METHOD FOR LASER PROCESSING A WORKPIECE, PROCESSING OPTICS AND LASER PROCESSING DEVICE

Description

[0001] The present invention relates to a method for laser processing of a workpiece, a processing optic for laser processing of a workpiece, and a laser processing device with such a processing optic and with a laser source, preferably with an ultrashort pulse laser source.

[0002] In laser processing of a workpiece, particularly in laser ablation, laser cutting, surface texturing, laser welding, laser drilling, etc., it is advantageous to split an input laser beam into several partial beams that strike or are focused at different locations on the workpiece. This splitting can be achieved at a polarizer element, where typically two partial beams, each with one of two different polarization states (e.g., two perpendicularly polarized partial beams), are generated from a single input laser beam as output laser beams. It is also possible for multiple input laser beams, spatially offset, to strike the polarizer element. In this case, each input laser beam is split into a pair of partial beams, each with one of two different polarization states.

[0003] WO2015 / 128833A1 describes a laser cutting head that includes a polarizing beam offset element positioned in the beam path of a laser beam to generate two linearly polarized partial beams. The polarizing beam offset element is located in a divergent or convergent section of the laser beam path. The beam offset element can be made of a birefringent material. When using a focusing, magnifying optic and a beam offset element positioned downstream of the focusing optic, partial superposition of the two partial beams can occur in the focal plane.

[0004] From WO2015 / 5114032 A1, a laser processing device for workpiece processing is known, which has a processing optic in which an input laser beam is split into two perpendicularly polarized partial beams at a polarizer. The processing optic has a longer path length for the second partial beam than for the first partial beam, resulting in a longer transit time for the second partial beam. The second partial beam is modified in at least one geometric beam property compared to the first partial beam. The modified second partial beam is superimposed on the first partial beam in such a way that both partial beams form a common output laser beam.WO2018 / 020145A1 describes a method for cutting dielectric or semiconductor material using a pulsed laser, in which a laser beam is split into two partial beams that strike the material in two spatially separated zones offset from each other. The distance is set to a value below a threshold to create a straight-line micro-fracture in the material, running in a predetermined direction between the two offset zones. Beam shaping can be performed on the two partial beams to generate a spatial distribution on the material in the form of a Bessel beam.

[0005] WO2016 / 089799A1 describes a system for laser cutting at least one glass article using a pulsed laser assembly that includes a beam-shaping optical element for converting an input beam into a quasi-diffractive beam, for example, a Bessel beam. The laser assembly also includes a beam transformation element for converting the quasi-diffractive beam into several partial beams spaced between 1 µm and 500 µm apart.

[0006] DE 10 2019 205 394.7 describes a machining optic for workpiece processing, comprising a birefringent polarizer element for splitting at least one input laser beam into a pair of mutually polarized partial beams, and a focusing optic arranged in the beam path downstream of the polarizer element for focusing the partial beams onto focus zones. The machining optic is configured to generate focus zones of the mutually polarized partial beams that overlap at least partially. The machining optic can be configured to generate a plurality of pairs of at least partially overlapping focus zones along a predefined contour in a focal plane, with focus zones of each pair of mutually polarized partial beams from immediately adjacent pairs overlapping at least partially.In WO 2019 / 197423 A1, a method according to the preamble of claim 1 and a processing optic according to the preamble of claim 12 are described. Aufgabe der Erfindung

[0007] The invention is based on the objective of providing a method for laser processing, a processing optic and a laser processing device with such a processing optic that enables three-dimensional workpiece processing, in particular the processing of surfaces or edges of the workpiece. Gegenstand der Erfindung

[0008] This problem is solved according to the invention by a method according to claim 1. The laser beam can, for example, be generated in a solid-state laser, in particular in a disk laser or in a fiber laser.

[0009] For the purposes of this application, partial beams with different polarization states are understood to be linearly polarized partial beams whose polarization directions are aligned at an angle of 90° to each other. However, partial beams with different polarization states also include circularly polarized partial beams with opposite directions of rotation, i.e., two left- and right-circularly polarized partial beams. The conversion of linearly polarized partial beams with polarization directions perpendicular to each other into circularly polarized partial beams with opposite directions of rotation can be achieved, for example, using a suitably oriented retardation plate (λ / 4 plate).

[0010] If a (pulsed) laser beam, such as one generated by a single-mode laser and exhibiting a Gaussian beam profile, is split into two or more partial beams and these beams are at least partially superimposed, this can lead to undesirable interference effects if the partial beams have the same or a similar polarization. Therefore, when focusing the partial beams, the focus zones or focus cross-sections cannot be arbitrarily close to each other; consequently, the partial beams are typically focused at spaced-apart focus zones or partial areas on the workpiece.

[0011] When focusing partial beams with different polarization states onto immediately adjacent sub-areas or focus zones, interference effects of the laser radiation from different spatial or angular regions do not occur during (partial) superposition, provided the polarization state of the respective partial beams is uniform across the entire relevant beam cross-section or focus zone. The polarization of each partial beam should therefore vary as little as possible across the beam cross-section or focus zone / sub-area. In this case, the adjacent focus zones can be arbitrarily close to each other, partially or even completely overlap, and even form homogeneous focus zones, both transversely (i.e., perpendicular to the propagation direction of the partial beams) and longitudinally (i.e., in the propagation direction of the partial beams).

[0012] The sub-areas are typically arranged along the continuous interaction region; that is, each sub-area (except for the sub-areas at both ends of the interaction region) borders exactly two adjacent sub-areas and partially overlaps with these two adjacent sub-areas. Within the continuous interaction region, the adjacent sub-areas thus typically overlap only to the extent that they do not overlap with the differently polarized partial beam of another adjacent sub-area, so that no superposition of identically polarized partial beams occurs. The continuous interaction region forms a predefined, continuous contour, which is also referred to as the (curved) multispot focus contour or, in the case of a straight contour, as the multispot focus line.

[0013] As an alternative to using fully or partially overlapping partial beams with different polarization states, fully or partially overlapping partial beams can also be used that have a time offset large enough to practically eliminate interference effects. This is typically the case when the time offset is at least on the order of the pulse duration or the coherence length. The minimum time offset is usually set at 50% of the smaller of the two values ​​(pulse duration or coherence length).

[0014] The splitting of the laser beam into the majority of partial beams, each exhibiting one of two different polarization states, is typically performed in a processing optic.

[0015] In one variant, the laser beam, when split into multiple partial beams, passes through a preferably diffractive beam splitter and at least one preferably birefringent polarizer element. The (e.g., diffractive) beam splitter allows the laser beam to be split into multiple partial beams, thus creating several sub-areas or focus zones (spots) within the working volume of the (preferably transparent) workpiece material. The focus zones generated within the working volume without the polarizer are spaced apart to avoid the interference effects described above. The polarizer...The polarizer element serves to split each input laser beam, generated by the beam splitter optics, into two partial beams with different polarization states. This fills the gaps between the focal zones and creates a continuous interaction area. Along this continuous interaction area, a beam shape or intensity distribution is generated that typically exhibits a continuous transition, meaning there are no zero points in the intensity distribution between the partial beams or between the focal zones / sub-areas.

[0016] It is understood that, unlike the description above, the laser beam first passes through the polarizer element(s) and only then through the beam splitter element or beam splitter optics. The beam splitter optics can, for example, be in the form of a diffractive optical element, but they can also be another type of beam splitter optics, such as geometric beam splitter optics.

[0017] Although the following description often refers only to one birefringent polarizer element, two or more (birefringent) polarizer elements can, in principle, be incorporated into the processing optics. For example, in this case, the laser beam generated by an (ultrashort pulse) laser source and entering the processing optics can be split into two or more partial beams, each representing an input laser beam for a corresponding birefringent polarizer element, or the laser beams of several laser sources can be used as input laser beams.

[0018] In one variant, splitting the laser beam into multiple partial beams at a birefringent polarizer element generates a lateral (positional) offset and / or an angular offset between two partial beams that are focused onto adjacent sub-areas of the contiguous interaction zone. In this case, the birefringent polarizer element can be configured to generate either a lateral (positional) offset, an angular offset, or a combination of both between the two mutually polarized partial beams.

[0019] Using a birefringent polarizer element, typically in the form of a birefringent crystal, the input laser beam can be selectively split into its polarization components when polarized appropriately, for example, with an unpolarized input laser beam or one with undefined or circular polarization. Depending on the design of the birefringent polarizer element, a well-defined, pure spatial offset, a well-defined, pure angular offset, or a combination of spatial and angular offsets can be generated between the two partial beams with the different polarization states.

[0020] To generate the spatial offset (without angular offset), the birefringent polarizer element can, for example, have parallel, usually planar, beam entry and exit surfaces. In this case, the optical axis of the birefringent crystal is typically oriented at an angle to the beam entry surface. If the input laser beam strikes the beam entry surface perpendicularly, a pure spatial offset is generated at the beam exit surface.

[0021] To generate angular displacement (without spatial displacement), the birefringent polarizer element can have a beam exit surface inclined at an angle to the beam entrance surface. In this case, the optical axis of the birefringent crystal is typically aligned parallel to the beam entrance surface. The two partial beams then exit the birefringent crystal at the same location and with a defined angular displacement. To generate a combination of spatial and angular displacement, a polarizer element in the form of a conventional prism polarizer can be used, such as a Nicol prism, a Rochon prism, a Glan-Thompson prism, or another type of prism polarizer (see, for example, "https: / / de.wikipedia.org / wiki / Polarisator" or "https: / / www.b-halle.de / produkte / Polarisatoren.html").

[0022] According to the invention, when the laser beam is split into a plurality of partial beams at a birefringent polarizer element, in particular at a birefringent lens element, a longitudinal offset is generated between two partial beams, which are preferably focused on adjacent sub-areas of the continuous interaction zone. For generating the longitudinal offset between the partial beams, a birefringent imaging optical element, in particular a lens element, can be used, for example. The birefringent lens element can be configured to focus (e.g., as a converging lens) or to diverge (e.g., as a diverging lens). In the first case, the lens element can form a focusing optic of the processing optics. However, it has proven advantageous to use a non-birefringent lens element (focusing lens) as the focusing optic.If the birefringent lens element has a focusing effect, it can form part of the focusing optics. In the present application, the term "focusing optics" is often used to refer to the optical element with the greatest refractive power, which is typically designed as a focusing lens (objective lens).

[0023] The arrangement of the birefringent polarizer element(s) in the beam path of the processing optics depends, in addition to the type of laser processing, on whether a lateral or longitudinal spatial offset and / or an angular offset is to be generated. For examples of the arrangement of birefringent polarizer elements in processing optics, reference is made to DE 10 2019 205 394.7 cited above, which is incorporated in its entirety by reference into the content of this application. It is understood that by a suitable selection of birefringent polarizer elements, both a longitudinal and a lateral offset of the focal zones or of the sub-regions of the continuous interaction area can be generated.

[0024] The sub-areas or focus zones of the contiguous interaction area can lie in a common plane, which typically corresponds to the focus plane of the processing optics.

[0025] Preferably, at least two of the sub-areas of the connected interaction region are offset in the longitudinal direction (e.g., Z-direction), meaning they do not lie in a common focal plane. In this variant, the connected interaction region typically deviates from a linear shape, i.e., it forms a generally curved contour extending in the longitudinal direction. By implementing an additional offset of the sub-areas in the lateral direction (e.g., X-direction), the connected interaction region can form virtually any geometry or contour line in the XZ-plane. It is also fundamentally possible to generate a lateral offset of the partial rays in two directions (e.g., in the X-direction and the Y-direction), meaning the connected interaction region does not necessarily have to lie in a single plane.

[0026] In another variant, during laser processing, the connected interaction area and the workpiece are moved relative to each other, preferably along a feed direction. This relative movement moves the interaction area along a processing path, where, for example, material can be removed from the workpiece or the workpiece material can be structurally modified. The feed direction during laser processing can be constant, but it is also possible for the feed direction to vary. In the simplest case, the workpiece and the interaction area are fed linearly relative to each other in a direction that is transverse, and in particular perpendicular, to the plane (e.g., the XZ plane) in which the interaction area lies.

[0027] Laser processing, or workpiece machining, can involve processes such as laser ablation, laser cutting, surface texturing, laser welding, laser drilling, and more. It is understood that, depending on the type of laser processing, the relative movement can be repeated multiple times, for example, to remove several layers of the workpiece material successively during laser ablation.

[0028] In one variant, the interaction zone forms an ablation zone for removing material from the workpiece. In this case, the workpiece can be machined by removing material layer by layer. The continuous interaction zone can be linear and lie in a focal plane. By moving the linear interaction zone and the workpiece relative to each other along the feed direction, each layer of the workpiece can be removed. It is also possible to create an interaction zone with a geometry or profile adapted to the contour to be removed, for example, a V-shaped or U-shaped profile to create a V-shaped or U-shaped groove in the workpiece.An interaction zone with such a customized profile can be lowered deeper and deeper into the workpiece volume in several successive ablation steps to create the V-shaped or U-shaped groove and, if necessary, to divide the workpiece into two segments. The profile of the interaction zone can be modified during laser processing. In particular, with successive ablation steps, in which material is removed in each step, a steeper profile of the interaction zone can be selected, i.e., the longitudinal extent of the profile increases. For example, in this case, a V-shaped profile can be made progressively steeper in successive ablation steps to create a V-shaped groove in the workpiece.

[0029] In another variant, the ablation zone is formed on an entry-side surface of the workpiece or on an exit-side surface of the workpiece, wherein a predetermined, in particular three-dimensional, surface shape is preferably generated on the entry-side or exit-side surface during laser processing. In this variant, the laser processing modifies a surface shape or geometry to adapt it to a predetermined surface shape, e.g., to form a wedge-shaped, cylindrical, or freeform surface. For this purpose, the profile or geometry of the interaction zone is adapted to the predetermined surface shape, more precisely to a cross-sectional profile of the predetermined surface shape, and the interaction zone is moved along the processing path relative to the workpiece to generate the predetermined surface shape on the surface.In this way, surfaces with virtually any shape can be created. After laser processing, the surface can undergo modifying post-processing, for example, polishing.

[0030] If the ablation zone is formed on the exit surface of the workpiece, the workpiece is transparent to the wavelength of the laser beam. In back-side ablative laser processing, it is advantageous that the ablation products, unlike in entrance-side processing, do not affect beam propagation to the processing zone. With a transparent workpiece, both the entrance and exit surfaces can be processed without having to remove or rotate the workpiece from its respective holding fixture. The transparent workpiece can, in particular, be made of glass.

[0031] In another variant, the interaction zone forms a modification zone for the structural modification of the workpiece material, wherein the workpiece preferably consists of a material transparent to the laser beam, in particular glass. In this variant, the workpiece material is not removed during laser processing, but rather undergoes a structural modification of the workpiece material. Such structural modification can consist of a rearrangement of chemical bonds, the formation of microcracks, etc., upon irradiation with ultrashort pulse laser radiation. The structural modification can, in particular, induce or promote cracking of the glass material. The glass material can be, for example, quartz glass or another type of (optical) glass. In the case of a transparent material, the structural modification is not limited to the surface.The process is not limited to a near-surface volume region, but can be introduced practically anywhere within the volume of the workpiece. Structural modification of the workpiece surface is also possible; for example, structural modification can result in polishing (local melting) of the surface.

[0032] It can be advantageous if the geometry of the sub-areas or focus zones of the interaction area specifies or determines a preferred direction for crack formation. This can be achieved, for example, by an elliptical or oval shape of the focus zones, since crack formation preferentially occurs along the long axis of the oval or elliptical focus zones.

[0033] In another variant, after structural modification, the workpiece is separated into two segments along a modification contour formed within the workpiece volume during laser processing. This separation is preferably achieved through a mechanical, thermal, or etching process. In this variant, the structural modification serves to pre-damage the workpiece material; the workpiece is typically separated only after the structural modification is complete. In the mechanical separation process, for example, a force or mechanical stress can be applied to the workpiece to separate or break it into two segments. In the thermal separation process, the workpiece can be heated to create a temperature gradient that generates mechanical stress in the workpiece material, leading to separation.The thermal treatment of the workpiece can be carried out, for example, using laser radiation that is absorbed by the workpiece material. This is the case, for instance, with the laser radiation from a CO₂ laser, as it generates laser radiation at a wavelength of approximately 10 µm, which is absorbed by most materials, including quartz glass. For the thermal treatment or thermal separation process, a CO₂ laser beam can be directed onto the surface of the workpiece. Separating the workpiece into two segments can also be achieved through an etching process, in which the workpiece, after structural modification, is placed in an etching bath.

[0034] For separation, it is advantageous if the modification contour extends as far as possible into the workpiece's volume. Ideally, the modification structure connects the top and bottom surfaces of the workpiece. This can be achieved through a suitable three-dimensional profile of the continuous interaction area, which in this case extends across the entire thickness of the workpiece. To generate the greatest possible extent of the sub-areas or focus zones in the longitudinal direction or thickness direction of the workpiece, the laser beam, or more precisely the sub-beams, can also have a Bessel-shaped beam profile. In this case, a linear interaction area can also be used to generate the modification contour, where the sub-areas are not necessarily offset from each other in the longitudinal direction.

[0035] The invention also relates to a processing optic according to claim 12. In this case, too, the sub-areas are typically arranged along the continuous interaction area.

[0036] In one embodiment, the processing optics comprise at least one birefringent polarizer element for generating a lateral (positional) offset and / or an angular offset between two partial beams with different polarization states. Regarding the various possibilities for realizing the lateral offset and / or the angular offset, reference is made to the above explanations in connection with the method.

[0037] Depending on the specific processing application, it may be advantageous to use either a birefringent polarizer element that produces an angular offset but only an insignificant spatial offset (2 f setup, e.g., in beam splitter applications or laser ablation) or a birefringent polarizer element that produces a spatial offset but only an insignificant angular offset (4 f setup, for example, when using Bessel-like beam profiles for glass cutting or glass cutting).

[0038] According to the invention, the processing optics comprise at least one birefringent polarizer element, in particular a birefringent lens element, for generating a longitudinal offset between two partial beams with different polarization states, which are preferably focused into adjacent sub-regions of the continuous interaction area. As described above, a longitudinal offset between differently polarized partial beams can be generated by means of a birefringent lens element.

[0039] As described above, the birefringent lens element can, in principle, form the focusing optics, i.e., the processing optics do not have any further focusing element to focus the partial rays in the focus zones or in the sub-areas of the interaction area, which are preferably focused into adjacent sub-areas of the connected interaction area.

[0040] Since the size or diameter of the sub-areas or focus zones is determined in this case by the focal length of the birefringent lens element and only a limited number of birefringent materials are available for manufacturing the lens element, the longitudinal offset between the sub-areas or focus zones is predetermined in this case.

[0041] It has therefore proven advantageous for the focusing optics to include a non-birefringent focusing element, in particular another lens element made of a non-birefringent material, or to consist of a focusing lens made of a non-birefringent material. In combination with the birefringent lens element, a desired effective focal length of the focusing optics can be determined, and a desired longitudinal offset of the partial beams can be specified or adjusted.

[0042] The invention also relates to a laser processing device comprising: processing optics as described above and a laser source, in particular an ultrashort pulse laser source, for generating a laser beam, in particular a laser beam with a Gaussian beam profile. The laser source is preferably configured to generate a single-mode laser beam with a Gaussian beam profile, but this is not mandatory.

[0043] The processing optics can be housed, for example, in a laser processing head or in the housing of a laser processing head that is movable relative to the workpiece. The laser processing device can alternatively or additionally include a scanner to align the partial beams onto the workpiece or to different positions on the workpiece. In addition to the optics described above, the processing optics can also include other optics. The laser processing device can also include a motion device, such as a linear drive, for moving, in particular for displacing, the workpiece along a feed direction.

[0044] Further advantages of the invention will become apparent from the description and the drawing.

[0045] They show: Fig. 1a,b schematic representations of two birefringent polarizer elements for generating an angular or spatial offset between two mutually polarized partial beams, Fig. 2a,b schematic representations of a processing optic with a birefringent lens element for generating a longitudinal offset between focus zones of two mutually polarized partial beams, Fig. 2c a schematic representation of a processing optic analogous to Fig. 2b with the in Fig. 1a The polarizer element shown is used to generate an additional lateral offset of the two focus zones. Figures 3a and 3b show schematic representations of a subtractive laser processing operation on a workpiece. Figures 4a and 4b show schematic representations of a laser processing operation modifying the workpiece material to separate the workpiece along a modification contour. Figures 5a and 5b show schematic representations of a laser processing operation modifying the workpiece material to prepare for an etching process. Figures 6a and 6b show schematic representations of a subtractive laser processing operation for surface treatment of a workpiece.

[0046] In the following description of the drawings, identical reference symbols are used for identical or functionally equivalent components.

[0047] Fig. 1a ,bFigures 1a and 1b schematically depict birefringent polarizer elements in the form of birefringent crystals. Various birefringent materials can be used as crystal materials for polarizer elements 1a and 1b, such as alpha-BBO (alpha-barium borate), YVO4 (yttrium vananate), crystalline quartz, etc. The birefringent polarizer element 1a of Fig. 1a The polarizer element 1a is wedge-shaped, meaning that a flat beam entry surface 2a for the entry of an input laser beam 3 and a flat beam exit surface 2b are aligned at a (wedge) angle to each other. The optical axis 4 of the crystal material is aligned parallel to the beam entry surface 2a.

[0048] The unpolarized or circularly polarized input laser beam 3, entering the birefringent polarizer element 1a perpendicular to the beam entrance surface 2a, is split into two partial beams 5a, 5b at the beam exit surface 2b, which is inclined at an angle to the beam entrance surface 2a. These partial beams are perpendicular to each other (s- and p-polarized, respectively), i.e., they exhibit one of two different polarization states. Fig. 1a As is generally customary, the s-polarized partial beam 5a is indicated by a dot, while the second, p-polarized partial beam 5b is indicated by a double arrow. The first, p-polarized partial beam 5a is refracted less strongly upon exiting the birefringent polarizer element 1a than the second, s-polarized partial beam 5a, resulting in an angular offset Δα between the first and second partial beams 5a, 5b. The first and second partial beams 5a, 5b exit the birefringent polarizer element 1a at the same point on the beam exit surface 2b; that is, the angular offset Δα is generated, but no spatial offset occurs between the two partial beams 5a, 5b.

[0049] At the in Fig. 1b In the polarizer element 1b shown, the beam entrance surface 2a and the beam exit surface 2b are aligned parallel to each other, and the optical axis 4 of the crystal material is oriented at an angle of 45° to the beam entrance surface 2a. The input beam 3, incident perpendicularly to the beam entrance surface 2a, is split at the beam entrance surface 2a into a first, ordinary partial beam 5a and a second, extraordinary partial beam 5b. The two partial beams 5a, 5b emerge parallel at the beam exit surface 2b, i.e., without an angular offset, but with a spatial offset. Δx out of.

[0050] The two in Fig. 1a and in Fig. 1b The birefringent polarizer elements 1a and 1b shown here differ fundamentally in that the in Fig. 1a The polarizer element 1a shown exhibits an angular offset Δα (without spatial offset) and that the in Fig. 1b The polarizer element 1b shown generates a spatial offset Δx (without angular offset). It is understood that, for example, the one shown in Fig. 1a The wedge-shaped polarizer element 1a shown can also be designed to produce both a spatial offset Δx and an angular offset Δα, as is the case with conventional prism polarizers, which usually have two birefringent optical elements.

[0051] Fig. 2a -c Each figure shows a polarizer element in the form of a birefringent, focusing lens element 6, onto which a collimated input laser beam 3 is directed. The input laser beam 3 is split by the birefringent lens element 6 into two partial beams 5a, 5b, which are perpendicular to each other (s- and p-polarized, respectively). In the case of the Fig. 2a In the example shown, the first, s-polarized partial beam 5a is refracted more strongly upon exiting the birefringent lens element 6 than the second, p-polarized partial beam 5b, so that a longitudinal (spatial) offset Δz is generated between a focal zone 8a of the first partial beam 5a and a focal zone 8b of the second partial beam 5a, 5b. The two focal zones 8a, 8b are in Fig. 2a-c For the sake of simplicity, they are shown as points, but overlap in the longitudinal direction (Z-direction). The birefringent lens element 6, like the polarizer elements 1a and 1b, is formed from a birefringent crystal.

[0052] In Fig. 2b The birefringent focusing lens element 6 divides as in Fig. 2a The input laser beam 3 is split into two partial beams 5a, 5b. The first partial beam 5a, which is refracted more strongly at the birefringent lens element 6, is refracted less strongly at another, non-birefringent lens element 7 than the second partial beam 5b, thereby also generating a longitudinal offset Δz between the two focal zones 8a, 8b. In the Fig. 2b In the example shown, the focus zone 8a of the first partial beam 5a is, however, further away from the birefringent lens element 4 in the longitudinal direction Z than the focus zone 8b of the second partial beam 5b.

[0053] At the in Fig. 2c In the example shown, the wedge-shaped birefringent polarizer element 1a is located in the beam path of the input laser beam 3 immediately after the birefringent lens element 6. Fig. 1a arranged. The wedge-shaped polarizer element 1a generates an additional lateral offset Δx of the focus zones 8a, 8b of the two partial beams 5a, 5b.

[0054] The in Fig. 2a-c The lens elements 6, 7 and the wedge-shaped polarizer element 1a shown are part of a processing optic 10, which also includes a diffractive beam splitter optic 9. The processing optic 10 is part of a laser processing device 13, which additionally includes a laser source 11 in the form of an ultrashort pulse laser source. The laser source 11 generates a laser beam 12, which in the example shown has a Gaussian beam profile and which enters the processing optic 10. At the diffractive beam splitter optic 9, the laser beam 12 is split into a plurality of beam bundles, which are, for example, aligned parallel to each other and each form an input laser beam 3 for the birefringent lens element 7. For the sake of simplicity, the following is shown in Fig. 2a-c only a single input laser beam 3 is shown, which is split into two partial beams 5a, 5b.

[0055] At the in Fig. 2a In the example shown, the diffractive beam splitter optics 9 are arranged at a distance equal to the entrance focal length f' in front of the birefringent lens element 6. In this case, the birefringent lens element 6 forms the focusing optics of the processing optics 10 and focuses the partial beams 5a, 5b at approximately their exit focal length f. In the example shown... Fig. 2b In the examples shown, focusing is achieved primarily by the additional, non-birefringent lens element 7. The birefringent lens element 6 is – as is the one in Fig. 2c The wedge-shaped polarizer element 1a shown is arranged approximately at a distance of the entrance focal length f from the further lens element 7, which has a significantly greater refractive power than the birefringent lens element 6 and is therefore subsequently also referred to as the focusing lens or focusing optics. The order of the arrangement of the birefringent lens element 6, the wedge-shaped polarizer element 1a, and the diffractive beam splitter element 9 in the beam path is fundamentally arbitrary, but should be considered in the diagram shown. Fig. 2c The example shown is typically arranged at a distance of approximately the entrance-side focal length f' from the focusing lens 7.

[0056] With the help of the in Fig. 2a-c In the processing optics 10 and the laser processing device 13 shown, the two partial beams 5a, 5b can be focused into two adjacent focus zones 8a, 8b, which overlap at least partially. The beam splitter optics 9 can generate a plurality of input laser beams 3, which are split at the polarizer elements 1a, 6 into a plurality of pairs of partial beams 5a, 5b and focused into corresponding pairs of focus zones 8a, 8b. In this way, a continuous interaction area for processing a workpiece can be formed from the partially overlapping focus zones 8a, 8b, as described in more detail below.

[0057] Due to the possibility of generating both a lateral offset Δx and a longitudinal offset Δz of the focus zones 8a, 8b, a continuous interaction area can be formed that describes an almost arbitrary three-dimensional curve in space or in the XZ plane.

[0058] In particular, the connected interaction area can have several focus zones 8a, 8b or sub-areas offset from each other in the longitudinal direction Δz, as described in more detail below.

[0059] In the following examples, laser processing of a workpiece is achieved by moving a continuous interaction zone along a processing path, i.e., by accumulating adjacent, continuous interaction zones that form ablation or modification zones. For the sake of simplicity, the following examples assume that the workpiece is fed linearly to move the continuous interaction zone. It is understood that any other feed geometry or processing path is generally possible. In particular, not only the workpiece but also the processing optics or a laser processing head in which the processing optics are located can be moved.

[0060] With regard to successive modification / ablation areas in the feed direction, the geometry of the incident laser radiation, for example an angular range of the beam cross-section of the laser radiation, can be chosen such that, in a series of modification / ablation areas in the feed direction, a previously introduced modification or a previously processed ablation area has only an insignificant influence on the formation of the subsequent modifications / ablation areas.

[0061] Fig. 3a Figure 1 shows a laser processing process in the form of a laser ablation process in which material is removed from the top surface 23A of a plate-shaped workpiece 23 by focusing a plurality of partial beams 22 onto the top surface 23A of the plate-shaped workpiece 23, forming a linear, continuous interaction zone 25. Within the interaction zone 25, the sub-zones 25A (focus zones) onto which the partial beams 22 are focused are arranged side by side with alternating, different polarization states (e.g., s or p) in the X-direction of an XYZ coordinate system, with adjacent sub-zones 25A partially overlapping. The alternating polarization states (e.g., s or p) are indicated by light and dark areas within the interaction zone 25 and prevent interference between adjacent partial beams 22.

[0062] In Fig. 3a There is no offset of the sub-areas 25A in the Z-direction, which corresponds to the propagation direction of the laser radiation (longitudinal direction), i.e., the sub-areas 25A lie in a (focus) plane that is oriented perpendicular to the longitudinal direction Z. A Fig. 3a Arrow 27 illustrates a relative movement of the interaction area 25 transverse to the alignment direction (X-direction) in the form of a displacement of the workpiece 23 in the Y-direction. With a linear feed rate, laser processing results in an ablated strip 29 with the width of the continuous interaction area 25 and a depth corresponding to the ablation power of the partial beams 22 in the partial areas 25A (i.e., the focus zones).

[0063] Fig. 3b Figure 1 also shows laser processing in the form of a laser ablation process, in which material is removed from the top surface 23A of a plate-shaped workpiece 23'. As in Figure 2 Fig. 3a will also be in Fig. 3b For this purpose, a plurality of partial beams 22' are focused onto the plate-shaped workpiece 23, forming a continuous interaction area 25. In contrast to Fig. 3a The sub-areas 25A' are not only offset in the lateral direction (X-direction), but also additionally in the longitudinal direction (Z-direction) and in Fig. 3b for example, arranged in a V-shape. Due to the relative movement of the workpiece 23' in the Y-direction, i.e., transverse to a plane spanned by the V-shaped profile of the interaction area 25 (in Fig. 3b (the XZ-plane) results in a cut-off section 31 with the V-shape of the connected interaction area 25. Also in the case of the in Fig. 3b In the example shown, the alternating polarization states – again indicated by bright and dark areas – of immediately adjacent partial beams 22' cause a homogeneous erosion that is not influenced by the interference of neighboring partial beams 22'. To generate the Fig. 3b In the depicted ablated incision 31, the workpiece 23' can be moved in the Y-direction in several successive ablation steps, whereby between successive ablation steps the interaction area 25 with the V-shaped profile is moved in the Z-direction, i.e., lowered further onto the workpiece 23'. Alternatively or additionally, the geometry of the V-shaped interaction area 25 can be changed during the ablation laser processing; for example, the extent of the V-shaped interaction area 25 in the longitudinal Z-direction can be gradually increased, i.e., the V-shaped interaction area 25 becomes increasingly pointed with successive ablation steps. Regarding the material of the workpiece 23, 23', which is in Fig. 3a,b The material being processed by abrasive means could be, for example, a metallic material, a glass material, etc.

[0064] Fig. 4a Figure 23 shows a laser processing method for generating a structural modification of the material of a plate-shaped workpiece 23", which extends from the top surface 23A of the workpiece 23" along the propagation direction (Z-direction) of the incident laser radiation or partial beams 22" into the (transparent) workpiece 23". For this purpose, a continuous interaction area 25 is formed by an array of adjacent (in Fig. 4a elongated sub-areas 25A" (focus zones) extending in the Y-direction, partially overlapping, are formed by a plurality of partial beams 22". As in Fig. 3a There is no offset of the sub-areas 25A" in the Z-direction. Alternating polarization states (s and p) are again indicated by light and dark areas. Examples are shown in Fig. 4a Four elongated sub-regions 25A" are shown, which are caused by a suitable phase imprinting onto the partial beams 22", such that, for example, elongated focus zones or sub-regions 25A" of Bessel beams or inverted Bessel beams are formed. The elongated sub-regions 25A" can be generated by means of a beam-shaping optic of the processing optic 10, which may, for example, have an axicon or a diffractive optical element. For details of such a beam-shaping optic, reference is made to DE 10 2019 205 394.7 cited above. In order to also generate the structural modification in the volume of the workpiece 23", this is formed from a material transparent to the laser beam 12 or to the wavelength of the laser beam 12, in the example shown, glass.

[0065] During a relative movement along the alignment direction, i.e., in the Y-direction, a material modification of a narrow strip 33 with the width of a single sub-area 25A" results. The depth of the strip 33 in the Z-direction is determined by the length of the elongated focus zones or sub-areas 25A". As in Fig. 4a The partial beams 22, represented by dotted semicircles indicating the beam cross-section of the processing partial beams 22, are preferably limited to the leading angular component or angular range, so that no disturbance of the laser beam and thus of the interaction occurs during the feed due to modifications already created. In the example shown, the structural modification of the workpiece material 23" leads to the formation of microcracks, which weaken the glass material within the modified strip 33.

[0066] Fig. 4b Figure 1 shows how the workpiece 23" is partially placed on or off a support 37 and a force (arrow 35) is exerted on the unsupported side of the workpiece 23". A crack 39 forms below the modified strip 33, which represents a modification contour, through the entire thickness of the workpiece 23", resulting in the workpiece 23" separating into two segments.

[0067] Fig. 5a shows a non-linear, curved arrangement of sub-areas 59A of a continuous interaction area 59 in a (transparent) material of a plate-shaped workpiece 57. As in Fig. 4a,b A material modification is generated by means of the continuous interaction area 59, which extends in a curved path through the workpiece 57 from its top surface 57A to its bottom surface 57B. Adjacent sub-areas or focus zones 59A of the interaction area 59 partially overlap, so that a continuous / uninterrupted curved modification contour in the form of a modification plane 61 is formed in the material by a relative movement of the workpiece 57 and the interaction area 59 (arrow 27).

[0068] Fig. 5b Figure 1 shows the modified workpiece 57 in an etching tank 63 (etching bath), in which the material of the workpiece 57 in the area of ​​the modification plane 61 is etched away in the example shown. This causes, as in Figure 2, the following: Fig. 4a,b The result is a separation of workpiece 57 into two segments.

[0069] In the modification-based separation processes described above, segment separation can occur spontaneously, directly or following laser processing, or it can be induced by a further process, e.g., by the process associated with Fig. 4a,b described mechanical separation process, which is associated with Fig. 5a,b described etching process or by a thermal separation process not shown in the illustration.

[0070] In addition to the ablation or separation laser processing described above, it is also possible to perform surface processing using the multispot arrangement described above or using (at least) a continuous interaction area, i.e. the laser radiation or the laser processing device 13 serves as a forming tool. Fig. 6a shows an example of laser beam entry-side processing of a workpiece 101 and Fig. 6b a laser beam exit-side processing of a workpiece 107.

[0071] When machining the beam entrance side using a continuous interaction area (multispot arrangement) as a forming tool, primarily subtractive or locally modifying processes are considered. Modifying processes include, for example, polishing via local melting and exploitation of existing surface tension.

[0072] Fig. 6a Figure 1 shows the use of a multispot laser forming tool for laser entry-side ablation on a workpiece 101. Optionally, a top surface 102 of the workpiece 101 is coarsely pre-structured in a first processing step. This can be done, for example, with a throughput-optimized laser processing process with reduced precision, resulting in a coarsely structured surface 102A, which is to be transformed into a desired freeform surface 102B using the laser forming tool or by means of laser processing. A multispot focus curve or focus line adapted to the desired freeform surface 102B, in the form of a continuous interaction area 103, is positioned at the correct location above the coarsely structured top surface 102A and lowered onto it (arrow 105A) in order to remove material from the workpiece 101 in the area of ​​the (curved) focus line 103. As illustrated above, points orCircles of the focus line 103 adjacent sub-areas with different polarization components, so that interference between neighboring sub-areas is avoided.

[0073] Following the lowering process, a relative movement (arrow 105B) occurs between the multispot focus curve or interaction area 103 and the workpiece 101, so that the surface 102A of the top surface 102 acquires the desired shape. Furthermore, surface roughness 102B can optionally be reduced by offsetting the spots of the multispot focus curve 103 in the direction of the focus line (arrow 105C) (e.g., SLM ("spatial light modulator") controlled). Alternatively or additionally, the multispot focus curve or interaction area 103 as a whole can be rotated around the workpiece 101 within a small angular range to reduce roughness. Additionally, the process parameters can be adjusted during the machining process to achieve, for example, a surface quality comparable to grinding (finer focus line) and then polishing (local melting) after a laser milling or ablation step.

[0074] Fig. 6b Figure 1 shows the use of a multi-spot laser forming cutter for processing the laser exit side of a workpiece 107, i.e., on its underside 108. The processing steps are essentially analogous to those shown in Figure 1. Fig. 6aThe machining process shown (rough structuring of the laser exit-side surface 108A, forming a multispot focus line or multispot focus curve 109 according to a desired freeform surface 108B, raising the multispot focus curve 109 or, if necessary, lowering the workpiece 107 (arrow 105A'), performing a relative movement (arrow 105B') between multispot focus curve 109 and workpiece 107, optionally reducing roughness (arrow 105C')). Machining of the laser exit side (underside 108) of the workpiece 107 requires a transparency of the workpiece 107 with corresponding optical quality of the entry side (top side 102) and the volume of the workpiece 107, so that the energy of the laser radiation can be guided through the entry surface and the volume to the laser exit side 108A of the workpiece 107.

[0075] In general, under these conditions, similar machining processes to those performed on the entry side can be realized on the exit side using a laser forming tool, whereby remaining propagation-influencing properties of the volume and entry surface of the workpiece 107 can be taken into account during beam shaping. For back-side ablation processes with a laser forming tool designed for a high ablation rate, it is advantageous that the ablation products, unlike in entry-side machining, do not influence the beam propagation up to the machining zone.

[0076] It should also be mentioned that laser processing can simultaneously create several interconnected interaction zones, each spaced apart from the others. For example, multiple modifications of the material (e.g., inside the workpiece for marking) or ablation zones that run parallel due to the same relative movement can be formed simultaneously.

[0077] The ablation or modification geometry is determined by shaping the laser beam or partial beams 22, 22', 22". Spatial gradients in adjacent focus zones or areas of effect 25A, 25A', 25A" can be generated using suitable optical systems or processing optics. Temporal gradients can be generated by forming pulse groups or by pulse shaping the ultrashort pulse laser beam 12. For rapid processing, a single ablation or modification geometry can be generated simultaneously with a single laser pulse or laser pulse group, so that a position on the workpiece is approached only once.

Claims

1. A method for laser processing a workpiece (23, 23', 23", 59, 101, 107), comprising: splitting a preferably pulsed laser beam (12, 3) into a plurality of partial beams (22, 22', 22", 5a, 5b), each having one of two different polarization states (s, p), processing the workpiece (23, 23', 23", 59, 101, 107) by focusing the plurality of partial beams (22, 22', 22") in a plurality of at least partially overlapping partial regions (25A, 25A', 25A", 59A) of a continuous interaction region (25, 59, 103, 109), wherein partial beams (22, 22', 22") with respectively different polarization states (s, p) are focused into adjacent partial regions (25A, 25A', 25A", 59A) of the continuous interaction region (25, 59, 103, 109), characterized in that at least two partial regions (25A', 59A) of the continuous interaction region (25, 59, 103, 109) are offset relative to one another in the longitudinal direction (Z), i.e. in the propagation direction of the partial beams (22, 22', 22"), wherein a longitudinal offset (Δz) between two partial beams (22, 22', 22", 5a, 5b) with different polarization states (s, p) is generated when the laser beam (3) is split at at least one birefringent lens element (6).

2. The method according to claim 1, in which the laser beam (3) passes through a preferably diffractive beam-splitter optic (9) and at least one preferably birefringent polarizer element (6, 1a) when being split into the plurality of partial beams (22, 22', 22", 5a, 5b).

3. The method according to claim 1 or 2, in which, when the laser beam (3) is split at at least one birefringent polarizer element (1a, 1b), a lateral offset (Δx) and / or an angular offset (Δα) between two partial beams (22, 22', 22", 5a, 5b) with different polarization states (s, p) is generated, which preferably focuses into adjacent partial regions (25A, 25A', 25A", 59A) of the continuous interaction region (25, 59, 103, 109).

4. The method according to any one of the preceding claims, in which the longitudinal offset (Δz) between two partial beams (22, 22', 22", 5a, 5b) with different polarization states (s, p) is generated in such a way, that these are focused into adjacent partial regions (25A, 25A', 25A", 59A) of the continuous interaction region (25, 59, 103, 109).

5. The method according to any one of the preceding claims, wherein the partial regions (25A', 59A) of the continuous interaction region (25, 59, 103, 109) have an additional offset in the lateral direction (Δx).

6. The method according to any one of the preceding claims, wherein the continuous interaction region (25, 59, 103, 109) has a curved contour, which extends in particular in the longitudinal direction (Z), and / or wherein the continuous interaction region (25, 59, 103, 109) does not lie in one plane.

7. The method according to any one of the preceding claims, in which the continuous interaction region (25, 59, 103, 109) and the workpiece (3, 59, 101, 107) are moved relative to one another during the laser processing, wherein the movement preferably takes place along a feed direction (27, 105B, 105B').

8. The method according to any one of the preceding claims, in which the interaction region forms an ablation region (25, 103, 109) for the removal of material from the workpiece (23, 23', 101, 107).

9. The method according to claim 8, in which the ablation region (25, 103) is formed on an entry-side surface (23A, 102) of the workpiece (23, 23', 101) or on an exit-side surface (108) of the workpiece (107), wherein preferably a predetermined, in particular three-dimensional, surface form (102B, 108B) is generated on the entry-side or on the exit-side surface (102, 108) during processing.

10. The method according to one of claims 1 to 7, in which the interaction region forms a modification region (25, 59) for structurally modifying a material of the workpiece (23", 59), wherein the workpiece (23", 59) preferably consists of a material that is transparent to the laser beam (3), in particular glass.

11. The method according to claim 10, in which the workpiece (23", 59) is separated after the structural modification along a modification structure (33, 61) formed during the laser processing in the volume of the workpiece (23", 59), wherein the separation preferably takes place by way of a mechanical separation process, a thermal separation process, or by way of an etching process.

12. A processing optic (10) for laser processing of a workpiece (23, 59, 101, 107), comprising: a preferably diffractive beam-splitter optic (9) and at least one birefringent polarizer element (6, 1a, 1b) for splitting a preferably pulsed laser beam (12, 3) into a plurality of partial beams (22, 22', 22", 5a, 5b), each having one of two different polarization states (s, p), a focusing optic (6, 7) for focusing the plurality of partial beams (22, 22', 22") in a plurality of at least partially overlapping partial regions (25A, 25A', 25A", 59A) of a continuous interaction region (25, 59, 103, 109), wherein the processing optic (10) is designed to focus partial beams (22, 22', 22", 5a, 5b) with respectively different polarization states (s, p) into adjacent partial regions (25A, 25A', 25A", 59A) of the continuous interaction region (25, 59, 103, 109), characterized in that the at least one birefringent polarizer element (6) generates a longitudinal offset (Δz), i.e. in the propagation direction of the partial beams (22, 22', 22"), between two partial beams (22, 22', 22") with different polarization states (s, p).

13. The processing optic according to claim 12, which has at least one birefringent polarizer element (1a, 1b) for generating a lateral offset (Δx) and / or an angular offset (Δα) between two partial beams (22, 22', 22") with different polarization states (s, p).

14. The processing optic according to claim 12 or 13, characterized in that the at least one birefringent polarizer element for generating the longitudinal offset (Δz) between two partial beams (22, 22', 22") with different polarization states (s, p) is a birefringent lens element (6).

15. A laser processing device (13), comprising: a processing optic (10) according to one of claims 12 to 14, and a laser source, in particular an ultra-short-pulse laser source (11) for generating a laser beam (12), in particular for generating a laser beam (12) with a Gaussian beam profile.