Beam shaper optics for laser materials processing.

Abstract

An optical beam shaping element for performing beam shaping of a multimode laser beam resulting in a uniform annular intensity distribution at the focal length of a focusing lens. An optical beam shaping element having a surface with radial arms twisted to be curved to give a helical configuration, as compared to the known Siemens star beam shaper. An embodiment is described in which each of the arms in the helical configuration is additionally modified by a radially varying tilt and / or curvature to optimize the far-field distribution. Relative rotation between two optical beam shaping elements forms an adjustable trident that varies the power between the annulus and the central spot. The optical beam shaping element finds application in laser material processing, where the helical curvature can be configured to eliminate hot spots and improve through-focus performance and input sensitivity.

Description

[Technical field]

[0001] The present invention relates to an optical beam shaper for laser material processing applications. In particular, the present invention relates to an optical beam shaping element in which the optical components of the Siemens star beam shaper are twisted around their center to produce a helical or spiral configuration. This optical beam shaping element converts the laser intensity distribution into an annular distribution with uniform intensity at and around the focal plane of a focusing lens. [Background technology]

[0002] Laser beams with annular intensity profiles are often required in laser material processing such as welding, cutting, thin film material ablation, solar cell manufacturing, PCB laser drilling, and ophthalmology. To generate annular intensity distributions in the focal plane of a focusing lens, beam shapers such as classical axicons, conical lenses, rotationally symmetric prisms, etc. are often used.

[0003] US4275288 discloses a glass cone or axicon that converts the Gaussian energy distribution of a laser beam into an energy distribution of radiation impinging on a workpiece that has a circular cross section. These simple axicons are sensitive to alignment and input intensity distribution.

[0004] US10620444 discloses a diffractive optical beam shaping element for imparting a phase distribution to a laser beam intended for laser processing of a material, comprising a phase mask shaped as an area and configured to impart a plurality of beam shaping phase distributions in a laser beam incident on the phase mask. A virtual optical image is derived from at least one of the plurality of beam shaping phase distributions, which can be imaged into an elongated focus zone for effecting a modification in the material to be processed. A plurality of such elongated focus zones can be spatially added and interfere with each other to modify the intensity distribution in the material, for example to produce an asymmetric modification zone. These diffractive optical components suffer from low transmission efficiency, typically 75-95%, and are wavelength dependent.

[0005] US10444521 discloses a device for machining materials by laser radiation, comprising a focusing optical system for focusing the laser beam on the workpiece, and an adjustment optical system for adjusting the intensity distribution, comprising at least two plate-like optical elements arranged back to back in the beam path of the laser beam, rotatable relative to each other in the circumferential direction, each having a surface with a circular pattern of fan-shaped facets that are alternately inclined in the circumferential direction relative to the respective plate plane. Each plate-like optical element can be considered as a Siemens star beam shaper due to the circular pattern of fan-shaped facets according to the known Siemens star for testing imaging quality. Figure 1(a) shows a Siemens star beam shaper A according to the prior art, in which the alternately inclined fan-shaped facets B provide a circular pattern of spokes or arms C radiating from a central point D. The fan-shaped facets B in the Siemens star beam shaper are planar or curved, which results in hot spots in the annular intensity distribution, as shown in Figure 1(b). Hot spots are undesirable in laser processing applications as they can lead to localized damage and poor quality finishes. Summary of the Invention [Problem to be solved by the invention]

[0006] It is therefore an object of the present invention to provide an optical beam shaping element, and a method for manufacturing a refractive optical beam shaping element, that avoids or mitigates at least some of the disadvantages of the prior art. [Means for solving the problem]

[0007] According to a first aspect of the invention, there is provided an optical beam shaping element comprising a plate having a first surface with sector-shaped facets in a circular pattern, the element comprising: The fan-shaped facets are inclined alternately with respect to the plane of the plate in a circumferential direction from a central point; a plurality of arms radiating from a central point, each arm defining an edge between adjacent sector-shaped facets; An optical beam shaping element is provided, characterized in that the edges are curved and that the arms are curved to extend radially outward in a spiral star configuration.

[0008] In this way, the prior art Siemens star beam shaper can be thought of as twisting around its center to produce a spiral or helical star configuration, as its straight lines now become non-straight and curved, so that light that would otherwise be concentrated in a hot spot is spread out into a ring-like angular annular distribution, thus eliminating the hot spot at and around the focus of the annular distribution.

[0009] The curved edge of the spiral may be formed in a clockwise direction. Alternatively, the curved edge of the spiral may be formed in a counterclockwise direction.

[0010] Preferably, the optical beam shaping element is a refractive optical component. Alternatively, the optical beam shaping element may be a reflective optical component.

[0011] Preferably, the edges are tilted by a constant amount and rotated as a function of r, where r is the radial position.

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[0012] Preferably, each edge has a radial z scaling. Thus, the height of each edge varies radially from the center point. In this way, the added divergence that occurs can be recovered. Preferably, the radial z scaling imparts a slope to the height. More preferably, the slope decreases as a function of r, where r is the radial position.

[0013] Preferably, each facet has a curvature. Alternatively, each facet is planar, like the Siemens Star Beam Shaper. The curvature determines the amount of light that is scattered outside the annulus and the ability to combine hot spots to result in an annulus of uniform distribution.

[0014] A particularly uniform distribution of the laser energy in the ring-shaped profile can be achieved if the number of even facets is between 18 and 72, preferably between 24 and 40, in particular 36. This assumes that two facets are required for the edge forming the arms, where there can be either an even or an odd number of arms.

[0015] The optical beam shaping element may include a first surface nested within a second surface. Preferably, the direction of curvature is reversed between the first and second surfaces. The optical beam shaping element may include a first surface nested within a surface of a Siemens Star Beam Shaper.

[0016] Preferably, the optical beam shaping element includes a focus lens to provide the desired annular spot at the focal length of the focus lens. In one embodiment, the optical beam shaping element and the focus lens are separate elements and spaced apart to provide the optical system. In an alternative embodiment, the first correcting surface is combined on the entrance surface of the focus lens to provide a single optical element as the optical system.

[0017] Preferably, the optical system includes a laser, the beam of which is directed through the optical system to provide an annular intensity profile of the focused laser beam at the focal length of the focusing lens. The laser beam may be directed through a fiber. The optical system may also include a collimating lens between the laser and the optical beam shaping element. In this way, the present invention may be used in laser welding, laser cutting, thin film material ablation, solar cell manufacturing, PCB laser drilling, and ophthalmology.

[0018] There may be a second optical beam shaping element, where the first correction surface of the second optical beam shaping element is a mirror image of the first correction surface of the optical beam shaping element. Preferably, the second optical beam shaping element is configured with the first surfaces facing each other. Alternatively, the second optical beam shaping element is configured with the first surfaces facing away from each other. In this way, the first surfaces provide opposite refractive effects. In the second optical system, there are a first optical beam shaping element and a second optical beam shaping element, a collimating lens, and a focusing lens. The second optical system may include a rotation mount configured to rotate the first optical beam shaping element and the second optical beam shaping element relative to each other about a central optical axis through the optical system. By rotating the first optical beam shaping element and the second optical beam shaping element relative to each other, the intensity profile of the beam of the laser directed through the optical system can be switched between an annular intensity profile and a spot-like intensity profile when the arms of each optical beam shaping element are aligned or completely misaligned. Partial rotation may be used to create a trident where the power ratio between the core spot and the annulus can be controlled.

[0019] According to a second aspect of the present invention, there is provided a method for manufacturing an optical beam shaping element according to claim 1, comprising the steps of: (a) defining a target output far-field distribution; (b) determining the number of arms to obtain an angular distribution θ in each sector corresponding to a target output far-field distribution; (c) determining a curvature of the edge of each arm to result in a first surface having curved edges that provide a helical star configuration; (d) machining a profile of a first surface on the substrate plate to provide an optical beam shaping element.

[0020] In this way, an improved annular output beam can be formed for laser machining.

[0021] Preferably, in step (c), the curvature of the edge of each arm is

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[0022] Preferably, the method comprises in step (c) the further step of applying a curvature to each facet.

[0023] The step of adding curvature may be to widen the spot in the far field as each facet produces a spot in the far field to combine with the nearest neighbors, thus matching the beam input size, so if there are 12 arms, add 30 degrees to the spot to combine.

[0024] Alternatively, the step of adding curvature may be to vary the curvature depending on the input intensity in order to maintain uniform illumination at the annulus, thus matching the beam input size and intensity profile. For example, for a Gaussian input, the curvature needs to vary more gradually towards the periphery of the optic than in the center:

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[0025] Optionally, the step of adding curvature may be to overlap the spots much more than their angular separation, thus making them less sensitive to beam size and profile (within tolerances). The angle added to each spot is much larger than the angular separation in the far field, which has an averaging effect making it less sensitive to changes in input size and intensity profile.

[0026] Preferably, in step (b), the height of the edge relative to the plane of the plate is scaled as a function of radial position, in this way recovering the radial scattering outside the annulus caused by the added curvature, more preferably the height decreases in slope as a function of r, where r is the radial position.

[0027] According to a third aspect of the invention there is provided a method for producing an annular intensity profile from a beam of a laser, comprising the steps of: (a) providing a first optical beam shaper element according to a first aspect; (b) disposing a first optical beam shaper element in an optical system including a collimating lens and a focusing lens; (c) positioning an optical system between the laser beam and the workpiece to produce an annular intensity profile on the workpiece.

[0028] In this manner, the optical beam shaper can be used in laser processing applications to provide a laser beam having an annular intensity profile on a work piece.

[0029] Preferably, the laser beam is from a fiber. The laser beam may be a multimode beam.

[0030] The method may include providing a second optical beam shaper element in the optical system. More preferably, the second optical beam shaper element is a mirror image of the first optical beam shaper element, with their first surfaces configured to face each other. The method may include rotating at least one of the first optical beam shaper element and the second optical beam shaper element about a central optical axis of the optical system such that the first optical beam shaper element and the second optical beam shaper element rotate relative to each other. More preferably, the rotation comprises: a first configuration, in which edges of the arms at a first surface of the first optical beam shaper element and the second optical beam shaper element are aligned to generate an annular intensity profile at the workpiece; a second configuration in which edges of the arms on the first surface of the first optical beam shaper element are aligned with valleys between the arms on the first surface of the second optical beam shaper element to generate a spot-like intensity profile at the workpiece.

[0031] In this way, the optical system can provide switching between a spot-like intensity profile and an annular intensity profile. If the laser beam is from a fiber, the spot-like intensity profile may be an image of the fiber core.

[0032] Preferably, the method includes rotating at least one of the first and second optical beam shaper elements relative to one another between a first configuration and a second configuration, thereby varying the power in the intensity profile, thus forming an adjustable trident.

[0033] In the following description, the drawings are not necessarily drawn to scale. Certain features of the invention may be shown in exaggerated scale or somewhat schematic form, and some details of conventional elements may not be shown in terms of clarity and conciseness. It should be appreciated that the various features and teachings of the embodiments discussed below can be employed individually or in any suitable combination to produce the desired results.

[0034] Embodiments of the present invention will now be described, by way of example only, and with reference to the following figures. [Brief description of the drawings]

[0035] [Figure 1a] FIG. 1 is a schematic diagram of a Siemens star beam shaper according to the prior art. [Figure 1b] 1 is a modeled intensity distribution of the output annular spot of a Siemens star beam shaper according to the prior art. [Figure 2a] 1 is a modeled surface design of a prior art Siemens star beam shaper. [Figure 2b] 1 is a modeled surface design of an optical beam shaping element according to an embodiment of the present invention. [Diagram 3] 1 is an optical system according to an embodiment of the present invention incorporating a refractive optical beam shaping element according to an embodiment of the present invention. [Figure 4] 4 is a sequence of intensity distributions of an output beam passing through a focal point for an optical beam shaping element according to an embodiment of the present invention. [Diagram 5] 5 is a sequence of intensity distributions of the output beam passing through the focal point for a prior art Siemens star beam shaper for comparison with FIG. 4 . [Figure 6a] 11 is a graph illustrating the geometry used in calculations in an example calculation for an optical beam shaping element according to an embodiment of the present invention. [Figure 6b] 11 is a graph illustrating the geometry used in calculations in an example calculation for an optical beam shaping element according to an embodiment of the present invention. [Figure 6c] 11 is a graph illustrating the geometry used in calculations in an example calculation for an optical beam shaping element according to an embodiment of the present invention. [Figure 6d] 11 is a graph illustrating the geometry used in calculations in an example calculation for an optical beam shaping element according to an embodiment of the present invention. [Figure 7a] 3A-3C are schematic diagrams of curved edges in an optical beam shaping element according to an embodiment of the present invention for a flat top; [Figure 7b] FIG. 2 is a schematic illustration of curved edges in an optical beam shaping element according to an embodiment of the present invention for a Gaussian input laser beam; [Figure 8a] 1 is a modeled intensity distribution showing no curvature applied to an optical beam shaping element according to an embodiment of the present invention. [Figure 8b] 1 is a modeled intensity distribution showing an optimized curvature applied to an optical beam shaping element according to an embodiment of the present invention. [Figure 8c] 1 is a modeled intensity distribution showing too little curvature applied to an optical beam shaping element according to an embodiment of the present invention; [Figure 8d] 1 is a modeled intensity distribution showing too high a curvature applied to an optical beam shaping element according to an embodiment of the present invention; [Figure 9a] 13 is a modeled intensity distribution showing the annulus being widened after applying curvature. [Figure 9b] 9(b) is a modeled intensity distribution showing a corrected annulus after applying a pre-scaling slope factor to the optical beam shaping element of FIG. 9(a). [Figure 10] 11 is a height map of a surface of nested optical beam shaping elements according to an embodiment of the present invention. [Figure 11] 13 is a height map of a surface of nested optical beam shaping elements according to a further embodiment of the present invention; [Figure 12]1 is an optical system according to an embodiment of the present invention incorporating a first optical beam shaping element and a second optical beam shaping element according to an embodiment of the present invention; [Figure 13a] 13 is a modeled surface design of a first optical beam shaping element for use in the optical system of FIG. 12. [Figure 13b] 13 is a modeled surface design of a second optical beam shaping element for use in the optical system of FIG. 12. [Figure 14a] FIG. 13 is a schematic diagram of the alignment of the arms between a first optical beam shaping element and a second optical beam shaping element in a first configuration in the optical system of FIG. 12; [Figure 14b] FIG. 13 is a schematic diagram of the alignment of the arms between the first and second optical beam shaping elements in the optical system of FIG. 12 in a second configuration. [Figure 15a] A sequence of intensity distributions of an output beam passing through the optical system of Figure 12 as the first optical beam shaping element and the second optical beam shaping element are rotated relative to each other from a first configuration, through a second configuration, and back to the first configuration. [Figure 15b] A sequence of intensity distributions of an output beam passing through the optical system of Figure 12 as the first optical beam shaping element and the second optical beam shaping element are rotated relative to each other from a first configuration, through a second configuration, and back to the first configuration. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] Reference is first made to Figure 2(a), which shows the surface of an optical beam shaping element, a prior art Siemens star beam shaper, generally designated by reference numeral 10. Although shown as a square, it can be of any shape, typically a round 25 mm square made of fused silica, quartz glass, sapphire or ZnSe. 2The surface 12 is formed by micromachining a square or rectangular 1 mm thick substrate plate. The surface 12 is shown on the height map as a circular pattern of fan-shaped facets 16. The edges 18 of the facets 16 are straight and provide spokes or arms 20 radiating from a central point 22 representing a Siemens Star imaging target, as is known in the art. At each edge 18 the surface is tilted by a constant amount, resulting in ridges and valleys that are at constant heights across the surface. Twenty-four facets 16 are shown, although there may be any even number.

[0037] Reference is now made to Fig. 2(b), which shows a surface 112 of an optical beam shaping element 100 according to an embodiment of the present invention. Similar parts to those in Fig. 2(a) are given the same reference numerals, with 100 added to aid clarity. Surface 112 is modelled against surface 12, and has the same number of facets 116, edges 118 and arms 120, but edges 118 are curved rather than straight, radiating from a centre point 122. Edges 112 describe an arc that can be considered to be formed by twisting surface 12 in a clockwise direction around centre point 122. Facets 116 now appear as spirals, and edges 118 are spiralled. Arms 120 are no longer straight spokes 20.

[0038] In use, the optical beam shaping element 100 is placed in the optical system 24 as shown in FIG. 3. The optical beam shaping element 100 consists of a single optically refractive surface 112. In this figure, the optical beam shaping element 100 is refractive, but may also be configured as a reflective optical element. A laser 26, typically multimode through a fiber 28, provides an input beam 30 configured to be incident on the surface 112 of the refractive optical beam shaping element 100. A collimator 32 provides a collimated input beam 30. The element 100 modifies the far field on the input beam into a ring-like or annular distribution by splitting the input beam 30 into multiple beamlets 34, which are then stretched and overlapped in the far field. The transmitted beamlets 34 pass through a focusing lens 36, resulting in an annular spot 40 at the focal length 38 of the lens 36. This location may be configured to be incident on a workpiece 42 for irradiation with an output beam 44. A uniform annular intensity distribution is obtained not only at the focus, but also before and after the focus. In this configuration, there is a separation between element 100 and focusing lens 36, each of which is a separate optical component in system 24.

[0039] The refractive optical beam shaping element 100 of the present invention advantageously removes the hotspot from the annular intensity distribution seen in the axicon and in the Siemens star beam shaper (see FIG. 1(b)), because by twisting the arms 120, the light that would otherwise be concentrated in the hotspot spreads out into a ring-shaped angular distribution. The axicon suffers from a sharp change in the through-focus behavior as a result, because the rays in the outer part of the collimated beam become radial rays. The use of the Siemens star beam shaper provides better results than the axicon, because the rays in the outer part of the collimated beam become skew rays not only at the focal plane but also near the focal plane. For the present invention, the radial component increases, but is still mainly skew, and the number of arms reduces the skew component. Reference is now made to FIGS. 4 and 5, which show comparative through-focus propagation intensity distribution sequences for the refractive optical beam shaping element 100 of the present invention and for the Siemens star beam shaper, respectively. Here, the focal length of the focus lens 36 is 150 mm. The element 100 exhibits a beam intensity distribution that exhibits a torsional effect, but has a higher degree of uniformity and a smaller spot size than the prior art.

[0040] Considering the beam path through the optical system 24, starting with the Siemens star beam shaper, consider the edge 18 at a spoke 20 where two facets 16 meet. This provides a roof prism 46 that deflects the beam from each facet by an angle α, as shown in Figure 6(a). In the far field, two spots 48a,b are produced at angular radius α and planar angle θ+ / -(π / 2). This is shown in Figure 6(b) and occurs at each spoke 20.

[0041] If the incident power density varies rotationally symmetrically as I(r) (see Fig. 6(c)), the surrounded power is

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[0042] In the present invention, twisting the spokes into a spiral effectively "joins the points." The roof prism 46 is now on a curve or spiral (see FIG. 6(e)). For continuous loops, uniform power at every angular interval is desired. For N spokes, the angle

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[0043] Referring to FIG. 6(f) and FIG. 6(g),

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[0044]

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[0045] Thus, the curvature of the arms 120 on the correction surface 112 for a flat-top input beam gives a true spiral, as shown in Figure 7(a). For a Gaussian, the spots start and end radially, but rather it becomes a twisted spiral, as the end of each spoke is at the angle of the start of the next spoke (see Figure 7(b)).

[0046] Thus, in the method of manufacturing the optical beam shaping element 100, the starting point is the surface of a Siemens star beam shaper, which has a circular pattern of sector-shaped facets, each with the same constant magnitude of inclination, but with a direction perpendicular to r. The angular distribution in each section corresponds to the desired output far-field distribution. The arms 20 extending radially at θ about the surface of the prior art Siemens star beam shaper are now

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[0047] Curvature is then added to each facet 116 along its edge 118. There are several ways to do this.

[0048] Option 1: Match input beam size. Each facet 116 results in a spot in the far field (see FIG. 8(a)). Add enough curvature to spread the spot in the far field, thereby combining with the nearest spots, as in FIG. 8(c). Thus, for 12 arms 120, 30 degrees is added to the spot 48 to combine.

[0049] Option 2: Match the input beam size and intensity profile. Vary the curvature depending on the input intensity to maintain uniform illumination at the annulus. For example, for a Gaussian input, the curvature should vary more gradually towards the periphery of the optical element 100 than in the center:

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[0050] Option 3: Make it insensitive to input beam size and intensity profile (within an acceptable range). Overlap the spots 48 by much larger than their angular separation. Thus the angle added to each spot 48 is much larger than their angular separation in the far field. This has an averaging effect that makes it insensitive to changes in the input beam size and intensity profile.

[0051] Each option will provide a different first surface 112 for the optical beam shaper element 100 of the present invention. Note that each option will add an element of radial scattering outside the annulus. Adding a small curvature to the tool will result in hot spots being formed as the spots 48 are not coupled, as shown in FIG. 8(c). If too much curvature is added, the curvature of the facets will have the effect of widening the annulus, changing the slope of the surface to the point where the light is scattered outside the annulus, as seen in FIG. 8(d). The objective is not to widen the annulus, but to add curvature to couple the hot spots, which will vary depending on the system setup and the relative sizes of the imaged fiber and the target annular spot 40.

[0052] The widening of the annulus can be compensated for by scaling the z height of the first surface 12. In the Siemens star beam shaper 10, each spoke 20 has the same height in the z axis (shown in greyscale in FIG. 2(a)). Looking at the far field in polar coordinates, as shown in FIG. 9(a), the widening of the annulus is mainly in θ, with a slight effect of widening the annulus in r. The widening in r can be reduced by scaling the height as a function of r, thus reducing the tilt. In the first surface 112, the height is scaled as a function of r. In this way, the absolute tilt of each arm 120 decreases as r increases. This narrows the annulus, as shown in FIG. 9(b). The annulus may then be increased again by iteratively adding curvature to arrive at an optimal design.

[0053] Essentially, by rotating the sag value as a function of r, a "twist" is added to the Siemens star beam shaper design. This means that the facets on the sector are no longer flat and therefore do not have all the light incident at a constant number of angles resulting in hot spots. This creates the problem that the absolute deflection angle of the facets is no longer constant and therefore the annulus is widened in the far field. This can be corrected by pre-scaling the star sag value to decrease the tilt as a function of r, which is then re-corrected by the twist.

[0054] Once the first surface 112 is defined, the optical beam shaper element 100 is constructed by known laser optical machining processes, such as direct writing on the substrate, to produce the profile of the modified surface 112 on the plate.

[0055] The optical beam shaper element 100 of the present invention, and in particular the first surface 112, are suitable for components in nested optics. For example, an axicon can be shaped at its center to the profile of the first surface 112. Referring to FIG. 10, a height map of a nested optic 50 is shown, in which the central circular section is formed by a first surface 112a with a counterclockwise twist, and the outer section is formed by a second surface 112b with a curvature in the opposite direction to the first surface 112a. An alternative nested optic 50a is shown in FIG. 11. The nested optic 50a has a first surface 112 within the surface 12 of the Siemens Star Beam Shaper. Such optics are easier to manufacture and less sensitive to changes in the input beam. Nesting twist improves the symmetry of the spot 40 away from the focus, an important consideration in laser metal cutting.

[0056] Reference is now made to FIG. 12 of the drawings, which shows an optical system 224 in which the first optical beam shaping element 110 and the second optical beam shaping element 210 are present. The first optical beam shaping element 110 is provided as described above for the optical beam shaping element 100 and is a beam shaper consisting of a single optical refractive surface 212a with a spiral Siemens star profile. The second optical beam shaping element 210 is a mirror image of the first optical beam shaping element 110. In the illustrated embodiment, the elements 110, 210 are configured in the optical system 224 such that the machined refractive surface 212b of the second beam shaping element 210 faces the surface 212a of the first beam shaping element 110. Alternatively, the elements 110, 210 may be configured such that the surfaces 212a and 212b face away from each other.

[0057] The design flow resulting in the surfaces 212a,b is the same as the standard single plate helical beam shaper 100 as described above, with two additional steps resulting in the second surface 212b. Because the curved facets of the optical surfaces 212a, 212b need to line up, this means that one must be a mirror image of the other. One way to do this is to redesign applying the opposite curvature, but a quicker way is to invert the z-values ​​in x or y to get a mirror image of the original surface. The next step is to divide the z-values ​​of the surfaces by 2, which means that each facet on each plate has half the intended deflection, and when both are used in combination, the required spot size is produced. Height maps of the surfaces 212a and 212b are shown for the example design in Figures 13(a) and 13(b), respectively. These show the mirror images of each other when the surfaces 212a, 212b are arranged facing each other and when they are arranged facing away from each other.

[0058] Returning to Fig. 12, the optical system 224 is typically configured with a multimode laser 226 through a fiber 228 to provide an input beam 230 configured to be incident on a surface 212a of the first refractive optical beam shaping element 110 facing a surface 212b of the second refractive optical beam shaping element 210. The elements 110, 210 modify the input beam 230 as described above to provide a number of beamlets 234 that are collimated by a collimator 232. The collimated beamlets 234 are passed through a focusing lens 236 resulting in a spot 240 at a focal length 238 of the lens 236. This position may be configured to be incident on a workpiece 242 for irradiation with an output beam 244.

[0059] In this configuration, the first optical beam shaping element 110 and the second optical beam shaping element 210 can rotate relative to each other around the optical axis of the system 224. A rotation mount 15 is shown connected to element 210 for this purpose, but may be connected to either or both elements if desired. Consider each arm or spoke 220a,b having edges 218a,b that can be described as peaks 17a,b with valleys 19a,b between adjacent peaks on each surface 212a,b, as shown in Figures 13(a) and 13(b). When the surfaces 212a,b face each other, it is clear that there are various stages of relative rotational alignment where the surfaces 212a,b are perfectly aligned from peak 17a to peak 17b or from peak 17a to valley 19b. The alignment from peak 17a to peak 17b maximizes the phase difference through the optical system, producing an annular intensity profile on the spot 240. Aligning the peak 17a to the valley 19b minimizes the phase difference so that at the focus we see an image of the fiber core, i.e., a spot-like intensity profile at spot 240. Points between these two extremes lie on a continuum so that the amount of power in the center or ring can be adjusted, forming an adjustable trident.

[0060] This alignment is shown in Figures 14(a) and 14(b). Figure 14(a) shows the alignment from peak 17a to peak 17b, and Figure 14(b) shows the alignment from peak 17a to valley 19b. If the peaks were aligned at 0 degrees, and therefore there was no rotational misalignment, then in this neutral position, an annular spot 240 would result. To move from the peak to the valley position where the spot is visible, one would need to move half a period. For example, if one had 24 arms 220a,b, one would need to move 7.5 degrees (each arm would appear as a roof prism and occupy 360 / 24 degrees). In Figure 14(a), the 24 arms 220a,b are positioned from peak 17a to peak 17b, so from point to point they occupy 15 degrees in polar coordinates. If element 212b is rotated out of angle space, then distance "A" would be 15 degrees. In this first configuration, the phase difference is maximized and a spot 240 with an annular intensity profile is produced. Referring now to FIG. 14(b), a half period shift is depicted. The distance "B" is 7.5 degrees for the 24 arms 220a,b when the peaks 17a and valleys 19b are aligned. This second configuration minimizes the phase difference and the two elements 110, 210 cancel, so that the image of the core of the fiber 228 is produced as a spot 240 at the workpiece 242. Therefore, the optical system 224 can be considered to provide an on / off configuration for laser processing.

[0061] Reference is now made to Figures 15(a) and 15(b) of the drawings which show a sequence of modelled intensity distributions of a spot 240 when an element 110, 210 having 24 arms 220a,b is rotated by 15 degrees relative to each other as explained above with reference to Figures 12 to 14. At 0 and 15 degrees an annular intensity distribution is seen, at 7 to 8 degrees a central spot-like intensity distribution results, between this first and second configuration there is a continuous power transfer between the centre and the annulus forming an adjustable trident such that the amount of power at the centre or at the annulus can be adjusted.

[0062] A primary advantage of the present invention is that it provides an optical beam shaping element that provides an output beam having a uniform annular intensity distribution with reduced hot spots suitable for laser material processing.

[0063] A further advantage of the present invention is that it provides a method for manufacturing an optical beam shaping element, in which the surface of a known Siemens star beam shaper is modified by introducing a twist.

[0064] A further advantage of embodiments of the present invention is that they provide an apparatus and method for providing a beam for laser processing that is switchable between a ring and a center intensity distribution while forming an adjustable trident that varies power between the center or the ring.

[0065] It will be apparent to those skilled in the art that the present invention can be applied in various ways, such as that disclosed in US10444521, where multiple stacked optical beam shaping elements can be used in the optical system, the optical beam shaping elements can be rotated during use, and the input laser beam can be switched on and off. Also, the optical system may be positioned on a structure such that it can be moved over the workpiece.

Claims

1. 1. An optical beam shaping element including a plate having a first surface with sector-shaped facets in a circular pattern, the sector-shaped facets are inclined in alternating directions from a central point in a circumferential direction relative to the plane of the plate; a plurality of arms radiating from said central point, each arm defining an edge between adjacent sector-shaped facets; An optical beam shaping element, wherein the edges are curved, and the arms are curved as they extend radially outward in a spiral star configuration.

2. 2. The optical beam shaping element of claim 1, wherein the facets on either side of each edge are tilted by a constant amount and rotated as a function of r, where r is radial position.

3. Each arm is [0010] 2. The optical beam shaping element of claim 1, wherein r is the radial position and θ is an angle equal to 360 divided by the number of arms.

4. The optical beam shaping element of claim 1 , wherein each edge has a radial z-scaling.

5. 5. The optical beam shaping element of claim 4, wherein the radial z scaling imparts a slope to the height, the slope decreasing as a function of r, where r is the radial position.

6. The optical beam shaping element of claim 1 , wherein each facet has a curvature.

7. The optical beam shaping element of claim 1 , wherein the optical beam shaping element comprises the first surface nested within a second surface.

8. The optical beam shaping element of claim 7 , wherein the direction of the spiral is reversed between the first surface and the second surface.

9. The optical beam shaping element of claim 1 , wherein the first surface comprises a surface having a plurality of arms with no curvature nested within the surface in a Siemens Star configuration.

10. the optical beam shaping element includes a focus lens, the optical beam shaping element and the focus lens being separate elements and spaced apart to provide an optical system; 2. The optical beam shaping element of claim 1, wherein the optical system includes a laser, the beam of the laser being directed through the optical system to provide an annular intensity profile of the focused laser beam at a focal length of the focusing lens.

11. The optical beam shaping element of claim 10 , wherein the laser beam is directed through a fiber.

12. The optical beam shaping element of claim 10 , wherein there is a second optical beam shaping element having a first surface that is a mirror image of the first surface of the optical beam shaping element.

13. 1. A method for producing an annular intensity profile from a beam of a laser, comprising: (a) providing a first optical beam shaper element according to claim 1; (b) disposing the first optical beam shaper element in an optical system including a collimating lens and a focusing lens; (c) positioning the optical system between the laser beam and the workpiece so as to provide an annular intensity profile on the workpiece.

14. (d) the additional step of providing a second optical beam shaper element, the second optical beam shaper element being a mirror image of the first optical beam shaper element; (e) rotating at least one of the first optical beam shaper element and the second optical beam shaper element about a central optical axis of the optical system such that the first optical beam shaper element and the second optical beam shaper element rotate relative to each other to obtain two operating configurations, specifically: a first configuration, wherein the edges of the arms at the first surface of the first optical beam shaper element and the second optical beam shaper element are aligned to generate an annular intensity profile at the workpiece; 14. The method of claim 13, comprising the additional step of providing a second configuration in which the edges of the arms at the first surface of the first optical beam shaper element are aligned with valleys between the arms at the first surface of the second optical beam shaper element to produce a spot-like intensity profile at the workpiece.

15. 15. The method of producing an annular intensity profile from a beam of a laser as described in claim 14, the method comprising rotating at least one of the first and second optical beam shaper elements relative to one another between the first and second configurations, thereby varying power in the intensity profile to form an adjustable trident.

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