Dynamic beam laser systems and methods

Abstract

A laser welding system including a coherent beam combining (CBC) laser operative to provide a laser output for welding of a workpiece having a contoured surface, at least one of an angle of incidence of the laser output with respect to the surface and a distance between the CBC laser and the surface, varying across the surface, and a phase control sub-system electronically connected to the CBC laser, the phase control sub- system being operative to provide a first phase variation to vary a phase of the laser output, to compensate for the varying of at least one of the angle of incidence of the laser output with respect to the surface and the distance between the CBC laser and the surface.

Description

[0001] DYNAMIC BEAM LASER SYSTEMS AND METHODS

[0002] RELATED APPLICATIONS

[0003] Reference is hereby made to U.S. Provisional Patent Application No. 63 / 655,381, entitled ‘DYNAMIC BEAM LASER SYSTEMS AND METHODS’, filed

[0004] June 3, 2024, the disclosure of which is hereby incorporated by reference and priority of which is hereby claimed pursuant to 37 CFR 1.78(a)(4) and (5)(i).

[0005] FIELD OF THE INVENTION

[0006] The present invention relates generally to lasers and more particularly to dynamic beam lasers.

[0007] BACKGROUND OF THE INVENTION

[0008] Various types of dynamic beam laser systems and methods are known in the art.

[0009] SUMMARY OF THE INVENTION

[0010] The present invention seeks to provide improved systems and methods for optical-phased-array (OPA) coherent-beam-combining (CBC) lasers outputting dynamic laser beams, particularly useful for material processing and optical communication applications.

[0011] There is thus provided in accordance with a preferred embodiment of the present invention a laser welding system including a coherent beam combining (CBC) laser operative to provide a laser output for welding of a workpiece having a contoured surface, at least one of an angle of incidence of the laser output with respect to the surface and a distance between the CBC laser and the surface, varying across the surface, and a phase control sub-system electronically connected to the CBC laser, the phase control sub-system being operative to provide a first phase variation to vary a phase of the laser output, to compensate for the varying of at least one of the angle of incidence of the laser output with respect to the surface and the distance between the CBC laser and the surface.

[0012] Preferably, the phase control sub-system being operative to vary the phase of the laser output includes the phase control sub-system being operative to dynamically control both a shape and a position of the laser output across the surface to maintain a constant weld profile across the surface, during the welding.

[0013] Preferably, the phase control sub-system is operative to vary the phase of the laser output, to move the laser output over the surface and is further operative to dynamically control the shape of the laser output as the laser output traverses the surface, to maintain the constant weld profile at each point of the surface.

[0014] Preferably, the phase control sub-system is operative to provide the first phase variation to vary a phase of the laser output, to deliver a generally constant energy, by the laser output, to the surface at each point thereof.

[0015] Preferably, the surface is curved.

[0016] Preferably, the phase control sub-system is additionally operative to provide a second phase variation to vary a phase of the laser output to cancel out noise of the laser output, the second phase variation being provided, by the phase control subsystem, during time interstices between provision of the first phase variation. Preferably, the phase control sub-system is operative to provide the second phase variation during provision of the first phase variation and without causing significant disruption of the control, by the first phase variation, of the laser output.

[0017] Preferably, the CBC laser is a single-mode laser.

[0018] Preferably, the CBC laser operates in a power range of several watts to several hundred kilowatts.

[0019] Preferably, the CBC laser operates in a power range of 10W - 400kW.

[0020] Preferably, the workpiece includes an extensive region spanning an area of up to 200 m by 200 m.

[0021] Preferably, the workpiece includes a panel of a liquid natural gas (LNG) tank.

[0022] Preferably, the CBC laser includes a multiplicity of optical elements wherethrough the laser output passes, the multiplicity of optical elements including subbeam alignment optics operative to align sub-beams including the laser output with respect to one another and focusing optics operative to focus the sub-beams, once aligned, upon the workpiece.

[0023] Preferably, the sub-beam alignment optics are housed in an optical head (OH) and the focusing optics are housed in a welding head, separate from the OH, wherein the focusing optics are physically separated from the sub-beam alignment optics by a distance of less than or equal to 100 meters, and the laser output propagates, from the subbeam alignment optics to the focusing optics, through free space.

[0024] Preferably, the noise is generated, at least in part, by the multiplicity of optical elements.

[0025] Preferably, the system also includes at least one detector operative to sense the noise generated by the multiplicity of optical elements and the phase control subsystem is operative to provide the second phase variation to cancel out the noise of the laser output, based on taking into consideration the noise, generated, at least in part, by the multiplicity of optical elements as sensed by the at least one detector.

[0026] Preferably, substantially all of the multiplicity of optical elements are located upstream from the detector, such that substantially all of the noise generated by the multiplicity of optical elements is sensed by the at least one detector. Preferably, all of the multiplicity of optical elements are located upstream from the detector.

[0027] Preferably, an Optical Head (OH) housing the sub-beam alignment optics is connected, via an optical fiber bundle, to other components of the laser and the at least one detector is operative to additionally sense noise generated by the optical fiber bundle.

[0028] Preferably, the system also includes a beam splitter operative to direct a portion of the laser output to be incident upon the at least one detector, wherein a mechanical distance between the beam splitter and the workpiece is greater than a mechanical distance between the beam spitter and the at least one detector.

[0029] There is also provided in accordance with another preferred embodiment of the present invention a method for laser welding including providing, by a coherent beam combining (CBC) laser, a laser output for welding of a workpiece having a contoured surface, at least one of an angle of incidence of the laser output with respect to the surface and a distance between the CBC laser and the surface varying across the surface and varying, by a phase control sub-system electronically connected to the CBC laser, a phase of the laser output, to compensate for the variation of at least one of the angle of incidence of the laser output with respect to the surface and the distance between the CBC laser and the surface.

[0030] Preferably, the varying the phase of the laser output dynamically controls both a shape and a position of the laser output across the surface, to maintain a constant weld profile across the surface during the welding.

[0031] Preferably, the varying the phase of the laser output causes movement of the laser output over the surface and dynamically controls the shape of the laser output as the laser output traverses the surface, to maintain the constant weld profile at each point of the surface.

[0032] Preferably, the varying the phase of the laser output causes delivery of a generally constant energy, by the laser output, to the surface at each point thereof.

[0033] Preferably, the surface is curved.

[0034] Preferably, the method also includes additionally varying, by the phase control sub-system, an additional phase of the laser output to cancel out noise of the laser output, the varying of the additional phase being carried out by the phase control subsystem during time interstices between the varying of the phase. Preferably, the additionally varying the additional phase to cancel out noise of the laser output is performed, by the phase control sub-system, during the varying of the phase and without causing significant disruption of the control, by the varying of the phase, of the laser output.

[0035] Preferably, the CBC laser is a single-mode laser.

[0036] Preferably, the CBC laser operates in a power range of several watts to several hundred kilowatts.

[0037] Preferably, the CBC laser operates in a power range of 10W - 400kW.

[0038] Preferably, the workpiece includes an extensive region spanning an area of up to 200 m by 200 m.

[0039] Preferably, the workpiece includes a panel of a liquid natural gas (LNG) tank.

[0040] Preferably, the CBC laser includes a multiplicity of optical elements wherethrough the laser output passes, the multiplicity of optical elements including subbeam alignment optics operative to align sub-beams including the laser output with respect to one another and focusing optics operative to focus the sub-beams, once aligned, upon the workpiece.

[0041] Preferably, the sub-beam alignment optics are housed in an optical head (OH) and the focusing optics are housed in a welding head, separate from the OH, wherein the focusing optics are physically separated from the sub-beam alignment optics by a distance of less than or equal to 100 meters, and the laser output propagates, from the subbeam alignment optics to the focusing optics, through free space.

[0042] Preferably, the noise is generated, at least in part, by the multiplicity of optical elements.

[0043] Preferably, the method also includes detecting, by at least one detector, the noise generated by the multiplicity of optical elements and providing the additional phase variation to cancel out the noise of the laser output, based on taking into consideration the noise, generated, at least in part, by the multiplicity of optical elements, as detected by the at least one detector.

[0044] Preferably, substantially all of the multiplicity of optical elements are located upstream from the detector, such that substantially all of the noise generated by the multiplicity of optical elements is detected by the at least one detector. Preferably, all of the multiplicity of optical elements are located upstream from the detector.

[0045] Preferably, the method also includes connecting, via an optical fiber bundle, an Optical Head (OH) housing the sub-beam alignment optics to other components of the laser and detecting, by the at least one detector, noise generated by the optical fiber bundle.

[0046] Preferably, the method also includes directing, by a beam splitter, a portion of the laser output to be incident upon the at least one detector, wherein a mechanical distance between the beam splitter and the workpiece is greater than a mechanical distance between the beam spitter and the at least one detector.

[0047] There is further provided in accordance with another preferred embodiment of the present invention a laser welding system including a coherent beam combining (CBC) laser operative to provide a laser output for welding of a workpiece, the CBC laser including a multiplicity of optical elements wherethrough the laser output passes, the multiplicity of optical elements including sub-beam alignment optics, housed in an Optical Head (OH) and operative to align sub-beams including the laser output with respect to one another and focusing optics, not housed in the OH and operative to focus the sub-beams, once aligned, upon the workpiece, the focusing optics being physically separated from the sub-beam alignment optics by a distance of less than or equal to 100 meters, and the laser output propagating, from the sub-beam alignment optics to the focusing optics, through free space and a phase control sub-system electronically connected to the CBC laser, the phase control sub-system being operative to provide at least a spatial modification phase variation to vary a phase of the laser output, to dynamically control at least one of a shape and a position of the laser output during the welding.

[0048] Preferably, the focusing optics are physically separated from the subbeam alignment optics by a distance of 50m - 100m.

[0049] Preferably, the focusing optics are fixed in position with respect to the OH, the focusing optics being moveable in tandem with the OH during the welding or moveable with respect to the OH, the OH being stationary and the focusing optics being moveable during the welding. In accordance with one preferred embodiment of the present invention, the system also includes a wagon for mounting the laser welding system thereon, the OH and the focusing optics being movable in tandem along a scaffolding, by the wagon, during the welding.

[0050] Alternatively, the system also includes a stage for mounting the laser welding system thereon, the OH and the focusing optics being moveable in tandem along a hydraulic pole, by the stage, during the welding.

[0051] Preferably, the OH is stationary and the focusing optics are mounted on a moveable stage on a hydraulic pole, the laser output being directed, through free space, from the OH to the focusing optics and the focusing optics being moveable by the stage, during the welding, to moveably focus the laser output on the workpiece.

[0052] Alternatively, the OH is stationary and the focusing optics are mounted on a drone, the laser output being directed, through free space, from the OH to the focusing optics, the focusing optics being moveable by the drone, during the welding, to moveably focus the laser output on the workpiece.

[0053] Preferably, the sub -beam alignment optics and the focusing optics are housed in a welding head, also including the OH.

[0054] Preferably, the welding head also includes a detector including a confocal telescope and a camera.

[0055] Preferably, the system also includes a galvo-scanner.

[0056] There is yet further provided in accordance with another preferred embodiment of the present invention a method for laser welding including providing, by a coherent beam combining (CBC) laser, a laser output for welding of a workpiece, the CBC laser including a multiplicity of optical elements wherethrough the laser output passes, the multiplicity of optical elements including sub-beam alignment optic, housed in an Optical Head (OH), and being operative to align sub-beams including the laser output with respect to one another and focusing optics, not housed in the OH and being operative to focus the sub-beams, once aligned, upon the workpiece, the focusing optics being physically separated from the sub-beam alignment optics by a distance of less than or equal to 100 meters, and the laser output propagating, from the sub-beam alignment optics to the focusing optics, through free space and varying, by a phase control subsystem electronically connected to the CBC laser, a phase of the laser output, to dynamically control at least one of a shape and a position of the laser output during the welding.

[0057] Preferably, the focusing optics are physically separated from the subbeam alignment optics by a distance of 50m - 100m.

[0058] Preferably, the focusing optics are fixed in position with respect to the OH, the focusing optics being moveable in tandem with the OH during the welding or moveable with respect to the OH, the OH being stationary and the focusing optics being moveable during the welding.

[0059] In accordance with a preferred embodiment of the present invention, the method also includes mounting the laser system on a wagon, the OH and the focusing optics being movable in tandem along a scaffolding, by the wagon, during the welding.

[0060] Alternatively, the method also includes mounting the laser system on a stage, the OH and the focusing optics being moveable in tandem along a hydraulic pole, by the stage, during the welding.

[0061] Preferably, the method also includes mounting the focusing optics on a moveable stage on a hydraulic pole, wherein the OH is stationary and directing the laser output, through free space, from the OH to the focusing optics, the focusing optics being moveable by the stage, during the welding, to moveably focus the laser output on the workpiece.

[0062] Alternatively, the method also includes mounting the focusing optics on a drone, wherein the OH is stationary and directing the laser output, through free space, from the OH to the focusing optics, the focusing optics being moveable by the drone, during the welding, to moveably focus the laser output on the workpiece.

[0063] Preferably, the sub-beam alignment optics and the focusing optics are housed in a welding head, also including the OH.

[0064] Preferably, the welding head also includes a detector, the detector including a confocal telescope and a camera.

[0065] Preferably, the method also includes scanning the laser output, by a galvo-scanner.

[0066] There is further provided in accordance with still another preferred embodiment of the present invention a laser welding system including a coherent beam combining (CBC) laser operative to provide a laser output for butt welding of a workpiece having a gap, the gap having a width of at least 1mm and a phase control sub-system electronically connected to the CBC laser, the phase control sub-system being operative to provide a first phase variation to vary a phase of the laser output, to dynamically control at least one of a shape and a position of the laser output incident upon the workpiece, to perform butt welding across an entirety of the gap.

[0067] Preferably, the phase control sub-system is additionally operative to provide a second phase variation to vary a phase of the laser output to cancel out noise of the laser output, the second phase variation being provided, by the phase control subsystem, during time interstices between provision of the first phase variation.

[0068] Preferably, the phase control sub-system is operative to provide the second phase variation during provision of the first phase variation and without causing significant disruption of the control, by the first phase variation, of the laser output.

[0069] Preferably, the CBC laser is a single-mode laser.

[0070] Preferably, the CBC laser operates in a power range of several watts to several hundred kilowatts.

[0071] Preferably, the CBC laser operates in a power range of 10W - 400kW.

[0072] Preferably, the CBC laser includes a laser splitting and combining subsystem, operative to split an output of the CBC laser into a multiplicity of sub-beams and subsequently combine the multiplicity of sub-beams to form the laser output.

[0073] Preferably, the laser splitting and combining subsystem includes a focal lens for focusing the laser output on the workpiece, the focal lens having a focal length of at least 3m.

[0074] Preferably, the width of the gap is at least 2mm.

[0075] Preferably, the phase control subsystem being operative to dynamically control the shape and position of the laser output incident upon the workpiece includes the phase control subsystem being operative to continuously move at least one high intensity region of a far field intensity pattern of the laser output from one side of the gap to another, during the welding of the gap, without involving mechanical motion of the CBC laser.

[0076] There is also provided in accordance with a further preferred embodiment of the present invention a laser welding method including providing, by a coherent beam combining (CBC) laser, a laser output incident upon a workpiece having a gap, the gap having a width of at least 1mm, varying, by a phase control sub-system electronically connected to the CBC laser, a first phase of the laser output, to dynamically control at least one of a shape and a position of the laser output incident upon the workpiece and performing butt welding, by the laser output incident upon the workpiece, across an entirety of the width of the gap.

[0077] Preferably, the method also includes varying, by the phase control subsystem, a second phase of the laser output to cancel out noise of the laser output, the varying of the second phase being performed, by the phase control sub- system, during time interstices between the varying of the first phase.

[0078] Preferably, the varying of the second phase is performed, by the phase control sub-system, during the varying of the first phase and without causing significant disruption of the control, by the first phase varying, of the laser output.

[0079] Preferably, the CBC laser is a single-mode laser.

[0080] Preferably, the CBC laser operates in a power range of several watts to several hundred kilowatts.

[0081] Preferably, the CBC laser operates in a power range of 10W - 400kW.

[0082] Preferably, the CBC laser includes a laser splitting and combining subsystem, for splitting an output of the CBC laser into a multiplicity of sub-beams and subsequently combining the multiplicity of sub-beams to form the laser output.

[0083] Preferably, the method also includes focusing, by a focal lens, the laser output on the workpiece, the focal lens having a focal length of at least 3mm.

[0084] Preferably, the width of the gap is at least 2mm.

[0085] Preferably, the varying, by the phase control sub-system, a first phase of the laser output, to dynamically control at least one of a shape and a position of the laser output includes continuously moving at least one high intensity region of a far field intensity pattern of the laser output from one side of the gap to another, during the welding of the gap, without involving mechanical motion of the CBC laser.

[0086] There is still further provided in accordance with yet another preferred embodiment of the present invention a laser system including a seed laser operative to provide a laser output, a laser beam splitting and combining subsystem including a multiplicity of optical elements through which the laser output passes, and operative to receive the laser output from the seed laser, split the laser output into a plurality of sub- beams and combine the plurality of sub-beams into a combined laser output having noise generated, at least in part, by the multiplicity of optical elements, at least one detector operative to sense the noise generated at least in part by the multiplicity of optical elements, a spatial modification phase-variation subsystem operative to vary phases of sub-beams of the plurality of sub-beams, to control at least one of a shape and a position of the combined laser output and a noise cancellation phase variation subsystem operative to provide a noise cancellation phase correction output to sub-beams of the plurality of sub-beams, based on taking into consideration the noise as sensed by the detector.

[0087] Preferably, the multiplicity of optical elements includes at least a beam alignment subsystem operative to align ones of the plurality of sub-beams with one another, a beam focusing subsystem operative to focus the plurality of sub-beams, once aligned, and a beam splitting subsystem operative to direct a portion of the plurality of sub-beams towards the detector, the detector is operative to sense the noise generated by the beam alignment subsystem, the beam focusing subsystem and the beam splitting subsystem and the noise cancellation subsystem is operative to provide a noise cancellation phase correction output to sub-beams of the plurality of sub-beams, based on taking into consideration the noise generated, at least in part, by the beam alignment subsystem, the beam focusing subsystem and the beam splitting subsystem, as sensed by the detector.

[0088] Preferably, substantially all of the multiplicity of optical elements are located upstream from the detector, such that substantially all of the noise generated by the multiplicity of optical elements is sensed by the detector.

[0089] Preferably, all of the multiplicity of optical elements are located upstream from the detector.

[0090] Preferably, the beam alignment subsystem includes a plurality of collimating lenses corresponding to the plurality of sub-beams.

[0091] Preferably, the beam alignment subsystem is housed in an optical head connected, by an optical fiber bundle, to at least the seed laser, the detector is operative to additionally sense the noise generated by the optical fiber bundle and the noise cancellation subsystem is operative to provide a noise cancellation phase correction output to sub-beams of the plurality of sub-beams, based on additionally taking into consideration the noise generated by the optical fiber bundle, as sensed by the detector. Preferably, the spatial modification phase-variation subsystem is operative to vary phases of sub-beams of the plurality of sub-beams, to control at least one of a shape and a position of the combined laser output, for laser manufacturing of a workpiece.

[0092] Preferably, a mechanical distance from the beam splitting and combining subsystem to the workpiece is greater than a mechanical distance from the beam splitting and combining subsystem to the detector.

[0093] Preferably, the system also includes a confocal telescope positioned between the beam splitting and combining subsystem and the detector, for focusing the portion of the plurality of sub-beams, from the beam splitting and combining subsystem, on the detector.

[0094] Preferably, the beam focusing subsystem is physically distant from the beam alignment subsystem by a distance of up to about 100 meters, the plurality of subbeams propagating, from the sub-beam alignment subsystem to the beam focusing subsystem, through free space.

[0095] There is also provided in accordance with another preferred embodiment of the present invention a method for performing phase variation of a laser output, including providing, by a seed laser, a laser output, splitting the laser output into a plurality of sub-beams and combining the plurality of sub-beams into a combined laser output having noise generated, at least in part, by a multiplicity of optical elements through which the laser output passes, sensing, by at least one detector, the noise generated, at least in part, by the multiplicity of optical elements, varying, by a spatial modification phase variation sub-system, phases of sub-beams of the plurality of subbeams, to control at least one of a shape and a position of the combined laser output and providing, by a noise cancellation phase variation sub-system, a noise cancellation phase correction output to sub-beams of the plurality of sub-beams, based on taking into consideration the noise.

[0096] Preferably, the multiplicity of optical elements includes at least a beam alignment subsystem operative to align ones of the plurality of sub-beams with one another, a beam focusing subsystem operative to focus the plurality of sub-beams, once aligned, and a beam splitting subsystem operative to direct a portion of the plurality of sub-beams towards the detector, sensing, by the at least one detector, the noise generated, at least in part, by the multiplicity of optical elements including sensing, by the at least one detector, noise generated by the beam alignment subsystem, the beam focusing subsystem and the beam splitting subsystem and providing, by the noise cancellation phase variation sub-system, a noise cancellation phase correction output to sub-beams of the plurality of sub-beams, based on taking into consideration the noise, including providing, by the noise cancellation subsystem, a noise cancellation phase correction output to sub-beams of the plurality of sub-beams, based on taking into consideration the noise generated, at least in part, by the beam alignment subsystem, the beam focusing subsystem and the beam splitting subsystem, as sensed by the detector.

[0097] Preferably, the method also includes locating substantially all of the multiplicity of optical elements upstream from the detector, such that substantially all of the noise generated by the multiplicity of optical elements is sensed by the detector.

[0098] Preferably, the method also includes locating all of the multiplicity of optical elements upstream from the detector.

[0099] Preferably, the beam alignment subsystem includes a plurality of collimating lenses corresponding to the plurality of sub-beams.

[0100] Preferably, the method also includes housing the beam alignment subsystem in an optical head connected, by an optical fiber bundle, at least to the seed laser, sensing, by the at least one detector, noise generated by the optical fiber bundle and providing, by the noise cancellation phase variation subsystem, a noise cancellation phase correction output to sub-beams of the plurality of sub-beams, based on additionally taking into consideration the noise generated by the optical fiber bundle, as sensed by the at least one detector.

[0101] Preferably, the method includes a method for laser manufacturing of a workpiece, including directing the spatially modified, noise corrected, laser output to a workpiece, for performance of laser manufacturing of the workpiece.

[0102] Preferably, a mechanical distance from the beam focusing subsystem to the workpiece is greater than a mechanical distance from the beam focusing subsystem to the detector.

[0103] Preferably, the method also includes focusing, by a confocal telescope positioned between the beam splitting subsystem and the detector, the portion of the plurality of sub-beams, from the beam splitting subsystem, on the detector. Preferably, the method also includes housing the beam focusing subsystem in a welding head, the optical head being physically distant from the welding head by a distance of up to 100 meters, the plurality of sub-beams propagating, from the sub-beam alignment subsystem to the beam focusing subsystem, through free space.

[0104] BRIEF DESCRIPTION OF DRAWINGS

[0105] The present invention will be understood and appreciated from the following detailed description, taken in conjunction with the drawings in which:

[0106] Fig. 1A is a simplified block-diagram illustration of a laser system, constructed and operative in accordance with a preferred embodiment of the present invention;

[0107] Fig. IB is a highly simplified schematic illustration of a laser system of a type shown in Fig. 1A, constructed and operative in accordance with a preferred embodiment of the present invention;

[0108] Fig. 2A is a simplified block-diagram illustration of a laser system, constructed and operative in accordance with another preferred embodiment of the present invention;

[0109] Fig. 2B is a highly simplified schematic illustration of a laser system of a type shown in Fig. 2A, constructed and operative in accordance with a preferred embodiment of the present invention;

[0110] Fig. 3A is a simplified block-diagram illustration of a laser system, constructed and operative in accordance with a further preferred embodiment of the present invention;

[0111] Fig. 3B is a highly simplified schematic illustration of a laser system of a type shown in Fig. 3A, constructed and operative in accordance with a preferred embodiment of the present invention;

[0112] Fig. 3C is a simplified schematic illustration of a beam shape output by a laser system of the type shown in Figs. 3 A and 3B;

[0113] Fig. 4 is a simplified schematic illustration of a preferred embodiment of a laser system of a type shown in any one of Figs. 1A - 3B;

[0114] Fig. 5 is a simplified schematic illustration of a further preferred embodiment of a laser system of a type shown in any one of Figs. 1A - 3B;

[0115] Fig. 6 is a simplified schematic illustration of yet a further preferred embodiment of a laser system of a type shown in any one of Figs. 1A - 3B;

[0116] Figs. 7A - 7E are simplified respective first perspective, second perspective, front planar, side planar and cross-sectional view illustrations of a preferred embodiment of a portion of a laser system of a type shown in any one of Figs. 1A - 3B, Fig. 7E being taken along the line 7E-7E in Fig. 7C;

[0117] Figs. 8A - 8E are simplified respective first perspective, second perspective, front planar, side planar and cross-sectional view illustrations of another preferred embodiment of a portion of a laser system of a type shown in any one of Figs. 1A - 3B, Fig. 8E being taken along the line 8E-8E in Fig. 8C;

[0118] Fig. 9 is a simplified schematic illustration of a further preferred embodiment of a laser system of a type shown in any one of Figs. 1A - 3B;

[0119] Figs. 10A and 10B are simplified respective schematic illustrations of first and second portions of yet a further preferred embodiment of a laser system of a type shown in any one of Figs. 1A - 3B;

[0120] Figs. 11 A and 1 IB are simplified respective schematic illustrations of first and second portions of yet another preferred embodiment of a laser system of a type shown in any one of Figs. 1A - 3B;

[0121] Fig. 12A is a simplified schematic perspective view illustration of still another preferred embodiment of a laser system of a type shown in any one of Figs. 1 A - 3B;

[0122] Fig. 12B is a simplified side view illustration of the laser system of Fig. 12A in a first operative position thereof;

[0123] Fig. 12C is a simplified schematic illustration of a beam shape corresponding to the first operative position of the laser system shown in Fig. 12B;

[0124] Fig. 12D is a simplified side view illustration of the laser system of Fig. 12A in a second operative position thereof;

[0125] Fig. 12E is a simplified schematic illustration of a beam shape corresponding to the second operative position of the laser system shown in Fig. 12D;

[0126] Fig. 12F is a simplified side view illustration of the laser system of Fig. 12A in a third operative position thereof;

[0127] Fig. 12G is a simplified schematic illustration of a beam shape corresponding to the third operative position of the laser system shown in Fig. 12F;

[0128] Fig. 12H is a simplified side view illustration of the laser system of Fig. 12A in a fourth operative position thereof; Fig. 121 is a simplified schematic illustration of a beam shape corresponding to the fourth operative position of the laser system shown in Fig. 12H;

[0129] Fig. 13 is a simplified flow chart showing a method for laser operation, in accordance with a preferred embodiment of the present invention; and Fig. 14 is a simplified flow chart showing steps in operation of a laser welding system in accordance with another preferred embodiment of the present invention.

[0130] DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

[0131] Reference is now made to Fig. 1A, which is a simplified block-diagram illustration of a laser system, constructed and operative in accordance with a preferred embodiment of the present invention; and to Fig. IB, which is a simplified schematic illustration of a laser system of a type shown in Fig. 1A, constructed and operative in accordance with a preferred embodiment of the present invention.

[0132] As seen in Figs. 1A and IB, there is provided a laser system 100, preferably including an optical-phased-array coherent-beam-combining (OPA CBC) laser 102 operative to provide a dynamic laser beam output. OPA CBC laser 102 preferably outputs a multiplicity of laser sub-beams, which multiplicity of laser sub-beams are combined in the far-field to form a combined beam. The shape and / or position of the combined beam may be dynamically varied at least by phase control functionality incorporated in OPA CBC laser 102, as is detailed henceforth below.

[0133] As seen in Fig. 1A, OPA CBC laser 102 may include laser components 104 and optics 106. Laser components 104 may be operative to provide a multiplicity of laser sub-beams to optics 106. Optics 106 may include laser sub-beam alignment optics, functional to align the multiplicity of individual laser sub-beams relative to each other. Optics 106 may also include focusing optics, functional to focus the laser sub-beams, following alignment thereof by laser sub-beam alignment optics, for example on a workpiece 110. In other embodiments of OPA CBC laser 102, the focused laser subbeams may propagate through free space, rather than be focused upon a workpiece, for example for use in free space optical communications.

[0134] Optics 106 may include transmissive and / or reflective optical components, such as one or more lenses, mirrors, beamsplitters and / or other optical components. In some embodiments of OPA CBC laser 102, both sub-beam alignment optics and focusing optics may be included within (integrated with) the body of OPA CBC laser 102. In other embodiments of OPA CBC laser 102, focusing optics may be included in a separate component, external to the body of OPA CBC laser 102, such as a welding head, as is further detailed henceforth with reference to Figs. 2A and 2B. In some embodiments of OPA CBC laser 102, at least some optical components of optics 106 may be housed separately from other components of OPA CBC laser 102, for example in an optical head (OH). For example, larger, heavier parts of OPA CBC laser 102 (for example, laser components 104) may be housed in one or more housings or enclosures and optics 106 may be housed in an OH, which may be moveable, for example with respect to other laser components 104 and workpiece 110. The OH may be separate from but connected to other components 104 of OPA CBC laser 102. The multiplicity of sub-beams provided by laser components 104 to optics 106 may propagate through free-space or may be conveyed to optics 106 via optical fibers. In other embodiments of OPA CBC laser 102, optics 106 may be arranged in a same housing as, or may be integrated with, other components 104 of OPA CBC laser 102. In some embodiments of OPA CBC laser 102, the OH may include at least some of optics 106 in addition to other components 104 of OPA CBC laser 102.

[0135] Various possible arrangements of OPA CBC laser 102 are detailed herein, with respect to Figs. IB - 12A. It is understood, however, that these arrangements are provided by way of example only and that other arrangements, in which components of OPA CBC laser 102 are differently arranged (for example, separated or divided or housed) are also possible.

[0136] The combined laser output provided by OPA CBC laser 102 typically has noise. The noise in the combined laser output may be due to mechanical, thermal, intensity, amplification or other effects within system 100. Herein, noise (for example, phase noise) may refer to any variation from a predetermined or desired phase, regardless of whether such noise changes over time or is constant over time. Noise may be caused by mechanical movement, mechanical stress, thermal effects for example causing thermal focus shift, amplification noise, intensity noise or other effects in the optical elements (for example, lenses, mirrors, windows, beam splitters, phase plates, polarization elements, fibers etc.), effects in the mechanical elements holding the optics and effects in the air or space between the optical elements. Noise may also or alternatively be caused by manufacturing imperfections in the optical or mechanical elements or in the assembly thereof. The noise may also or alternatively be caused by the operation of the laser itself, such as by the heat created by the high-power laser beams, and / or may be amplification noise created by non-linear effects or noise in the electronics; as well as external effects such as acoustic noise, vibrations, wind, temperature variations of the surroundings and so on.

[0137] Optics 106 may contribute to noise in the combined laser output, for example, but not limited to, due to heating of optics 106, by the high-power laser beams, during operation of OPA CBC laser 102. Such heating may distort optical elements of optics 106 and may create thermal focus shift effects. Thermal distortions of optics 106 may create (for example, generate or cause) noise in the combined laser output. Additionally or alternatively, optics 106 may create noise in the combined laser output due to distortions thereof arising from other causes, for example physical defects or misalignment.

[0138] Furthermore, in the case that OPA CBC laser 102 includes an OH connected to the other laser components (e.g. the main laser body 104) by an optical fiber bundle, the optical fibers may also create phase noise in the combined laser output. This is particularly so in embodiments in which the OH (e.g. optics 106 in the OH) is moved with respect to the other laser components (e.g. other laser components 104), wherein movement of the optical fiber bundle may create phase noise in the combined laser output.

[0139] Noise in the combined laser output provided by OPA CBC laser 102 may be detected by at least one detector, here shown to be embodied, by way of example, as a single detector 120. Preferably, a portion of the combined laser output may be made incident upon detector 120. Detector 120 is preferably operative to sense noise in the laser output incident thereupon. The operation of laser component 104 may be adjusted based on noise sensed by detector 120, as indicated by a feedback arrow 122. More specifically, a noise detection phase correction may be applied to the laser output based on the noise in the laser output, as detected by detector 120.

[0140] It is a particular feature of a preferred embodiment of the present invention that detector 120 is preferably downstream of optics 106, such that detector 120 is preferably operative to sense noise in the combined laser output including noise arising from optics 106 (for example, optical thermal distortions due to optics 106, such as thermal focus shift). The noise detection phase correction, applied based on the noise detected by detector 120, may then be operative to take this noise into account and hence to apply an appropriate correction to the laser output, including correction for noise arising from optics 106. It is appreciated that should detector 120 be positioned upstream from some or all of optics 106, phase noise in the laser output caused by the laser output propagating through optics 106 would not be sensed, or would be only partially sensed, by detector 120 and hence would not be corrected for, or would be only partially corrected for, based on the feedback 122 provided by detector 120 to laser components 104.

[0141] Detector 120 may be located downstream of optics 106, in the case that optics 106 are entirely included in OPA CBC laser 102. Detector 120 may be located downstream of optics 106 also in the case that optics 106 are partly included in OPA CBC laser 102 and partly included in an external component connected thereto, as is further detailed henceforth in relation to Fig. IB. Notwithstanding the particular distribution and arrangement of optics 106, detector 120 is preferably located downstream from all significant optical components of optics 106, such that detector 120 is operative to sense phase noise in the combined laser output arising from all significant components of optics 106. In some embodiments, detector 120 may be located downstream of the entirety (for example, all) of optics 106. In other embodiment, detector 120 may be located downstream of a significant portion but not necessarily all of optics 106, such that detector 120 is operative to sense phase noise in the combined laser output arising from a significant portion, although not necessarily all, of optics 106.

[0142] The arrows in the block diagram of Fig. 1A thus may be understood to show a progression of the laser output through system 100 in a sense of sequence and direction of travel. It is understood that the arrows indicate progression of the laser output in a highly simplified manner, to aid appreciation of the downstream location of detector 120 with respect to other elements of OPA CBC laser 102. Furthermore, it is understood that although detector 120 is shown as a separate element with respect to laser components 104 and optics 106, detector 120 may be integrated into OPA CBC laser 102, for example included in an OH also housing optics 106. It is appreciated that the feedback 122 from detector 120 to laser components 104 is indicated by a dashed line, in order to distinguish feedback 122 from the other arrows in the block diagram of Fig. 1A indicating the progression of the laser beams through system 100.

[0143] In the case that OPA CBC laser 102 includes an OH, detector 120 is preferably located downstream of the OH and of the bundle of optical fibers which may connect the OH (for example, optics 106 in the OH) to other laser components (for example, laser components 104). Noise in the combined laser output due to the bundle of optical fibers, for example caused by motion thereof, is thus also sensed by detector 120 and may be corrected for by a phase noise correction.

[0144] This arrangement of detector 120 with respect to optics 106 has been found to be particularly advantageous in providing noise correction of the combined laser beam, including noise correction for noise generated by optics 106 (for example due to thermal focus shift of optics 106 and noise arising from optical fibers connecting the OH to other laser components 104), even during high-power operation of laser system 100. OPA CBC laser 102 is preferably a single mode laser operating at high power. Particularly preferably, OPA CBC laser 102 may operate in a power range of several watts to several hundred kilowatts, and even more preferably a power range of 10W - 400kW. Laser system 100 is thus particularly useful for stable, distortion-free operation for a variety of high-power applications, including laser welding, cutting, additive manufacturing and free space optical communication.

[0145] Turning now to Fig. IB, a preferred embodiment of laser system 100 is shown. OPA CBC laser 102 may include a seed laser 130 and a laser beam splitting and combining subsystem 132. Splitting and combining subsystem 132 preferably receives an output laser beam from seed laser 130 and splits the output laser beam into a plurality of sub-beams along a corresponding plurality of channels 134. Here, by way of example only, an output from seed laser 130 is shown to be split into four sub-beams along four channels 134 although it is appreciated that splitting and combining subsystem 132 typically may include a far greater number of channels, typically arranged in a three- dimensional matrix, along which the output of seed laser 130 is split. By way of example, splitting and combining subsystem 132 may include 32 or more channels arranged in a three-dimensional matrix. The four channels 134 shown in Fig. IB thus may be considered to illustrate a side-view of a three-dimensional matrix of channels.

[0146] The relative phase of each sub-beam may be individually modulated by a phase modulator 140, preferably located along each of channels 134. Phase modulators 140 are preferably electro-optical phase modulators, each operative to modify a phase of the sub-beam passing therethrough. Phase modulated sub-beams produced by the splitting and subsequent phase modulation of the output of seed laser 130 are preferably mutually relatively aligned by sub-beam alignment optics 142, here shown to comprise a plurality of collimating lenses 142. Preferably, each phase modulated sub-beam propagate towards a corresponding collimating lens. The individually collimated, phase modulated subbeams are subsequently combined and focused by focusing optics 146, here embodied by way of example as a focal lens 146, to form a combined beam 148.

[0147] Splitting and combining subsystem 132 may also provide laser amplification of the sub-beams, preferably following the splitting of the output beam of seed laser 130 into sub-beams and prior to the combining of the sub-beams to form output beam 148. Here, by way of example, splitting and combining subsystem 132 is shown to include a plurality of optical amplifiers 150 located along corresponding ones of channels 134 for amplifying each sub-beam. It is appreciated, however, that such amplification is optional and may be omitted, depending on the power output requirements of laser 102. Sub-beams may be delivered, following optional amplification thereof by optical amplifiers 150, to sub-beam alignment optics 142, by a corresponding plurality of optical fibers 152. The sub-beams may propagate through free space from sub-beam alignment optics 142 to focusing optics 146.

[0148] It is a particular feature of a preferred embodiment of the present invention that focusing optics 146 may be located at a physically large distance from sub-beam alignment optics 142. For example, focusing optics may be located at a distance of up to about 100m from sub-beam alignment optics 142 or even at a distance of greater than 100m. The plurality of sub-beams preferably propagates through free space over the distance between sub-beam alignment optics 142 and focusing optics 146.

[0149] The phase of combined beam 148, and hence the position and shape of a far-field intensity output pattern thereof, is controlled, at least in part, by the relative phases of the constituent sub-beams combined to form beam 148. In many applications, such as laser manufacturing and free-space communications, it is desirable to dynamically move and shape the far-field intensity pattern of the output beam. This may be achieved in laser system 100 by laser splitting and combining subsystem 132 dynamically varying the relative phases of the individual sub-beams and thereby varying the phase of the combined laser output 148 so as dynamically to control the position and shape of the far- field intensity pattern thereof.

[0150] The relative phases of the sub-beams are preferably predetermined in accordance with a desired laser output pattern, for example for the processing of workpiece 110. Particularly preferably, the varying relative phases are applied by a spatial modification phase control subsystem 160. Spatial modification phase control subsystem 160 preferably forms a part of a control electronics module 162 in OPA laser 102 and preferably controls each phase modulator 140 so as to dynamically modulate the relative phases of the sub-beams along channels 134 so as to produce a dynamically varying laser output pattern.

[0151] Seed laser 130, possibly in combination with other components such as amplifiers 150, may be a preferred embodiment of laser components 104 (Fig. 1A). Subbeam alignment optics 142 and focusing optics 146 may combinedly be a preferred embodiment of optics 106 (Fig. 1A). Sub-beam alignment optics 142 and focusing optics 146 may be housed in an OH forming a part of OPA CBC laser 102. Alternatively, subbeam alignment optics 142 may be housed in the OH and focusing optics 146 may be housed in a separate system component external to the OH. The OH may be connected to other components of the laser 104 by the plurality of optical fibers 152 through which the multiplicity of laser sub-beams may travel. Optics 142 and 146 may be subject to thermal distortions due to heating by the sub-beams of OPA CBC laser 102 during operation thereof, thereby causing distortion (for example, creating phase noise) of the laser output. Furthermore, movement of the optical fibers 152 connecting the OH to other laser components 104 may create phase noise. Distortions arising from optical elements in laser 102 (for example, phase noise) contribute to noise in output beam 148. Noise in combined beam 148 may additionally be created by other thermal or mechanical effects and / or by the amplification process in the case that optical amplifiers 150 are present in OPA system 100.

[0152] In order to cancel out noise in the laser output of system 100, system 100 preferably includes a noise cancellation phase variation subsystem 164. Noise cancellation phase variation subsystem 164 is preferably operative to provide a noise cancellation phase correction output in order to cancel out the noise in combined beam 148.

[0153] Particularly preferably, noise cancellation phase variation subsystem 164 employs an algorithm to sense and correct phase noise in the combined laser output. The noise cancellation phase correction output is preferably provided by noise cancellation phase variation subsystem 164 to phase modulators 140 so as to correct phase noise in combined beam 148 and thus avoid distortion of the shape and position of the far field intensity output pattern of combined beam 148 that would otherwise be caused by the noise. Noise cancellation phase variation subsystem 164 may be included in control electronics module 162.

[0154] In order to facilitate application of phase variation and noise correction to combined beam 148, a portion of the output of OPA laser 102 is preferably extracted and directed towards at least one detector 120. Detector 120 may be embodied as a single detector, as illustrated in Fig. IB, or may alternatively be embodied as multiple detectors. The extracted portion of the output beam preferably functions as a reference beam, based on characteristics of which the required noise correction and / or phase variation may be calculated. In the embodiment shown in Fig. IB, combined beam 148 is directed towards a beam splitter 170. Beam splitter 170 preferably splits combined beam 148 into a reflected portion 172 and a transmitted portion 174 in accordance with a predetermined ratio. For example, beam splitter 170 may split each sub-beam with a 99.9% reflected: 0.01% transmitted ratio.

[0155] The reflected portion 172 of the sub-beams preferably forms a combined output beam 178 having a far-field intensity pattern 180 incident upon workpiece 110. The transmitted portion 174 of the sub-beams is preferably transmitted to form an output reference beam 182 having a far-field intensity pattern incident 184 on a surface of detector 120.

[0156] As described hereinabove, the shape and position of the far-field intensity pattern 180 of the output beam 172, 178 and correspondingly of the far-field intensity pattern 184 of the reference beam 174, 182 are constantly changing, due to the ongoing variation of the relative phases of the sub-beams, as applied by phase modulators 140 controlled by spatial modification phase control subsystem 160. As a result, the far-field intensity pattern 184 of the reference beam 182 is not fixed upon detector 120 but rather is constantly being moved around with respect to detector 120 depending on the combined relative phases of the constituent sub-beams. However, in order for detector 120 to sense noise in reference beam 182 and thus provide the required feedback to noise cancellation phase variation subsystem 164, the far-field intensity pattern 184 of reference beam 182 must be incident upon detector 120 in order for detector to measure the intensity and thereby noise of the far- field intensity pattern, seemingly requiring a fixed output beam.

[0157] The conflict between the dynamic nature of far-field intensity pattern due to the phase-variation thereof and the fixed nature required of the far-field intensity pattern 184 of reference beam 182 in order to derive and ultimately apply noise correction thereto, is preferably resolved in a preferred embodiment of the present invention by providing the noise cancellation phase variation and spatial modification phase variation at mutually different times and rates.

[0158] The noise cancellation phase correction output is provided based on taking into consideration noise measured at detector 120 at a noise sampling rate. The output beam 148 is controlled in such a way that the far-field intensity pattern 184 of reference beam 182 is incident upon detector 120 during the course of the dynamic changes to the shape and position of the output and reference beams at a rate that is equal to or higher than the required noise sampling rate. The noise in reference beam 182 is taken into consideration during those intermittent times at which the far-field intensity pattern 184 is returned to detector 120. Noise cancellation phase variation subsystem 164 is operative to receive an output from detector 120 indicative of noise in reference beam 182 and apply a noise cancellation phase variation to phase modulators 140 based thereon at intermittent times.

[0159] At time interstices between the intermittent times at which the far-field intensity pattern 184 of reference beam 182 is incident upon detector 120 and a noise cancellation phase variation applied to phase modulators 140 by noise cancellation phase variation subsystem 164, the phase of the combined output beam 148 and hence reference beam 182 is continuously varied under the control of spatial modification phase variation subsystem 160, in order to dynamically change the shape and position of the far-field intensity pattern 180 thereof as required, for example to perform laser processing of workpiece 110 or for other applications. The combined laser output is varied, by spatial modification phase variation subsystem 160, at a phase varying rate which exceeds the noise sampling rate, in order to rapidly change the phase and hence shape and position of the far-field intensity pattern. By way of example, the noise sampling rate may be of the order of 10 - 1000 Hz whereas the phase varying rate may be greater than 10,000 Hz. Further details pertaining to particular exemplary algorithms useful for performing spatial modification phase variation and noise cancellation phase variation in the present invention, are described in WO2019 / 092702, the entirety of which is incorporated herein by reference.

[0160] The second phase variation to produce noise cancellation is preferably provided, by noise cancellation phase variation subsystem 164, during the course of the first phase variation for spatial modulation of the combined output beam 178, provided by spatial modification phase variation subsystem 160, without needing to significantly pause or disrupt the desired laser output pattern created and controlled by the first phase variation. It is appreciated that spatial modification phase variation subsystem 160 and noise cancellation phase variation subsystem 164 preferably have separate functionalities and hence are shown herein for clarity as separate modules, but may be implemented in the same (for example, common) physical components within control electronics 162.

[0161] Detector 120 is preferably operative to detect noise in the laser output incident thereupon, including noise arising from optical elements upstream from detector 120, such as optics 142 and 146. It is understood that the particular structure and configuration of beam splitting and recombining elements shown herein, including beam splitter 170, sub-beam alignment optics 142 and focusing optics 146, is exemplary only and depicted in a highly simplified form. It is appreciated that OPA laser system 100 may include a variety of such elements, as well as additional optical elements, including, by way of example only, additional or alternative lenses, optical fibers and coherent free- space far-field combiners. Preferably, most and even more preferably all of such additional optical elements are located upstream of detector 120, such that detector 120 is preferably operative to detect phase noise in the combined laser output generated by (arising from) such optical elements.

[0162] It is appreciated that should only some, but not all, of the optical elements be located upstream from detector 120, then detector 120 would not be capable of sensing noise in the combined laser output generated by that portion of the optics located downstream of detector 120 and the far field intensity pattern of the combined laser output 148 would be degraded by noise which would not be corrected for by noise correction phase variation module 164. By way of example, should beam-alignment optics 142 be located upstream from detector 120 but focusing optics 146 be located downstream from detector 120, detector 120 would not detect noise in combined laser output 148 generated by focusing optics 146, for example due to thermal focus shift of focusing optics 146, and thus the far field intensity pattern of combined laser output 178 would be degraded by noise arising from focusing optics 146 and be of poorer quality. For example, a thermal focus shift of focusing optics 146 may cause output beam 178 to shift by several mm or tens of mm from a desired position thereof. Should focusing optics 146 be located downstream from detector 120, such a shift in output beam 178 would not be detected by detector 120 and hence would remain uncorrected.

[0163] The Power in the Bucket (PIB) metric may be used to define beam quality. Deterioration in beam quality, due to noise and including thermal focus shift-related deterioration, may be quantified as the measured PIB. The measured PIB expresses how much energy is delivered by the beam to the desired location on the workpiece, compared to the energy delivery to the desired location by an ideal beam. Locating all of the optical elements of the laser of the present invention upstream from the detector, such that noise arising from the optical elements including thermal focus shift-related noise caused by focusing optics 406 is detected and hence corrected for, may result in an improvement in the PIB of the combined output beam of several percent, such as 10%, 20%, 30% or more.

[0164] Detector 120 may include additional optics as required to optimize the sensing of the noise (for example, phase noise). For example, additional optics for detector 120 may be located between detector 120 and beam splitter 170. Such optics may, for example, be operative to focus the combined output on the detector at a mechanical distance from beam splitter 170 that is different from the mechanical distance between beam splitter 170 and workpiece 110. For example, the mechanical distance from beam splitter 170 to detector 120 may be shorter than the mechanical distance from beam splitter 170 to workpiece 110, which may be helpful in minimizing the physical dimensions of system 100. Since the optics in the detector are not subject to high-power, due to only a small portion of the total output being directed towards detector 120, the optics in the detector may be formed by a variety of optical elements without being subject to thermal focusing or thermal distortion effects. For example, optics for detector 120 may have a confocal arrangement that allows a long effective focal length with a short back focal length, as is detailed henceforth with reference to Figs. 7A - 8E. As a result of the single-mode nature of the laser output, the laser output is highly sensitive to distortions. Distortions in the laser output may be corrected, in part, by the application, via phase modulators 140 controlled by noise cancellation phase variation subsystem 164, of a phase variation for noise cancellation. Distortions may further be minimized by careful construction and maintenance of laser system 100. Various exemplary features of laser system 100, which features preferably serve to minimize distortion of the single-mode output provided thereby, are listed below:

[0165] • Due to the single-mode nature of the laser output, the laser output must be transmitted in a very narrow optical fiber. This results in a high power-density in the fiber, leading to non-linear effects. In order to minimize such non-linear effects, the laser output in the present invention may be transmitted over relatively large distances through free space, rather than within optical fibers, for example between sub-beam alignment optics 142 and focusing optics 146.

[0166] • Due to the single mode high power nature of the laser output, the laser output is very sensitive to distortions caused by optical elements in laser system 100. Optical elements in laser system 100, such as lenses, mirrors and beamsplitters, are therefore preferably formed by pure fused silica glass which creates a minimum amount of distortion. There is therefore no variation in glass type in the optics (for example, optics 142 and 146, beam splitter 170) of system 100 and correspondingly no variation in refractive indices of different ones of the optical elements. Differences in refractive indices therefore cannot be used in lens design, making lens design more limited and hence more difficult.

[0167] • In some applications, the focal length of focusing optics 146 may be several meters long whereas the working distance between focusing optics 146 and workpiece 110 may be less than 1 meter long. As a result, the beam diameter on the downstream elements of optics 146 may be a few millimeters only. This small diameter combined with the high power of the laser, may result in high power density on these downstream optical elements which may result in distortion. In the present invention, most and preferably all optical elements including focusing optics 146 are located upstream of detector 120, such that any distortions may be sensed by detector and hence corrected for by phase control functionality included in control module 162. The dynamic laser output of OPA CBC laser 102, as spatially controlled by the first phase variation and noise-corrected by the second variation, has been found to be particularly well suited for laser manufacturing, including laser cutting, welding and additive manufacturing as well as for free space optical communications.

[0168] A particularly preferred embodiment of system 100, adapted for laser welding of curved surfaces and / or extensive surfaces, is shown in Figs. 2A and 2B. Turning now to Figs. 2A and 2B, there is provided a laser system 200, preferably including an OPA CBC laser 202 operative to provide a dynamic laser beam output. Laser system 200 may be a particularly preferred embodiment of laser system 100. OPA CBC laser 202 preferably outputs a multiplicity of laser sub-beams, which multiplicity of laser sub-beams are combined in the far-field to form a combined beam. The shape and / or position of the combined beam may be dynamically varied at least by phase control functionality incorporated in OPA CBC laser 202, as is detailed henceforth below, in order to perform welding of curved and / or extensive surfaces.

[0169] As seen in Fig. 2A, OPA CBC laser 202 may include laser components 204, sub-beam alignment optics 206 and focusing optics 208. Laser components 204 may be operative to provide a multiplicity of laser sub-beams to sub-beam alignment optics 206. Sub-beam alignment optics 206 may be functional to align the multiplicity of individual laser sub-beams relative to each other. Sub-beam alignment optics 206 are particularly preferably, although not necessarily, housed (located or positioned) in an OH separate from the body of laser components 204. Focusing optics 208 are preferably functional to focus the laser sub-beams, following alignment thereof by laser sub-beam alignment optics 206, for example on a workpiece 210 for welding thereof. Focusing optics 208 are preferably housed (located or positioned) in a welding head, separately from sub-beam alignment optics 206 and laser components 204. Focusing optics 208 may alternatively be arranged in alternative configurations or enclosures, rather than housed in a welding head.

[0170] Optics 206 and 208 may include transmissive and / or reflective optical components, such as one or more lenses, mirrors, beamsplitters and / or other optical components.

[0171] Optics 206, optics 208 or a combination thereof may be moveable with respect to each other, to workpiece 210 and / or other components 204 (such as heavier, larger components) of the laser 202. The multiplicity of sub-beams provided by laser components 204 to sub-beam alignment optics 206 may propagate through free-space or may be conveyed to optics 206 via a bundle of optical fibers 212. The aligned sub-beams output by optics 206 may propagate through free-space to a welding head housing focusing optics 208, whereat and whereby the sub-beams are focused on workpiece 210. In some cases, the welding head housing focusing optics 208 may be distant from the OH housing alignment optics 206, for example by tens of meters, a hundred meters or more.

[0172] Various possible arrangements of OPA CBC laser 202 are detailed herein, with respect to Figs. 2B - 12A. It is understood, however, that these arrangements are provided by way of example only and that other arrangements, in which components of OPA CBC laser 202 are differently arranged (for example, separated or divided or housed) are also possible.

[0173] The combined laser output provided by OPA CBC laser 202 typically has noise. The noise in the combined laser output may be due to mechanical, thermal, intensity, amplification or other effects within system 200. Herein, noise (for example, phase noise) may refer to any variation from a predetermined or desired phase, regardless of whether such noise changes over time or is constant over time. Noise may be caused by mechanical movement, mechanical stress, thermal effects for example causing thermal focus shift, amplification noise, intensity noise or other effects in the optical elements (for example, lenses, mirrors, windows, beam splitters, phase plates, polarization elements, fibers etc.), effects in the mechanical elements holding the optics and effects in the air or space between the optical elements. Noise may also or alternatively be caused by manufacturing imperfections in the optical or mechanical elements or in the assembly thereof. The noise may also or alternatively be caused by the operation of the laser itself, such as by the heat created by the high-power laser beams, and / or may be amplification noise created by non-linear effects or noise in the electronics; as well as external effects such as acoustic noise, vibrations, wind, temperature variations of the surroundings and so on.

[0174] Optics 206 and 208 may contribute to noise in the combined laser output, for example, but not limited to, due to heating of optics 206 and 208, by the high-power laser beams, during operation of OPA CBC laser 202. Such heating may distort optical elements of optics 206 and 208 and may create thermal focus shift effects. Thermal distortions of optics 206 and 208 may create (for example, generate or cause) noise in the combined laser output. Additionally or alternatively, optics 206 and 208 may create noise in the combined laser output due to distortions thereof arising from other causes, for example physical defects or misalignment.

[0175] Furthermore, in the case that OPA CBC laser 202 includes an OH connected to the other laser components (e.g. the main laser body 204) by optical fiber bundle 212, the optical fibers 212 may also create phase noise in the combined laser output. This is particularly so in embodiments in which the OH (e.g. optics 206 in the OH) is moved with respect to the other laser components (e.g. other laser components 204), wherein movement of the optical fiber bundle 212 may create phase noise in the combined laser output.

[0176] Noise in the combined laser output provided by OPA CBC laser 202 may be detected by at least one detector, here shown to be embodied, by way of example, as a single detector 220. Preferably, a portion of the combined laser output may be made incident upon detector 220. Detector 220 is preferably operative to sense noise in the laser output incident thereupon. The operation of laser component 204 may be adjusted based on noise sensed by detector 220, as indicated by a feedback arrow 222. More specifically, a noise detection phase correction may be applied to the laser output based on the noise in the laser output, as detected by detector 220.

[0177] It is a particular feature of a preferred embodiment of the present invention that detector 220 is preferably downstream of alignment optics 206 and focusing optics 208, such that detector 220 is preferably operative to sense noise in the combined laser output including noise arising from alignment optics 206 and focusing optics 208 (for example, optical thermal distortions due to optics 206 and 208, such as thermal focus shift). The noise detection phase correction, applied based on the noise detected by detector 220, may then be operative to take this noise into account and hence to apply an appropriate correction to the laser output, including correction for noise arising from alignment optics 206 and focusing optics 208. It is appreciated that should detector 220 be positioned upstream from some or all of alignment optics 206 and focusing optics 208, phase noise in the laser output caused by the laser output propagating through alignment optics 206 and focusing optics 208 would not be sensed, or would be only partially sensed, by detector 220 and hence would not be corrected for, or would be only partially corrected for, based on the feedback 222 provided by detector 220 to laser components 204.

[0178] In some embodiments, detector 220 may be located downstream of the entirety (for example, all) of alignment optics 206 and focusing optics 208. In other embodiment, detector 220 may be located downstream of a significant portion but not necessarily all of alignment optics 206 and focusing optics 208, such that detector 220 is operative to sense phase noise in the combined laser output arising from a significant portion, although not necessarily all, of alignment optics 206 and focusing optics 208.

[0179] The arrows in the block diagram of Fig. 2A thus may be understood to show a progression of the laser output through system 200 in a sense of sequence and direction of travel. It is understood that the arrows indicate progression of the laser output in a highly simplified manner, to aid appreciation of the downstream location of detector 220 with respect to other elements of OPA CBC laser 202. Furthermore, it is understood that although detector 220 is shown as a separate element with respect to laser components 204 and alignment optics 206 and focusing optics 208, detector 220 may be integrated with other components of OPA CBC laser 102, for example included in a welding head also housing focusing optics 208. It is appreciated that the feedback 222 from detector 220 to laser components 204 is indicated by a dashed line, in order to distinguish feedback 222 from the other arrows in the block diagram of Fig. 2A indicating the progression of the laser beams through system 200.

[0180] Furthermore, in the case that OPA CBC laser 202 includes an OH (for example, housing alignment optics 206) connected to laser components 204 by optical fibers 212, detector 220 is preferably located downstream of the bundle of optical fibers 212. Noise in the combined laser output due to the bundle of optical fibers, for example caused by motion thereof, is thus also sensed by detector 220 and may be corrected for by a phase noise correction.

[0181] This arrangement of detector 220 with respect to alignment optics 206 and focusing optics 208 has been found to be particularly advantageous in providing noise correction of the combined laser beam, including noise correction for optical thermal aberrations (for example due to thermal focus shift of optics 206 and 208 and noise arising from optical fibers connecting the OH to other laser components 204), even during high- power operation of laser system 200. OPA CBC laser 202 is preferably a single mode laser operating at high power. Particularly preferably, OPA CBC laser 202 may operate in a power range of several watts to several hundred kilowatts, and even more preferably a power range of 10W - 400kW. Laser system 200 is thus well-suited for stable, distortion-free operation for a variety of high-power applications, particularly for high- power laser welding of curved substrates, such as workpiece 210, as is further detailed henceforth with reference to Fig. 2B.

[0182] Turning now to Fig. 2B, a preferred embodiment of laser system 200 is shown. OPA CBC laser 202 may include a seed laser 230 and a laser beam splitting and combining subsystem 232. Splitting and combining subsystem 232 preferably receives an output laser beam from seed laser 230 and splits the output laser beam into a plurality of sub-beams along a corresponding plurality of channels 234. Here, by way of example only, an output from seed laser 230 is shown to be split into four sub-beams along four channels 234 although it is appreciated that splitting and combining subsystem 232 typically may include a far greater number of channels, typically arranged in a three- dimensional matrix, along which the output of seed laser 230 is split. By way of example, splitting and combining subsystem 232 may include 32 or more channels arranged in a three-dimensional matrix. The four channels 234 shown in Fig. 2B thus may be considered to illustrate a side-view of a three-dimensional matrix of channels.

[0183] The relative phase of each sub-beam may be individually modulated by a phase modulator 240, preferably located along each of channels 234. Phase modulators 240 are preferably electro-optical phase modulators, each operative to modify a phase of the sub-beam passing therethrough. Phase modulated sub-beams produced by the splitting and subsequent phase modulation of the output of seed laser 230 are preferably mutually relatively aligned by sub-beam alignment optics 242, here shown to comprise a plurality of collimating lenses 242. Preferably, each phase modulated sub-beam propagates towards a corresponding collimating lens. The individually collimated, phase modulated sub-beams are subsequently combined and focused by focusing optics 246, here embodied by way of example as a focal lens 246, to form a combined beam 248.

[0184] Splitting and combining subsystem 232 may also provide laser amplification of the sub-beams, preferably following the splitting of the output beam of seed laser 230 into sub-beams and prior to the combining of the sub-beams to form combined beam 248. Here, by way of example, splitting and combining subsystem 232 is shown to include a plurality of optical amplifiers 250 located along corresponding ones of channels 234 for amplifying each sub-beam. It is appreciated, however, that such amplification is optional and may be omitted, depending on the power output requirements of laser 202. Sub-beams may be delivered, following optional amplification thereof by optical amplifiers 250, to sub-beam alignment optics 242, by a corresponding plurality of optical fibers 252. The sub-beams may propagate through free space from sub-beam alignment optics 242 to focusing optics 246.

[0185] It is a particular feature of a preferred embodiment of the present invention that focusing optics 246 may be located at a physically large distance from sub-beam alignment optics 242. For example, focusing optics may be located at a distance of up to about 100m from sub-beam alignment optics 242 or even at a distance of greater than 100m. The plurality of sub-beams preferably propagates through free space over the distance between sub-beam alignment optics 242 and focusing optics 246.

[0186] The phase of combined beam 248, and hence the position and shape of the far-field intensity output pattern thereof, is controlled, at least in part, by the relative phases of the constituent sub-beams combined to form beam 248. In laser welding it is desirable to dynamically move and shape the far-field intensity pattern of the output beam. This may be achieved in laser system 200 by laser splitting and combining subsystem 232 dynamically varying the relative phases of the individual sub-beams and thereby varying the phase of the combined laser output 248 so as dynamically to control the position and shape of the far-field intensity pattern thereof.

[0187] The relative phases of the sub-beams are preferably predetermined in accordance with a desired laser output pattern, for example for the welding of workpiece 210. Particularly preferably, the varying relative phases are applied by a spatial modification curvature compensation phase control subsystem 260. Spatial modification curvature compensation phase control subsystem 260 preferably forms a part of a control electronics module 262 in OPA laser 202 and preferably controls each phase modulator 240 so as to dynamically modulate the relative phases of the sub-beams along channels 234 so as to produce a dynamically varying laser output pattern. Particularly preferably, spatial modification curvature compensation phase control subsystem 260 is operative to continuously dynamically modulate phases of the individual sub-beams comprising the combined laser output 248 so as to compensate for variation of at least one of the angle of incidence of the laser output with respect to curved workpiece 210 and a distance between laser 202 and curved workpiece 210, in a manner detailed henceforth.

[0188] Seed laser 230, possibly in combination with other components such as amplifiers 250, may be a preferred embodiment of laser components 204 (Fig. 2A). Subbeam alignment optics 242 may be a preferred embodiment of sub-beam alignment optics 206 (Fig. 2A) and focusing optics 246 may be a preferred embodiment of focusing optics 208 (Fig. 2A). Sub-beam alignment optics 242 are preferably housed (located) in an OH forming a part of OPA CBC laser 202. Focusing optics 246 are preferably housed (located) in a welding head, which welding head may be separate from both the OH and other components 104 of laser 202. The OH housing sub-beam alignment optics 206 may be connected to other components of the laser 204 by the plurality of optical fibers 252 through which the multiplicity of laser sub-beams may travel. Plurality of optical fibers 252 may be a preferred embodiment of optical fiber bundle 212 (Fig. 2A).

[0189] Optics 242 and 246 may be subject to thermal distortions due to heating by the sub-beams of OPA CBC laser 202 during operation thereof, thereby causing distortion (for example, creating phase noise) of the laser output. Furthermore, movement of the optical fibers 252 connecting the OH to other laser components 204 may create phase noise. Distortions arising from optical elements in laser 202 (for example, phase noise) contribute to noise in combined beam 248. Noise in combined beam 248 may additionally be created by other thermal or mechanical effects and / or by the amplification process in the case that optical amplifiers 250 are present in OPA system 200.

[0190] In order to cancel out noise in the laser output of system 200, system 200 preferably includes a noise cancellation phase variation subsystem 264. Noise cancellation phase variation subsystem 264 is preferably operative to provide a noise cancellation phase correction output in order to cancel out the noise in combined beam 248.

[0191] Particularly preferably, noise cancellation phase variation subsystem 264 employs an algorithm to sense and correct phase noise in the combined laser output. The noise cancellation phase correction output is preferably provided by noise cancellation phase variation subsystem 264 to phase modulators 240 so as to correct phase noise in combined beam 248 and thus avoid distortion of the shape and position of the far field intensity output pattern of combined beam 248 that would otherwise be caused by the noise. Noise cancellation phase variation subsystem 264 may be included in control electronics module 262.

[0192] In order to facilitate application of phase variation and noise correction to combined beam 248, a portion of the output of OPA laser 202 is preferably extracted and directed towards at least one detector 220. Detector 220 may be embodied as a single detector, as illustrated in Fig. 2B, or may alternatively be embodied as multiple detectors. The extracted portion of the output beam preferably functions as a reference beam, based on characteristics of which the required noise correction and / or phase variation may be calculated. In the embodiment shown in Fig. 2B, combined beam 248 is directed towards a beam splitter 270. Beam splitter 270 preferably splits combined beam 248 into a reflected portion 272 and a transmitted portion 274 in accordance with a predetermined ratio. For example, beam splitter 270 may split each sub-beam with a 99.9% reflected: 0.01% transmitted ratio.

[0193] The reflected portion 272 of the sub-beams preferably forms a combined output beam 278 having a far-field intensity pattern 280 incident upon workpiece 210. The transmitted portion 274 of the sub-beams is preferably transmitted to form an output reference beam 282 having a far-field intensity pattern 284 incident on a surface of detector 220.

[0194] As described hereinabove, the shape and position of the far-field intensity pattern 280 of the output beam 272, 278 and correspondingly of the far-field intensity pattern 284 of the reference beam 274, 282 are constantly changing, due to the ongoing variation of the relative phases of the sub-beams, as applied by phase modulators 240 controlled by spatial modification curvature compensation phase control subsystem 260. As a result, the far-field intensity pattern 284 of the reference beam 282 is not fixed upon detector 220 but rather is constantly being moved around with respect to detector 220 depending on the combined relative phases of the constituent sub-beams. However, in order for detector 220 to sense noise in reference beam 282 and thus provide the required feedback to noise cancellation phase variation subsystem 264, the far-field intensity pattern 284 of reference beam 282 must be incident upon detector 220 in order for detector to measure the intensity and thereby noise of the far-field intensity pattern, seemingly requiring a fixed output beam.

[0195] The conflict between the dynamic nature of far-field intensity pattern due to the phase-variation thereof and the fixed nature required of the far-field intensity pattern of reference beam 282 in order to derive and ultimately apply noise correction thereto, is preferably resolved in a preferred embodiment of the present invention by providing the noise cancellation phase variation and spatial modification phase variation at mutually different times and rates.

[0196] The noise cancellation phase correction output is provided based on taking into consideration noise measured at detector 220 at a noise sampling rate. The output beam 248 is controlled in such a way that the far-field intensity pattern 284 of reference beam 282 is incident upon detector 220 during the course of the dynamic changes to the shape and position of the output and reference beams at a rate that is equal to or higher than the required noise sampling rate. The noise in reference beam 282 is taken into consideration during those intermittent times at which the far-field intensity pattern is returned to detector 220. Noise cancellation phase variation subsystem 264 is operative to receive an output from detector 220 indicative of noise in reference beam 282 and apply a noise cancellation phase variation to phase modulators 240 based thereon at intermittent times.

[0197] At time interstices between the intermittent times at which the far-field intensity pattern of reference beam 282 is incident upon detector 220 and a noise cancellation phase variation applied to phase modulators 240 by noise cancellation phase variation subsystem 264, the phase of the combined output beams 248 and hence reference beam 282 is continuously varied under the control of spatial modification curvature compensation phase variation subsystem 260, in order to dynamically change the shape and position of the far-field intensity pattern 280 thereof as required, for example to perform laser welding of workpiece 110. The combined laser output is varied, by spatial modification curvature compensation phase variation subsystem 260, at a phase varying rate which exceeds the noise sampling rate, in order to rapidly change the phase and hence shape and position of the far-field intensity pattern. By way of example, the noise sampling rate may be of the order of 10 - 1000 Hz whereas the phase varying rate may be greater than 10,000 Hz. Further details pertaining to particular exemplary algorithms useful for performing spatial modification phase variation and noise cancellation phase variation in the present invention, are described in WO2019 / 092702, the entirety of which is incorporated herein by reference.

[0198] The second phase variation to produce noise cancellation is preferably provided, by noise cancellation phase variation subsystem 264, during the course of the first phase variation for spatial modulation of the combined output beam 278, provided by spatial modification curvature compensation phase variation subsystem 260, without needing to significantly pause or disrupt the desired laser output pattern created and controlled by the first phase variation. It is appreciated that spatial modification curvature compensation phase variation subsystem 260 and noise cancellation phase variation subsystem 264 preferably have separate functionalities and hence are shown herein for clarity as separate modules, but may be implemented in the same (for example, common) physical components within control electronics 262.

[0199] Detector 220 is preferably operative to detect noise in the laser output incident thereupon, including noise arising from optical elements upstream from detector 220, such as optics 242 and 246. It is understood that the particular structure and configuration of beam splitting and recombining elements shown herein, including beam splitter 270, sub-beam alignment optics 242 and focusing optics 246, is exemplary only and depicted in a highly simplified form. It is appreciated that OPA laser system 200 may include a variety of such elements, as well as additional optical elements, including, by way of example only, additional or alternative lenses, optical fibers and coherent free- space far-field combiners. Preferably, most and even more preferably all of such additional optical elements are located upstream of detector 220, such that detector 220 is preferably operative to detect phase noise in the combined laser output generated by (arising from) such optical elements.

[0200] It is appreciated that should only some, but not all, of the optical elements be located upstream from detector 220, then detector 220 would not be capable of sensing noise in the combined laser output generated by that portion of the optics located downstream of detector 220 and the far field intensity pattern 280 of the combined laser output 248 would be degraded by noise which would not be corrected for by noise correction phase variation module 264. By way of example, should beam-alignment optics 242 be located upstream from detector 220 but focusing optics 246 be located downstream from detector 220, detector 220 would not detect noise in combined laser output 248 generated by focusing optics 246, for example due to thermal focus shift of focusing optics 246, and thus the far field intensity pattern of combined laser output 278 would be degraded by noise arising from focusing optics 246 and be of poorer quality. For example, a thermal focus shift of focusing optics 246 may cause output beam 278 to shift by several mm or tens of mm from a desired position thereof. Should focusing optics 246 be located downstream from detector 220, such a shift in output beam 278 would not be detected by detector 220 and hence would remain uncorrected.

[0201] The Power in the Bucket (PIB) metric may be used to define beam quality. Deterioration in beam quality, due to noise and including thermal focus shift-related deterioration, may be quantified as the measured PIB. The measured PIB expresses how much energy is delivered by the beam to the desired location on the workpiece, compared to the energy delivery to the desired location by an ideal beam. Locating all of the optical elements of the laser of the present invention upstream from the detector, such that noise arising from the optical elements including thermal focus shift-related noise caused by focusing optics 246 is detected and hence corrected for, may result in an improvement in the PIB of the combined output beam of several percent, such as 10%, 20%, 30% or more.

[0202] Detector 220 may include additional optics as required to optimize the sensing of the noise (for example, phase noise). For example, additional optics for detector 220 may be located between detector 220 and beam splitter 270. Such optics may, for example, be operative to focus the combined output on the detector at a mechanical distance from beam splitter 270 that is different from the mechanical distance between beam splitter 270 and workpiece 210. For example, the mechanical distance from beam splitter 270 to detector 220 may be shorter than the mechanical distance from beam splitter 270 to workpiece 210, which may be helpful in minimizing the physical dimensions of system 200. Since the optics in the detector are not subject to high-power, due to only a small portion of the total output being directed towards detector 220, the optics in the detector may be formed by a variety of optical elements without being subject to thermal focusing or thermal distortion effects. For example, optics for detector 220 may have a confocal arrangement that allows a long effective focal length with a short back focal length, as is detailed henceforth with reference to Figs. 7A - 8E.

[0203] As a result of the single-mode nature of the laser output, the laser output is highly sensitive to distortions. Distortions in the laser output may be corrected, in part, by the application, via phase modulators 240 controlled by noise cancellation phase variation subsystem 264, of a phase variation for noise cancellation. Distortions may further be minimized by careful construction and maintenance of laser system 200. Various exemplary features of laser system 200, which features preferably serve to minimize distortion of the single-mode output provided thereby, are listed below:

[0204] • Due to the single-mode nature of the laser output, the laser output must be transmitted in a very narrow optical fiber. This results in a high power-density in the fiber, leading to non-linear effects. In order to minimize such non-linear effects, the laser output in the present invention may be transmitted over relatively large distances through free space, rather than within optical fibers, for example between sub-beam alignment optics 242 and focusing optics 246.

[0205] • Due to the single mode high power nature of the laser output, the laser output is very sensitive to distortions caused by optical elements in laser system 200. Optical elements in laser system 200, such as lenses, mirrors and beamsplitters, are therefore preferably formed by pure fused silica glass which creates a minimum amount of distortion. There is therefore no variation in glass type in the optics (for example, optics 242 and 246, beam splitter 270) of system 200 and correspondingly no variation in refractive indices of different ones of the optical elements. Differences in refractive indices therefore cannot be used in lens design, making lens design more limited and hence more difficult.

[0206] • In some applications, the focal length of focusing optics 246 may be several meters long whereas the working distance between focusing optics 246 and workpiece 210 may be less than 1 meter long. As a result, the beam diameter on the downstream elements of optics 246 may be a few millimeters only. This small diameter combined with the high power of the laser, may result in high power density on these downstream optical elements which may result in distortion. In the present invention, most and preferably all optical elements including focusing optics 246 are located upstream of detector 220, such that any distortions may be sensed by detector and hence corrected for by phase control functionality included in control module 262.

[0207] The dynamic laser output of OPA CBC laser 202, as spatially controlled by the first phase variation and noise-corrected by the second variation, has been found to be particularly well suited for laser welding of contoured workpieces, wherein the contoured surface of the workpiece causes variation, across a surface of the workpiece, of at least one of an angle of incidence of the laser output with respect to the surface and a distance between the focusing optics 246 and the surface. For example, in the case of workpiece 210 including a plurality of curved ridges 290, both an angle of incidence of the laser output 278 with respect to the surface of workpiece 210 and a distance between focusing optics 246 and the surface of workpiece 210, vary over the surface of workpiece 210. As is well known in the art, this variation in angle of incidence and distance would tend to cause a variation in parameters of the weld produced by laser 202 over the surface of workpiece 210. In many welding applications, it is desirable to maintain a constant or near-constant weld profile over the welded surface, notwithstanding irregularities in the contours of the surface.

[0208] In accordance with a preferred embodiment of the present invention, a shape of output beam 278 is varied with the varying angle of incidence and distance to the surface of workpiece 210, as far-field intensity pattern 280 of output beam 278 is moved across the surface of workpiece 210, in order to maintain a constant or nearconstant weld profile over the welded surface. More specifically, spatial modification curvature compensation phase control subsystem 260 is preferably operative to vary the phase of the laser output, by controlling operation of phase modulators 240 on the individual sub-beams comprising the combined laser output, so as to move the laser output over surface 210. Spatial modification curvature compensation phase control subsystem 260 is further operative to dynamically control the shape of the laser output, as the laser output is moved over the surface of workpiece 210, to maintain a constant weld profile across each point of the surface. Moreover, spatial modification curvature compensation phase control subsystem 260 is preferably operative to vary the phase of the laser output, by controlling operation of phase modulators 240 on the individual subbeams comprising the combined laser output, to deliver a generally constant energy, by the laser output, at each point across the surface of workpiece 210. Variation in angle of incidence of the laser output on the curved surface, and hence variation in power density delivery during welding of the curved surface as well as the resulting variation of the effective thickness required to be welded and other properties effected by the incident angle, are preferably compensated for by control of the shape and position of the laser output.

[0209] Various exemplary shapes of a combined laser output which may be made incident upon curved workpiece 210 are detailed henceforth with reference to Figs. 12C, 12E, 12G and 121. One or more of these shapes, or other shapes, may provide optimum welding at various locations on workpiece 210. By adjusting the first spatial modification phase variation during welding, the laser output shape may be adjusted accordingly, in an uninterrupted manner, during the course of welding and in accordance with the geometry of workpiece 210. Furthermore, by adjusting the second noise correction phase variation, noise in the laser output may be cancelled, such that a desired laser output shape is maintained in a non-degraded manner.

[0210] Different combined beam shapes may be achieved by phase variation of the various sub-beams, under the control of spatial modification curvature compensation phase variation subsystem 260, thereby changing the combined beam shape in the far field. The beam shape may be adjusted without necessarily changing the beam position. Additionally or alternatively, a position of the combined output beam may be moved, by phase variation of the constituent sub-beams, by phase modulators 240. The position of the combined output beam 278 may be changed in an arbitrary manner and at any arbitrary speed or may be changed in accordance with a predetermined desired pattern, for example based on a priori knowledge of a surface geometry of workpiece 210 and / or a desired weld pattern. Movement of the beam may generate trajectories of varying shapes and at various speeds. The various different beam shapes and beam trajectories, in combination with the varying speed of movement of the beam, may be controlled so as to control temperature distribution in space and time over the welded area. In addition, variation of the beam parameters such as one or more of beam shape, beam trajectory and beam speed, allows control of flow of molten material in the melt pool of the welded area. These controls in turn provide means to adjust various parameters of the weld such as solidification rate, stability of the weld process, geometry of the weld, spatter formation, crack formation, porosity, humping and / or other properties. The laser output may thus be optimized for changes in angle of incidence between the laser and workpiece 210, and for changes in the distance between the welding head housing focusing optics 246 and workpiece 210, by changing phases of the laser output and thus parameters thereof. These phase changes may be implemented rapidly during welding as required. This avoids the need for changing beam parameters during welding using mechanical or optical elements, or for mechanically changing the height and position of the laser to follow changes in workpiece 210 during welding, which would otherwise be required. Rather, laser system 200 may remain at a fixed height with respect to workpiece 210 and variations in workpiece 210, such as curvature, be compensated for by phase variation.

[0211] Focusing optics 246 may comprise at least one lens having a large focal length and large depth of focus. As a result, even in the case of an uneven workpiece 210 exhibiting variations in surface height or having individual features thereon on varying heights, workpiece 210 may remain within the borders of the depth of focus of CBC laser 202. Furthermore, the focus of the laser output on workpiece 210 may be rapidly electrooptically adapted by phase control of the output beam. Possible focal lengths may range from about 1 meter up to about 6 meters or more. The depth of focus may range from several millimeters up to many tens of millimeters or more. The electrooptical adaptation may increase the effective depth of focus by a factor ranging from x 1,5 to more than x3.

[0212] It will be appreciated that the provision of a high-power laser operating in single-mode is highly advantageous and differs from conventional single-mode lasers which are typically low-power. The single-mode output of OPA CBC laser 202 provides many advantages, including extremely precise welding, very high power density, the ability to weld from a distance of several meters or more and large depth of focus. For example, the laser spot of the combined laser beam 278 of system 200 may be of a size of 10 microns to greater than 500 microns.

[0213] Furthermore, the single-mode nature of the laser output of laser 202 means that the laser output may travel over long distances without significant beam divergence, such that a precise weld may be produced by a laser located relatively distant from the workpiece 210. In some embodiments, the single mode sub-beams may travel in free space for 100m or more and then be focused onto the work piece 210 to be welded. For example, the sub-beams originating from seed laser 230 and aligned by sub-beam alignment optics 242 (for example, in an OH) may subsequently travel in free space over a distance of more than 100 m, to a welding head holding focusing optics 246 and subsequently be focused, by focusing optics 246 in the welding head, upon workpiece 210 for performing welding thereof.

[0214] The ability to transmit the laser beams over large distances in free space, without significant divergence of the beams, may be particularly advantageous when welding very large regions. For example, panels of Liquid Natural Gas (LNG) tanks may have dimensions, in one example, of approximately 40m x 40 m x 40m or in another example of up to approximately 200m x 200m x 200m. In operation of laser system 200 during welding of extensive surfaces, such as LNG tanks, the laser system may be located in one position and the aligned sub-beams transmitted from beam alignment optics 242, through free space, over tens or even hundreds of meters, to focusing optics 246, for example in a welding head. The welding head may be easily moveable around the surface to be welded, such as a surface of an LNG tank, thus avoiding the need for moving the entire cumbersome laser with its associated parts (for example, laser components 204 including seed laser 230) around the extensive surface during welding.

[0215] It is appreciated that although the welding of extensive surfaces, such as panels of an LNG tank, is described with reference to Fig. 2B in the context of welding of a contoured surface of curved workpiece 210, the welding of extensive surfaces may be performed by system 200 for surfaces which are not necessarily curved, such as flat panels. In such a case, the curvature compensation functionality of spatial modification curvature compensation phase variation subsystem 260 may be obviated, since curvature compensation may not be required.

[0216] In conventional laser systems in which the laser output is directed to a distant substrate, it is typically challenging to precisely control the position of the output beam on the substrate. In contrast, in the present invention, the position of the output beam on workpiece 210 may be precisely controlled by a combination of the first phase variation for spatial modulation, provided by of spatial modification curvature compensation phase variation subsystem 260; focusing optics 246 used for focusing the laser beam on the workpiece; and optionally also mechanical motion of the welding head and / or galvo-scanner in which focusing optics 246 may be housed. Mechanical motion provided by a welding head and / or galvo-scanner may complement beam motion due to phase variation. It understood, however, that in some embodiments of the present invention the laser output may be dynamically spatially modified without involving any moving parts, by way of phase variation only.

[0217] A particularly preferred embodiment of system 200, adapted for laser butt welding of relatively wide gaps, is shown in Figs. 3 A and 3B. Turning now to Figs. 3 A and 3B, there is provided a laser system 300, preferably including an OPA CBC laser 302 operative to provide a dynamic laser beam output. Laser system 300 may be a particularly preferred embodiment of laser system 200. OPA CBC laser 302 preferably outputs a multiplicity of laser sub-beams, which multiplicity of laser sub-beams are combined in the far-field to form a combined beam. The shape and / or position of the combined beam may be dynamically varied at least by phase control functionality incorporated in OPA CBC laser 302, as is detailed henceforth below, in order to perform butt welding across relatively wide gaps, such as gaps of about 1mm or more.

[0218] As seen in Fig. 3A, OPA CBC laser 302 may include laser components 304, sub-beam alignment optics 306 and focusing optics 308. Laser components 304 may be operative to provide a multiplicity of laser sub-beams to sub-beam alignment optics 306. Sub-beam alignment optics 306 may be functional to align the multiplicity of individual laser sub-beams relative to each other. Sub-beam alignment optics 306 are particularly preferably, although not necessarily, housed (located or positioned) in an OH separate from the body of laser components 304. Focusing optics 308 are preferably functional to focus the laser sub-beams, following alignment thereof by laser sub-beam alignment optics 306, for example on a workpiece 310 for butt welding thereof. Focusing optics 308 may be housed (located or positioned) in a welding head, separately from subbeam alignment optics 306 and laser components 304. Focusing optics 308 may alternatively be arranged in alternative configurations or enclosures, rather than housed in a welding head.

[0219] Preferably, workpiece 310 includes a first piece or segment 310A and a second piece or segment 310B, separated by a gap 311. Preferably, first and second pieces 310A and 310B are co-planar. Gap 311 between first and second pieces 310A and 310B may have a width of 1mm or more, such as a width of 1mm or 2mm or between 1mm - 2mm or more. It is a particular feature of a preferred embodiment of the present invention that laser 302 is capable of performing butt welding across gap 311 between first and second pieces 310A and 310B, over a gap width of 1mm or more.

[0220] Optics 306 and 308 may include transmissive and / or reflective optical components, such as one or more lenses, mirrors, beamsplitters and / or other optical components.

[0221] Optics 306, optics 308 or a combination thereof, may be moveable with respect to each other, to workpiece 310 and / or other components 304 (such as heavier, larger components) of the laser 302. The multiplicity of sub-beams provided by laser components 304 to sub-beam alignment optics 306 may propagate through free-space or may be conveyed to optics 306 via a bundle of optical fibers 312. The aligned sub-beams output by optics 306 may propagate through free-space to a welding head housing focusing optics 308, whereat and whereby the sub-beams are focused on workpiece 310. In some cases, the welding head housing focusing optics 308 may be distant from the OH housing alignment optics 306, for example by tens of meters, a hundred meters or more.

[0222] Various possible arrangements of OPA CBC laser 302 are detailed herein, with respect to Figs. 3B - 12A. It is understood, however, that these arrangements are provided by way of example only and that other arrangements, in which components of OPA CBC laser 302 are differently arranged (for example, separated or divided or housed) are also possible.

[0223] The combined laser output provided by OPA CBC laser 302 typically has noise. The noise in the combined laser output may be due to mechanical, thermal, intensity, amplification or other effects within system 300. Herein, noise (for example, phase noise) may refer to any variation from a predetermined or desired phase, regardless of whether such noise changes over time or is constant over time. Noise may be caused by mechanical movement, mechanical stress, thermal effects for example causing thermal focus shift, amplification noise, intensity noise or other effects in the optical elements (for example, lenses, mirrors, windows, beam splitters, phase plates, polarization elements, fibers etc.), effects in the mechanical elements holding the optics and effects in the air or space between the optical elements. Noise may also or alternatively be caused by manufacturing imperfections in the optical or mechanical elements or in the assembly thereof. The noise may also or alternatively be caused by the operation of the laser itself, such as by the heat created by the high-power laser beams, and / or may be amplification noise created by non-linear effects or noise in the electronics; as well as external effects such as acoustic noise, vibrations, wind, temperature variations of the surroundings and so on.

[0224] Optics 306 and 308 may contribute to noise in the combined laser output, for example, but not limited to, due to heating of optics 306 and 308, by the high-power laser beams, during operation of OPA CBC laser 302. Such heating may distort optical elements of optics 306 and 308 and may create thermal focus shift effects. Thermal distortions of optics 306 and 308 may create (for example, generate or cause) noise in the combined laser output. Additionally or alternatively, optics 306 and 308 may create noise in the combined laser output due to distortions thereof arising from other causes, for example physical defects or misalignment.

[0225] Furthermore, in the case that OPA CBC laser 302 includes an OH connected to the other laser components (e.g. the main laser body 304) by optical fiber bundle 312, the optical fibers 312 may also create phase noise in the combined laser output. This is particularly so in embodiments in which the OH (e.g. beam alignment optics 306 in the OH) is moved with respect to the other laser components (e.g. other laser components 304), wherein movement of the optical fiber bundle 312 may create phase noise in the combined laser output.

[0226] Noise in the combined laser output provided by OPA CBC laser 302 may be detected by at least one detector, here shown to be embodied, by way of example, as a single detector 320. Preferably, a portion of the combined laser output may be made incident upon detector 320. Detector 320 is preferably operative to sense noise in the laser output incident thereupon. The operation of laser component 304 may be adjusted based on noise sensed by detector 320, as indicated by a feedback arrow 322. More specifically, a noise detection phase correction may be applied to the laser output based on the noise in the laser output, as detected by detector 320.

[0227] It is a particular feature of a preferred embodiment of the present invention that detector 320 is preferably downstream of sub-beam alignment optics 306 and focusing optics 308, such that detector 320 is preferably operative to sense noise in the combined laser output including noise arising from sub-beam alignment optics 306 and focusing optics 308 (for example, optical thermal distortions due to optics 306 and 308, such as thermal focus shift). The noise detection phase correction, applied based on the noise detected by detector 320, may then be operative to take this noise into account and hence to apply an appropriate correction to the laser output, including correction for noise arising from sub-beam alignment optics 306 and focusing optics 308. It is appreciated that should detector 320 be positioned upstream from some or all of alignment optics 306 and focusing optics 308, phase noise in the laser output caused by the laser output propagating through alignment optics 306 and focusing optics 308 would not be sensed, or would be only partially sensed, by detector 320 and hence would not be corrected for, or would be only partially corrected for, based on the feedback 322 provided by detector 320 to laser components 304.

[0228] In some embodiments, detector 320 may be located downstream of the entirety (for example, all) of alignment optics 306 and focusing optics 308. In other embodiment, detector 320 may be located downstream of a significant portion but not necessarily all of alignment optics 306 and focusing optics 308, such that detector 320 is operative to sense phase noise in the combined laser output arising from a significant portion, although not necessarily all, of alignment optics 306 and focusing optics 308.

[0229] The arrows in the block diagram of Fig. 3A thus may be understood to show a progression of the laser output through system 300 in a sense of sequence and direction of travel. It is understood that the arrows indicate progression of the laser output in a highly simplified manner, to aid appreciation of the downstream location of detector 320 with respect to other elements of OPA CBC laser 302. Furthermore, it is understood that although detector 320 is shown as a separate element with respect to laser components 304 and alignment optics 306 and focusing optics 308, detector 320 may be integrated with other components of OPA CBC laser 302, for example included in a welding head also housing focusing optics 308. It is appreciated that the feedback 322 from detector 320 to laser components 304 is indicated by a dashed line, in order to distinguish feedback 322 from the other arrows in the block diagram of Fig. 3A indicating the progression of the laser beams through system 300.

[0230] Furthermore, in the case that OPA CBC laser 302 includes an OH (for example, housing beam alignment optics 306) connected to laser components 304 by optical fibers 312, detector 320 is preferably located downstream of the bundle of optical fibers 312. Noise in the combined laser output due to the bundle of optical fibers, for example caused by motion thereof, is thus also sensed by detector 320 and may be corrected for by a phase noise correction.

[0231] This arrangement of detector 320 with respect to alignment optics 306 and focusing optics 308 has been found to be particularly advantageous in providing noise correction of the combined laser beam, including noise correction for optical thermal aberrations (for example due to thermal focus shift of optics 306 and 308 and noise arising from optical fibers connecting the OH to other laser components 304), even during high- power operation of laser system 300. OPA CBC laser 302 is preferably a single mode laser operating at high power. Particularly preferably, OPA CBC laser 302 may operate in a power range of several watts to several hundred kilowatts, and even more preferably a power range of 10W - 400kW.

[0232] Turning now to Fig. 3B, a preferred embodiment of laser system 300 is shown. OPA CBC laser 302 may include a seed laser 330 and a laser beam splitting and combining subsystem 332. Splitting and combining subsystem 332 preferably receives an output laser beam from seed laser 330 and splits the output laser beam into a plurality of sub-beams along a corresponding plurality of channels 334. Here, by way of example only, an output from seed laser 330 is shown to be split into four sub-beams along four channels 334 although it is appreciated that splitting and combining subsystem 332 typically may include a far greater number of channels, typically arranged in a three- dimensional matrix, along which the output of seed laser 330 is split. By way of example, splitting and combining subsystem 332 may include 32 or more channels arranged in a three-dimensional matrix. The four channels 334 shown in Fig. 3B thus may be considered to illustrate a side-view of a three-dimensional matrix of channels.

[0233] The relative phase of each sub-beam may be individually modulated by a phase modulator 340, preferably located along each of channels 334. Phase modulators 340 are preferably electro-optical phase modulators, each operative to modify a phase of the sub-beam passing therethrough. Phase modulated sub-beams produced by the splitting and subsequent phase modulation of the output of seed laser 330 are preferably mutually relatively aligned by sub-beam alignment optics 342, here shown to comprise a plurality of collimating lenses 342. Preferably, each phase modulated sub-beam propagates towards a corresponding collimating lens. The individually collimated, phase modulated sub-beams are subsequently combined and focused by focusing optics 346, here embodied by way of example as a focal lens 346, to form a combined beam 348.

[0234] Splitting and combining subsystem 332 may also provide laser amplification of the sub-beams, preferably following the splitting of the output beam of seed laser 330 into sub-beams and prior to the combining of the sub-beams to form combined beam 348. Here, by way of example, splitting and combining subsystem 332 is shown to include a plurality of optical amplifiers 350 located along corresponding ones of channels 334 for amplifying each sub-beam. It is appreciated, however, that such amplification is optional and may be omitted, depending on the power output requirements of laser 302. Sub-beams may be delivered, following optional amplification thereof by optical amplifiers 350, to sub-beam alignment optics 342, by a corresponding plurality of optical fibers 352. The sub-beams may propagate through free space from sub-beam alignment optics 342 to focusing optics 346.

[0235] It is a particular feature of a preferred embodiment of the present invention that focusing optics 346 may be located at a physically large distance from sub-beam alignment optics 342. For example, focusing optics may be located at a distance of up to about 100m from sub-beam alignment optics 342 or even at a distance of greater than 100m. The plurality of sub-beams preferably propagates through free space over the distance between sub-beam alignment optics 342 and focusing optics 346.

[0236] The phase of combined beam 348, and hence the position and shape of the far-field intensity output pattern thereof, is controlled, at least in part, by the relative phases of the constituent sub-beams combined to form beam 348. In laser butt welding it is desirable to dynamically move and shape the far-field intensity pattern of the output beam. This may be achieved in laser system 300 by laser splitting and combining subsystem 332 dynamically varying the relative phases of the individual sub-beams and thereby varying the phase of the combined laser output 348 so as dynamically to control the position and shape of the far-field intensity pattern thereof.

[0237] The relative phases of the sub-beams are preferably predetermined in accordance with a desired laser output pattern, for example for the welding of workpiece 310 across gap 311. Particularly preferably, the varying relative phases are applied by a spatial modification butt welding phase control subsystem 360. Spatial modification butt welding phase control subsystem 360 preferably forms a part of a control electronics module 362 in OPA laser 302 and preferably controls each phase modulator 340 so as to dynamically modulate the relative phases of the sub-beams along channels 334 so as to produce a dynamically varying laser output pattern. Particularly preferably, spatial modification butt welding phase control subsystem 360 is operative to continuously dynamically modulate phases of the individual sub-beams comprising the combined laser output 348 so as to perform butt welding across gap 311 between first and second pieces 310A and 310B of workpiece 310, in a manner detailed henceforth.

[0238] Seed laser 330, possibly in combination with other components such as amplifiers 350, may be a preferred embodiment of laser components 304 (Fig. 3A). Subbeam alignment optics 342 may be a preferred embodiment of sub-beam alignment optics 306 (Fig. 3A) and focusing optics 346 may be a preferred embodiment of focusing optics 308 (Fig. 3A). Sub-beam alignment optics 342 are preferably housed (located) in an OH forming a part of OPA CBC laser 302. Focusing optics 346 are preferably housed (located) in a welding head, which welding head may be separate from both the OH and other components 304 of laser 302. The OH housing sub-beam alignment optics 306 may be connected to other components of the laser 304 by the plurality of optical fibers 352 through which the multiplicity of laser sub-beams may travel. Plurality of optical fibers 352 may be a preferred embodiment of optical fiber bundle 312 (Fig. 3A).

[0239] Optics 342 and 346 may be subject to thermal distortions due to heating by the sub-beams of OPA CBC laser 302 during operation thereof, thereby causing distortion (for example, creating phase noise) of the laser output. Furthermore, movement of the optical fibers 352 connecting the OH to other laser components 304 may create phase noise. Distortions arising from optical elements in laser 302 (for example, phase noise) contribute to noise in combined beam 348. Noise in combined beam 348 may additionally be created by other thermal or mechanical effects and / or by the amplification process in the case that optical amplifiers 350 are present in OPA system 300.

[0240] In order to cancel out noise in the laser output of system 300, system 300 preferably includes a noise cancellation phase variation subsystem 364. Noise cancellation phase variation subsystem 364 is preferably operative to provide a noise cancellation phase correction output in order to cancel out the noise in combined beam 348. Particularly preferably, noise cancellation phase variation subsystem 364 employs an algorithm to sense and correct phase noise in the combined laser output. The noise cancellation phase correction output is preferably provided by noise cancellation phase variation subsystem 364 to phase modulators 340 so as to correct phase noise in combined beam 348 and thus avoid distortion of the shape and position of the far field intensity output pattern of combined beam 348 that would otherwise be caused by the noise. Noise cancellation phase variation subsystem 364 may be included in control electronics module 362.

[0241] In order to facilitate application of phase variation and noise correction to combined beam 348, a portion of the output of OPA laser 302 is preferably extracted and directed towards at least one detector 320. Detector 320 may be embodied as a single detector, as illustrated in Fig. 3B, or may alternatively be embodied as multiple detectors. The extracted portion of the output beam preferably functions as a reference beam, based on characteristics of which the required noise correction and / or phase variation may be calculated. In the embodiment shown in Fig. 3B, combined beam 348 is directed towards a beam splitter 370. Beam splitter 370 preferably splits combined beam 348 into a reflected portion 372 and a transmitted portion 374 in accordance with a predetermined ratio. For example, beam splitter 370 may split each sub-beam with a 99.9% reflected: 0.01% transmitted ratio.

[0242] The reflected portion 372 of the sub-beams preferably forms a combined output beam 378 having a far-field intensity pattern 380 incident upon workpiece 310. The transmitted portion 374 of the sub-beams is preferably transmitted to form an output reference beam 382 having a far-field intensity pattern 384 incident on a surface of detector 320.

[0243] As described hereinabove, the shape and position of the far-field intensity pattern 380 of the output beam 372, 378 and correspondingly of the far-field intensity pattern 384 of the reference beam 374, 380 are constantly changing, due to the ongoing variation of the relative phases of the sub-beams, as applied by phase modulators 340 controlled by spatial modification butt welding phase control subsystem 360. As a result, the far-field intensity pattern 384 of the reference beam 382 is not fixed upon detector 320 but rather is constantly being moved around with respect to detector 320 depending on the combined relative phases of the constituent sub-beams. However, in order for detector 320 to sense noise in reference beam 382 and thus provide the required feedback to noise cancellation phase variation subsystem 364, the far-field intensity pattern 384 of reference beam 382 must be incident upon detector 320 in order for detector to measure the intensity and thereby noise of the far-field intensity pattern, seemingly requiring a fixed output beam.

[0244] The conflict between the dynamic nature of far-field intensity pattern due to the phase-variation thereof and the fixed nature required of the far-field intensity pattern of reference beam 382 in order to derive and ultimately apply noise correction thereto, is preferably resolved in a preferred embodiment of the present invention by providing the noise cancellation phase variation and spatial modification phase variation at mutually different times and rates.

[0245] The noise cancellation phase correction output is provided based on taking into consideration noise measured at detector 320 at a noise sampling rate. The output beam 348 is controlled in such a way that the far-field intensity pattern 384 of reference beam 382 is incident upon detector 320 during the course of the dynamic changes to the shape and position of the output and reference beams at a rate that is equal to or higher than the required noise sampling rate. The noise in reference beam 382 is taken into consideration during those intermittent times at which the far-field intensity pattern is returned to detector 320. Noise cancellation phase variation subsystem 364 is operative to receive an output from detector 320 indicative of noise in reference beam 382 and apply a noise cancellation phase variation to phase modulators 340 based thereon at intermittent times.

[0246] At time interstices between the intermittent times at which the far-field intensity pattern of reference beam 382 is incident upon detector 320 and a noise cancellation phase variation applied to phase modulators 340 by noise cancellation phase variation subsystem 364, the phase of the combined output beams 348 and hence reference beam 382 is continuously varied under the control of spatial modification butt welding phase variation subsystem 360, in order to dynamically change the shape and position of the far-field intensity pattern thereof as required, for example to perform laser butt welding of workpiece 310. The combined laser output is varied, by spatial modification butt welding phase variation subsystem 360, at a phase varying rate which exceeds the noise sampling rate, in order to rapidly change the phase and hence shape and position of the far-field intensity pattern. By way of example, the noise sampling rate may be of the order of 10 - 1000 Hz whereas the phase varying rate may be greater than 10,000 Hz. Further details pertaining to particular exemplary algorithms useful for performing spatial modification phase variation and noise cancellation phase variation in the present invention, are described in WO2019 / 092702, the entirety of which is incorporated herein by reference.

[0247] The second phase variation to produce noise cancellation is preferably provided, by noise cancellation phase variation subsystem 364, during the course of the first phase variation for spatial modulation of the combined output beam 378, provided by spatial modification butt welding phase variation subsystem 360, without needing to significantly pause or disrupt the desired laser output pattern created and controlled by the first phase variation. It is appreciated that spatial modification butt welding phase variation subsystem 360 and noise cancellation phase variation subsystem 364 preferably have separate functionalities and hence are shown herein for clarity as separate modules, but may be implemented in the same (for example, common) physical components within control electronics 362.

[0248] Detector 320 is preferably operative to detect noise in the laser output incident thereupon, including noise arising from optical elements upstream from detector 320, such as optics 342 and 346. It is understood that the particular structure and configuration of beam splitting and recombining elements shown herein, including beam splitter 370, sub-beam alignment optics 342 and focusing optics 346, is exemplary only and depicted in a highly simplified form. It is appreciated that OPA laser system 300 may include a variety of such elements, as well as additional optical elements, including, by way of example only, additional or alternative lenses, optical fibers and coherent free- space far-field combiners. Preferably, most and even more preferably all of such additional optical elements are located upstream of detector 320, such that detector 320 is preferably operative to detect phase noise in the combined laser output generated by (arising from) such optical elements. It is appreciated that should only some, but not all, of the optical elements be located upstream from detector 320, then detector 320 would not be capable of sensing noise in the combined laser output generated by that portion of the optics located downstream of detector 320 and the far field intensity pattern of the combined laser output 348 would be degraded by noise which would not be corrected for by noise correction phase variation module 364. By way of example, should beam alignment optics 342 be located upstream from detector 320 but focusing optics 346 be located downstream from detector 320, detector 320 would not detect noise in combined laser output 348 generated by focusing optics 346, for example due to thermal focus shift of focusing optics 346, and thus the far field intensity pattern of combined laser output 378 would be degraded by noise arising from focusing optics 346 and be of poorer quality. For example, a thermal focus shift of focusing optics 346 may cause output beam 378 to shift by several mm or tens of mm from a desired position thereof. Should focusing optics 346 be located downstream from detector 320, such a shift in output beam 378 would not be detected by detector 320 and hence would remain uncorrected.

[0249] The Power in the Bucket (PIB) metric may be used to define beam quality. Deterioration in beam quality, due to noise and including thermal focus shift-related deterioration, may be quantified as the measured PIB. The measured PIB expresses how much energy is delivered by the beam to the desired location on the workpiece, compared to the energy delivery to the desired location by an ideal beam. Locating all of the optical elements of the laser of the present invention upstream from the detector, such that noise arising from the optical elements including thermal focus shift-related noise caused by focusing optics 346 is detected and hence corrected for, may result in an improvement in the PIB of the combined output beam of several percent, such as 10%, 20%, 30% or more.

[0250] Detector 320 may include additional optics as required to optimize the sensing of the noise (for example, phase noise). For example, additional optics for detector 320 may be located between detector 320 and beam splitter 370. Such optics may, for example, be operative to focus the combined output on the detector at a mechanical distance from beam splitter 370 that is different from the mechanical distance between beam splitter 370 and workpiece 310. For example, the mechanical distance from beam splitter 370 to detector 320 may be shorter than the mechanical distance from beam splitter 370 to workpiece 310, which may be helpful in minimizing the physical dimensions of system 300. Since the optics in the detector are not subject to high-power, due to only a small portion of the total output being directed towards detector 320, the optics in the detector may be formed by a variety of optical elements without being subject to thermal focusing or thermal distortion effects. For example, optics for detector 320 may have a confocal arrangement that allows a long effective focal length with a short back focal length, as is detailed henceforth with reference to Figs. 7A - 8E.

[0251] As a result of the single-mode nature of the laser output, the laser output is highly sensitive to distortions. Distortions in the laser output may be corrected, in part, by the application, via phase modulators 340 controlled by noise cancellation phase variation subsystem 364, of a phase variation for noise cancellation. Distortions may further be minimized by careful construction and maintenance of laser system 300. Various exemplary features of laser system 300, which features preferably serve to minimize distortion of the single-mode output provided thereby, are listed below:

[0252] • Due to the single-mode nature of the laser output, the laser output must be transmitted in a very narrow optical fiber. This results in a high power-density in the fiber, leading to non-linear effects. In order to minimize such non-linear effects, the laser output in the present invention may be transmitted over relatively large distances through free space, rather than within optical fibers, for example between sub-beam alignment optics 342 and focusing optics 346.

[0253] • Due to the single mode high power nature of the laser output, the laser output is very sensitive to distortions caused by optical elements in laser system 300. Optical elements in laser system 300, such as lenses, mirrors and beamsplitters, are therefore preferably formed by pure fused silica glass which creates a minimum amount of distortion. There is therefore no variation in glass type in the optics (for example, optics 342 and 346, beam splitter 370) of system 300 and correspondingly no variation in refractive indices of different ones of the optical elements. Differences in refractive indices therefore cannot be used in lens design, making lens design more limited and hence more difficult.

[0254] • In some applications, the focal length of focusing optics 346 may be several meters long whereas the working distance between focusing optics 346 and workpiece 310 may be less than 1 meter long. As a result, the beam diameter on the downstream elements of optics 346 may be a few millimeters only. This small diameter combined with the high power of the laser, may result in high power density on these downstream optical elements which may result in distortion. In the present invention, most and preferably all optical elements including focusing optics 346 are located upstream of detector 320, such that any distortions may be sensed by detector and hence corrected for by phase control functionality included in control module 362.

[0255] The dynamic laser output of OPA CBC laser 302, as spatially controlled by the first phase variation and noise-corrected by the second variation, has been found to be particularly well suited for laser butt welding across relatively wide gaps, such as gaps having a width of about 1mm, 2mm or more.

[0256] It is appreciated that far field intensity pattern 380, as incident upon workpiece 310, does not have a constant intensity distribution thereacross. Rather, depending on the relative phases of the combined sub-beams contributing to far field intensity pattern 380, far field intensity pattern 380 includes some regions of higher intensity than others. Regions of high intensity within far field intensity pattern 380 are preferably localized at specific points, whereat the beam energy is concentrated.

[0257] In accordance with a preferred embodiment of the present invention, spatial modification butt welding phase variation subsystem 360 may be operative to dynamically control phases of the constituent sub-beams in order to create a combined output beam having a far field intensity pattern including localized points at which energy is concentrated and may be further operative to control the shape and position of the output beam so as to causes these high energy points to be incident upon adjacent segments 310A and 310B of workpiece 310, rather than to fall upon gap 311.

[0258] Particularly preferably, spatial modification butt welding phase variation subsystem 360 may be operative to dynamically control the shape and position of the combined laser output so as to cause the high energy points within the far field intensity pattern 380 to jump from side to side of gap 311, back and forth between segments 310A and 310B, in order to push material from segments 310A and 310B into gap 311 and thereby weld gap 311 closed. Energy of the beam is thus preferably concentrated upon the material bordering gap 311, such that material is pushed into gap 311, rather than the beam energy being wasted within gap 311. This is in contrast to conventional laser butt welding systems, wherein a significant portion of the laser output typically travels through the gap and is wasted, rather than being utilized for welding.

[0259] By way of example, spatial modification butt welding phase variation subsystem 360 may be operative to dynamically control phases of the sub-beams in order to create a combined output beam having a far field intensity pattern spanning a width of gap 311. For example, far field intensity pattern 380 of combined output beam 378 may span a width of 3mm and thus may extend across an entire width or area of gap 311 having a width of at least 1mm. The combined beam shape and position, and thus the energy distribution thereof, may be controlled so as to deposit energy by high intensity regions of the far field intensity pattern in a localized manner, on either side of gap 311. Yet further additionally or alternatively, the combined output beam may be varied along a length of gap 311 to adjust (compensate for) variations in properties of the welded gap, such as angle, thickness and distance from focusing optics 346.

[0260] It is appreciated that, by way of controlling the phases of the constituent sub-beams, the combined output beam thus may be formed at one point or position on one side of gap 311 and, as a result of changing the phases of the constituent sub-beams, may subsequently be formed at a different point or position on the other side of gap 311. As the output beam changes position, the output beam does not travel over the gap 311. Rather, the output beam ‘disappears’ from (is removed from) the initial position thereof on one side of gap 311 and ‘appears’ (is reformed) at the subsequent position thereof on the other side of gap 311. This is in contrast to conventional mechanical steering of the beam, in which the beam is moved from one side to the other of the gap, but in doing so traverses the gap, thereby wasting beam energy.

[0261] An exemplary beam shape, useful for gap welding, is shown in Fig. 3C. It is appreciated that the exemplary beam shape is illustrative only and that a preferred beam shape employed in a given gap welding application may depend upon the process material and parameters.

[0262] As seen in Fig. 3C, an exemplary beam shape 390 for gap welding may be u-shaped. It is appreciated that beam 390 is not a static image of the beam shape incident on the workpiece at a single point in time but rather is an image of the pattern formed or path traversed by the beam over a multiplicity of consecutive points in time, such as about 20, 30, 40 or more consecutive points in time. By way of example, the image shown in Fig. 3C may be a composite image comprising multiple frames rapidly captured by a camera incorporated within system 300, as further detailed henceforth with reference to Figs. 7A - 8E. At any given point in time, the output beam may be located at a particular position along beam shape 390 and have a correspondingly positioned far field intensity pattern on workpiece 310.

[0263] Initially, the beam is preferably located at a far edge of beam shape 390, for example at a position generally indicated in Fig. 3C as position 1 (Pl). Pl preferably lies on a first side of gap 311, for example upon segment 310A of workpiece 310. Subsequently, the beam is preferably repositioned at the oppositive far edge of beam shape 390, for example at a position generally indicated in Fig. 3C as position 2 (P2). P2 preferably lies on a second side of gap 311, for example upon segment 310B of workpiece 310. It is appreciated that the beam does not traverse gap 311 as the beam is repositioned from Pl to P2 but rather is simply removed from Pl and reformed at P2, thereby avoiding loss of energy within gap 311.

[0264] As the beam melts workpiece 310 and pushes material inwards towards gap 311, the beam is subsequently repositioned at a plurality of points increasingly inwards from the edge of beam shape 390 and towards the center of closing gap 311, for example at points P3, P4, P5 and P6, in that sequence. The beam preferably jumps back and forth across gap 311 from one point to a consecutive point, continuously moving inwards towards a center of gap 311 as the gap is closed by material being pushed inwards by the beam. The overall beam pattern comprising a multiplicity of individual beam positions is thus u-shaped.

[0265] It is understood that the u-shaped beam pattern 390 of Fig. 3C is exemplary only and a variety of other beam shapes may be used, depending on the specific processing requirements. Additionally, it is understood that points Pl - P6 are shown in a highly simplified form and provided for clarity of explanation only. Beam pattern 390 may be formed by a far greater number of points, which points may be positioned much more closely with respect to one another than shown in Fig. 3C.

[0266] The performance of butt welding electro -optic ally across a gap of about 1mm or more, without necessarily requiring mechanical movement of laser components, is highly advantageous. In order to perform butt welding across such a relatively wide gap 311, it is preferable that focusing optics 246 comprises at least one lens having a large focal length. By way of example, a lens comprising optics 246 may have a focal length of about 3m.

[0267] It will be appreciated that the provision of a high-power laser operating in single-mode is highly advantageous and differs from conventional single-mode lasers which are typically low-power. The single-mode output of OPA CBC laser 302 provides many advantages, including extremely precise welding, very high power density, the ability to weld from a distance of several meters or more and large depth of focus. For example, the laser spot of the combined laser beam 378 of system 300 may be of a size of 10 microns to greater than 500 microns.

[0268] Furthermore, the single-mode nature of the laser output of laser 302 means that the laser output may travel over long distances without significant beam divergence, such that a precise weld may be produced by a laser located relatively distant from the workpiece 310. In some embodiments, the single mode sub-beams may travel in free space for 100m or more and then be focused onto the work piece 310 to be welded. For example, the sub-beams originating from seed laser 330 and aligned by sub-beam alignment optics 342 (for example, in an OH) may subsequently travel in free space over a distance of more than 100 m, to a welding head holding focusing optics 346 and subsequently be focused, by focusing optics 346 in the welding head, upon workpiece 310 for performing welding thereof.

[0269] In conventional laser systems in which the laser output is directed to a distant substrate, it is typically challenging to precisely control the position of the output beam on the substrate. In contrast, in the present invention, the position of the output beam on workpiece 310 may be precisely controlled by a combination of the first phase variation for spatial modulation, provided by of spatial modification butt welding phase variation subsystem 360; focusing optics 346 used for focusing the laser beam on the workpiece; and optionally also mechanical motion of the welding head and / or galvo- scanner in which focusing optics 346 may be housed. Mechanical motion provided by a welding head and / or galvo-scanner may complement beam motion due to phase variation. It understood, however, that in some embodiments of the present invention the laser output may be dynamically spatially modified without involving any moving parts, by way of phase variation only.

[0270] Laser systems 100, 200 and 300 may be used in a fixed optics configuration or in a flying optics configuration. Various exemplary embodiments of laser systems 100 - 300 are shown in Figs. 4 - 1 IB. In a fixed optics configuration, the focusing optics 146, 208, 308 (for example, although not necessarily, located in a welding head) are fixed in position with respect to the OH, which OH includes at least a part of laser 102, 202, 302 (for example, sub-beam alignment optics 142, 206, 306). In a fixed optics configuration, both the focusing optics and OH may move in tandem with respect to the workpiece 110, 210, 310. Other laser components (for example, laser components 104, 204, 304) may or may not also be moveable in this configuration, depending on the required separation between the various components.

[0271] In a flying optics configuration, the focusing optics 146, 208, 308 (for example, although not necessarily, located in a welding head) may move with respect to a static OH, which OH includes at least a part of laser 102, 202, 302 (for example, subbeam alignment optics 142, 206, 306). In a flying optics configuration, laser output from laser 102, 202, 302 (for example, laser output having been aligned by sub-beam alignment optics 142, 206, 306) may be transmitted over free space to at least a portion of focusing optics 146, 208, 308. Focusing optics 146, 208, 308 may comprise one or more moveable optical elements, such as mirrors and / or lenses, which are used to focus and move the laser output with respect to workpiece 110, 210, 310. It is appreciated that in both fixed and flying optics configurations, detector 120, 220, 320 may be arranged downstream of the optical elements, in order to sense and allow correction of noise arising therefrom. In some embodiments, detector 120, 220, 320 may be integrated within the welding head or other entity housing the focusing optics.

[0272] Turning now to Figs. 4 - 8E, various exemplary fixed optics configurations are shown. As seen in Fig. 4, an OH 400 may be mounted on a welding robot 402. OH 400 may, for example, include beam alignment optics 206 or 306 (not shown). Focusing optics 408, which may comprise focusing optics 208 or focusing optics 308, is fixed in position with respect to OH 400 and focusing optics 408 and OH 400 are moved in tandem by robot 402 during welding and with respect to workpiece 410. In this example, a main body of the laser 412, which may include laser components 204 or 304 including seed laser 230 or 330 and associated components such as cooling components, is also fixed in position and connected to the OH 400 via a bundle of optical fibers 414. A detector, such as detector 220 or 320, may be located downstream of some or all of optical fiber bundle 414, OH 400 including beam alignment optics, and focusing optics 408, in order to sense and therefore allow correction of noise in the laser output, including substantially all or all noise arising from the optics, such as noise created by thermal aberrations of the optics. Phase variation functionality, including spatial modification and noise correction functionality, is preferably housed in an electronics control module (not shown), for example embodied as computerized hardware and / or software components.

[0273] As seen in Fig. 5, in a further preferred embodiment of a fixed optics configuration, a laser system 500, which may be an embodiment of laser system 200 or 300, may be mounted on a wagon 502. An OH 504 may be mounted on wagon 502. OH 504 may, for example, include beam alignment optics 206 or 306 (not shown). Focusing optics 508, which may comprise focusing optics 208 or focusing optics 308, is fixed in position with respect to OH 504 and focusing optics 508 and OH 504 are moved in tandem by wagon 502 during welding and with respect to a workpiece (not shown). In this example, a main body of the laser 512, which may include laser components 204 or 304 and associated components such as cooling components, is also portably mounted on wagon 502 and connected to the OH 504 via a bundle of optical fibers 514. A detector ( not shown), such as detector 220 or 320, may be located downstream of some or all of optical fiber bundle 514, OH 504 including beam alignment optics, and focusing optics 508, in order to sense and therefore allow correction of noise in the laser output, including substantially all or all noise arising from the optics, such as noise created by thermal aberrations of the optics. Phase variation functionality, including spatial modification and noise correction functionality, is preferably housed in an electronics control module (not shown), for example embodied as computerized hardware and / or software components.

[0274] As seen in Fig. 6, in yet a further preferred embodiment of a fixed optics configuration, a laser system 600, which may be an embodiment of laser system 200 or 300, may be mounted on a stage 602, moveable along a hydraulic pole 604. An OH 606 may be mounted on a robot 608, mounted in turn on stage 602. OH 606 may, for example, include beam alignment optics 206 or 306 (not shown). Focusing optics 610, which may comprise focusing optics 208 or focusing optics 308, is fixed in position with respect to OH 606 and focusing optics 610 and OH 606 are moved in tandem both by robot 608 and stage 602 during welding and with respect to workpiece 612. Here, by way of example, workpiece 612 is shown to be an extensive workpiece, for example a panel of an LNG tank. In this example, a main body of the laser 614, which may include laser components 204 or 304 including seed laser 230 or 330 and associated components such as cooling components, is also portably mounted on stage 602 and connected to the OH 606 via a bundle of optical fibers 616. A detector (not shown), such as detector 220 or 320, may be located downstream of some or all of optical fiber bundle 616, OH 606 including beam alignment optics, and focusing optics 610, in order to sense and therefore allow correction of noise in the laser output, including substantially all or all noise arising from the optics, such as noise created by thermal aberrations of the optics. Phase variation functionality, including spatial modification and noise correction functionality, is preferably housed in an electronics control module (not shown), for example embodied as computerized hardware and / or software components.

[0275] As seen in Figs. 7A - 7E, in another preferred embodiment of a fixed optics configuration, a welding head 700, which may form a part of laser system 200 or 300, may include an OH 702. OH 702 preferably receives, at an input port 704 thereof, an output from a seed laser (not shown). OH 702 preferably includes beam alignment optics, such as beam alignment optics 206 or 306, operative to spatially align a plurality of subbeams 706 following the phase modification and optional amplification thereof. As best seen in Figs. 7B and 7E, sub-beams 706 are output from OH 702 in parallel to one another and with a predetermined mutual spatial separation. Sub-beam alignment output optics 708, from which aligned sub-beams 706 emerge, are best seen in Fig. 7E.

[0276] Aligned sub-beams 706 emerging from OH 702 are preferably focused by a focusing lens 710, which may be a preferred embodiment of focusing optics 208 or focusing optics 308. Focusing lens 710 is preferably fixed in position with respect to OH 702 and preferably causes sub-beams 706 to converge and combine in a direction towards a beam splitter 712. At beam splitter 712 the combined output beam is split. A majority portion of the combined beam is reflected towards a workpiece (not shown) in a direction indicated by an arrow 716 in Fig. 7A. A minority portion of the combined beam, which functions as a reference beam, is transmitted through beam splitter 712 towards a detector system 720. Welding head 700 preferably includes a first co-axial camera 722 for imaging the workpiece, during welding thereof.

[0277] The reference beam, transmitted through beam splitter 712, is preferably bent by a bender mirror 726 in a direction towards detector system 720. Detector system 720 may be seen most clearly in Fig. 7B, which shows the welding head 700 of Fig. 7A with protective covers 728 removed therefrom, as well as Fig. 7D. Detector system 720 preferably includes a telescope 730 and a second camera 732. A beam splitter enclosure 734 housing a beam splitter (not shown) is preferably located at the exit of telescope 730 and is preferably operative to split the reference beam into reflected and transmitted portions. One portion propagates towards second camera 732. Second camera 732 is preferably operative to capture and monitor the far field pattern of the combined beam. The other portion is preferably directed towards an optical fiber 736, which is preferably operative to deliver that portion to at least one detector (not shown). The at least one detector is preferably operative to detect noise in the laser output, based on which a noise correction phase variation is preferably applied to the laser output, as detailed hereinabove with reference to Figs. 1A - 3B. In an alternative embodiment of the present invention, optical fiber 736 may be obviated and the detector itself may be located within detector system 720.

[0278] As best seen in Figs. 7D and 7E, telescope 730 is preferably operative to focus the reference portion of the combined output of aligned sub-beams onto the second camera 732. The mechanical distance from focusing lens 710 to second camera 732 may be different (for example, smaller) than the mechanical distance from focusing lens 710 to the workpiece. This may be helpful in minimizing the mechanical dimensions of welding head 700. It is appreciated that the optics in telescope 730 are not subject to high power and therefore may be composed from a variety of optical elements without being subject to thermal focusing or thermal distortion effects, unlike other optics in welding head 700. In a preferred embodiment of the present invention, telescope 730 may have a confocal arrangement that allows for a long effective focal length with short back focal length, in order to focus the reference beam upon second camera 732.

[0279] It is appreciated that first coaxial camera 722 and second camera 732 are preferably operative to capture images of a same far field pattern of the combined beam. However, first coaxial camera 722 preferably has a significantly larger field of view than that of second camera 732, in order for first coaxial camera 722 to image a welded region of the workpiece. Additionally, since the laser beam incident upon the workpiece creates a large amount of light, the light reflected from the workpiece and incident upon first coaxial camera 722 is preferably filtered. It is therefore advantageous to employ second camera 732 for monitoring the far field pattern of the output beam, which second camera 732 has a smaller field of view and does not require a filtered input, rather than utilizing the far field pattern imaged by the first camera 722 for this purpose.

[0280] In many welding applications, a large beam diameter is useful. The physical size of the beam is a function of the product of the beam angle and focal length of the focusing lens. In some cases, a large focal length, such as approximately 5 m, may be required. However, it may be undesirable to work at such a large distance between the focusing lens and the workpiece. In certain embodiments of welding head 700, focusing lens 710 may therefore be embodied as a confocal lens having a relatively long effective focal length but relatively short working distance, in order to maintain a desired beam diameter but nonetheless allow the workpiece to be positioned relatively close to the welding head 700.

[0281] As seen in Figs. 8A - 8E, welding head 700 may be adapted to include a galvo-scanner 800 including x-direction and y-direction scanning mirrors 802 and 804, seen most clearly in Fig. 8E. First co-axial camera 722 is preferably oriented orthogonally in the embodiment of Figs. 8A - 8E compared to that of Figs. 7A - 7E. Scanning mirrors 802 and 804 are preferably operative to scan the combined laser output beam across the workpiece in accordance with a desired pattern. The mechanical movement of the scanning mirrors in order to adjust the position of the output beam may be applied in combination with the electro-optical adjustment of the position of the output beam using phase control functionality, as detailed above with reference to Figs. 1A - 3B.

[0282] It is appreciated that detector system 720 in welding head 700 is preferably located downstream from the beam alignment optics, focusing lens 710 and additional optics, including beam splitter 712, mirror 726 and telescope 730. This arrangement allows detector system 720 to sense, and therefore allows correction of noise in the laser output arising from, most or preferably all of the optical elements in welding head 700, such as substantially all or all noise created by thermal aberrations of the optics. Figs. 4 - 8E illustrate some examples of fixed optics arrangements, preferably including a detector downstream from the optical elements. Other examples are also possible.

[0283] Turning now to Figs. 9 - 11B, various exemplary possible flying optics configurations are shown.

[0284] As seen in Fig. 9, an OH 900, including sub-beam alignment optics (not shown) such as sub-beam alignment optics 206 or 306, may be static. OH 900 preferably receives, at an input port 904 thereof, an output from a seed laser (not shown). The mutually aligned sub-beams output from OH 900 may be directed, by way of a multiplicity of optical mirrors and focusing elements 908, towards a workpiece 910. Here, by way of example only, focusing elements 908 preferably include a first optical element 912 moveable along the y-axis, a second optical element 914 moveable along the x-axes and a third optical element 916, here embodied as a focusing lens for focusing the laser beam onto workpiece 910, moveable along the z-axes.

[0285] The combined laser output, focused by third optical element 916, may be incident upon a beam splitter 920. A majority portion of the combined beam may be transmitted towards workpiece 910 and a minority portion of the combined beam may be reflected towards a detector 922. It is appreciated that detector 922 is preferably located downstream from the beam alignment optics, focusing optics 908 including focusing lens 916, and additional optics, including beam splitter 920. This arrangement allows detector system 922 to sense, and therefore allows correction of noise in the laser output arising from most, and preferably all, of the optical elements, such as noise created by thermal aberrations of the optics.

[0286] It is appreciated that third optical element 916, functioning as the focusing lens, may be located at a considerable distance from OH 900, for example up to 100 m from OH 900 or at an even greater distance therefrom. This creates great flexibility in the arrangement and operation of OH 900.

[0287] As seen in Figs. 10A and 10B, in another preferred embodiment of a flying optics configuration, an OH 1000 may be static. OH 1000 may, for example, include beam alignment optics 206 or 306. In this example, a main body of the laser 1002, which may include laser components 204 or 304 and associated components such as cooling components, is also fixed in position (static) and connected to the OH 1000 via a bundle of optical fibers 1004. A welding head 1008 may be mounted on a stage 1010 moveable along a hydraulic pole 1012. Welding head 1008 may include focusing optics, which may comprise focusing optics 208 or focusing optics 308. Additional focusing optics 1014 may be movably mounted on hydraulic pole 1012 and may be operative to direct a laser output 1016 from OH 1000 towards welding head 1008. A combined beam 1018, output by welding head 1008, is preferably incident upon workpiece 1020, here embodied, by way of example, as an extensive panel such as a panel of an LNG tank.

[0288] It is appreciated that welding head 1008 may be located at a considerable distance from OH 1000. For example, welding head 1008 may be located at a distance of up to 100 m or more from OH 1000. This allows great flexibility in the use of welding head 1008 for welding extensive surfaces, since welding head 1008 may be readily shifted around the surface to be welded, whereas OH 1000 and other heavier components of the laser, such as laser body 1002, may remain fixed in place.

[0289] A detector 1022, such as detector 220 or 320, may be located downstream of some or all of optical fiber bundle 1004, OH 1000 including beam alignment optics, and focusing optics 1014. For example, detector 1022 may be mounted on welding head 1008. Detector 1022 is preferably operative to sense and therefore allow correction of noise in the laser output, including most, and particularly preferably substantially all noise, arising from the optics, such as noise created by thermal aberrations of the optics. Phase variation functionality, including spatial modification and noise correction functionality, is preferably housed in an electronics control module (not shown), for example embodied as computerized hardware and / or software components.

[0290] As seen in Figs. 11 A and 1 IB, in another preferred embodiment of a flying optics configuration, an OH 1100 may be static. OH 1100 may, for example, include beam alignment optics 206 or 306. In this example, a main body of the laser 1102, which may include laser components 204 or 304 and associated components such as cooling components, is also fixed in position (static) and connected to the OH 1100 via a bundle of optical fibers 1104. A welding head 1108 may be mounted on a drone 1110, moveable with respect to OH 1100. Welding head 1108 may include focusing optics, which may comprise focusing optics 208 or focusing optics 308. Additional focusing optics 1114 may also be mounted on drone 1110, external to welding head 1108. Additional focusing optics 1114 may be operative to direct a laser output 1116 from OH 1100 towards welding head 1108. A combined beam 1118, output by welding head 1108, is preferably incident upon workpiece 1120, here embodied, by way of example, as an extensive panel such as a panel of an LNG tank.

[0291] It is appreciated that welding head 1108 on drone 1110 may be located at a considerable distance from OH 1100. For example, drone 1110 may move welding head 1108 so as to be located at a distance of up to 100 m or more from OH 1100. This allows great flexibility in the use of welding head 1108 for welding extensive surfaces, since welding head 1108 may be readily repositioned by drone 1110 around the surface to be welded, whereas OH 1100 and other heavier components of the laser, such as laser body 1102, may remain fixed in place.

[0292] A detector 1122, such as detector 220 or 320, may be located downstream of some or all of optical fiber bundle 1104, OH 1100 including beam alignment optics, and focusing optics 1114. For example, detector 1122 may be mounted on welding head 1108. Detector 1122 is preferably operative to sense and therefore allow correction of noise in the laser output, including most, and particularly preferably substantially all noise, arising from the optics, such as noise created by thermal aberrations of the optics. Phase variation functionality, including spatial modification and noise correction functionality, is preferably housed in an electronics control module (not shown), for example embodied as computerized hardware and / or software components.

[0293] Figs. 9 - 11B illustrate some examples of flying optics arrangements, preferably including a detector downstream from the optical elements. Other flying optics arrangements are also possible. Flying optics arrangements, such as those shown in Figs. 9 - 1 IB, avoid the need for moving all or most of the laser system (for example, the OH and the seed laser) with respect to the workpiece.

[0294] In any flying optics or fixed optics configuration, a wired or wireless communication channel may be provided between detector and the laser (for example, laser components 204, 304) in order to transmit thereto the signal detected by the detector, for feedback control of the phase correction.

[0295] As described above with reference to Figs. 2A and 2B, the laser system of the present invention may be particularly well suited for the welding of curved surfaces, in which a distance between the laser and welded surface as well as an angle of incidence of the combined output beam with respect to the surface, varies over the surface of the curved workpiece. A preferred embodiment of the laser system of the present invention, particularly well-suited for the welding of curved surfaces, is shown in Figs. 12A - 121.

[0296] Turning first to Fig. 12A, a welding head 1200 may be mounted with respect to a curved workpiece 1202 to be welded. Welding head 1200 may be embodied, by way of example as welding head 700 of Figs. 7A - 7E and may include a galvoscanner as shown in Figs. 8A - 8E. Welding head 1200 may be mounted at a fixed height above workpiece 1202. A combined laser output beam 1210 may emerge from welding head 1200 and is focused upon workpiece 1202. Welding head 1200 is preferably operative to perform welding of workpiece 1202 using combined laser output beam 1210.

[0297] Turning now to Fig. 12B, combined laser output beam 1210 may be initially incident upon a generally flat portion of workpiece 1202. In this position of combined laser output 1210 with respect to workpiece 1202, the far field intensity pattern of combined laser output 1210 upon workpiece 1202 may have a shape as shown in Fig. 12C. A weld having a characteristic weld profile may be produced by combined laser output 1210 incident upon workpiece 1202. It is appreciated that the far field intensity pattern of combined laser output 1210 is controlled by the relative phases of the subbeams constituting the combined laser output 1210, which relative phases are controlled in turn by a spatial modification phase variation sub-system such as spatial modification curvature compensation phase variation sub-system 260 (Fig. 2B). Noise in the far field intensity pattern of combined laser output 1210 is preferably detected and corrected for by a noise cancellation phase variation sub-system such as noise cancellation phase variation sub-system 264 (Fig. 2B).

[0298] As seen in the progression from Fig. 12B to Fig. 12D, laser output beam 1210 may be scanned across a surface of workpiece 1202, whilst the position (distance and angle) of welding head 1200 remains fixed with respect to workpiece 1202. As further seen in the progression from Fig. 12B to Fig. 12D, laser output beam 1210 may begin to ascend a curved portion 1220 of workpiece 1202. The motion of laser output beam 1202 in the progression from Fig. 12B to Fig. 12D is due to a combination of motion created by a galvo- scanner, if present in welding head 1200, and modification of the phases of the sub-beams comprising laser output beam 1210.

[0299] As laser output beam 1210 ascends curve 1220, a spatial modification phase variation may be applied to the sub-beams constituting the combined laser output 1210, in order to adjust the shape and position of the output beam 1210. The phase modification of the shape and position of the output beam 1210 ensures that the output beam 120 remains focused upon curve 1220, as well as adjusts the energy distribution in space and time as required, to workpiece 1202 in the region of curve 1220, despite the continuously changing angle of incidence of beam 1210 with respect to curve 1220 and continuously changing distance between welding head 1200 and curve 1220.

[0300] In the position of combined laser output 1210 with respect to workpiece 1202 shown in Fig. 12D, the far field intensity pattern of combined laser output 1210 upon workpiece 1202 may have a shape as shown in Fig. 12E. A weld having a characteristic weld profile may be produced by combined laser output 1210 incident upon workpiece 1202. It is appreciated that the beam shape shown in Fig. 12E differs from that shown in Fig. 12C, due to the variation in phase and hence combined output pattern of the output beam. However, the weld profile of the weld created by the beam shape of Fig. 12D is preferably highly similar to the weld profile of the weld created by the beam shape of Fig. 12C, due to a generally constant weld profile being maintained during welding across curve 1220. It is appreciated that the maintenance of a constant weld profile across workpiece 1202, despite the curvature thereof, is achieved due to the changing of the beam shape and position as the beam ascends curve 1220. Should a fixed beam shape be used, the weld profile would undesirably change, since the variation in welding distance and welding angle would not be compensated for.

[0301] As further seen in the progression from Fig. 12D to 12F, welding head 1200 may be mechanically moved with respect to workpiece 1202, in a direction indicated by an arrow 1230. Concurrently, laser output beam 1210 may reach a peak of curve 1220, the motion of laser output 1210 being controlled by a combination of the gross mechanical movement of welding head 1200, motion created by a galvo-scanner, if present in welding head 1200, and modification of the phases of the sub-beams comprising laser output beam 1210.

[0302] As laser output beam 1210 reaches a peak of curve 1220, a spatial modification phase variation may be applied to the sub-beams constituting the combined laser output 1210, in order to further adjust the shape and position of the output beam 1210. The phase modification of the shape and position of the output beam 1210 ensures that the output beam 1210 remains focused upon curve 1220, as well as adjusts the energy distribution in space and time as required, to workpiece 1202 in the region of curve 1220, despite the continuously changing angle of incidence of beam 1210 with respect to curve 1220 and continuously changing distance between welding head 1200 and curve 1220.

[0303] In the position of combined laser output 1210 with respect to workpiece 1202 shown in Fig. 12F, the far field intensity pattern of combined laser output 1210 upon workpiece 1202 may have a shape as shown in Fig. 12G. A weld having a characteristic weld profile may be produced by combined laser output 1210 incident upon workpiece 1202. It is appreciated that the beam shape shown in Fig. 12G differs from that shown in Fig. 12C and 12E, due to the variation in phase and hence combined output pattern of the output beam. However, the weld profile produced by the output beams of Figs. 12C, 12E and 12G are preferably highly similar to each other, due to a generally constant weld profile being maintained during welding across curve 1220. It is appreciated that the maintenance of a generally constant weld profile across workpiece 1202, despite the curvature thereof, is achieved due to the changing of the beam shape and position as the beam ascends curve 1220. Should a fixed beam shape be used, the weld profile would undesirably change, since the variation in welding distance and welding angle would not be compensated for.

[0304] As further seen in the progression from Fig. 12F to 12H, welding head 1200 may be additionally mechanically moved with respect to workpiece 1202, in a direction indicated by an arrow 1240. Concurrently, laser output beam 1210 may begin to descend curve 1220, the motion of laser output 1210 being controlled by a combination of the gross mechanical movement of welding head 1200, motion created by a galvo- scanner, if present in welding head 1200, and modification of the phases of the sub-beams comprising laser output beam 1210.

[0305] As laser output beam 1210 descends curve 1220, a spatial modification phase variation may be applied to the sub-beams constituting the combined laser output 1210, in order to further adjust the shape and position of the output beam 1210. The phase modification of the shape and position of the output beam 1210 ensures that the output beam 120 remains focused upon curve 1220, as well as adjusts the energy distribution in space and time as required to workpiece 1202 in the region of curve 1220, despite the continuously changing angle of incidence of beam 1210 with respect to curve 1220 and continuously changing distance between welding head 1200 and curve 1220. In the position of combined laser output 1210 with respect to workpiece 1202 shown in Fig. 12H, the far field intensity pattern of combined laser output 1210 upon workpiece 1202 may have a shape as shown in Fig. 121. A weld having a characteristic weld profile may be produced by combined laser output 1210 incident upon workpiece 1202. It is appreciated that the beam shape shown in Fig. 121 differs from that shown in Figs. 12C and 12G due to the variation in phase and hence combined output pattern of the output beam . However, the weld profile of the output beam of Fig. 121 may be highly similar to the weld profile produced by the output beams of Figs. 12C, 12E and 12G due to a generally constant weld profile being maintained during welding across curve 1220. It is appreciated that the maintenance of a constant weld profile across workpiece 1202, despite the curvature thereof, is achieved due to the changing of the beam shape and position as the beam ascends curve 1220. Should a fixed beam shape be used, the weld profile would undesirably change, since the variation in welding distance and welding angle would not be compensated for.

[0306] It is understood that although particular beam shapes are shown in Figs. 12C, 12E, 12G and 121, these beam shapes are generally illustrative and exemplary only. In practice, a particular beam shape employed in a given process may be selected based on the processed material and other process parameters. It is further understood that each illustrated beam shape is not a static image of the beam shape incident on the workpiece at a single point in time but rather is an image of the pattern formed or path traversed by the beam over a multiplicity of consecutive points in time, such as about 20, 30, 40 or more consecutive points in time. By way of example, the images shown in Figs. 12C, 12E, 12G and 121 may each be a composite image comprising multiple frames rapidly captured by a camera, such as camera 732 in Figs. 7A - 8E.

[0307] It is further understood that although a particular ‘fixed optics’ arrangement is shown in Figs. 12A - 12H, alternative fixed optics arrangements or flying optics arrangements are also possible.

[0308] Reference is now made to Fig. 13, which is a simplified flow chart showing steps in operation of a laser welding system of the present invention.

[0309] As seen in Fig. 13, a method 1300 is provided for noise detection during laser operation of an OPA CBC laser. As seen at step 1302, a laser output may be provided by an OPA CBC laser. The laser output may be focused, by focusing optics (step 1304). Noise in the laser output may be detected by a detector, downstream from the focusing optics (step 1306), including phase noise arising from the focusing optics.

[0310] Reference is now made to Fig. 14, which is a simplified flow chart showing additional or alternative steps in operation of a laser welding system of the present invention.

[0311] As seen in Fig. 14, a method 1400 is provided for welding of a workpiece by an OPA CBC laser. It is appreciated that although the method of Fig. 14 is described in the context of welding of a curved substrate, a similar method may be used for welding of substrates having other geometries, such as extensive substrates spanning a large area, seamed substrates including large gaps of the order of 1mm or more, and uneven substrates which are not necessarily curved. It is also appreciated that the method 1400 may be combined with the method 1300, for noise detection during welding.

[0312] As seen at step 1402, a laser output may be provided by an OPA CBC laser, such as laser 202 of laser system 200 shown in Figs. 2A and 2B or laser 302 of laser system 300 shown in Figs. 3 A and 3B. The laser output may be spatially modified by a first phase variation (step 1404) and noise in the laser output may be corrected for by application of a second phase variation (step 1406). For example, the first phase variation of step 1404 may be applied by phase modulators controlled by spatial modification curvature compensation phase variation subsystem 260 of Fig. 2B. Further by way of example, the second phase variation of step 1406 may be applied by phase modulators controlled by noise cancellation phase variation subsystem 264 of Fig. 2B. The laser output may be directed to a curved surface by fixed or flying optics, in conjunction with the first phase variation for spatial modification (step 1408). The laser output may be tailored, by application of the first phase variation at step 1404 and optics at step 1408, to take into account and compensate for curvature of the surface during welding (step 1410). For example, the focus of the laser output may be adjusted. Additionally or alternatively, variations in power density delivery to the surface and changes in the effective thickness of the substrate to be welded due to changing angle of incidence and distance caused by surface curvature, may be compensated for by controlling the shape and time spent by the laser output at various regions of the surface during welding. Further additionally or alternatively, a position of the laser output may be shifted. This may be achieved by phase control of the laser output, mechanical motion of the laser, or a combination of both. It will be appreciated by persons skilled in the art that the present invention is not limited by what has been described hereinabove. Rather the present invention includes both combinations and sub-combinations of features described hereinabove as well as modifications thereof which are not in the prior art.

Claims

CLAIMS1. A laser welding system comprising: a coherent beam combining (CBC) laser operative to provide a laser output for welding of a workpiece having a contoured surface, at least one of an angle of incidence of said laser output with respect to said surface and a distance between said CBC laser and said surface, varying across said surface; and a phase control sub-system electronically connected to said CBC laser, said phase control sub-system being operative to provide a first phase variation to vary a phase of said laser output, to compensate for said varying of at least one of said angle of incidence of said laser output with respect to said surface and said distance between said CBC laser and said surface.

2. A system according to claim 1, wherein said phase control sub-system being operative to vary said phase of said laser output comprises said phase control sub-system being operative to dynamically control both a shape and a position of said laser output across said surface to maintain a constant weld profile across said surface, during said welding.

3. A system according to claim 2, wherein said phase control sub-system is operative to vary said phase of said laser output, to move said laser output over said surface and is further operative to dynamically control said shape of said laser output as said laser output traverses said surface, to maintain said constant weld profile at each point of said surface.

4. A system according to claim 3, wherein said phase control sub-system is operative to provide said first phase variation to vary a phase of said laser output, to deliver a generally constant energy, by said laser output, to said surface at each said point thereof.

5. A system according to any one of the preceding claims, wherein said surface is curved.

6. A system according to any one of the preceding claims, wherein said phase control sub-system is additionally operative to provide a second phase variation to vary a phaseof said laser output to cancel out noise of said laser output, said second phase variation being provided, by said phase control sub-system, during time interstices between provision of said first phase variation.

7. A system according to claim 6, wherein said phase control sub-system is operative to provide said second phase variation during provision of said first phase variation and without causing significant disruption of said control, by said first phase variation, of said laser output.

8. A system according to any one of the preceding claims, wherein said CBC laser is a single-mode laser.

9. A system according to claim 8, wherein said CBC laser operates in a power range of several watts to several hundred kilowatts.

10. A system according to claim 9, wherein said CBC laser operates in a power range of 10W - 400kW.

11. A system according to any one of the preceding claims, wherein said workpiece comprises an extensive region spanning an area of up to 200 m by 200 m.

12. A system according to claim 11, wherein said workpiece comprises a panel of a liquid natural gas (LNG) tank.

13. A system according to claim 6 or claim 7, wherein said CBC laser comprises a multiplicity of optical elements wherethrough said laser output passes, said multiplicity of optical elements comprising: sub-beam alignment optics operative to align sub-beams comprising said laser output with respect to one another; and focusing optics operative to focus said sub-beams, once aligned, upon said workpiece.

14. A system according to claim 13, wherein said sub-beam alignment optics are housed in an optical head (OH) and said focusing optics are housed in a welding head,separate from said OH, wherein said focusing optics are physically separated from said sub-beam alignment optics by a distance of less than or equal to 100 meters, and said laser output propagates, from said sub-beam alignment optics to said focusing optics, through free space.

15. A system according to claim 13 or claim 14, wherein said noise is generated, at least in part, by said multiplicity of optical elements.

16. A system according to claim 15, and also comprising at least one detector operative to sense said noise generated by said multiplicity of optical elements; and said phase control sub-system is operative to provide said second phase variation to cancel out said noise of said laser output, based on taking into consideration said noise, generated, at least in part, by said multiplicity of optical elements as sensed by said at least one detector.

17. A system according to claim 16, wherein substantially all of said multiplicity of optical elements are located upstream from said detector, such that substantially all of said noise generated by said multiplicity of optical elements is sensed by said at least one detector.

18. A system according to claim 17, wherein all of said multiplicity of optical elements are located upstream from said detector.

19. A system according to any one of claims 16 - 18, wherein an Optical Head (OH) housing said sub-beam alignment optics is connected, via an optical fiber bundle, to other components of said laser and said at least one detector is operative to additionally sense noise generated by said optical fiber bundle.

20. A system according to any one of claims 16 - 19, and also comprising a beam splitter operative to direct a portion of said laser output to be incident upon said at least one detector, wherein a mechanical distance between said beam splitter and said workpiece is greater than a mechanical distance between said beam spitter and said at least one detector.

21. A method for laser welding comprising: providing, by a coherent beam combining (CBC) laser, a laser output for welding of a workpiece having a contoured surface, at least one of an angle of incidence of said laser output with respect to said surface and a distance between said CBC laser and said surface varying across said surface; and varying, by a phase control sub-system electronically connected to said CBC laser, a phase of said laser output, to compensate for said variation of at least one of said angle of incidence of said laser output with respect to said surface and said distance between said CBC laser and said surface.

22. A method according to claim 21, wherein said varying said phase of said laser output dynamically controls both a shape and a position of said laser output across said surface, to maintain a constant weld profile across said surface during said welding.

23. A method according to claim 22, wherein said varying said phase of said laser output causes movement of said laser output over said surface and dynamically controls said shape of said laser output as said laser output traverses said surface, to maintain said constant weld profile at each point of said surface.

24. A method according to claim 23, wherein said varying said phase of said laser output causes delivery of a generally constant energy, by said laser output, to said surface at each said point thereof.

25. A method according to any one of claims 21 - 24, wherein said surface is curved.

26. A method according to any one of claims 21 - 25, and also comprising additionally varying, by said phase control sub-system, an additional phase of said laser output to cancel out noise of said laser output, said varying of said additional phase being carried out by said phase control sub-system during time interstices between said varying of said phase.

27. A method according to claim 26, wherein said additionally varying said additional phase to cancel out noise of said laser output is performed, by said phase control subsystem, during said varying of said phase and without causing significant disruption of said control, by said varying of said phase, of said laser output.

28. A method according to any one of claims 21 - 27, wherein said CBC laser is a single-mode laser.

29. A method according to claim 28, wherein said CBC laser operates in a power range of several watts to several hundred kilowatts.

30. A method according to claim 29, wherein said CBC laser operates in a power range of 10W - 400kW.

31. A method according to any one of claims 21 - 30, wherein said workpiece comprises an extensive region spanning an area of up to 200 m by 200 m.

32. A method according to claim 31, wherein said workpiece comprises a panel of a liquid natural gas (LNG) tank.

33. A method according to claim 26 or claim 27, wherein said CBC laser comprises a multiplicity of optical elements wherethrough said laser output passes, said multiplicity of optical elements comprising: sub-beam alignment optics operative to align sub-beams comprising said laser output with respect to one another; and focusing optics operative to focus said sub-beams, once aligned, upon said workpiece.

34. A method according to claim 33, wherein said sub-beam alignment optics are housed in an optical head (OH) and said focusing optics are housed in a welding head, separate from said OH, wherein said focusing optics are physically separated from said sub-beam alignment optics by a distance of less than or equal to 100 meters, and said laser output propagates, from said sub-beam alignment optics to said focusing optics, through free space.

35. A method according to claim 33 or claim 34, wherein said noise is generated, at least in part, by said multiplicity of optical elements.

36. A method according to claim 35, and also comprising detecting, by at least one detector, said noise generated by said multiplicity of optical elements; and providing said additional phase variation to cancel out said noise of said laser output, based on taking into consideration said noise, generated, at least in part, by said multiplicity of optical elements, as detected by said at least one detector.

37. A method according to claim 36, wherein substantially all of said multiplicity of optical elements are located upstream from said detector, such that substantially all of said noise generated by said multiplicity of optical elements is detected by said at least one detector.

38. A method according to claim 37, wherein all of said multiplicity of optical elements are located upstream from said detector.

39. A method according to any one of claims 36 - 38, and also comprising connecting, via an optical fiber bundle, an Optical Head (OH) housing said sub-beam alignment optics to other components of said laser; and detecting, by said at least one detector, noise generated by said optical fiber bundle.

40. A method according to any one of claims 36 - 39, and also comprising directing, by a beam splitter, a portion of said laser output to be incident upon said at least one detector, wherein a mechanical distance between said beam splitter and said workpiece is greater than a mechanical distance between said beam spitter and said at least one detector.

41. A laser welding system comprising: a coherent beam combining (CBC) laser operative to provide a laser output for welding of a workpiece, said CBC laser comprising a multiplicity of optical elements wherethrough said laser output passes, said multiplicity of optical elements comprising:sub-beam alignment optics, housed in an Optical Head (OH) and operative to align sub-beams comprising said laser output with respect to one another; and focusing optics, not housed in said OH and operative to focus said subbeams, once aligned, upon said workpiece, said focusing optics being physically separated from said sub-beam alignment optics by a distance of less than or equal to 100 meters, and said laser output propagating, from said sub-beam alignment optics to said focusing optics, through free space; and a phase control sub-system electronically connected to said CBC laser, said phase control sub-system being operative to provide at least a spatial modification phase variation to vary a phase of said laser output, to dynamically control at least one of a shape and a position of said laser output during said welding.

42. A system according to claim 41, wherein said focusing optics are physically separated from said sub-beam alignment optics by a distance of 50m - 100m.

43. A system according to claim 41 or claim 42, wherein said focusing optics are: fixed in position with respect to said OH, said focusing optics being moveable in tandem with said OH during said welding; or moveable with respect to said OH, said OH being stationary and said focusing optics being moveable during said welding.

44. A system according to claim 43, and also comprising a wagon for mounting said laser welding system thereon, said OH and said focusing optics being movable in tandem along a scaffolding, by said wagon, during said welding.

45. A system according to claim 43, and also comprising a stage for mounting said laser welding system thereon, said OH and said focusing optics being moveable in tandem along a hydraulic pole, by said stage, during said welding.

46. A system according to claim 43, wherein said OH is stationary and said focusing optics are mounted on a moveable stage on a hydraulic pole, said laser output being directed, through free space, from said OH to said focusing optics; and said focusing optics being moveable by said stage, during said welding, to moveably focus said laser output on said workpiece.

47. A system according to claim 43, wherein said OH is stationary and said focusing optics are mounted on a drone, said laser output being directed, through free space, from said OH to said focusing optics, said focusing optics being moveable by said drone, during said welding, to moveably focus said laser output on said workpiece.

48. A system according to claim 43, wherein said sub-beam alignment optics and said focusing optics are housed in a welding head, also comprising said OH.

49. A system according to claim 48, wherein said welding head also comprises a detector comprising a confocal telescope and a camera.

50. A system according to claim 48 or claim 49, and also comprising a galvo- scanner.

51. A method for laser welding comprising: providing, by a coherent beam combining (CBC) laser, a laser output for welding of a workpiece, said CBC laser comprising a multiplicity of optical elements wherethrough said laser output passes, said multiplicity of optical elements comprising: sub-beam alignment optic, housed in an Optical Head (OH), and being operative to align sub-beams comprising said laser output with respect to one another; and focusing optics, not housed in said OH and being operative to focus said sub-beams, once aligned, upon said workpiece,said focusing optics being physically separated from said sub-beam alignment optics by a distance of less than or equal to 100 meters, and said laser output propagating, from said sub-beam alignment optics to said focusing optics, through free space; and varying, by a phase control sub-system electronically connected to said CBC laser, a phase of said laser output, to dynamically control at least one of a shape and a position of said laser output during said welding.

52. A method according to claim 51, wherein said focusing optics are physically separated from said sub-beam alignment optics by a distance of 50m - 100m.

53. A method according to claim 51 or claim 52, wherein said focusing optics are: fixed in position with respect to said OH, said focusing optics being moveable in tandem with said OH during said welding; or moveable with respect to said OH, said OH being stationary and said focusing optics being moveable during said welding.

54. A method according to claim 53, and also comprising mounting said laser system on a wagon, said OH and said focusing optics being movable in tandem along a scaffolding, by said wagon, during said welding.

55. A method according to claim 53, and also comprising mounting said laser system on a stage, said OH and said focusing optics being moveable in tandem along a hydraulic pole, by said stage, during said welding.

56. A method according to claim 53, and also comprising mounting said focusing optics on a moveable stage on a hydraulic pole, wherein said OH is stationary; and directing said laser output, through free space, from said OH to said focusing optics, said focusing optics being moveable by said stage, during said welding, to moveably focus said laser output on said workpiece.

57. A method according to claim 53, and also comprising mounting said focusing optics on a drone, wherein said OH is stationary; and directing said laser output, through free space, from said OH to said focusing optics, said focusing optics being moveable by said drone, during said welding, to moveably focus said laser output on said workpiece.

58. A method according to claim 53, wherein said sub -beam alignment optics and said focusing optics are housed in a welding head, also comprising said OH.

59. A method according to claim 58, wherein said welding head also comprises a detector, said detector comprising a confocal telescope and a camera.

60. A method according to claim 58 or claim 59, and also comprising scanning said laser output, by a galvo- scanner.

61. A laser welding system comprising: a coherent beam combining (CBC) laser operative to provide a laser output for butt welding of a workpiece having a gap, said gap having a width of at least 1mm; and a phase control sub-system electronically connected to said CBC laser, said phase control sub-system being operative to provide a first phase variation to vary a phase of said laser output, to dynamically control at least one of a shape and a position of said laser output incident upon said workpiece, to perform butt welding across an entirety of said gap-62. A system according to claim 61, wherein said phase control sub-system is additionally operative to provide a second phase variation to vary a phase of said laser output to cancel out noise of said laser output, said second phase variation being provided, by said phase control sub-system, during time interstices between provision of said first phase variation.

63. A system according to claim 62, wherein said phase control sub-system is operative to provide said second phase variation during provision of said first phasevariation and without causing significant disruption of said control, by said first phase variation, of said laser output.

64. A system according to any one of claims 61 - 63, wherein said CBC laser is a single-mode laser.

65. A system according to claim 64, wherein said CBC laser operates in a power range of several watts to several hundred kilowatts.

66. A system according to claim 65, wherein said CBC laser operates in a power range of 10W - 400kW.

67. A system according to any one of claims 61 - 66, wherein said CBC laser comprises a laser splitting and combining subsystem, operative to split an output of said CBC laser into a multiplicity of sub-beams and subsequently combine said multiplicity of sub-beams to form said laser output.

68. A system according to claim 67, wherein said laser splitting and combining subsystem comprises a focal lens for focusing said laser output on said workpiece, said focal lens having a focal length of at least 3m.

69. A system according to said 68, wherein said width of said gap is at least 2mm.

70. A system according to any one of claims 61 - 69, wherein said phase control subsystem being operative to dynamically control said shape and position of said laser output incident upon said workpiece comprises said phase control subsystem being operative to continuously move at least one high intensity region of a far field intensity pattern of said laser output from one side of said gap to another, during said welding of said gap, without involving mechanical motion of said CBC laser.

71. A laser welding method comprising: providing, by a coherent beam combining (CBC) laser, a laser output incident upon a workpiece having a gap, said gap having a width of at least 1mm;varying, by a phase control sub-system electronically connected to said CBC laser, a first phase of said laser output, to dynamically control at least one of a shape and a position of said laser output incident upon said workpiece; and performing butt welding, by said laser output incident upon said workpiece, across an entirety of said width of said gap.

72. A method according to claim 71, and also comprising varying, by said phase control sub-system, a second phase of said laser output to cancel out noise of said laser output, said varying of said second phase being performed, by said phase control subsystem, during time interstices between said varying of said first phase.

73. A method according to claim 72, wherein said varying of said second phase is performed, by said phase control sub-system, during said varying of said first phase and without causing significant disruption of said control, by said first phase varying, of said laser output.

74. A method according to any one of claims 71 - 73, wherein said CBC laser is a single-mode laser.

75. A method according to claim 74, wherein said CBC laser operates in a power range of several watts to several hundred kilowatts.

76. A method according to claim 75, wherein said CBC laser operates in a power range of 10W - 400kW.

77. A method according to any one of claims 71 - 76, wherein said CBC laser comprises a laser splitting and combining subsystem, for splititng an output of said CBC laser into a multiplicity of sub-beams and subsequently combining said multiplicity of sub-beams to form said laser output.

78. A method according to claim 77, and also comprising focusing, by a focal lens, said laser output on said workpiece, said focal lens having a focal length of at least 3mm.

79. A method according to said 78, wherein said width of said gap is at least 2mm.

80. A method according to any one of claims 71 - 79, wherein said varying, by said phase control sub-system, a first phase of said laser output, to dynamically control at least one of a shape and a position of said laser output comprises continuously moving at least one high intensity region of a far field intensity pattern of said laser output from one side of said gap to another, during said welding of said gap, without involving mechanical motion of said CBC laser.

81. A laser system comprising: a seed laser operative to provide a laser output; a laser beam splitting and combining subsystem comprising a multiplicity of optical elements through which said laser output passes, and operative to receive said laser output from said seed laser, split said laser output into a plurality of sub-beams and combine said plurality of sub-beams into a combined laser output having noise generated, at least in part, by said multiplicity of optical elements; at least one detector operative to sense said noise generated at least in part by said multiplicity of optical elements; a spatial modification phase-variation subsystem operative to vary phases of sub-beams of said plurality of sub-beams, to control at least one of a shape and a position of said combined laser output; and a noise cancellation phase variation subsystem operative to provide a noise cancellation phase correction output to sub-beams of said plurality of sub-beams, based on taking into consideration said noise as sensed by said detector.

82. A laser system according to claim 81, wherein: said multiplicity of optical elements comprises at least a beam alignment subsystem operative to align ones of said plurality of sub-beams with one another, a beam focusing subsystem operative to focus said plurality of sub-beams, once aligned, and a beam splitting subsystem operative to direct a portion of said plurality of sub-beams towards said detector; said detector is operative to sense said noise generated by said beam alignment subsystem, said beam focusing subsystem and said beam splitting subsystem; andsaid noise cancellation subsystem is operative to provide a noise cancellation phase correction output to sub-beams of said plurality of sub-beams, based on taking into consideration said noise generated, at least in part, by said beam alignment subsystem, said beam focusing subsystem and said beam splitting subsystem, as sensed by said detector.

83. A laser system according to claim 81 or claim 82, wherein substantially all of said multiplicity of optical elements are located upstream from said detector, such that substantially all of said noise generated by said multiplicity of optical elements is sensed by said detector.

84. A laser system according to claim 83, wherein all of said multiplicity of optical elements are located upstream from said detector.

85. A laser system according to claim 82, wherein said beam alignment subsystem comprises a plurality of collimating lenses corresponding to said plurality of sub-beams.

86. A laser system according to claim 85, wherein: said beam alignment subsystem is housed in an optical head connected, by an optical fiber bundle, to at least said seed laser; said detector is operative to additionally sense said noise generated by said optical fiber bundle; and said noise cancellation subsystem is operative to provide a noise cancellation phase correction output to sub-beams of said plurality of sub-beams, based on additionally taking into consideration said noise generated by said optical fiber bundle, as sensed by said detector.

87. A laser system according to any one of claims 81 - 86, wherein: said spatial modification phase-variation subsystem is operative to vary phases of sub-beams of said plurality of sub-beams, to control at least one of a shape and a position of said combined laser output, for laser manufacturing of a workpiece.

88. A laser system according to claim 82, wherein a mechanical distance from said beam splitting and combining subsystem to said workpiece is greater than a mechanical distance from said beam splitting and combining subsystem to said detector.

89. A laser system according to claim 88, and also comprising a confocal telescope positioned between said beam splitting and combining subsystem and said detector, for focusing said portion of said plurality of sub-beams, from said beam splitting and combining subsystem, on said detector.

90. A laser system according to claim 82, wherein said beam focusing subsystem is physically distant from said beam alignment subsystem by a distance of up to about 100 meters, said plurality of sub-beams propagating, from said sub-beam alignment subsystem to said beam focusing subsystem, through free space.

91. A method for performing phase variation of a laser output, comprising: providing, by a seed laser, a laser output; splitting said laser output into a plurality of sub-beams and combining said plurality of sub-beams into a combined laser output having noise generated, at least in part, by a multiplicity of optical elements through which said laser output passes; sensing, by at least one detector, said noise generated, at least in part, by said multiplicity of optical elements; varying, by a spatial modification phase variation sub-system, phases of subbeams of said plurality of sub-beams, to control at least one of a shape and a position of said combined laser output; and providing, by a noise cancellation phase variation sub-system, a noise cancellation phase correction output to sub-beams of said plurality of sub-beams, based on taking into consideration said noise.

92. A method according to claim 91, wherein: said multiplicity of optical elements comprises at least a beam alignment subsystem operative to align ones of said plurality of sub-beams with one another, a beam focusing subsystem operative to focus said plurality of sub-beams, once aligned, and abeam splitting subsystem operative to direct a portion of said plurality of sub-beams towards said detector; sensing, by said at least one detector, said noise generated, at least in part, by said multiplicity of optical elements comprising sensing, by said at least one detector, noise generated by said beam alignment subsystem, said beam focusing subsystem and said beam splitting subsystem; and providing, by said noise cancellation phase variation sub-system, a noise cancellation phase correction output to sub-beams of said plurality of sub-beams, based on taking into consideration said noise, comprising providing, by said noise cancellation subsystem, a noise cancellation phase correction output to sub-beams of said plurality of sub-beams, based on taking into consideration said noise generated, at least in part, by said beam alignment subsystem, said beam focusing subsystem and said beam splitting subsystem, as sensed by said detector.

93. A method according to claim 91 or claim 92, comprising locating substantially all of said multiplicity of optical elements upstream from said detector, such that substantially all of said noise generated by said multiplicity of optical elements is sensed by said detector.

94. A method according to claim 93, comprising locating all of said multiplicity of optical elements upstream from said detector.

95. A method according to claim 92, wherein said beam alignment subsystem comprises a plurality of collimating lenses corresponding to said plurality of sub-beams.

96. A method according to claim 95, comprising: housing said beam alignment subsystem in an optical head connected, by an optical fiber bundle, at least to said seed laser; sensing, by said at least one detector, noise generated by said optical fiber bundle; and providing, by said noise cancellation phase variation subsystem, a noise cancellation phase correction output to sub-beams of said plurality of sub-beams, basedon additionally taking into consideration said noise generated by said optical fiber bundle, as sensed by said at least one detector.

97. A method for laser manufacturing of a workpiece, according to any one of claims 91 - 96, and also comprising: directing said spatially modified, noise corrected, laser output to a workpiece, for performance of laser manufacturing of said workpiece.

98. A method according to claim 92, wherein a mechanical distance from said beam focusing subsystem to said workpiece is greater than a mechanical distance from said beam focusing subsystem to said detector.

99. A method according to claim 98, and also comprising focusing, by a confocal telescope positioned between said beam splitting subsystem and said detector, said portion of said plurality of sub-beams, from said beam splitting subsystem, on said detector.

100. A method according to claim 98 or claim 99, and also comprising housing said beam focusing subsystem in a welding head, said optical head being physically distant from said welding head by a distance of up to 100 meters, said plurality of sub-beams propagating, from said sub-beam alignment subsystem to said beam focusing subsystem, through free space.

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