PROCESSING OPTICS, LASER PROCESSING DEVICE AND METHOD FOR LASER PROCESSING

Description

[0001] The present invention relates to a processing optics for workpiece processing according to claim 1. The invention also relates to a laser processing device with such a processing optics according to claim 16, as well as to a method for laser processing a workpiece by means of a processing optics according to claim 17.

[0002] When laser processing a workpiece, especially during laser ablation, laser cutting, surface structuring, laser welding, laser drilling, etc., it is advantageous to split an input laser beam into several sub-beams that impinge on the workpiece or are focused at different locations. The splitting can occur at a polarizer element, with one input laser beam being converted into two perpendicularly polarized sub-beams as output laser beams. It is possible for several spatially offset input laser beams to impinge on the polarizer element. In this case, each of the input laser beams is split into a pair of perpendicularly polarized sub-beams.

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

[0004] WO2015 / 5114032 A1 discloses a laser processing device for workpiece processing, which comprises processing optics in which an input laser beam is split into two perpendicularly polarized partial beams by a polarizer. The processing optics have a longer path length for the second partial beam than for the first partial beam, whereby the second partial beam has a longer propagation time than the first 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 such that both partial beams form a common output laser beam.

[0005] WO2018 / 020145A1 describes a method for cutting dielectric or semiconductor material using a pulsed laser. A laser beam is split into two partial beams that impinge on the material in two spatially separated zones offset by a certain distance. The distance is set to a value below a threshold to create a linear micro-fracture in the material that runs 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.

[0006] WO2016 / 089799A1 describes a system for laser cutting at least one glass article using a pulsed laser assembly comprising a beam-shaping optical element for converting an input beam into a quasi-non-diffracting beam, for example, a Bessel beam. The laser assembly also comprises a beam transformation element for converting the quasi-non-diffracting beam into a plurality of sub-beams spaced between 1 µm and 500 µm apart. Further laser cutting systems are known from EP1721695 and WO2018 / 162356. WO2018 / 020145 further discloses a system for laser cutting using a quasi-non-diffracting laser beam. Aufgabe der Erfindung

[0007] The invention is based on the object of providing a processing optics, a laser processing device therewith and a method for laser processing in which undesirable interference effects during workpiece processing can be avoided. Gegenstand der Erfindung

[0008] This object is achieved according to the invention by a processing optics of the type mentioned at the outset, in which the processing optics are designed to generate at least partially overlapping focus zones of the partial beams polarized perpendicular to one another, preferably in the focal plane.

[0009] For the purposes of this application, perpendicularly polarized partial beams are understood to be linearly polarized partial beams whose polarization directions are aligned at an angle of 90° to each other. Perpendicularly polarized partial beams are also understood to be 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 perpendicularly polarized directions of polarization 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 laser beam, generated, for example, by a single-mode laser and featuring a Gaussian beam profile, is split into two or more partial beams and the partial beams are at least partially superimposed, this can lead to undesirable interference effects if the partial beams have the same or similar polarization. Therefore, when focusing the partial beams, the focal zones or focus cross-sections cannot be positioned arbitrarily close to one another, so the partial beams are usually focused at spaced-apart focal zones on the workpiece.

[0011] When using partial beams that have polarization states that are perpendicular to one another, there is no interference effect from the laser radiation from different spatial or angular ranges during (partial) superposition, provided that the polarization state of the respective partial beams is uniform across the entire relevant beam cross-section or the respective focus zone. The polarization of each partial beam should therefore vary as little as possible depending on the location across the beam cross-section or the focus zone. In this case, the focus zones can be as close to one another as desired, partially or completely overlap, and even form homogeneous focus zones, both transversely, i.e. perpendicular to the direction of propagation of the partial beams, and longitudinally, i.e. in the direction of propagation of the partial beams.

[0012] As an alternative to using fully or partially overlapping partial beams with polarization states perpendicular to one another, fully or partially overlapping partial beams can also be used with a time offset so large that virtually no interference effects occur. This is typically the case when the time offset is at least the order of magnitude of the pulse duration or the order of magnitude of the coherence length. The minimum time offset is usually 50% of the smaller of the two values (pulse duration or coherence length).

[0013] Although only one birefringent polarizer element is described in the following description, two or more birefringent polarizer elements can in principle also be provided in the processing optics. For example, in this case, the laser beam generated by a laser source and entering the processing optics can be split into two or more sub-beams, each of which represents an input laser beam for a corresponding birefringent polarizer element, or the laser beams from multiple laser sources can be used as input laser beams.

[0014] If the partial beams have a quasi-non-diffracting beam profile, e.g., a Bessel-like beam profile, they are focused by the focusing optics into a comparatively long focal volume (e.g., on the order of millimeters) compared to the diameter of the focal zone (e.g., on the order of micrometers). However, for the sake of simplicity, this application also refers to such beam profiles as focusing into a focal plane. The focal plane, or the planes described below, are determined by the properties of the respective optics (regardless of the type of beam profile).

[0015] In one embodiment, the birefringent polarizer element is designed either to generate a spatial offset or to generate an angular offset, or to generate a combination of an angular offset and a spatial offset between the two perpendicularly polarized partial beams. With the aid of a birefringent polarizer element, typically in the form of a birefringent crystal, the targeted spatial splitting of the input laser beam into its polarization components is enabled with a suitable polarization of the input laser beam, e.g., with an unpolarized input laser beam or with an input laser beam 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 offset and angular offset can be generated.

[0016] To generate the spatial offset (without angular offset), the birefringent polarizer element can, for example, have parallel, usually flat, beam entrance and exit surfaces. In this case, the optical axis of the birefringent crystal is typically aligned at an angle to the beam entrance surface. If the input laser beam strikes the beam entrance surface perpendicularly, a pure spatial offset is generated at the beam exit surface.

[0017] To generate the angular offset (without spatial offset), 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 exit the birefringent crystal at the same location at the beam exit surface and with a defined angular offset.

[0018] The arrangement of the birefringent polarizer element in the beam path of the processing optics depends not only on the type of laser processing but also on whether a purely spatial or purely angular offset is to be created. Creating a combination of both spatial and angular offsets is generally unfavorable for the present applications; however, in certain applications, a combination of spatial and angular offsets in the focal plane may be acceptable. Such a combination of spatial and angular offsets can also be advantageous when rotating the polarizer element (see below).

[0019] To generate a combination of spatial and angular offset, a polarizer element in the form of a conventional prism polarizer can be used, for example a Nicols 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").

[0020] In a further development, the birefringent polarizer element is designed to generate an angular offset and is arranged in a plane optically conjugate to the focal plane. A plane optically conjugate to the focal plane is understood to be a plane that is correlated with the focal plane by a Fourier transformation, i.e. an angle-to-position transformation. Assuming that the focusing optics have an (effective) image-side focal length f 2, the conjugate plane with the polarizer element, which is designed to generate an angular offset, is typically arranged at a distance of the object-side focal length f 1 of the focusing optics. For the special case that f 1 = f 2 = f, the birefringent polarizer element is arranged at a distance of 2 f (or generally 2 f + N x 4 f, N greater than or equal to 0, N is an integer) from the focal plane.For the sake of simplicity, we will refer to a 2f setup below, even if the condition f 1 = f 2 = f is not met.

[0021] In an alternative embodiment, the birefringent polarizer element is designed to generate a spatial offset and is arranged in the beam path upstream of a further, preferably collimating optical unit, wherein the processing optical unit is designed to image the spatial offset between the partial beams polarized perpendicular to one another at the polarizer element into the focal plane. In this case, the birefringent polarizer element can be arranged in a plane corresponding to the focal plane upstream of the further optical unit. Such a plane is correlated with the focal plane, for example, via two angle-to-position transformations. Assuming that the focusing optical unit has an (effective) focal length of f, the plane corresponding to the focal plane can, in a special case in which the same focal lengths are used for collimation and focusing, be arranged at a distance of 4 f (orgenerally 4 f + N x 4 f, N greater than or equal to zero, N is an integer) from the focal plane. For the sake of simplicity, we will refer to a 4f setup below, even if the optical elements used do not necessarily have a uniform focal length f. In the event that the birefringent polarizer element is arranged in the (essentially) collimated beam path, the precise arrangement of the polarizer element at a given distance from the focal plane is generally not important; only a (large-scale) position-to-position transformation is essential, i.e. an imaging between the plane with the polarizer element and the focal plane.

[0022] However, the birefringent polarizer element should be arranged in the beam path upstream of the additional optics, which can be designed, for example, as collimating optics to generate an angle-to-position transformation. Together with the angle-to-position transformation (or equivalently, position-to-angle transformation) generated by the focusing optics, the spatial offset of the partial beams generated at the polarizer element is converted or imaged into a spatial offset in the focal plane. The additional optics, e.g., collimating optics, together with the focusing optics, can image the plane with the birefringent polarizer element onto the focal plane, i.e., onto a plane linked to the focal zone, with a predetermined, e.g., reducing, image scale.

[0023] In a further embodiment, the processing optics are designed to generate a plurality of pairs of at least partially overlapping focus zones along a predetermined contour, in particular along a preferred direction, in the focal plane, wherein focus zones of two partial beams polarized perpendicular to one another from immediately adjacent pairs at least partially overlap. In this embodiment, at least two pairs of partial beams are generated whose focus zones each overlap one another, so that a beam shape or intensity distribution - in the case of a preferred direction, a line-shaped one - is created along the predetermined, not necessarily rectilinear contour, which generally has a continuous transition, i.e., no zeros in the intensity distribution between the partial beams or between the focus zones.In this case, partial beams of the respective pairs that are polarized perpendicular to each other overlap, but only to the extent that they do not overlap with the differently polarized partial beam of a respective pair, so that in this case, too, no superposition of identically polarized partial beams occurs.

[0024] In a further embodiment, the processing optics preferably comprise a diffractive beam splitter optic for generating a plurality of pairs of partial beams polarized perpendicular to one another. The beam splitter optic can, for example, be in the form of a diffractive optical element, but it can also be a different type of beam splitter optic, for example a geometric beam splitter optic. The beam splitter optic can be arranged upstream of the polarizer element in the beam path of the laser beam entering the processing optics and generate a plurality of input laser beams, each of which is split at the polarizer element into a pair of partial beams polarized perpendicular to one another. The reverse is also possible, i.e. the beam splitter optic can be arranged downstream of the birefringent polarizer element in the beam path.In this case, a plurality of pairs of partial beams are generated from the pair of partial beams generated by the polarizer element by means of the beam splitter optics, the focus zones of which can partially overlap along a preferred direction, in particular as described above.

[0025] In a further embodiment, the beam splitter optics are arranged in a plane optically conjugate to the focal plane. In the plane conjugate to the focal plane, an angular offset can be generated between the pairs of partial beams, which is transformed by the focusing optics into a spatial offset in the focal plane. In this case, the beam splitter optics can be arranged, for example, in a plane optically conjugate to the focal plane between the further imaging optics described above and the focusing optics in order to generate the plurality of pairs of partial beams from a pair of partial beams generated by the polarizer element.

[0026] In a further development, the beam splitter optics are arranged together with the birefringent polarizer element in the plane optically conjugate to the focal plane. In this case, the polarizer element is generally designed to generate an angular offset. The polarizer element and the beam splitter optics can in this case, for example, be designed in the form of plate-shaped optical elements that are connected to one another at their end faces or that abut one another. For the purposes of this application, a joint arrangement in the plane optically conjugate to the focal plane is understood to mean that the optically conjugate plane runs through one of these two optical elements or between the two optical elements. In this case, the polarizer element can be arranged after the beam splitter optics in the beam path, but the reverse is also possible.

[0027] In a further development of this embodiment, the preferably diffractive beam splitter optics are designed as beam-shaping optics for converting an incoming laser beam with a Gaussian beam profile into an outgoing laser beam with a flat-top beam profile. Shaping a laser beam with a flat-top beam profile, i.e. with a beam profile that has a substantially homogeneous intensity distribution with steeply sloping edges, enables the intensity distribution to be controlled on a surface that is oriented substantially perpendicular to the propagation direction. The flat-top beam profile can, for example, have a round or rectangular geometry, with one side of the rectangle preferably being aligned along the preferred direction generated by the polarization splitting on the polarizer element.If partial beams with such a rectangular flat-top beam profile overlap at the respective edge areas of their focus zones, a linear beam distribution with approximately constant intensity can be generated on the workpiece. It is understood that the flat-top beam profile can also have a different geometry than a round or rectangular one, for example, a geometry in the shape of a rhombus, a circle with circular cutouts, etc., in which the partial beams complement each other homogeneously when arranged along a given contour, particularly along a preferred direction.

[0028] In a further development of this embodiment, the processing optics comprises a filter optic arranged downstream of the beam splitter optic in the beam path. Particularly if the beam splitter optic is also configured as a beam-shaping optic for generating a flat-top beam profile, it may be advantageous to use a filter optic, which can be configured, for example, as a phase mask or phase filter, or in the form of an iris diaphragm or spatial aperture, to suppress higher diffraction orders generated during beam shaping.

[0029] It is understood that the processing optics may also comprise a beam-shaping optic designed to convert an incoming laser beam with a Gaussian beam profile into an outgoing laser beam with a flat-top beam profile, which is not designed as a beam splitter optic. In this case, the processing optics may additionally comprise a beam splitter optic, but this is not mandatory.

[0030] According to the claimed invention, the processing optics comprise beam-shaping optics for converting an incoming laser beam with a Gaussian beam profile into an outgoing laser beam with a quasi-non-diffracting beam profile, in particular with a Bessel-type beam profile. The use of a quasi-non-diffracting beam profile has proven particularly advantageous for glass-cutting applications or for selective laser etching, since with such a beam profile, a substantially homogeneous beam profile can be maintained in the longitudinal direction over a comparatively long distance, thereby creating a modification volume with a preferred direction. A Bessel beam has proven particularly advantageous in this case, but other non-diffracting beam profiles, e.g., an Airy beam profile, a Weber beam profile, or a Mathieu beam profile, can also be generated using the beam-shaping optics.The beam-shaping optics can be designed to generate a quasi-non-diffracting beam profile with a beam cross-section that is rotationally symmetrical to the propagation direction.

[0031] In a further development, the beam-shaping optics are designed to generate a quasi-non-diffracting beam profile with a non-rotationally symmetric beam cross-section, in particular with a preferred direction. It has proven advantageous if the beam-shaping optics in this case are designed as diffractive optics. The preferred direction of the non-diffracting beam profile generally corresponds to the (preferred) direction or the plane in which the polarizer element generates the two partial beams. The quasi-non-diffracting beam profile can have a plurality of spaced-apart (secondary) maxima along the preferred direction, so that the beam-shaping optics acts like a beam splitter optics and generates, for example, a so-called multi-Bessel beam profile. In this case, the gaps between the maxima of the beam profile are filled by the splitting into two partial beams at the polarizer element.In this way, a plurality of pairs of at least partially overlapping focus zones can be generated in the focal plane along a predetermined contour, usually along the preferred direction, with focus zones of two perpendicularly polarized partial beams of immediately adjacent pairs at least partially overlapping. In a further embodiment, the beam-shaping optics comprises an axicon and / or a diffractive optical element. The generation of a (quasi-)non-diffracting beam profile, for example in the form of a Bessel beam, can advantageously be achieved using an axicon, which typically comprises at least one substantially conical surface. The axicon or the conical surface can be modified if necessary to create a preferred direction of the beam profile, to homogenize the beam profile, etc.Alternatively or additionally, a diffractive optical element can be used to generate the (quasi-)non-diffracting beam profile. Using such a diffractive optical element, the properties of an axicon can be simulated. Alternatively or additionally, the beam-shaping optics can be configured to generate an exiting laser beam with a flat-top beam profile from an incoming laser beam with a Gaussian beam profile, etc.

[0032] In a further embodiment, the processing optics comprises a rotary drive for rotating the birefringent polarizer element and preferably the beam splitter optics and / or the beam-shaping optics about a (common) rotation axis. The rotation is particularly useful when partially overlapping focus zones are to be generated along a predetermined contour, in particular along a preferred direction. When rotating, it is advantageous that the birefringent polarizer element represents a component that is not critical for adjustment, which particularly favors its use in adaptive optics. However, the spatial offset or the angular offset generated by the polarizer element is generally not symmetrical to the propagation direction of the input beam or to the rotation axis. When rotating the polarizer element about a rotation axis, which generally runs in the longitudinal direction, ieAlong the propagation direction of the input beam, which enables tracking or rotation of the preferred direction of the focus zones described above depending on the respective application or the relative movement between the processing optics and the workpiece, an undesirable angular and / or spatial offset of the partial beams may occur, depending on the angle of rotation. To compensate for this offset, a suitably designed polarizer element can be used, for example, a Rochon prism, through which the ordinary partial beam passes without deflection, while the extraordinary partial beam experiences both an angular and spatial offset, which compensates for the offset upon rotation of the Rochon prism.

[0033] When machining a workpiece using a laser cutting process to cut glass along a processing path, it may be necessary or advantageous to change the preferred direction of the focus zones depending on a location-dependently variable feed direction during movement relative to the workpiece in order to promote crack propagation in the glass along the feed direction. The targeted alignment of cracks during glass cutting enables working in a process regime that significantly simplifies glass separation. In such a glass cutting application, the focus zones of two or more Bessel (Gaussian) beams are usually at least partially spatially superimposed, as described in more detail above. In this case, to change the preferred direction, it is not necessary to rotate optical elements that are critical for alignment, such as lenses, even though such rotation is also possible in principle.

[0034] In a further embodiment, the processing optics comprise a polarization-influencing device for generating a circularly polarized input laser beam. The laser source generally generates a linearly polarized input laser beam, which can be converted into a circularly polarized input laser beam by the polarization-influencing device, for example in the form of a suitably oriented λ / 4 plate. This is particularly advantageous if, as described above, the polarizer element is rotated by means of the rotary drive. When the polarizer element is rotated (without rotating the λ / 4 plate), in the case of a circularly polarized input laser beam, in contrast to a linearly polarized input beam, the splitting ratio of the intensities of the two perpendicularly polarized partial beams does not change during the rotation, i.e., it is not dependent on the angle of rotation.

[0035] If the splitting ratio of the intensity or power of the two partial beams generated at the polarizer element is to be specifically influenced, the polarization direction or the polarization plane of the input beam (in this case, linearly polarized, incident on the polarizer element) can be specifically rotated. For this purpose, a delay device, such as a λ / 2 plate or a λ / 4 plate, can be used. When using a λ / 2 plate, the input beam incident on it is typically linearly polarized. In this case, by rotating the λ / 2 plate, the polarization direction of the linearly polarized input laser beam can be rotated, whereby the splitting ratio of the power of the input laser beam between the two perpendicularly polarized partial beams can be adjusted.When using a λ / 4 plate, the input laser beam incident on it is usually circularly polarized and is converted by the λ / 4 plate into a linearly polarized input laser beam. In this case, too, the polarization direction of the input laser beam can be reversed by rotating the λ / 4 plate, thus adjusting the splitting ratio.

[0036] 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 designed to generate a single-mode laser beam with a Gaussian beam profile, but this is not absolutely necessary. The processing optics can, for example, be accommodated in a laser processing head or in a housing of a laser processing head that is movable relative to the workpiece. The laser processing device can alternatively or additionally comprise a scanner device for aligning the partial beams onto the workpiece or onto different positions on the workpiece.In addition to the optics described above, the processing optics can also comprise other optics that enable, for example, spatial filtering or spatial rearrangement of the input laser beam to facilitate beam shaping, e.g., homogenization of a Bessel-like beam profile, mask imaging, etc.

[0037] The invention also relates to a method of the type mentioned above, in which the perpendicularly polarized partial beams are focused in the focal plane onto at least partially overlapping focus zones. This method offers the advantages described above in connection with the processing optics.

[0038] Laser processing or workpiece processing can involve laser ablation, laser cutting, surface structuring, laser welding, laser drilling, etc. Depending on the specific processing application, it may be advantageous to use either a birefringent beam splitter element, which generates an angular offset but only an insignificant spatial offset (2 f setup, e.g., in beam splitter applications or laser ablation) or a birefringent beam splitter element, which generates a spatial offset but only an insignificant angular offset (4 f setup, e.g., when using Bessel-like beam profiles in glass separation or glass cutting).

[0039] Further advantages of the invention will become apparent from the description and the drawings. Likewise, the above-mentioned and further listed features can be used individually or in combination. The embodiments shown and described are not intended to be exhaustive, but rather serve as examples for describing the invention.

[0040] They show: Fig. 1a,bschematic representations of two birefringent polarizer elements for generating an angular offset or a spatial offset between two perpendicularly polarized partial beams, Fig. 2a,bschematic representations of a processing optics with the polarizer element of Fig. 1a or from Fig. 1b for generating two partially overlapping focus zones of the two partial beams in one focus plane, Fig. 3a,bschematic representations analogous to Fig. 2a,b with a diffractive beam splitter optics for generating a plurality of pairs of partial beams whose focus zones partially overlap, Fig. 4a,b schematic representations of a processing optics according to the claimed invention analogous to Fig. 2a,b with a beam-forming optic for generating two partially overlapping partial beams with a Bessel-shaped beam profile, Fig. 5a,b schematic representations of a processing optic according to the claimed invention analogous to Fig. 4a,b with an additional beam splitter optics for generating a plurality of pairs of partially overlapping partial beams with a Bessel-shaped beam profile, Fig. 6 a schematic representation of a processing optics analogous to Fig. 3a with a flat-top beam profile forming optics for generating partially overlapping focus zones that form a substantially homogeneous beam profile, Fig. 7a,b schematic representations of a processing optics of Fig. 4a ,b generated transverse Bessel beam profile, Fig. 8schematic representations of a beam profile generated with the processing optics of Fig. 5a ,b generated longitudinal Bessel beam profile, Fig. 9a,b schematic representations of a flat-top beam profile generated with the processing optics of Fig. 6a,b, Fig. 10a,b schematic representations of an embodiment of the processing optics of Fig. 3b , as well as Fig. 11a-cschematic representations of the processing optics of Fig. 4b with a beam-forming optic in the form of an axicon.

[0041] In the following description of the drawings, identical reference symbols are used for identical or functionally identical components.

[0042] Fig. 1a,b show schematically a birefringent polarizer element 1a, 1b in the form of a birefringent crystal. Different birefringent materials can be used as crystal material for the polarizer element 1a, 1b, e.g. alpha-BBO (alpha-barium borate), YVO4 (yttrium vandanate), crystalline quartz, etc. The birefringent polarizer element 1a of Fig. 1a is wedge-shaped, ie a flat beam entry surface 2a to the entry of an input laser beam 3 and a flat beam exit surface 2b of the polarizer element 1a are aligned at a (wedge) angle to each other. The or an optical axis 4 of the crystal material is aligned parallel to the beam entrance surface 2a.

[0043] 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 at the beam exit surface 2b inclined at an angle to the beam entrance surface 2a 5a, 5b which are perpendicular to each other (s- and p-polarized). Fig. 1a As is generally the case, the s-polarized partial beam 5a is marked by a dot, while the second, p-polarized partial beam 5b is marked 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, so that 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, ie, although the angular offset Δα is generated, no spatial offset is generated between the two partial beams 5a, 5b.

[0044] In the 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 aligned at an angle of 45° to the beam entrance surface 2a. The input beam 3, which is perpendicular to the beam entrance surface 2a, is in this case 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 at the beam exit surface 2b parallel, i.e. without an angular offset, but with a spatial offset. Δx out of.

[0045] The two in Fig. 1a and in Fig. 1b The birefringent polarizer elements 1a, 1b shown in the figure thus differ fundamentally in that the Fig. 1a shown polarizer element 1a has an angular offset Δa (without spatial offset) and that the Fig. 1b The polarizer element 1b shown generates a spatial offset Δx (without angular offset). Both polarizer elements 1a, 1b can be a component of a processing optics 6 form, for example, as in Fig. 2a,b It is understood that the processing optics 6 can also have polarizer elements that generate both a spatial offset Δx and an angular offset Δα, as is the case with conventional prism polarizers, which generally have two birefringent optical elements. In particular, the processing optics 6 can have a polarizer element that compensates for an angular offset and / or spatial offset occurring upon rotation of the polarizer element (see below). For example, a Rochon prism can be used as the polarizer element in this case.

[0046] The Fig. 2a,b The processing optics 6 shown has a focusing optics 7which are used to focus the two partial beams 5a, 5b on a focal plane 8 serves, which in Fig. 2a,b on the top of a workpiece to be machined 9 Unlike in Fig. 2a,b As shown, the focal plane 8 can also be in the beam path 10 the processing optics 6 just before the workpiece 9, in a plane within the workpiece 9 or just after the workpiece 9. The input laser beam 3, which strikes the birefringent polarizer element 1a, 1b, corresponds to a laser source 11 generated laser beam entering the processing optics 6 12. The Fig. 2a,b The processing optics 6 shown is designed to focus the two partial beams 5a, 5b on two focus zones 13a, 13b in the focal plane 8, which partially overlap and which are in Fig. 2a,b represented by a black and a white circle. The Fig. 2a The processing optics 6 shown together with the laser source 11 forms a laser processing device 14 for processing the workpiece 9, for example in the form of abrasive laser processing. For this purpose, the processing optics 6 can be moved relative to the workpiece 9 and / or have a scanner device for aligning the partial beams 5a, 5b to different locations in the focal plane 8.

[0047] At the Fig. 2a In the processing optics 6 shown, the birefringent polarizer element 1a is in a plane optically conjugated to the focal plane 8 15The optically conjugate plane 15 is linked to the focal plane 8 by an angle-to-position transformation (Fourier transformation) generated by the focusing optics 7. Angles in the optically conjugate plane 15 correspond to positions in the focal plane 8 and vice versa. The two partial beams 5a, 5b emerging from the polarizer element 1a with the angular offset Δα are therefore aligned with a position offset ΔX' of the two centers of the focus zones 13a,b in the focal plane 8, which is smaller than the diameter of the focus zones 13a,b, so that the two focus zones 13a,b overlap each other. Due to the absence of a spatial offset of the two partial beams 5a, 5b emerging from the polarizer element 1a, the two partial beams 5a, 5b are aligned parallel and perpendicular to the focal plane 8 after passing through the focusing optics 7. The distance between the focal plane 8 and the optically conjugate plane 15 is at the Fig. 2a shown example at 2 f, where f denotes the focal length of the focusing optics 7.

[0048] The Fig. 2b The processing optics 6 shown has a further imaging optics 16 which is arranged in the beam path 10 in front of the focusing optics 7. The imaging optics 16, together with the focusing optics 7, images the two partial beams 5a, 5b generated at the polarizer element 1b arranged in the beam path 10 in front of the further imaging or collimating optics 16 with a spatial offset Δx into the focal plane 8. The imaging scale for the imaging into the focal plane 8 is selected such that the diameter of the two partial beams 5a,b as well as the distance Δx' between the two partial beams 5a,b in the focal plane 8 is reduced. The polarizer element 1b is in the Fig. 2b illustrated example simplified at a distance of 4 f from the focal plane 8 in a further plane corresponding to the focal plane 8 17As a rule, the additional optics 16 and the focusing optics 7 have different focal lengths f 1 , f 2 , ie, the additional plane 17 is arranged at a distance of 2 (f 1 + f 2 ). By selecting suitable different focal lengths f 1 , f 2 , the image scale can be adjusted, for example, to achieve the reduction described above.

[0049] The spatial distribution in the further plane 17 corresponds to the spatial distribution in the focal plane 8 (with an adjustment of the scale). Since the polarizer element 1b is arranged in the collimated beam path 10 of the laser beam 12 entering the processing optics 6, it is not absolutely necessary for it to be positioned in the further plane 17; rather, it can also be arranged in the beam path 10 before or after the further plane 17.

[0050] Fig. 3a,b each show the processing optics 6 of Fig. 2a,b with an additional diffractive beam splitter optics 18, which produce a plurality of pairs 19 of focus zones 13a, 13b, which run along a preferred direction X in the focal plane 8, as shown in Fig. 3a,b The focus zones 13a,b of a pair 19 are formed by partial beams 5a, 5b which are polarized perpendicular to each other and partially overlap, as is also shown in Fig. 2a,b In addition, the focus zones 13a, 13b of two perpendicularly polarized partial beams 5a, 5b of two immediately adjacent pairs 19 overlap. In all Fig. 3a,b In the focus zones 13a, 13b shown, only partial beams 5a, 5b polarized perpendicular to one another overlap, so that no interference effects occur between the partial beams 5a, 5b. The essentially linear intensity distribution thus generated in the focal plane 8, which extends along the preferred direction X, increases the efficiency of laser ablation of the surface of, for example, a metallic workpiece 9.

[0051] At the Fig. 3a In the processing optics 6 shown, the beam splitter optics 18 are arranged in the beam path 10 after the polarizer element 1a. The diffractive beam splitter optics 18 are in Fig. 3a shown only as an example in the beam path 10 behind the polarizer element 1a and can alternatively also be arranged in front of the polarizer element 1a. Fig. 3b In the processing optics 6 shown, the beam splitter optics 18 is arranged in the beam path 10 between the further imaging optics 16 and the focusing optics 7, specifically in a plane 15 optically conjugated to the focal plane 8. In particular, both optical elements 1a, 18 can also be arranged in a common plane, as will be described in more detail below.

[0052] At the Fig. 4a,b The processing optics 6 shown is as shown in Fig. 2a,b the input laser beam 3 is split into two partial beams 5a,b, whose focus zones 13a,b overlap in the focus plane 8. The processing optics 6 of Fig. 4a,b According to the claimed invention, the device has a beam-shaping optic 20for converting a laser beam entering the processing optics 6, which in the example shown corresponds to the laser beam 12 generated by the laser source 11 with a Gaussian beam profile, into an input laser beam 3 with a quasi-non-diffracting beam profile, more precisely with a Bessel-like beam profile.

[0053] The Bessel-like beam profile can be rotationally symmetrical to the propagation direction, but it is also possible for the beam-shaping optics 20 to generate a non-rotationally symmetrical beam profile that has a preferred direction, i.e., the beam-shaping optics 20 acts like a beam splitter optic. Other or more complex beam profiles, e.g., non-diffractive beam profiles such as Airy beam profiles, Mathieu beam profiles, beam homogenization, the generation of a vortex, a bottle, etc., can also be generated using the beam-shaping optics 20. The beam-shaping optics 20 can be designed as a diffractive optical element, as an axicon, etc., or a combination of these elements. The beam-shaping optics 20 can also be designed as a diffractive optical element that functions as an axicon.

[0054] After the beam-shaping optics 20, in the present example, a beam profile is present which corresponds to a substantially rotationally symmetric Bessel beam, ie a radial intensity profile in the transverse direction in the form of a Bessel function. Fig. 4a The processing optics 6 shown additionally has an imaging or collimating optics 16, which is arranged in the beam path 10 between the beam-forming optics 20 and the polarizer element 1a and which serves for reduced imaging. At the location of the polarizer element 1a, Fig. 4a the far field of the Bessel-like beam profile. The generation of a beam profile in the form of a Bessel-like beam has proven advantageous for the separation of a workpiece 9 which is made of a transparent material, for example glass, and in which a separation and, if necessary, crack guidance along a predetermined direction is advantageous, which corresponds to the direction in Fig. 4a,b shown preferred direction X, which can also be aligned at a predetermined angle to the preferred direction X or, if necessary, form a predetermined contour deviating from a line. The fact that the longitudinal beam profile of the partial beams 5a, 5b, which penetrate the workpiece 9, is almost homogeneous over a comparatively large length, also facilitates the separation, possibly with the formation of cracks, and thus the separating processing of the glass material.

[0055] The Fig. 5a,b The processing optics 6 shown corresponds to the one shown in Fig. 4a,b processing optics 6 shown, but additionally has a beam splitter optics 18, which, as in connection with Fig. 3a,b described for generating a plurality of pairs 19 of focus zones 13a, 13b in the focus plane 8, which are arranged next to one another along the preferred direction X.

[0056] The one with the Fig. 4a,b The transverse beam profile generated by the processing optics 6 shown in the focal plane 8 (in X-direction) for one polarization direction, e.g. for s-polarized partial beams 5a, is shown in Fig. 7a In the example shown, the beam-shaping optics 20 are used to Fig. 7a shown, non-rotationally symmetric beam profile is generated, which has several maxima along a preferred direction (X-direction) (multi-Bessel), ie the beam-forming optics 20 acts in the manner of a beam splitter optics. Fig. 7b shows the transverse steel profile in the focal plane 8 during the partial superposition of the focus zones 13a, 13b of mutually perpendicularly polarized partial beams 5a, 5b, as these are generated by means of the polarizer element 1b of Fig. 4b is generated. Fig. 8 shows the longitudinal beam profile generated by the Fig. 5b shown processing optics 6 is generated without (in Fig. 8 above) and with (in Fig. 8 below) Superposition of the perpendicularly polarized partial beams 5a, 5b by means of the polarizer element 1b.

[0057] Fig. 6 shows a processing optics 6, which is Fig. 3a shown processing optics 6 and in which the beam splitter optics 18 is additionally designed as a beam-shaping optics for converting an incoming laser beam 12 into an outgoing laser beam with a flat-top beam profile. The beam splitter optics 18 is different from Fig. 3a arranged in the beam path 10 in front of the polarizer element 1a. Between the beam splitter optics 18 and the polarizer element 1a is a filter optics 21 arranged, which is an optical filter element 22 which separates parasitic radiation components from the useful radiation. The filter element 22 can, for example, be in the form of a diaphragm or a phase mask 22The filter element 22 is arranged between two further imaging (collimating or focusing) optics 22a, 22b The filter optics 21 are used to filter out unwanted diffraction components that are generated during beam shaping by means of the beam splitter optics 18 and prevent these parasitic radiation components from reaching the workpiece 9 or other locations where they have a disruptive effect. Fig. 6 In the example shown, instead of the polarizer element 1a, which is designed to generate an angular offset Δα (without spatial offset), a polarizer element 1b could be arranged adjacent to the filter element 22, which is designed to generate a spatial offset Δx (without angular offset).

[0058] The intensity profile generated in the focal plane 8 is for the focus zones 13a assigned to the first partial beams 5a in Fig. 9a As shown in Fig. 9a As can be seen, rectangular focus zones 13a are generated in the focal plane 8, which have an essentially constant radiation intensity. Fig. 9b shows the intensity profile in the focal plane 8 for the Fig. 6 overlapping focus zones 13a,b of the two perpendicularly polarized partial beams 5a, 5b. As shown in Fig. 9b As can be seen, with the help of the polarizer element 1a, an essentially homogeneous line-shaped intensity or beam profile is generated in the focal plane 8 along the preferred direction X. The Fig. 9a,b In principle, the intensity profile shown can also be (more compactly) calculated using the Fig. 3a,b The processing optics 6 shown in Figure 1 are also produced. Fig. 3a,b A filter optics 21 or a filter element 22 can be used in the processing optics 6 shown, which is arranged in the beam path 10 after the beam splitter optics 18.

[0059] The beam path 10 of the Fig. 3a schematically shown processing optics 6 is in Fig. 10a,b portrayed in a more realistic way. Fig. 10a shows the beam path 10 without the polarizer element 1a, ie only the diffractive, plate-shaped beam splitter optics 18, which from the laser beam 12 entering the processing optics 6 a plurality of, for example, five exiting laser beams 23a-e which are focused onto the focal plane 8 by means of the focusing optics 17. Fig. 10b shows the processing optics 6 of Fig. 10a , which additionally comprises the polarizer element 1a, which is arranged in the beam path 10 behind the diffractive optical element 18 and which splits each of the outgoing laser beams 23a-e into two perpendicularly polarized partial beams 5a, 5b. The focusing optics 7 in the form of a focusing lens aligns the partial beams 5a, 5b parallel to each other so that they impinge perpendicularly on the focal plane 8. The focus zones 13a, 13b (not shown) of the respective perpendicular partial beams 5a, 5b overlap each other. As in Fig. 10a ,b can also be seen, the processing optics 6 has a rotary drive indicated by an arrow 24 to rotate the plate-shaped diffractive optical element 18 together with the polarizer element 1a attached thereto around a rotation axis running centrally and parallel to the propagation direction of the input beam 12 25to rotate. By rotating, the alignment of the partial beams 5a, 5b in the focal plane 8 or the preferred direction X can be rotated.

[0060] In order to avoid an undesirable offset of the partial beams 23a-e in the focal plane 8, which is dependent on the angle of rotation around the axis of rotation 25, the Fig. 10b The processing optics 6 shown comprises a polarization-influencing device in the form of a λ / 4 plate 26 The λ / 4 plate 26 is suitably oriented to convert the linear polarization of the input laser beam 12 into a circular polarization. Due to the circular polarization of the input laser beam 12, in addition to the undesired offset, a generally undesirable variation in the distribution of the power of the input laser beam 12 between the two perpendicularly polarized partial beams 5a,b, which depends on the angle of rotation about the rotation axis 25, can be avoided.

[0061] Fig. 11a -ceach show a processing optics 6, which is similar to Fig. 4b The processing optics 6 have a refractive optical element in the form of an axicon 20 in order to generate a Bessel-like beam profile from the input beam 12 with the Gaussian beam profile. Instead of the axicon 20, a diffractive optical element can also be used as the beam-shaping optics. In particular, when using a diffractive optical element, a Bessel-like beam profile with a preferred direction (X-direction) can also be generated (cf. Fig. 7a ), ie the beam-forming optics 20 acts as a beam splitter optics. The polarizer element 1b following in the beam path splits the input beam 12 into the two perpendicularly polarized partial beams 5a, 5b, which are formed by the imaging optics 16 (with focal length f = 200 mm in Fig. 11a or with focal length f = 100 mm in Fig. 11b ) and the focusing optics 7 (with focal length f = 10 mm) onto the focal plane 8. In the focal plane 8, a comparatively elongated focus profile is created in the longitudinal direction 27, whose intensity distribution in Fig. 11a,b is shown on the right side.

[0062] The Fig. 11a The processing optics 6 shown differs from those shown in Fig. 11b,c processing optics 6 shown in that the Fig. 11a The Axicon 20 shown is an inverse Axicon in which the conical surface is concavely curved, while the Axicons shown in Fig. 11b,c The Axicon 20 shown is a conventional Axicon 20 in which the conical surface is convexly curved. It is understood that the Fig. 11b,c The Axicon 20 shown can be replaced by a suitably designed diffractive optical element or, if necessary, combined with it. Fig. 11c The processing optics 6 shown differs from the one shown in Fig. 11b processing optics 6 shown in that the further imaging optics 16 is arranged at a distance from the polarizer element 1b. With the in Fig. 11a-c A glass cutting application can be carried out particularly advantageously using the processing optics 6 shown. Depending on the application, it may be useful to generate circularly polarized partial beams 5a, 5b in the focal plane 8 instead of linearly polarized partial beams 5a, 5b on the left and right, respectively. For this purpose, a delay element, e.g., in the form of a λ / 4 plate, can be arranged at a suitable location in the beam path 10 after the polarizer element 1a, 1b.

Claims

1. A processing optics (6) for workpiece processing, comprising: a birefringent polarizer element (1a, 1b) for splitting at least one input laser beam (12) into a pair of partial beams (5a, 5b) polarized perpendicular to each other, and focusing optics (7) disposed in the beam path (10) after the polarizer element (1a, 1b) for focusing the partial beams (5a, 5b) onto focus zones (13a, 13b), preferably in a focal plane (8), characterized in that, the processing optics (6) is designed to generate at least partially overlapping focus zones (13a, 13b) of the partial beams (5a, 5b) polarized perpendicular to each other and that the processing optics (6) comprise a beam-shaping optics (20) for converting an incident laser beam (12) with a Gaussian beam profile into an emerging laser beam (3) with a quasi-non-diffractive beam profile, wherein the beam-shaping optics (20) is disposed in the beam path (10) in front of the birefringent polarizer element (1a, 1b).

2. The processing optics according to claim 1, in which the birefringent polarizer element (1a, 1b) is designed to generate either a spatial offset (Δx) or to generate an angular offset (△α) or to generate a combination of a spatial offset (Δx) and an angular offset (△α) between the two partial beams (5a, 5b) polarized perpendicular to each other.

3. The processing optics according to claim 2, wherein the birefringent polarizer element (1a) is designed to generate an angular offset (△α) and is disposed in a plane (15) optically conjugate to the focal plane (8).

4. The processing optics according to claim 2, wherein the polarizer element (1b) is designed to generate a spatial offset (Δx) and is disposed in the beam path (10) in front of a further, preferably collimating optics (16), wherein the processing optics (6) is designed to map the spatial offset (Δx) between the partial beams (5a, 5b) polarized perpendicular to each other into the focal plane (8).

5. The processing optics according to one of the preceding claims, which are designed to generate a plurality of pairs (19) of at least partially overlapping focus zones (13a, 13b) along a predetermined contour, in particular along a preferred direction (X), in the focal plane (8), wherein focus zones (13a, 13b) of two partial beams (5a, 5b) polarized perpendicular to each other of immediately adjoining pairs (19) at least partially overlap.

6. The processing optics according to claim 5, further comprising: a preferably diffractive beam splitter optics (18) for generating the plurality of pairs (19) of partial beams (5a, 5b) polarized perpendicular to each other.

7. The processing optics according to claim 6, wherein the beam splitter optics (18) are disposed in a plane (15) optically conjugate to the focal plane (8).

8. The processing optics according to claim 7, wherein the beam splitter optics (18) together with the birefringent polarizer element (1a) are disposed in the plane (15) optically conjugate to the focal plane (8).

9. The processing optics according to one of claims 6 to 8, wherein the beam splitter optics (18) are designed as beam-shaping optics for converting an incident laser beam (12) with a Gaussian beam profile into an emerging laser beam (3) with a flat-top beam profile.

10. The processing optics according to one of claims 6 to 9, further comprising: a filter optics (21) arranged downstream of the diffractive beam splitter optics (18).

11. The processing optics according to one of the preceding claims, characterized in that the beam-shaping optics (20) are designed for converting an incident laser beam (12) with a Gaussian beam profile into an emerging laser beam (3) with a Bessel-like beam profile.

12. The processing optics according to one of the preceding claims, wherein the beam-shaping optics (20) are designed to generate a non-rotationally symmetrical, quasi-non-diffractive beam profile which preferably has a preferred direction (X).

13. The processing optics according to one of the preceding claims, wherein the beam-shaping optics (20) are designed as an axicon or as a diffractive optical element.

14. The processing optics according to one of the preceding claims, further comprising: a rotary drive (24) for rotating the birefringent polarizer element (1a, 1b) and preferably the beam splitter optics (18) and / or the beam-shaping optics (20) about an axis of rotation (25).

15. The processing optics according to one of the preceding claims, further comprising: a polarization-influencing device (26) for generating a circularly polarized input laser beam (12).

16. A laser processing device (14), comprising: processing optics (6) according to one of the preceding claims, and a laser source (11), in particular an ultra-short pulse laser source (11), for generating a laser beam (12), in particular a laser beam (12) with a Gaussian beam profile.

17. A method for laser processing a workpiece (9) by means of processing optics (6), comprising: splitting at least one input laser beam (12) into a pair of partial beams (5a, 5b) polarized perpendicular to each other at a birefringent polarizer element (1a, 1b) of the processing optics (6), and focusing the partial beams (5a, 5b) on focus zones (13a, 13b), preferably in a focal plane (8), in the area of the workpiece (9) by means of a focusing device (7) of the processing optics (6), characterized in that, beam-shaping optics (20) of the processing optics (6) converts an incident laser beam (12) with a Gaussian beam profile into an emerging laser beam (3) with a quasi-non-diffractive beam profile, wherein the beam-shaping optics (20) is disposed in the beam path (10) in front of the birefringent polarizer element (1a, 1b), and that the partial beams (5a, 5b) polarized perpendicular to each other are focused onto at least partially overlapping focus zones (13a, 13b).