Laser optics and method for laser cutting by means of an annular intensity distribution and correspondingly designed laser system

Abstract

The invention relates to a laser system (1), optics (7) for same and a method for operating the laser system (1) for machining a workpiece (2). The optics (7) comprise a light guide (5) for simultaneously coaxially transporting a first laser beam (18) as a single-mode or quasi-single-mode laser beam (18) and a second laser beam (21) as a multi-mode laser beam (21). The optics (7) also comprise an optical device (14) arranged in the beam path of the first laser beam (18) for imposing a phase singularity and / or a polarisation singularity on the first laser beam (18) for generating an annular intensity distribution (18) of the first laser beam (18) with a central intensity minimum (19) on the optical axis (13) of the optics (7).

Description

[0001] Laser optics and method for laser cutting using an annular intensity distribution and correspondingly configured laser system

[0002] The present invention lies in the field of laser technology. The invention relates to an optics system for a laser system, which is particularly intended for laser cutting. Furthermore, the invention relates to such a laser system and a method for processing, in particular cutting, a workpiece therewith.

[0003] Lasers offer a wide range of useful possibilities for non-contact material processing, such as material removal or cutting a workpiece. The effect of laser light can melt and / or vaporize material, allowing a cutting gap to be created, for example, by guiding a laser beam over a workpiece. The cutting behavior and / or properties of the cutting gap or the resulting cutting edge of the remaining material can be influenced by adjusting the laser system and the laser light.

[0004] For example, WO 2019 / 150071 A1 describes a device for laser processing a material. This device comprises a pressure mechanism for compressing a periodically structured surface and an optical fiber. This allows a first optical mode and a second optical mode of laser radiation propagating in the optical fiber to be coupled. The resulting laser light is intended to enable material processing that reduces the disadvantages or undesirable effects known from other laser-based material processing methods.

[0005] A similar approach is also described in WO 2019 / 150070 A1. Therein, a device for laser processing a material is described, which device has a laser, an optical fiber, and a coupler. The optical fiber is designed such that laser radiation can propagate therein in a first optical mode, a second optical mode, and a third optical mode, wherein the mode order of the third optical mode is the largest and the mode order of the first optical mode is the smallest. The coupler is configured to convert laser radiation propagating in the first optical mode into laser radiation propagating in the second optical mode. Furthermore, the coupler is configured to convert laser radiation propagating in the second optical mode into laser radiation propagating in the third optical mode.This should also enable laser-based material processing that reduces known disadvantages and undesirable effects.

[0006] Despite the various known approaches to optimizing laser-based material processing, no optimal result can yet be reliably achieved, for example with regard to a precisely shaped cutting gap geometry and / or with regard to thermal effects due to a temperature gradient between the material exposed to the laser light and the material surrounding it and / or the like.

[0007] The object of the present invention is to enable improved cutting performance and cutting gap quality in laser cutting.

[0008] The problem is solved by the subject matter of the independent claims. Further possible embodiments of the invention are specified in the subclaims, the description, and the drawings. Features, advantages, and possible embodiments presented in the description for one of the subject matter of the independent claims are to be regarded at least analogously as features, advantages, and possible embodiments of the respective subject matter of the other independent claims, as well as any possible combination of the subject matter of the independent claims, optionally in conjunction with one or more of the subclaims.

[0009] The optics according to the invention can be used advantageously, in particular, in a laser system for laser cutting workpieces or materials. However, other applications are also possible. An optics system in the present sense can be understood, in particular, as an arrangement or combination of several components for transporting, guiding, influencing, or shaping or conditioning light, in particular laser light or at least one laser beam. The optics according to the invention comprise a light guide for the simultaneous coaxial transport, i.e., guiding or directing, of a first laser beam as a single-mode or quasi-single-mode laser beam and a second laser beam as a multimode laser beam.In other words, the optical fiber is designed, for example, to transport a first portion of light coupled into the optical fiber at the input side, corresponding to the first laser beam, in the fundamental mode or at least close to or largely in the fundamental mode, and a second portion of light coupled into the optical fiber at the input side, corresponding to the second laser beam, farther away from the fundamental mode, in a plurality of different modes. In other words, the first laser beam can have a smaller diffraction index M. 2, i.e., a greater or higher beam quality, than the second laser beam. The light guide can in particular be or comprise an optical waveguide or a fiber optic cable, i.e., an optical fiber or glass fiber. The laser beams can, for example, be completely or partially overlapped or separated from one another or guided separately in the light guide. The light guide can, for example, have a light guide region for both laser beams, into which the already different laser beams can be coupled on the input side. Likewise, the light guide can, for example, have multiple light guide regions.This means that, for example, the first laser beam can be guided only or primarily in a first light-guiding region of the optical fiber, while the second laser beam can be guided only or primarily in a different second light-guiding region, or, for example, partially in the first light-guiding region and partially in the second light-guiding region. The light-guiding regions can, for example, be directly adjacent to one another or separated or spaced apart from one another by a so-called cladding. This is explained in more detail elsewhere. The thickness of this cladding, if provided, in the radial direction can, for example, be selected depending on the design or requirements in the individual case.

[0010] The optical system according to the invention further comprises an optical device for imposing a phase singularity and / or a polarization singularity on the first laser beam, i.e., on the single-mode or quasi-single-mode portion of the light guided in the optical fiber or exiting the optical fiber at the output side. This optical device is thus configured or designed to generate an annular intensity distribution of the first laser beam with a central intensity minimum on the optical axis of the optical system. In other words, this optical device can convert, for example, an at least substantially Gaussian intensity distribution of the first laser beam into an annular intensity distribution. There are various ways to achieve this effect, and correspondingly various ways to specifically design the optical device, which will be explained in more detail elsewhere.For example, the optical device can be or include a spiral phase plate and / or a spatial light modulator, such as a liquid crystal display or a DMD (Digital Micromirror Device) for imposing the phase singularity and / or an S-wavelength retardation plate for imposing the polarization singularity. The correspondingly imposed phase or polarization singularity can also be verified metrologically, depending on the design, for example, using an interferometer or a liquid crystal display in combination with a camera, or using a rotating polarization filter or the like.

[0011] In the optics according to the invention, the optical device is arranged in the intended light or beam path of at least the first laser beam. Along the longitudinal direction of this beam path, i.e., in or along the intended beam propagation direction of the first laser beam in the optics or viewed through the optics, the optical device is arranged downstream of the light guide. The optical device can therefore be arranged directly at an output end of the light guide, for example, by plugging or splicing or the like, or can be arranged at a distance from the output end of the light guide, so that the first laser beam transported in the light guide can exit the light guide and then enter the optical device or radiate through it.Depending on the design, the optical device can be or comprise a single optically active element or component or an arrangement or combination of several components.

[0012] The optical device can also be arranged in the beam path of the second laser beam, i.e., can be traversed by it during operation. In practice, however, only the single-mode or quasi-single-mode portion of the laser light traversing the optical device is significantly influenced by the optical device. Thus, the phase and / or polarization singularity is imposed on the first laser beam by the optical device, thereby generating the annular intensity distribution, while the second laser beam can traverse the optical device at least substantially unchanged or unaffected, thus retaining its original intensity distribution, i.e., the intensity distribution existing before the optical device, and thus also after the optical device.

[0013] The first laser beam can be used for the actual cutting or melting of the material exposed to the laser beam. The first laser beam can therefore be used to create the actual cutting gap. The first laser beam can be optimized particularly effectively and specifically for this task, for example, by appropriately designing or adapting the optical device for a specific situation or application, such as the material to be cut.

[0014] At the same time, the second laser beam can be available or used for other tasks or effects. For example, the second laser beam can also or only hit the respective workpiece or material outside the actual cutting gap, or at least be essentially absorbed in the entry area of ​​the cutting gap. This can, for example, round off or fillet the otherwise sharp-edged geometry of the upper, i.e. entry-side, cutting edge of the cutting gap - for example, when the first laser beam is used alone. Such rounding can be particularly aerodynamic and thus, for example, enable more effective or efficient removal of molten or vaporized material from the cutting gap. In other words, the second laser beam can shape the upper area of ​​the cutting gap, viewed in cross-section, into a type of inlet funnel.In addition, by irradiating an area surrounding the actual cutting gap with the second laser beam, a temperature gradient in the respective workpiece or material can be flattened or adjusted. This can prevent or reduce corresponding undesirable thermal effects or stresses, etc.

[0015] The shared coaxial guidance of the laser beams in the optical fiber always ensures reliable and consistent overlap or spatial relationship between the first laser beam and the second laser beam. However, since the second laser beam, unlike the first laser beam, is a multimode laser beam, the optics enable different or selective influences on the two laser beams. This ultimately allows different individual intensity distributions of the two laser beams to be achieved despite the overlapped, coaxial, or concentric arrangement or guidance of the two laser beams. This enables particularly simple and flexible adaptation to different requirements or applications.

[0016] Furthermore, it has been shown that the annular intensity distribution of the first laser beam generated by the optical device, i.e. by the imposition of the phase and / or polarization singularity, is not only present in the central focal point, but can propagate, i.e. be maintained, in the longitudinal direction, i.e. in the direction of light or beam propagation along the beam path, over more than one Rayleigh length. In particular, the annular shape can propagate or be maintained, starting from the central focal point, in the positive and negative longitudinal direction or beam propagation direction for at least one Rayleigh length in each case, i.e. over a total of at least two Rayleigh lengths. Thus, the annular intensity distribution or its central intensity minimum can be reached or maintained over a length, depending on the application.which can be in the range of the thickness of the workpiece or material to be cut. This is typically not the case with previous approaches to generating or using an annular intensity distribution of a cutting laser beam and can represent a significant advantage in practice. With the present invention, particularly homogeneous, i.e. constant, absorbed intensities can then be achieved on the absorption front - within narrower limits than with previous approaches. This makes it possible, for example, to achieve an improved burr-free cutting gap or a resulting cutting edge when laser cutting sheet metal, particularly at high feed rates. The present invention therefore simultaneously enables a particularly high cutting gap quality and a particularly high feed rate, i.e. a particularly high cutting performance.

[0017] In addition, the present invention thus offers the possibility of specifically shaping the cutting gap in depth or in the lower region, i.e. in the exit region. The lower region or exit region here is the region of the cutting gap that is located on a side of the respective workpiece or material facing away from the optics during operation. The present invention can therefore provide a further degree of freedom for shaping the cutting gap by appropriately parameterizing or adapting the first laser beam using the appropriately designed optical device. This means that, for example, the region of the cutting gap that lies below the rounding that may have been generated on the input side by the second laser beam can also be adapted or specifically shaped.

[0018] The optics can also have or include further components, such as collimating optics, i.e. partial optics for collimating the laser light emerging from the light guide and / or focusing optics, i.e. partial optics for focusing the - optionally collimated - laser light into a focal point or focal area or onto the workpiece or material to be cut or machined, and / or an output-side or surrounding protective glass and / or an adjusting device for setting or adapting the optics, for example by moving at least one optical component along the optical axis, i.e. in the light or beam propagation of the laser beam, and / or perpendicular thereto, and / or corresponding holders for fixing the said components and / or a housing surrounding the said components and / or the like.

[0019] In a possible embodiment of the present invention, the optical fiber is designed or configured to direct the first laser beam with a diffraction index M 2 <2, especially M 2 < 1 ,7, and the second laser beam with a diffraction index M 2 > 2 or M 2 > 1.7. In other words, the first laser beam can be guided in the light guide with at least nearly limited diffraction, or at the diffraction limit, while the second laser beam can be guided without diffraction, i.e., further away from the diffraction limit. This can be achieved, for example, by using appropriate materials for the light-guiding regions, i.e., the light-guiding core regions, and the cladding regions surrounding them, and / or the diameter of the light-guiding region(s) – possibly depending on the wavelength(s) used for the laser beams.

[0020] For example, the first laser beam at M 2 < 1 ,3 as a pure single-mode laser beam and at M 2 < 1 .5 is considered a quasi-single-mode laser beam. The different diffraction coefficients M 2 The corresponding steel grades for the two laser beams have proven useful in practice. For example, even when both laser beams pass through the optical device, it can be reliably achieved that only, or at least primarily, the first laser beam is influenced, i.e., its intensity distribution is changed, while the second laser beam can remain at least essentially unaffected.

[0021] In a further possible embodiment of the present invention, the light guide has an inner core or light guide region for transporting the first laser beam and an outer core or light guide region for transporting the second laser beam. The outer light guide region surrounds the inner light guide region in a ring shape, resulting in an intensity distribution of the second laser beam that surrounds the first laser beam in a corresponding ring shape. This ring-shaped intensity distribution of the second laser beam results from the ring-shaped or tubular shape of the outer light guide region. The inner light guide region, on the other hand, can have a fully cylindrical shape, for example, and thus be circular disk-shaped in cross-section. The inner light guide region can in particular form the center of the light guide.The outer light guide region, however, can surround the center, i.e., the central longitudinal axis of the light guide, coaxially or concentrically. Since the second laser beam remains at least substantially unaffected by the optical device or can propagate past it, a ring-in-ring intensity distribution of the two laser beams is created downstream of the optical device, with an inner ring and an outer ring surrounding it. The inner ring of the intensity distribution is formed by the first laser beam, and the outer ring of the intensity distribution, concentrically surrounding it, is formed by the second laser beam.

[0022] For this purpose, the light guide can be designed, for example, as a so-called 2-in-1 fiber or n-in-1 fiber with n > 2 or as a so-called multiclad fiber or can comprise such an optical fiber. In this case, a cladding material or cladding region can be arranged in the radial direction between the inner light guide region and the outer light guide region in the cross-sectional plane perpendicular to the light propagation direction or to the longitudinal direction of the beam path or to the beam propagation direction of the laser beams. Likewise, the outer light guide region can be surrounded by such a cladding material or cladding region. This design can prevent unwanted coupling of the two laser beams. This can, for example, prevent the central or deeper region of the cutting gap from being influenced by the second laser beam.This, in turn, can enable particularly simple adjustment or implementation of the desired effect on the workpiece or material in a given application. For example, the intensity, power, or power density in the center of the cutting gap can be adjusted—and thus particularly easily—simply by adjusting the first laser beam.

[0023] By means of a cladding region, i.e. a cladding around the inner or first light guide region provided for guiding the first laser beam, the transfer of photons from the first laser beam into the surrounding outer or second light guide region provided for guiding the second laser beam can be prevented or at least reduced compared to a structure without such cladding between the light guide regions. This makes it possible to have a correspondingly higher power density of the first laser beam and better control or adjustability of the power in the outer ring of the overall intensity distribution, which is primarily formed by the second laser beam. This makes it possible to have particularly flexible and diverse uses for the optics according to the invention or of the corresponding laser system. Equally, however, a structure of the light guide with the inner or second light guide region provided for guiding the first laser beam is also possible.first light guide region and the outer or second light guide region surrounding it in a ring, intended for guiding the second laser beam, but without cladding arranged between these light guide regions. The light guide regions can then, for example, be directly adjacent to one another. In this case, the outer or second light guide region might not need to be separately exposed to laser light on the input side. This can potentially enable a simpler design of a corresponding laser system and represent a practical approach, for example, for laser cutting of components or materials in combination with hot forming.

[0024] In a further possible embodiment of the present invention, the optics have at least one focusing device for focusing the laser beams into a focal point or focal region located outside the optics on the output side. This focusing device is arranged after the light guide in the beam path in the longitudinal direction of the beam path or in the direction of beam propagation of the laser beams. In particular, the focusing device can be designed such that it is irradiated by both the first laser beam and the second laser beam. The focusing device can be or comprise a focusing lens, for example. The focusing device can therefore be a single focusing element or be designed as a multi-part partial optics of the optics according to the invention, i.e. possibly comprising a plurality of optical elements. In particular, the focusing device can be designed orbe designed to generate a focus diameter of no more than 600 pm, preferably no more than 300 pm, for the first laser beam. The focusing device can, for example, enable particularly effective and efficient laser cutting. The focus diameters proposed here can achieve a fluid-dynamic adaptation and optimization of the cutting gap geometry.

[0025] In a possible development of the present invention, the optical device, i.e., the element or assembly for generating the annular intensity distribution of the first laser beam, is arranged in the beam propagation direction, i.e., viewed along the beam path, between at least part of the focusing device and the focal point or focal region. The arrangement of the optical device proposed here can enable a particularly simple design of the optics. For example, the focusing device or any provided collimating device or collimating lens can be arranged particularly close to the output or end of the optical fiber. This easily prevents an unnecessarily large expansion of the laser beams.The optical device does not necessarily have to be positioned in the 2f plane of the focusing device, i.e., at a distance from it corresponding to twice the focal length. This also enables a particularly flexible arrangement of the optical device, adapted to the specific space constraints of the respective application, and thus a correspondingly flexible design of the optics as a whole.

[0026] In a possible further development of the present invention, the optics have a protective glass arranged on the output side in the beam path. This protective glass can therefore be arranged downstream of the focusing device, in particular along the beam propagation direction of the laser beams, i.e., viewed along the longitudinal direction of the beam path, but upstream of the focus area located outside the optics. Such a protective glass can, for example, prevent or minimize the ingress of dust or dirt into the optics. Furthermore, it is provided here that the optical device for generating the annular intensity distribution of the first laser beam is arranged on this protective glass or is formed in this protective glass. In the former case, the protective glass can therefore function, for example, as a holder or carrier for the optical device.In the latter case, the optical device can be formed, for example, by appropriately shaping or machining the protective glass, particularly its surface. In both cases, an additional mount for the optical device can be eliminated, enabling particularly robust and permanently reliable positioning of the optical device.

[0027] In another possible embodiment of the present invention, the optical device for generating the annular intensity distribution of the first laser beam is arranged at a longitudinal position along the beam path at which at least the first laser beam has its largest diameter. This applies at least to the region of the optics according to the invention, i.e., for example, the region from the light guide to the focal point or focal region located outside the optics on the output side. Since the power of the first laser beam is predetermined in each case, the surface energy density of the first laser beam is lowest at the point with the largest diameter. By arranging the optical device at this point along the beam path, each surface element of the optical device is exposed to as little intensity or power of the first laser beam as possible.This allows the corresponding load on the optical device to be minimized, for example, to prevent damage or increase its service life. For example, the optical device can be arranged on the side of the focusing device mentioned elsewhere, facing the light guide, as viewed along the beam path, in particular between the focusing device and the collimating device mentioned elsewhere.

[0028] In another possible embodiment of the present invention, the optics has an end element arranged directly at an output end of the light guide. This end element can therefore, for example, be plugged or spliced ​​onto the output end of the light guide. For example, the end element can be a fiber end connector if the light guide is an optical fiber. Furthermore, it is provided here that the optical device for generating the annular intensity distribution of the first laser beam is arranged or formed in this end element. Likewise, the end element can be an output end region of the light guide. In this case, the optical device can, for example, be formed directly on or in the output end, i.e. the corresponding end face of the light guide.The embodiment of the present invention proposed here makes it easy to ensure that the first laser beam and the second laser beam are already precisely and consistently arranged relative to one another or superimposed on one another upon entering the optical device. This means that additional beam shaping or beam guidance can then be dispensed with if necessary. Furthermore, it can be achieved here that at least the first laser beam always radiates through the optical device in the same way, for example in the same area and in the same direction, even in the event of vibrations or the like. This makes it possible to achieve a permanently consistent, i.e. constant intensity distribution and thus a particularly high level of consistency and reliability of the properties of the optics or of the laser system equipped therewith. The end element can be arranged in the longitudinal direction orin the direction of beam propagation, for example, they can extend up to a few centimeters.

[0029] In a possible further development of the present invention, the end element comprises a machined end region of the light guide. The optical device is then formed by a height profile formed on the output-side end face, through which the laser light passes during operation in the longitudinal direction or the beam propagation direction. Such a height profile can, for example, be etched onto or into the end face of the light guide or produced by selective material removal, for example by means of a laser lithographic process or the like. Thanks to the further development of the present invention proposed here, the optics can be constructed from particularly few components and in a particularly robust manner. For example, relative movement between the light guide and the optical device is thus excluded. This makes it possible to achieve particularly robust and permanently consistent output-side beam properties.Depending on the size and design of the light guide and the available manufacturing processes, the height profile forming the optical device can be formed across the entire end face of the light guide or only in the area of ​​the light guide that transports the first laser beam. The former variant can be particularly easy to manufacture, while the latter variant can completely prevent any influence on the second laser beam by the optical device.

[0030] According to a further possible embodiment of the present invention, the optical device is or comprises a spiral phase plate. Such a spiral phase plate can impart a phase singularity to the first laser beam. An annular intensity profile generated by such a spiral phase plate can, in particular for laser beams with a diffraction index M 2< 1.5, propagate, and thus are maintained, over a particularly long length or path in the direction of beam propagation or in the longitudinal direction of the beam path. This makes it possible to achieve a correspondingly uniform intensity application within the cutting gap, even with particularly thick materials on the workpiece to be cut. Likewise, a particularly large distance can be selected between the optics and the workpiece or material to be cut or processed without negatively affecting the cutting or processing result. This can enable correspondingly simple and safe relative positioning between the optics or laser system and the workpiece or material, as well as particularly effective and efficient removal of molten or vaporized material to the side.The use of a spiral phase plate for or as the optical device can enable particularly simple adaptation to different requirements or applications. For example, the number of 2TT phase jumps, i.e. the so-called topological charge, and / or the number of height steps and / or the modulation depth of the spiral phase plate can be varied. For practical applications, for example, an amount of topological charge m can be selected in the range from 1 to 50, in particular in the range from 1 to 5. In particular, the amount of topological charge can be selected or set to be smaller than the largest azimuthal mode order of the second laser beam. This can ensure that the second laser beam is not influenced, or not significantly influenced, by the optical device, in this case the spiral phase plate.

[0031] In a possible further development of the present invention, the spiral phase plate has at least 16 stages, i.e., height stages or different height levels, in particular at least 32 or at least 64 stages. This is based on the realization that, while fewer stages can in principle be used for the spiral phase plate, for example, 4 or 8 stages or the like, a larger number of stages enables greater efficiency. For example, with at least 32 stages, an efficiency of at least 97% can be achieved.

[0032] In a further possible embodiment of the present invention, the optical device is or comprises an S-waveplate. This can in particular be or comprise a component or material with location-dependent birefringence properties. This can impart a polarization singularity to the first laser beam, for example by forming a radial or azimuthal polarization or a mixed state thereof. An S-waveplate can, for example, convert a linear polarization into a radial or azimuthal polarization or convert a circular polarization into an optical vortex, i.e. an annular intensity distribution. With such an S-waveplate, particularly favorable propagation properties for the intensity distribution of the first laser beam can be achieved. In addition, the S-waveplate also causes no or only a marginal ornegligible influence on the second laser beam. A segmented polarization converter or a geometric-phase hologram (GPH) can also be used as the optical device or as part of it.

[0033] The present invention also relates to a laser system which can be configured in particular for laser cutting. The laser system according to the invention has at least one laser source, the optics according to the invention and a coupling device for coupling different laser light components or laser beams into the light guide of the optics. The laser system according to the invention can in particular be the laser system mentioned in connection with the optics according to the invention or correspond thereto. The laser system according to the invention can likewise have further components. For example, the laser system can have a power distribution device for setting a power distribution or a power ratio between the first laser beam and the second laser beam. This can in particular be configured for continuous adjustment of the power orof the power component of the first laser beam and / or the second laser beam, each between 0% and 100% of the respectively available power. Likewise, the laser system can, for example, have a control device, in particular a closed control loop, with which the power of the first laser beam and / or the second laser beam can be automatically controlled, for example as a function of the feed rate at which the optics or the focus area is moved relative to the workpiece or material to be processed. Likewise, the laser system can, for example, have a cutting or process gas system for generating and guiding a cutting or process gas stream coaxially to the laser beams, the flow direction of which corresponds to the propagation direction, i.e. the direction of light propagation of the laser beams. Such a process gas system can, for example, have a control unit for guiding and stabilizing a gas pressure of the cutting or process gas.process gas and / or a gas nozzle and / or more. The gas nozzle can, for example, surround the laser beams after the optics, viewed in the direction of propagation. Likewise, the laser system can have a distance sensor for monitoring a distance between the workpiece or material to be processed and a predefined reference point that is fixed in position relative to the laser system, for example a specific component or component point of the laser system, such as the gas nozzle. This can, for example, be coupled to a control device or a controlled drive in order to guide or hold the laser system or the respective reference point or the respective component, for example the gas nozzle or the optics, at a predetermined distance from the respective workpiece or material. Likewise, the laser system can have a drive oran adjustment device for generating a relative movement between the laser system, in particular the optics, and the workpiece or material to be cut or machined.

[0034] In one possible embodiment of the present invention, the laser system is configured to generate different wavelengths and / or different polarization states of the first laser beam and the second laser beam. In other words, the first laser beam and the second laser beam can have different wavelengths and / or polarization states during operation of the laser system. The use of different wavelengths can enable the use of maximum absorption conditions or an adaptation to maximum absorption conditions, taking into account the different primary beam incidence conditions of the two laser beams on the respective workpiece. For example, the first laser beam can primarily be incident in a grazing manner, for example at an angle between 70° and approximately 87°. The second laser beam, on the other hand, can primarily be incident orthogonally, for example at an angle between 0° and 45°.For maximum absorption under the primarily grazing beam incidence conditions of the first laser beam, a wavelength in the near infrared range may be particularly favorable. For maximum absorption under the primarily orthogonal beam incidence conditions of the second laser beam, however, a wavelength in the visible range may be particularly favorable. For example, a wavelength in the range of 0.8 pm to 2.1 pm can be used for the first laser beam. For the second laser beam, a wavelength in the range of 0.2 pm to 0.8 pm can be used.

[0035] Depending on the design and application, different polarization states can be used for the two laser beams, for example, circular, azimuthal, radial, or stochastically distributed polarization states, or combinations thereof. By selecting or using suitable polarization states, i.e., polarization states adapted to the respective conditions or application, the absorption efficiency or energy efficiency can be increased. Likewise, by adjusting the polarization states, the resulting temperature profile of the absorption front can be specifically influenced. Thus, the appropriate adaptation or adjustability of the laser system offers corresponding flexibility and adaptability to different situations and applications.

[0036] The present invention also relates to a method for operating a laser system according to the present invention for processing, in particular for cutting, a workpiece or material. In the method, laser light is generated by means of at least one laser source. Furthermore, a first portion of the laser light is transported as a single-mode or quasi-single-mode laser beam and a second portion of the laser light is transported as a multimode laser beam with an annular intensity distribution in the optical fiber. At least the single-mode or quasi-single-mode laser beam irradiates the optical device, thereby generating a coaxial or concentric ring-in-ring intensity distribution, in which the annular intensity distribution of the single-mode or quasi-single-mode laser beam generated by the optical device is surrounded in a ring by the larger annular intensity distribution of the multimode laser beam coaxial therewith.In this process, the two laser beams are focused on the workpiece to be processed, in particular cut, and the workpiece is processed, in particular cut, using the ring-in-ring intensity distribution. Thus, at least the first laser beam passes through the optical device between the laser source and the workpiece-side focus of the laser beams. To process or cut the workpiece, a relative movement can be generated between the focus of the laser beams and the respective workpiece, effectively guiding the focus of the laser beams over the workpiece, for example, along a path specified for the respective application.

[0037] Further features of the invention can be derived from the following description of the figures and from the drawings. The features and combinations of features mentioned above in the description, as well as the features and combinations of features shown below in the description of the figures and / or in the figures alone, can be used not only in the respective combinations specified, but also in other combinations or on their own, without departing from the scope of the invention.

[0038] The drawing shows:

[0039] Fig. 1 is a partial schematic representation of a laser system for cutting a workpiece using a ring-in-ring laser intensity distribution; and

[0040] Fig. 2 a cross-sectional view of a corresponding simulated ring-in-ring laser intensity distribution.

[0041] Fig. 1 shows a partial schematic representation to illustrate laser cutting by means of a laser system 1. This can be used to cut or machine a schematically indicated workpiece 2, for example. The laser system 1 comprises at least one beam or laser source 3. Downstream of this laser source 3 is a coupling device 4 for coupling laser beams generated by the laser source 3 into a light guide 5, also indicated schematically here, of the laser system 1. The light guide 5 can be an optical fiber, for example. This can in particular be a 2-in-1 fiber with an inner light guide region and an outer light guide region surrounding this. Laser light 6, indicated schematically here, can emerge from an output-side end of the light guide 5, i.e. the end opposite the coupling device 4 as viewed along the direction of light propagation.In order to be able to process the workpiece 2 effectively, the laser system 1 also comprises further optical elements or devices arranged downstream of the light guide 5. These, together with the light guide 5, can be referred to collectively as optics 7. In particular, the optics 7 comprise a collimation device, which is indicated here in the form of a collimating lens 8. The optics 7 also comprises a focusing device arranged downstream of the collimating lens 8, which is indicated here as a focusing lens 9. The laser light 6 can first be collimated by means of the collimating lens 8. The focusing lens 9 can then focus the collimated laser light 6 into a focus area 10 located outside the laser system 1. In this focus area 10, the maximum intensity or energy density of the laser light 6 can be achieved, and a cutting gap 11 can thereby be created in the workpiece 2.The optics 7 can be designed as a transmission optic, as indicated here, but also entirely or partially as a reflective optic.

[0042] For safety reasons and to protect the components, the laser system 1 can, for example, have a protective glass 12 on the output side, through which the laser light 6 can pass. Depending on the design, the protective glass 12 can, for example, be arranged downstream of the optics 7 or be part of the optics 7.

[0043] Depending on the requirements or application, the laser system 1 or its laser source 3 can be configured in different ways, for example, as a CO2 laser, a solid-state laser, such as a disk laser, a fiber laser, a diode laser, or similar. For typical laser cutting applications, the laser system 1 or the laser source 3 can, for example, have a laser power, in particular a continuous wave power, in the range of several kilowatts. This allows, for example, 3D sheets with a thickness of several millimeters to be cut. However, other applications or power levels are also possible.

[0044] In order to create not only a point-shaped hole but also the elongated cutting gap 11 in the workpiece 2, an adjustment or displacement device (not explicitly shown here for the sake of clarity) can be used to create a relative movement between the focus area 10 and the workpiece 2. This can, for example, be used to move the workpiece 2. Additionally or alternatively, the laser system 1 or its optics 7 can be moved, tilted, or adjusted.

[0045] In addition, the laser system 1 can comprise a cutting or process gas system, which is also not explicitly shown here for the sake of clarity. This allows a cutting or process gas flow to be directed onto the cutting gap 11. In particular, this cutting or process gas flow can be guided coaxially to an optical axis 13 of the optics 7, indicated schematically here. This optical axis 13 corresponds to the longitudinal direction of the beam path, i.e., the primary light or beam propagation direction of the laser light 6 - at least after leaving the light guide 5. For this purpose, for example, a gas nozzle can be arranged on the outside of the laser system 1, which can surround the laser light 6 emerging through the protective glass 12. The flow direction of the cutting or process gas flow can thus correspond to the primary propagation direction of the laser light 6.

[0046] The laser system 1 is designed here to achieve or enable a particularly high grade or quality of the cutting gap 11 with, at the same time, a particularly high cutting performance. For this purpose, a ring-in-ring shape of the laser light 6 is generated or used at least in the focus area 10. Fig. 2 shows a corresponding simulated ring-in-ring intensity distribution 17 in a cross-sectional plane perpendicular to the optical axis 13. For better understanding, an intensity scale is also shown here. The intensity distribution 17 here comprises an inner ring 18 with a central intensity minimum 19, which can lie in particular on the optical axis 13 or in the center of the cutting gap 11. The inner ring 18 is surrounded by an annular intensity minimum 20. An outer ring 21 is located again outside of this. The inner ring 18 and the outer ring 21 are therefore regions in which the laser light 6 propagates.

[0047] A portion of the laser light 6 that ultimately forms the inner ring 18 can be guided in the inner light guide region of the light guide 5, while the portion of the laser light 6 that ultimately forms the outer ring 21 can be guided in the outer light guide region of the light guide 5. The portion of the laser light that forms the inner ring 18, which is also referred to here as the first laser beam, can be guided in a diffraction-limited manner or at least relatively close to or closer to the diffraction limit, for example as a single-mode or quasi-single-mode laser beam with a diffraction index of M 2< 1.5. The first laser beam can therefore be guided in the optical fiber 5 at least primarily in the Gaussian or Gaussian-like fundamental mode. The portion of the laser light 6 forming the outer ring 21, which is also referred to here as the second laser beam, can, however, be guided as a multimode laser beam in the optical fiber 5. In this case, the outer light guiding region of the optical fiber 5 can already have an annular shape, from which the outer ring 21 can easily result. The second laser beam can be guided in the optical fiber 5 in a non-diffraction-limited manner, i.e., further away from the diffraction limit than the first laser beam, in particular with a diffraction index of M 2 > 1.5.

[0048] By means of the coupling device 4, corresponding modes can be selectively excited or coupled. In particular, different power components can be variably set for the inner ring 18 and the outer ring 21, for example, correspondingly different power components can be coupled into the inner light guide region and the outer light guide region of the light guide 5. Power components from 0% to 100% are possible in each case. During regular operation of the laser system 1, however, power components of more than 0% can be provided for the inner ring 18 as well as the outer ring 21, for example, both the inner light guide region and the outer light guide region can be supplied with power, i.e., laser light 6 generated by the laser source 3, simultaneously.

[0049] In order to shape the first laser beam into the inner ring 18, the laser system 1 has a singularity element 14. This allows a phase singularity or a polarization singularity to be impressed on the first laser beam. For this purpose, the singularity element 14 can be designed, for example, as a spiral phase plate or an S-shaped delay plate. As indicated in Fig. 1, the singularity element 14 can be arranged or formed, for example, on the inside of the protective glass 12. However, other arrangements are also possible, which are indicated here as a first alternative position 15 between the collimating lens 8 and the focusing lens 9 and as a second alternative position 16 at the output end of the light guide 5 or between the latter and the collimating lens 8.

[0050] The singularity element 14 thus allows the first laser beam to be shaped into the inner ring 18, while the second laser beam can remain at least substantially unaffected. This results in the ring-in-ring intensity distribution 17, which can be maintained in the focus area 10 in the direction along the optical axis 13, for example, over at least two Rayleigh lengths, i.e., for example, over several millimeters. This intensity distribution 17 can therefore be present, in particular, over at least a large part of the thickness or material thickness of the workpiece 2. Depending on the application, the laser system, in particular the properties of the laser light 6 or the intensity distribution 17, can be adapted or adjusted as required. For example, a fiber laser with an average power of approximately 3 kW at a wavelength of approximately 1070 nm can be used.For the optics 7, for example, a collimating lens 8 with a focal length of f = 200 mm and a focusing lens 9 with a focal length of f = 300 mm can be used. By selecting a focus diameter suitable for the respective application, a flow-dynamic adaptation and optimization of the final cutting gap geometry can be achieved. For example, in the focus area 10, a diameter ratio between the first laser beam and the second laser beam, i.e. the ratio of the diameter of the inner ring 18 to the diameter of the outer ring 21, of at most 1:8, preferably of at most 1:4, can be set. For example, in the focus area 10, a diameter of at most 600 pm, in particular at most 150 pm, can be set for the first laser beam, i.e. for the inner ring 18.

[0051] With regard to power, for example, a power distribution or power ratio of approximately 2:1 can be set between the inner ring 18 and the outer ring 21. Likewise, however, up to 95% of the total available laser power can be directed into the inner ring 18. The larger portion of the laser power in the inner ring 18 can enable particularly effective and rapid melting or vaporization of the material of the workpiece 2. The smaller portion of the laser power in the outer ring 21, on the other hand, can be sufficient to create a radius, i.e., a rounding, at an end of the cutting gap 11 facing the laser system 1. This allows the cutting or process gas to reach the cutting gap 11 particularly effectively and efficiently. This ultimately makes it possible to achieve a particularly smooth, i.e., burr-free cutting edge, i.e., a particularly high quality of the cutting gap 11.This applies both to relatively low and relatively high feed rates or feed speeds.

[0052] Likewise, suitable, in particular different, polarization states can be selected or set for the inner ring 18 and the outer ring 21. This can enable optimization of the absorption efficiency or the energetic efficiency during laser cutting using the laser system 1, as well as influencing a temperature profile of the absorption front or of the workpiece 2 in the region of the cutting gap 11. In particular, when using a spiral phase plate as the singularity element 14, for example, the first laser beam, i.e., the inner ring 18, can be linearly polarized, while the second laser beam, i.e., the outer ring 21, can be unpolarized. In particular, when using an S-wavelength delay plate, for example, the first laser beam, i.e., the inner ring 18, can be radially or azimuthally polarized, while the second laser beam, i.e., the outer ring 21, can be unpolarized.

[0053] Overall, the described examples show how a ring-in-ring beam profile can be realized for laser applications and used to achieve improved cutting or machining results.

[0054] LIST OF REFERENCE SYMBOLS

[0055] 1 laser system

[0056] 2 Workpiece

[0057] 3 Laser source

[0058] 4 coupling device

[0059] 5 light guides

[0060] 6 Laser light

[0061] 7 Optics

[0062] 8 Collimating lens

[0063] 9 Focusing lens

[0064] 10 Focus area

[0065] 11 Cutting gap

[0066] 12 protective glass

[0067] 13 optical axis

[0068] 14 Singularity element

[0069] 15 first alternative position

[0070] 16 second alternative position

[0071] 17 Intensity distribution

[0072] 18 inner ring

[0073] 19 central intensity minimum

[0074] 20 annular intensity minimum

[0075] 21 Outer ring

Claims

PATENT CLAIMS 1. Optics (7) for a laser system (1) for laser cutting, wherein the optics (7) has a light guide (5) for the simultaneous coaxial transport of a first laser beam (18) as a single-mode or quasi-single-mode laser beam (18) and a second laser beam (21) as a multi-mode laser beam (21), as well as an optical device (14) arranged in the beam path of the first laser beam (18) and, viewed in the direction of beam propagation thereof, downstream of the light guide (5) for imposing a phase singularity and / or a polarization singularity on the first laser beam (18) to generate an annular intensity distribution (18) of the first laser beam (18) with a central intensity minimum (19) on the optical axis (13) of the optics (7).

2. Optics (7) according to claim 1, characterized in that the light guide (5) is designed to direct the first laser beam (18) with a diffraction index M 2 < 2, especially M2 < 1 ,7, and the second laser beam (21) with a diffraction index M 2 > 2 to lead.

3. Optics (7) according to one of the preceding claims, characterized in that the light guide (5) has an inner light guide region for transporting the first laser beam (18) and an outer light guide region surrounding the latter in a ring shape for transporting the second laser beam (21), so that an intensity distribution (21) of the second laser beam (21) surrounding the first laser beam (18) in a ring shape is obtained.

4. Optics (7) according to one of the preceding claims, characterized in that the optics (7) has a focusing device (9) arranged after the light guide (5) in the beam path, viewed in the beam propagation direction, for focusing the laser beams into a focus area (10) located outside the optics (7) on the output side, in particular designed to generate a focus diameter of at most 600 pm, preferably of at most 300 pm, for the first laser beam (18).

5. Optics (7) according to claim 4, characterized in that the optical device (14) is arranged between the focusing device (9) and the focus area (10) as viewed in the beam propagation direction.

6. Optics (7) according to claim 5, characterized in that the optics (7) has a protective glass (12) arranged on the output side in the beam path and the optical device (14) is arranged on this protective glass (12) or is formed in this protective glass (12).

7. Optics (7) according to one of claims 1 to 4, characterized in that the optical device (14) is arranged at a longitudinal position (15) along the beam path at which at least the first laser beam (18) has its largest diameter.

8. Optics (7) according to one of claims 1 to 4, characterized in that the optics (7) has an end element arranged directly at an output-side end of the light guide (5) and the optical device (14) is arranged in this end element.

9. Optics (7) according to claim 8, characterized in that the end element comprises a machined end region of the light guide (5) and the optical device (14) is formed by a height profile formed on the output-side end face of the light guide (5).

10. Optics (7) according to one of the preceding claims, characterized in that the optical device (14) comprises a spiral phase plate.

11. Optics (7) according to claim 10, characterized in that the spiral phase plate has at least 16 stages, in particular at least 32 stages.

12. Optics (7) according to one of the preceding claims, characterized in that the optical device (14) comprises an S-wavelength retardation plate.

13. Laser system (1), comprising at least one laser source (3), an optic (7) according to one of the preceding claims and a coupling device (4) for coupling different laser light components (18, 21) into the light guide (5) of the optic (7).

14. Laser system (1) according to claim 13, characterized in that the laser system is configured to generate different wavelengths and / or different polarization states of the first laser beam (18) and the second laser beam (21).

15. A method for operating a laser system (1) according to claim 13 or 14 for processing, in particular cutting, a workpiece (2), wherein - laser light (6) is generated by means of a laser source (3), - a first portion (18) of the laser light (6) as a single-mode or quasi-single-mode laser beam (18) and a second portion (21) of the laser light (6) as a multi-mode laser beam (21) with annular intensity distribution (21) are transported in the optical fiber (5) to the optics (7), - at least the single-mode or quasi-single-mode laser beam (18) radiates through the optical device (14) and thereby generates a concentric ring-in-ring intensity distribution (17), in which the ring-shaped intensity distribution (18) of the single-mode or quasi-single-mode laser beam (18) generated by the optical device (14) is surrounded in a ring-shaped manner by the larger ring-shaped intensity distribution (21) of the multi-mode laser beam (21), - the two laser beams (18, 21) are focused on the workpiece (2) to be machined, in particular cut, and the workpiece (2) is machined, in particular cut, by means of the ring-in-ring intensity distribution (17).

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