METHOD AND DEVICE FOR LASER MACHINING A WORKPIECE

Description

[0001] The invention relates to a method for laser processing of a workpiece which has a material which is transparent for laser processing, in which method an input laser beam is split into a plurality of partial beams by means of a beam splitting element, wherein the splitting of the input laser beam is carried out by means of the beam splitting element by phase imprinting on a beam cross-section of the input laser beam, partial beams coupled out of the beam splitting element are focused by means of focusing optics, a plurality of focus elements are formed by focusing the partial beams, and in which the material of the workpiece for laser processing is exposed to at least a subset of the formed focus elements.

[0002] The invention further relates to a device for laser processing of a workpiece which has a material which is transparent for laser processing, comprising a beam splitting element for splitting an input laser beam coupled into the beam splitting element into a plurality of partial beams, wherein the splitting of the input laser beam is carried out by means of the beam splitting element by phase imprinting on a beam cross-section of the input laser beam, and a focusing optics for focusing partial beams coupled out of the beam splitting element, wherein a plurality of focus elements for laser processing of the workpiece are formed by focusing the partial beams.

[0003] From DE 10 2014 116 958 A1, a diffractive optical beam-shaping element for imprinting a phase profile on a laser beam intended for laser processing of a material that is largely transparent to the laser beam is known, comprising a phase mask that is designed to imprint a plurality of beam-shaping phase profiles on the laser beam falling on the phase mask, wherein at least one of the plurality of beam-shaping phase profiles is assigned a virtual optical image that can be imaged in at least one elongated focus zone to form a modification in the material to be processed.

[0004] From JP 2020 004 889 A, a device and a method for cutting, in particular a substrate, are known, wherein a plurality of focus points are generated by means of a spatial light modulator.

[0005] The invention is based on the object of providing a method and a device as mentioned above, by means of which the formation of material modifications in the material of the workpiece can be better controlled and / or reproduced, so that in particular an improved material separation is made possible.

[0006] This object is achieved according to the invention in the method mentioned at the outset in that the phase imprinting is carried out by means of the beam splitting element in such a way that at least two of the formed focus elements have a different intensity.

[0007] It has been shown that lower intensities are necessary to form material modifications close to the surface, i.e. material modifications located close to an outer side and / or upper side of the workpiece, than to form material modifications which are formed deep in the volume of the material, i.e. further away from the nearest outer side and / or upper side of the workpiece. By forming several focus elements with different intensities, material modifications can be formed in the material of the workpiece which have similar properties regardless of their depth positioning in the volume of the material. In particular, this makes it possible to improve the homogeneity of the material modifications in the thickness direction and / or depth direction of the material. In particular, this makes it possible to achieve material separation with improved quality and / or homogeneity.

[0008] In particular, at least two of the formed focus elements, with which the material of the workpiece is exposed for laser processing, have a different intensity.

[0009] In particular, the formed focus elements are each arranged at different spatial positions.

[0010] Different intensities of focus elements mean, in particular, that focus elements arranged at different spatial positions each have different intensities.

[0011] In particular, the intensity of a particular focus element is understood to be a spatial average intensity or a maximum intensity of the focus element.

[0012] In particular, the respective intensities of the focus elements within a specific medium are defined while neglecting absorption effects of that medium. For example, the intensity is defined in air and / or glass.

[0013] In particular, the intensities of the formed focus elements are at least approximately constant over time during laser processing of the workpiece.

[0014] In particular, different focus elements are spaced apart from one another and / or arranged at different spatial positions. It is generally possible for different focus elements to spatially overlap in sections.

[0015] The spatial position of a specific focus element is understood to mean, in particular, a center position of the corresponding focus element.

[0016] It can be advantageous to select the intensity of the focus elements such that exposure to the material with the focus elements creates similar material modifications in the material, and in particular, such modifications are created in the material regardless of the distance between the respective focus elements and an outer side of the workpiece closest to the respective focus elements. This results in optimized separability of the material along the formed material modifications. Separation can thus be achieved, for example, with increased homogeneity and / or with a smoother separating edge.

[0017] Similar material modifications are understood to mean, in particular, material modifications which have at least approximately the same selective etchability and / or the same spatial extent.

[0018] In particular, the similar material modifications exhibit identical or similar etching properties. This allows for optimized separation of the material by etching using a wet chemical solution.

[0019] It may be advantageous if the intensity of the focus elements is selected depending on a distance and / or distance range by which the respective focus elements are spaced from an outer side of the workpiece, and in particular from an outer side of the workpiece closest to the respective focus elements. This allows at least approximately similar material modifications to be formed in the material, regardless of their distance and / or distance range.

[0020] A distance range is understood to mean, in particular, distances within a certain interval to the outside and, in particular, the nearest outside of the workpiece.

[0021] In particular, a specific focus element is uniquely assigned to a specific distance range. In particular, different distance ranges do not overlap.

[0022] A spacing direction of the distance or spacing range is oriented in particular parallel to a thickness direction of the workpiece.

[0023] The workpiece is, for example, plate-shaped and / or panel-shaped.

[0024] It can be advantageous to increase the intensity of the focus elements as the distance between the respective focus elements and the closest outer surface of the workpiece increases. This allows material modifications located deeper within the workpiece volume to be formed at least approximately similarly to material modifications located less deeply.

[0025] For the same reason, it may be advantageous if an average intensity of respective focus elements assigned to a certain distance range is chosen to be increasingly larger with increasing mean distance of the respective distance range to the nearest outer side of the workpiece.

[0026] In particular, it can be provided that a relative intensity of the formed focus elements varies by a factor of at least 1.5 and / or at most 5.0, preferably of at least 2.0 and / or at most 3.0 and particularly preferably of 2.5.

[0027] If the relative intensity of the formed focus elements varies, for example, by a factor of 2.0, this means that the formed focus elements comprise at least one focus element with a smallest intensity and at least one focus element with a greatest intensity, wherein the intensity of the focus element with the greatest intensity is greater by a factor of 2.0 than the intensity of the focus element with the smallest intensity.

[0028] In particular, it can be provided that at least one distance range is provided, wherein the intensity of respective focus elements lying within this at least one distance range is at least approximately constant. For example, multiple distance ranges are then provided, the associated focus elements of which each have different intensities. For example, the intensity of the focus elements then varies in steps.

[0029] In particular, it can be provided that at least one spacing range is provided, wherein the intensity of respective focus elements lying within this at least one spacing range varies, and wherein, in particular, the intensity of the focus elements lying in this spacing range increases with increasing distance of these focus elements from the nearest outer side of the workpiece. In particular, the respective intensities of two or more or all of the focus elements lying in this spacing range are then different. For example, the intensity of adjacent focus elements is then different from each other.

[0030] For example, a first distance range is provided in which the intensity of respective focus elements lying within this first distance range varies, and a further distance range is provided in which the intensity of respective focus elements lying within this further distance range is at least approximately constant. The first distance range then borders, for example, on an outer side of the workpiece or encloses an outer side of the workpiece. The further distance range then lies, for example, entirely within the material of the workpiece and, in particular, borders the first distance range.

[0031] For example, an intensity of the focus elements of the further distance range is then greater than the intensity of the focus elements of the first distance range by a factor of at least 1.5 to 5.0, preferably from 2.0 to 3.0, particularly preferably from 2.5.

[0032] It can be advantageous if different focus elements are arranged along a predetermined processing line, and in particular if the different focus elements are spaced apart along the processing line and / or have such an intensity that, by applying these focus elements to the material of the workpiece, material modifications are formed in the material, which enable the material to be separated along this processing line. During laser processing of the material, this results in the formation of material modifications along this processing line or along a processing surface corresponding to this processing line. In particular, the material can be separated along this processing line or processing surface.

[0033] For example, the at least one processing line has a total length between 50 µm and 5000 µm.

[0034] In particular, it can be provided that the material of the workpiece is separable or is separated by applying thermal stress and / or mechanical tension and / or by etching using at least one wet chemical solution. For example, the etching takes place in an ultrasonically assisted etching bath.

[0035] In particular, it can be provided that the processing line is spatially continuous over a thickness of the material of the workpiece.

[0036] The processing line is not necessarily spatially contiguous, but may comprise various spatially separated sections. In particular, the processing line may have gaps and / or interruptions in which no focus elements are arranged.

[0037] In particular, the processing line is or comprises a connecting line between adjacent focus elements.

[0038] In particular, it can be provided that an angle of incidence between the processing line and an outer side of the workpiece, through which the focus elements for laser processing are coupled into the workpiece material, is at least 1° and / or at most 90°. This allows, for example, a vertical cut to be made on the workpiece or the workpiece to be chamfered at a specific angle.

[0039] In particular, it can be provided that the angle of attack of the processing line is constant at least in sections, and / or that the processing line has several sections with different angles of attack.

[0040] In particular, it can be provided that the processing line is at least partially a straight line and / or that the processing line is at least partially a curve.

[0041] By executing the machining line as a curve, rounded segments can be cut from the workpiece, for example, creating rounded edges.

[0042] When the machining line is designed as a curve, for example, the machining line is assigned a specific angle of attack range which the machining line has with respect to the outside of the workpiece.

[0043] It may be advantageous if one or more of the formed focus elements are arranged or are arranged outside a material of the workpiece, at least partially and / or at least temporarily, during laser processing of the workpiece. In particular, this ensures that the material of the workpiece continues to be exposed to focus elements in the outer region during laser processing in the event of thickness fluctuations and / or focus position fluctuations.

[0044] In particular, during laser processing, the processing line extends beyond at least one outer side of the workpiece in the thickness direction of the workpiece and / or at least temporarily beyond one outer side of the workpiece.

[0045] For example, focus elements arranged outside the material of the workpiece are spaced at a distance from an outer side of the workpiece closest to these focus elements.

[0046] For example, a section of the machining line arranged outside the material is a tangential continuation of the machining line to an end point and / or end section of the machining line arranged inside the material.

[0047] In particular, it can be provided that for laser processing of the workpiece, the focus elements are moved relative to the material of the workpiece at a feed rate.

[0048] In particular, the processing line with the focus elements for laser processing the workpiece is moved relative to the workpiece at a feed rate oriented in the feed direction. This creates, in particular, a processing surface corresponding to the processing line, along which material modifications are arranged.

[0049] Preferably, the focus elements each lie, at least in sections, in a plane that is oriented perpendicular to the feed direction. In particular, all formed focus elements lie in this plane.

[0050] It may be advantageous if a polarization beam splitting element is used to split the polarization beams so that the partial beams have one of at least two different polarization states. Focusing the partial beams using the focusing optics creates focus elements with different polarization states, and in particular, focus elements with different polarization states are arranged adjacent to one another. This prevents, in particular, interference between adjacent focus elements. This allows adjacent focus elements to be arranged at a particularly close distance from one another.

[0051] The material modifications introduced into transparent materials by ultrashort laser pulses are divided into three different classes, see K. Itoh et al., "Ultrafast Processes for Bulk Modification of Transparent Materials," MRS Bulletin, vol. 31, p. 620 (2006): Type I is an isotropic refractive index change; Type II is a birefringent refractive index change; and Type III is a so-called void. The material modification produced depends on the laser parameters of the laser beam from which the focus zone is formed, such as the pulse duration, wavelength, pulse energy, and repetition frequency of the laser beam, as well as on the material properties, including the electronic structure and thermal expansion coefficient, as well as the numerical aperture (NA) of the focusing.

[0052] Type I isotropic refractive index changes are attributed to localized melting by the laser pulses and rapid resolidification of the transparent material. For example, in fused silica, the density and refractive index of the material are higher when the fused silica is rapidly cooled from a higher temperature. Thus, when the material melts in the focal volume and then cools rapidly, the fused silica exhibits a higher refractive index in the modified areas than in the unmodified areas.

[0053] Type II birefringent refractive index changes can arise, for example, from interference between the ultrashort laser pulse and the electric field of the plasma generated by the laser pulse. This interference leads to periodic modulations in the electron plasma density, which, upon solidification, results in a birefringent property—i.e., direction-dependent refractive indices—of the transparent material. A Type II modification is also associated, for example, with the formation of so-called nanogratings.

[0054] The voids of Type III modifications can be created, for example, with high laser pulse energy. The formation of the voids is attributed to the explosive expansion of highly excited, vaporized material from the focal volume into the surrounding material. This process is also referred to as a microexplosion. Since this expansion occurs within the bulk of the material, the microexplosion leaves behind a less dense or hollow core (the void), or a microscopic defect in the submicrometer or atomic range, surrounded by a dense material shell. The densification at the shock front of the microexplosion creates stresses in the transparent material that can lead to or promote spontaneous crack formation.

[0055] In particular, the formation of voids can also be associated with Type I and Type II modifications. For example, Type I and Type II modifications can occur in the less stressed areas around the applied laser pulses. Therefore, when a Type III modification is introduced, a less dense or hollow core, or a defect, is always present. For example, in sapphire, a Type III modification does not create a cavity through microexplosion, but rather an area of lower density. Due to the material stresses that occur during a Type III modification, such a modification is often accompanied by or at least promotes crack formation. The formation of Type I and Type II modifications cannot be completely prevented or avoided when introducing Type III modifications. Therefore, the discovery of "pure" Type III modifications is unlikely.

[0056] At high repetition rates of the laser beam, the material cannot cool completely between pulses, so that cumulative effects of the heat introduced from pulse to pulse can influence the material modification. For example, the repetition frequency of the laser beam can be higher than the inverse of the material's thermal diffusion time, so that heat accumulation can occur at the focal elements through successive absorption of laser energy until the material's melting temperature is reached. Furthermore, the thermal transport of heat energy to the areas surrounding the focal elements can melt a larger area than the focal elements. After the introduction of ultrashort laser pulses, the heated material cools rapidly, so that the density and other structural properties of the high-temperature state are, to a certain extent, frozen in the material.

[0057] In particular, it can be provided that by applying the focus elements to the material of the workpiece, material modifications are formed in the material which are associated with crack formation in the material, and / or that by applying the focus elements to a material of the workpiece, type III material modifications are formed in the material.

[0058] The fact that the formation of material modifications is associated with crack formation means in particular that the formation of the material modifications is accompanied by crack formation in the material and / or that crack formation occurs in the material when the material modifications are formed.

[0059] In particular, it can be provided that by applying the focus elements to the material of the workpiece, material modifications are formed in the material which are associated with a change in a refractive index of the material, and / or that by applying the focus elements to a material of the workpiece, type I material modifications and / or type II material modifications are formed in the material.

[0060] The fact that the formation of material modifications is associated with a change in the refractive index means in particular that the formation of the material modifications is accompanied by a change in the refractive index in the material and / or that the formation of the material modifications results in a change in the refractive index in the material.

[0061] In the device for laser processing of a workpiece mentioned at the outset, it is provided according to the invention that the phase imprinting is carried out by means of the beam splitting element in such a way that at least two of the formed focus elements have a different intensity.

[0062] The device according to the invention has, in particular, one or more features and / or advantages of the method according to the invention. Advantageous embodiments of the device according to the invention have already been explained in connection with the method according to the invention.

[0063] In particular, the device comprises at least one polarization beam splitting element which is arranged upstream or downstream of the beam splitting element with respect to a beam propagation direction of the input laser beam, wherein a polarization beam splitting element is carried out by means of the polarization beam splitting element, that the partial beams incident on the focusing optics each have one of at least two different polarization states and that focus elements with different polarization states are formed by focusing the partial beams by means of the focusing optics.

[0064] In particular, the method according to the invention can be carried out by means of the device according to the invention or the method according to the invention is carried out by means of the device according to the invention.

[0065] In particular, the focus elements are formed from the input laser beam, wherein the focus elements are formed in particular by transforming and / or beam shaping of the input laser beam.

[0066] In particular, it can be provided that the input laser beam is split by means of the beam splitting element by phase manipulation of a phase of the input laser beam. In particular, the input laser beam is split exclusively by phase manipulation of the phase of the input laser beam.

[0067] The focusing optics are not necessarily designed as a separate optical element. It is also possible, in principle, for the focusing optics to be integrated into another component of the device, for example, into the beam splitting element and / or a polarization beam splitting element.

[0068] In particular, a phase imprint on the beam cross-section of the first input beam carried out by means of the beam splitting element can be variably adjusted and / or defined.

[0069] The beam splitting element is designed in particular as a diffractive beam splitting element and / or as a 3D beam splitting element.

[0070] In particular, the device according to the invention comprises a laser source for providing the input laser beam, which is in particular a pulsed laser beam and / or an ultrashort pulse laser beam.

[0071] In particular, the material of the workpiece is made of a material that is transparent to the input laser beam and / or to a laser beam from which the focus elements are formed.

[0072] A transparent material is understood to mean, in particular, a material through which at least 70% and in particular at least 80% and in particular at least 90% of the laser energy of a laser beam from which the focus elements are formed is transmitted.

[0073] In particular, the focus elements are formed from an ultrashort pulse laser beam or are provided by an ultrashort pulse laser beam. This ultrashort pulse laser beam comprises, in particular, ultrashort laser pulses.

[0074] For example, a wavelength of the input laser beam and / or the laser beam from which the focus elements are formed is at least 300 nm and / or at most 1500 nm. For example, the wavelength is 515 nm or 1030 nm.

[0075] In particular, the input laser beam and / or the laser beam from which the focus elements are formed has an average power of at least 1W to 1kW. For example, the laser beam comprises pulses with a pulse energy of at least 10 µJ and / or at most 50 mJ. It can be provided that the laser beam comprises individual pulses or bursts, wherein the bursts have 2 to 20 subpulses and, in particular, a time interval of approximately 20 ns.

[0076] In particular, a focus element is understood to be a radiation area with a specific spatial extent. To determine the spatial dimensions of a specific focus element, such as the diameter of the focus element, only intensity values above a certain intensity threshold are considered. The intensity threshold is chosen, for example, such that values below this intensity threshold have such low intensity that they are no longer relevant for interaction with the material to form material modifications. For example, the intensity threshold is 50% of a global intensity maximum of the focus element.

[0077] In particular, the terms "at least approximately" or "approximately" generally mean a deviation of no more than 10%. Unless otherwise stated, the terms "at least approximately" or "approximately" specifically mean that an actual value and / or distance and / or angle deviates by no more than 10% from an ideal value and / or distance and / or angle.

[0078] The following description of preferred embodiments, in conjunction with the drawings, serves to further explain the invention. They show: Fig. 1 shows a schematic representation of an embodiment of a device for laser processing of a workpiece; Fig. 2 shows a schematic cross-sectional representation of a section of a workpiece which is subjected to multiple focus elements for laser processing; Fig. 3 shows a schematic cross-sectional representation of a section of a workpiece subjected to multiple focus elements, wherein multiple focus elements are present which are positioned outside the workpiece; Fig. 4 shows a schematic cross-sectional representation of a section of a workpiece in which material modifications were created by subjecting the workpiece to focus elements, which modifications are accompanied by crack formation in the material; Fig. 5a shows a cross-sectional representation of a simulated intensity distribution of focus elements for laser processing of the workpiece; Fig. 5b shows the intensity distribution according to Fig. 5a associated phase distribution; Fig. 6a a schematic perspective view of a workpiece with material modifications formed thereon, which extend along a processing line and / or processing surface; and Fig. 6b a schematic view of two workpiece segments, which are formed by separating the workpiece according to Fig. 6a formed along the machining line and / or machining surface.

[0079] Identical or functionally equivalent elements are provided with the same reference numerals in all figures.

[0080] An embodiment of a device for laser processing of a workpiece is described in Fig. 1 and designated therein by 100. Using the device 100, localized material modifications, such as defects in the submicrometer range or atomic range, can be created in a material 102 of the workpiece 104, which result in a weakening of the material. At these material modifications, the workpiece 104 can be separated or, for example, a workpiece segment can be separated from the workpiece 104.

[0081] In particular, by means of the device 100, material modifications can be introduced into the material 102 at an angle of incidence, so that by separating a corresponding workpiece segment from the workpiece 104, an edge region of the workpiece 104 can be chamfered or beveled.

[0082] The device 100 comprises a beam splitting element 106 into which an input laser beam 108 is coupled. This input laser beam 108 is provided, for example, by a laser source 110. For example, the input laser beam 108 is a pulsed laser beam and / or an ultrashort pulse laser beam.

[0083] The input laser beam 108 is understood, in particular, to be a beam bundle comprising a plurality of, in particular, parallel beams. The input laser beam 108 has, in particular, a transverse beam cross-section 112 and / or a transverse beam extension with which the input laser beam 108 impinges on the beam splitting element 106.

[0084] The input laser beam 108 impinging on the beam splitting element 106 has, in particular, at least approximately planar wavefronts 114.

[0085] By means of the beam splitting element 106, the input laser beam 108 is split into a plurality of partial beams 116 and / or partial beam bundles. Fig. 1 In the example shown, two different partial beams 116a and 116b are indicated.

[0086] The partial beams 116 coupled out of the beam splitting element 106 have, in particular, a divergent beam profile.

[0087] To focus the partial beams 116 coupled out of the beam splitting element 106, the device 100 comprises a focusing optics 118 into which the partial beams 116 are coupled. The focusing optics 116 are designed, for example, as a microscope objective and / or lens element.

[0088] In particular, different partial beams 116 impinge on the focusing optics 118 with a spatial offset and / or angular offset.

[0089] The partial beams 116 are focused by means of the focusing optics 118, forming a plurality of focus elements 120, each arranged at different spatial positions. It is generally possible for adjacent focus elements 120 to spatially overlap in sections.

[0090] For example, one or more partial beams 116 and / or partial beam bundles are assigned to each respective focus element 120. For example, each focus element 120 is formed by focusing one or more partial beams 116 and / or partial beam bundles.

[0091] For laser processing of the workpiece 104, the focus elements 120 are introduced into the material 102 of the workpiece 104 and moved relative to the material 102.

[0092] A specific focus distribution is assigned to the input laser beam 108 coupled into the beam splitting element 106. This focus distribution describes a geometric shape and / or an intensity profile of a focus element that would be formed by focusing the input laser beam 108 before coupling into the beam splitting element 106. In particular, the geometric shape is understood to mean a spatial shape and / or spatial extent of the formed focus element.

[0093] For example, the input laser beam 108, when provided, for example, by the laser source 110, has a Gaussian beam profile. By focusing the input laser beam 108, a focus element would be formed in this case, which has a focus distribution with a Gaussian shape and / or a Gaussian intensity profile.

[0094] Alternatively, it may be provided, for example, that a Bessel-like beam profile is assigned to the input laser beam 108, so that by focusing the input laser beam 108, a focus element would be formed which has a focus distribution with a Bessel-like shape and / or a Bessel-like intensity profile.

[0095] The focus distribution of the input laser beam 108 is assigned to the partial beams 116 and / or partial beam bundles formed by splitting the input laser beam 108 by means of the beam splitting element 106 in such a way that by focusing the partial beams 116, the focus elements 120 are formed with this focus distribution and / or with a focus distribution based on this focus distribution.

[0096] In the Fig. 1 In the example shown, the input laser beam 108 has a Gaussian beam profile, i.e., a focus distribution with a Gaussian shape and / or Gaussian intensity profile is assigned to the input laser beam 108. The focus elements 120 then each have, for example, a focus distribution 121 with this Gaussian shape and / or this Gaussian intensity profile or with a shape and / or intensity profile based on this Gaussian shape and / or this Gaussian intensity profile.

[0097] The focus distribution 121 is a property of the respective focus elements 120 and describes their shape and / or intensity profile.

[0098] If, for example, a Bessel-like beam profile is assigned to the input laser beam 108, the focus elements 120 configured for laser processing the workpiece 104 each have a focus distribution 121 with this Bessel-like beam profile or with a beam profile based on this Bessel-like profile. The focus elements 120 can thus be configured, for example, with a focus distribution having an elongated shape and / or an elongated intensity profile.

[0099] It can be provided that the device 100 has a beam shaping device 122 for beam shaping the input laser beam 108 (indicated in Fig. 1 ). For example, this beam shaping device 122 is arranged in front of the beam splitting element 106 with respect to a beam propagation direction 124 of the input laser beam 108 and / or arranged between the laser source 110 and the beam splitting element 106.

[0100] By means of the beam shaping device 122, in particular a specific focus distribution and / or a specific beam profile can be assigned to the input laser beam 108.

[0101] The beam-shaping device 122 can, for example, be configured to form a laser beam with a quasi-non-diffractive and / or Bessel-like beam profile from a laser beam with a Gaussian beam profile. The input laser beam 108 coupled into the beam splitting element 106 then has the quasi-non-diffractive and / or Bessel-like beam profile.

[0102] Regarding the formation and properties of quasi-non-diffracting and / or Bessel-like beams with curved shapes, reference is made to the scientific publication "Bessel-like optical beams with arbitrary trajectories" by I. Chremmos et al., Optics Letters, Vol. 37, No. 23, December 1, 2012.

[0103] By beam splitting using the beam splitting element 106, the focus elements 120 are each formed as copies. In particular, one or more of the formed focus elements 120 have the same geometric shape and / or the same intensity profile.

[0104] In particular, a respective distance d and / or a spatial offset between adjacent focus elements 120 can be adjusted by means of the beam splitting element 106. A distance direction of the distance d adjustable by means of the beam splitting element 106 preferably lies in a plane which is oriented transversely and in particular perpendicular to a feed direction 126 with which the focus elements 120 are moved relative to the workpiece 104 for laser processing of the workpiece 104. For example, the distance d can be adjusted component by component in two spatial directions by means of the beam splitting element 106, which span the said plane or lie in the said plane (in the case of Fig. 1 shown example x-direction and z-direction).

[0105] The feed direction 126 is in the Fig. 1 In the example shown, it is oriented parallel to the y-direction, which is perpendicular to the x-direction and the z-direction.

[0106] In particular, to adjust the distance d, the partial beams 116 are formed such that they impinge on the focusing optics 118 with a specific spatial offset and / or with a specific convergence and / or divergence. The partial beams 116 are then focused by means of the focusing optics 118, so that the focus elements 120 are formed with the corresponding distance d and / or spatial offset.

[0107] Furthermore, a specific intensity I can be assigned to each of the formed focus elements 120 by means of the beam splitting element 106. In particular, the respective intensity I of a specific focus element 120 is adjusted by means of the beam splitting element 106 and, in particular, by phase imprinting on the input laser beam 108. By focusing the partial beams 116 coupled out of the beam splitting element 106, the focus elements 120 are then formed with a defined intensity I.

[0108] In particular, the intensity I of a specific focus element 120 is to be understood as an absolute intensity and / or an average intensity of the corresponding focus element 120.

[0109] It is provided that the beam splitting by means of the beam splitting element 106 takes place in such a way that two or more of the formed focus elements 120 each have a different intensity I.

[0110] To carry out the beam splitting by means of the beam splitting element 106, a defined transverse phase distribution is impressed on the transverse beam cross-section 112 of the input laser beam 108. A transverse beam cross-section or a transverse phase distribution is to be understood in particular as a beam cross-section or a phase distribution in a plane oriented transversely and in particular perpendicularly to the beam propagation direction 124. An example of a transverse phase distribution of beams coupled out of the beam splitting element 106 is shown in Fig. 5b shown.

[0111] The focus elements 120 are formed by interference of the focused partial beams 116, wherein, for example, constructive interference, destructive interference or intermediate cases thereof may occur, such as partially constructive or destructive interference.

[0112] To form the focus elements 120 with the respective distance d and / or spatial offset, the phase imprinting by means of the beam splitting element 106 is carried out in particular in such a way that the associated phase distribution for each focus element 120 has a specific optical grating component and / or optical lens component.

[0113] Due to the optical grating component, after focusing the partial beams 116, a corresponding spatial offset of the formed focus elements 120 results in a first spatial direction, e.g., in the x-direction. Due to the optical lens component, partial beams 116 or partial beam bundles impinge on the focusing optics 118 at different angles or with different convergence or divergence, which, after focusing, results in a spatial offset in a second spatial direction, e.g., in the z-direction.

[0114] The intensity of the respective focus elements 120 is determined by the phase positions of the focused partial beams 116 relative to one another. These phase positions can be defined by the aforementioned optical grating components and optical lens components. The phase positions of the focused partial beams 116 relative to one another can be selected during the design of the beam splitting element 106 such that the focus elements 120 each exhibit a desired intensity.

[0115] Regarding the technical implementation and properties of the beam splitting element 106, reference is made to the scientific publication "Structured light for ultrafast laser micro- and nanoprocessing" by D. Flamm et al., arXiv:2012.10119v1 [physics.optics], December 18, 2020. This publication is expressly incorporated by reference in its entirety.

[0116] For example, the beam splitting element 106 is designed as a 3D beam splitting element.

[0117] It can be provided that the device 100 has a polarization beam splitting element 128. By means of the polarization beam splitting element 128, a polarization beam splitting of the input laser beam 108 and / or a partial beam coupled out of the beam splitting element 106 is carried out into beams which each have one of at least two different polarization states.

[0118] With respect to the beam propagation direction 124 of the input laser beam 108, the polarization beam splitting element 128 can be arranged, for example, before or after the beam splitting element 106.

[0119] In particular, the polarization states mentioned are to be understood as linear polarization states, wherein, for example, two different polarization states are provided and / or polarization states oriented perpendicular to each other are provided.

[0120] In particular, beams coupled out of the polarization beam splitting element 128 are polarized such that an electric field is oriented in a plane perpendicular to the propagation direction of the beams (transverse electric).

[0121] For polarization beam splitting, the polarization beam splitting element 128 comprises, for example, a birefringent lens element and / or a birefringent wedge element. The birefringent lens element and / or the birefringent wedge element are, for example, made of a quartz crystal or comprise a quartz crystal.

[0122] With regard to the functionality and design of the polarization beam splitting element 128, reference is made to the German patent applications with file number 10 2020 207 715.0 (filing date: June 22, 2020) and with file number 10 2019 217 577.5 (filing date: November 14, 2019) of the same applicant. Express and full reference is made to these applications.

[0123] By splitting the polarization beam using the polarization beam splitting element 128, the partial beams 116 impinging on the focusing optics 118 each have one of at least two different polarization states, for example. By focusing these partial beams 116 using the focusing optics 118, the focus elements 120 can each be formed from beams with a specific polarization state. A specific polarization state can thus be assigned to each of the focus elements 120.

[0124] In particular, it can be provided that adjacent focus elements 120 each have a different polarization state.

[0125] In particular, the beam splitting element 106 and / or the polarization beam splitting element 128 are each designed as far-field beam shaping elements.

[0126] For laser processing of the workpiece 104, at least a subset and / or selection of the formed focus elements 120 is introduced into the material 102 ( Fig. 2 ).

[0127] Each of the formed focus elements 120 is assigned a specific local position x 0 , z 0 , at which a respective focus element 120 is arranged with respect to the material 102 of the workpiece 104. Furthermore, each of the focus elements 120 is assigned a specific intensity I.

[0128] In particular, the local positions of the respective focus elements 120 lie in a plane oriented perpendicular to the feed direction 126. In particular, all formed focus elements 120 lie, at least in sections, in this plane oriented perpendicular to the feed direction 126.

[0129] By means of the beam splitting element 106, both the spatial position x 0 , z 0 and the intensity I of the respective focus elements 120 can be defined. For this purpose, the phase distribution impressed on the beam cross-section 112 of the input laser beam 108 by means of the beam splitting element 106 is adjusted accordingly.

[0130] The coupling of the focus elements 120, which are introduced into the material 102 for laser processing of the workpiece 104, takes place, for example, through a first outer side 130 of the workpiece 104.

[0131] For example, the workpiece 104 is plate-shaped and / or panel-shaped. A second outer side 132 of the workpiece 104 is arranged at a distance from the first outer side 130, for example, in the thickness direction 134 and / or depth direction of the workpiece 104.

[0132] The feed direction 126 is oriented transversely and in particular perpendicularly to the thickness direction 134 of the workpiece 104.

[0133] In particular, the formed focus elements 120 are arranged along a defined processing line 136. This processing line 136 corresponds to a desired processing geometry with which the laser processing of the workpiece 104 is to be carried out.

[0134] The respective distances d and intensities I of the focus elements 130 arranged along the processing line 136 are selected such that material modifications 138 are formed by applying these focus elements 120 to the material 102 ( Fig. 4 ), which enable a separation of the material along this processing line 136 and / or a processing surface corresponding to this processing line 136.

[0135] In particular, it can be provided that the machining line 136 extends between the first outer side 130 and the second outer side 132 and in particular continuously between the first outer side and the second outer side 132 of the workpiece 104.

[0136] It can be provided that the processing line 136 has several different sections 140. For example, the processing line 136 in the Fig. 2 shown example, a first section 140a, a second section 140b and a third section 140c, wherein with respect to the thickness direction 134, the second section 140b adjoins the first section 140a and the third section 140c adjoins the second section 140b.

[0137] However, the processing line 136 is not necessarily continuous and / or differentiable. It may be provided that the processing line 136 has interruptions and / or gaps, at which, in particular, no focus elements 120 are arranged.

[0138] The processing line 136 and / or different sections 140 of the processing line 136 can be designed, for example, as a straight line or a curve.

[0139] Furthermore, the machining line 136 and / or the respective sections 140 of the machining line 136 are assigned a specific angle of attack α and / or angle of attack range, which the machining line 136 or the respective section 140 encloses with the first outer side 130 of the workpiece 104.

[0140] In the embodiment shown, the angle of attack α of the first section 140a and the third section 140c is 45° and that of the second section is 90°.

[0141] The focus elements 120 assigned to a specific section 140 can each have different intensities I.

[0142] It is provided that the respective intensity I of a specific focus element 120 is selected as a function of a distance d 0 and / or distance range dr by which the corresponding focus element 120 is spaced from an outer side 130, 132 of the workpiece 104 closest to the corresponding focus element 120. A spacing direction of the distance d 0 and / or the distance range dr is oriented in particular parallel to the thickness direction 134 of the workpiece 104.

[0143] The outer side closest to a focus element 120 is to be understood as that outer side 130, 132 of the workpiece which has the shortest distance to the corresponding focus element 120 and in particular the shortest distance with respect to the thickness direction 134. In the Fig. 2 In the example shown, the outer side closest to the focus element 120a is the first outer side 130 and the outer side closest to the focus element 120b is the second outer side 132.

[0144] Each distance range dr is assigned a center distance dr m, wherein the center distance dr m is understood to be a mean distance and / or an average distance of the corresponding distance range dr to the nearest outer side 130, 132 of the workpiece 104.

[0145] In the example according to Fig. 2 a first distance range dr 1 and a second distance range dr 2 are provided, wherein the focus elements 120 located in the first distance range dr 1 have a first intensity I 1 and the focus elements 120 located in the second distance range dr 2 have a second intensity I 2 different from the first intensity I 1. The intensity I 2 is greater than the intensity I 1 (indicated in Fig. 2 ).

[0146] For example, the first distance range dr 1 and the second distance range dr 2 are consecutive and / or non-overlapping distance ranges. Different focus elements 120 are thus uniquely assigned to a specific distance range dr.

[0147] In the Fig. 2 In the example shown, the respective intensities I 1 , I 2 of the focus elements 120 located in the first distance range dr 1 and those located in the second distance range dr 2 are at least approximately constant. However, it is also possible in principle to provide at least one distance range dr in which two or more of the focus elements 120 located therein have different intensities I from one another.

[0148] It can be provided that focus elements 120 are formed which are arranged at least partially outside the workpiece 104 at a specific time and / or at a specific position during the laser processing of the workpiece 104 ( Fig. 3 ). In this case, the processing line 136, along which the focus elements 120 are arranged, has at least one section 142 in which the processing line 136 projects beyond the first outer side 130 and / or the second outer side 132 of the workpiece 104.

[0149] In the example according to Fig. 3 the processing line has two sections 142.

[0150] The section 142 is, for example, a tangential continuation of the processing line 136 to an end point 144 arranged within the material 102 and / or end section of the processing line 136.

[0151] In particular, the section 142 of the processing line 136 arranged outside the material 102 projects up to a maximum distance d max beyond the outer side 130 or 132 of the workpiece 104 closest to the section 142, wherein a distance direction of the maximum distance d max is oriented in the thickness direction 134.

[0152] In particular, the maximum distance d max is a distance of a focus element 120c arranged outside the material 102, which has the greatest distance to the nearest outer side 130, 132.

[0153] The maximum distance d max is chosen in particular so that fluctuations in the thickness of the material 102 and / or axis tolerances can be compensated.

[0154] If the thickness of the material 102 increases in a certain area, for example in the feed direction 126, the material 102 in this area is exposed to focus elements 120 which were arranged in another area outside the material 102.

[0155] By applying and / or introducing the focus elements 120 into the material 102, localized material modifications 146 are formed, which are arranged at the respective local positions x 0 , z 0 of the corresponding focus elements 120 in the material 102 ( Fig. 4 ).

[0156] By appropriately selecting processing parameters, such as the respective distances d between the focus elements 120, their respective intensities I, a feed rate oriented in the feed direction 126, and the laser parameters of the input laser beam 108, the material modifications 146 can be formed, for example, as Type III modifications, which are accompanied by a spontaneous formation of cracks 148 in the material 102 of the workpiece 104. In particular, cracks 148 are formed between adjacent material modifications 146.

[0157] Alternatively, it is also possible, by suitable selection of the processing parameters, to form the material modifications 146 as type I and / or type II modifications, which are accompanied by a heat accumulation in the material 102 and / or by a change in a refractive index of the material 102.

[0158] The formation of the material modifications 146 as Type I and / or Type II modifications is associated with a heat accumulation in the material 102 of the workpiece 104. In particular, to form these material modifications 146, the respective distance d between the focus elements 120 is selected to be so small that this heat accumulation occurs when the material 102 is exposed to the focus elements.

[0159] Fig. 5a shows a simulated intensity distribution of a plurality of focus elements 120, wherein the focus elements arranged at the bottom with respect to the z-direction have a lower intensity I than the focus elements 120 arranged at the top. In the grayscale representation shown, brighter areas represent higher intensities.

[0160] Fig. 5b shows an intensity distribution according to Fig. 5a associated phase distribution of beams coupled out of the beam splitting element 106, wherein the grayscale ranges from white (phase +Pi) to black (phase - Pi).

[0161] The laser processing of the workpiece 104 by means of the device 100 functions as follows: To carry out the laser processing, the material 102 of the workpiece 104 is subjected to the focus elements 120 and the focus elements 120 are moved in the feed direction 126 relative to the workpiece 104 through its material 102.

[0162] The material 102 is a material that is transparent to a wavelength of rays from which the focus elements 120 are each formed. For example, the material 102 is a glass material.

[0163] By applying the focus elements 120 to the material 102, material modifications 146 are formed in the material 102, which are arranged along the processing line 136. In the Fig. 6 In the example shown, material modifications 146 are formed continuously over a thickness D of the material 102 oriented in the thickness direction 134.

[0164] By moving the focus elements 120 relative to the material 102 along a predetermined trajectory 150, a processing surface 152 corresponding to the processing line 136 is formed, on which the material modifications 146 are arranged. This results in a planar formation and / or arrangement of the material modifications 146 along the processing surface 152.

[0165] A distance between adjacent material modifications 138 in the feed direction 126 can be defined, for example, by setting a pulse duration of the input laser beam 108 and / or by setting the feed rate.

[0166] The material modifications 146 formed along the machining surface 152 result in, in particular, a reduction in the strength of the material 102. As a result, the material 102 can be separated into two different workpiece segments 154a and 154b after the material modifications 146 have been formed on the machining surface 152, for example by applying a mechanical force ( Fig. 6b ).

[0167] In the example shown, the workpiece segment 154b is a good piece segment with a desired edge shape that corresponds to the shape of the machining line 136. The workpiece segment 188b in this case is a residual workpiece segment and / or a waste segment.

[0168] The material 102 of the workpiece 104 is, for example, quartz glass. For example, to form the material modifications 146 as Type I and / or Type II modifications, a laser beam from which the focus elements 120 are formed has a wavelength of 1030 nm and a pulse duration of 1 ps. Furthermore, the numerical aperture assigned to the focusing optics 118 is 0.4, and the pulse energy assigned to a single focus element 120 is 50 to 200 nJ.

[0169] To form the material modifications 146 as type III modifications, with all other parameters remaining the same, the pulse energy assigned to a single focus element 120 is 500 to 2000 nJ. Bezugszeichenliste

[0170] αAngle of attack dDistance d 0 Distance d max Maximum distance drDistance range dr 1 Distance range dr 2 Distance range dr m Center distance DDickness I Intensity I 1 Intensity I 2 Intensity LProtrusion length x 0 Position in x-direction z 0 Position in y-direction 100Device 102Material 104Workpiece 106Beam splitting element 108Input laser beam 110Laser source 112Beam cross-section 114Wavefront 116Partial beams 116aPartial beam 116bPartial beam 118Focusing optics 120Focus elements 120aFocus element 120bFocus element 120cFocus element 121Focus distribution 122Beam shaping device 124Beam propagation direction 126Feed direction 128Polarization beam splitting element 130 First outer side 132 Second outer side 134 Thickness direction 136 Machining line 138 Material modification 140 Section 140a First section 140b Second section 140c Third section 142 Section 144 End point / End section 146 Material modification 148 Crack 150 Trajectory 152 Machining surface 154a Workpiece segment 154b Workpiece segment.

Claims

1. A method for laser processing a workpiece (104) which has a material (102) which is transparent for laser processing, in which an input laser beam (108) is divided by means of a beam-splitting element (106) into a plurality of partial beams (116), wherein the input laser beam (108) is split by means of the beam-splitting element (106) by phase imprinting on a beam cross-section (112) of the input laser beam (108), partial beams (116) coupled out of the beam-splitting element (106) are focused by means of a focusing optics (118), a plurality of focusing elements (120) are formed by focusing the partial beams (116), and in which the material (102) of the workpiece (104) is subjected to laser processing with at least a subset of the formed focusing elements (120), characterized in that the phase imprinting is effected by means of the beam-splitting element (106) in such a way that at least two of the formed focusing elements (120) have a different intensity (I).

2. The method according to claim 1, characterized in that the intensity (I) of the focusing elements (120) is selected such that, by applying the focusing elements (120) to the material (102), similar material modifications (138) are produced in the material (102) and, in particular, similar material modifications (138) are produced in the material (102) independent of a distance (d0) between the respective focusing elements (120) and an outer side (130, 132) of the workpiece (104) closest to the respective focusing elements (120).

3. The method according to any one of the preceding claims, characterized in that the intensity (I) of the focusing elements (120) is selected as a function of a distance (d0) and / or distance range (dr) with which the respective focusing elements (130) are spaced apart from an outer side (130, 132) of the workpiece (104) and, in particular, from an outer side (130, 132) of the workpiece (104) closest to the respective focusing elements (120).

4. The method according to claim 3, characterized in that the intensity (I) of the focusing elements (120) is selected to increase with an increasing distance (d0) of the respective focusing elements (120) from the nearest outer side (130, 132) of the workpiece (104).

5. The method according to any one of claims 3 or 4, characterized in that an average intensity (I) of the respective focusing elements (120) which are assigned to a specific distance range (dr) is selected to be increasingly greater with an increasing mean distance (drm) of the respective distance range (dr) to the nearest outer side (130, 132) of the workpiece.

6. The method according to any one of claims 3 to 5, characterized in that at least one distance range (dr) is provided, wherein the intensity (I) of the respective focusing elements which lie within this at least one distance range (dr) is at least approximately constant.

7. The method according to any one of claims 3 to 6, characterized in that at least one distance range (dr) is provided, wherein the intensity (I) of the respective focusing elements (120) which lie within this at least one distance range (dr) varies, and wherein, in particular, the intensity (I) of the focusing elements (120) lying in this distance range (dr) increases with an increasing distance (d) of these focusing elements (120) from the nearest outer side (130, 132) of the workpiece (104).

8. The method according to any one of the preceding claims, characterized in that focusing elements (120) which are different from one another are disposed along a predetermined processing line (136), and in particular characterized in that the focusing elements (120) which are different from one another are spaced apart along the processing line (136) and / or have such an intensity (I) that, by applying these focusing elements (120) to the material (102) of the workpiece (104), material modifications (138) are formed in the material (102) which enable the material (102) to be separated along this processing line (136).

9. The method according to claim 8, characterized in that an angle of incidence (α) between the processing line (136) and an outer side (130, 132) of the workpiece (104), through which the focusing elements (120) are coupled into the material (102) of the workpiece (104) for laser processing, is at least 1° and / or at most 90°.

10. The method according to any one of the preceding claims, characterized in that one or a plurality of the formed focusing elements (120) are disposed or are arranged at least in sections and / or at least temporarily outside a material (102) of the workpiece (104) during the laser processing of the workpiece (104).

11. The method according to any one of the preceding claims, characterized in that polarization beam splitting is performed by means of a polarization beam-splitting element (128) so that the partial beams (116) have one of at least two different polarization states, wherein focusing of the partial beams (116) by means of the focusing optics (118) produces focusing elements (120) with different polarization states, and wherein, in particular, focusing elements (120) with different polarization states are disposed adjoining one another.

12. The method according to any one of the preceding claims, characterized in that, by applying the focusing elements (120) to the material (102) of the workpiece (104), material modifications (138) are formed in the material (102), which are associated with crack formation in the material (102), and / or that type III material modifications (138) are formed in the material by applying the focusing elements (120) to a material (102) of the workpiece (104).

13. The method according to any one of the preceding claims, characterized in that, by applying the focusing elements (120) to the material (102) of the workpiece (104), material modifications (138) are formed in the material (102) which are associated with a change in the refractive index of the material (102), and / or that type I material modifications (138) and / or type II material modifications (138) are formed in the material by applying the focusing elements (120) to a material (102) of the workpiece (104).

14. An apparatus for laser processing a workpiece (104) which has a material (102) that is transparent to laser processing, comprising a beam-splitting element (106) for splitting an input laser beam (108) coupled into the beam-splitting element (106) into a plurality of partial beams (116), wherein the input laser beam (108) is split by means of the beam-splitting element (106) by phase imprinting on a beam cross-section (112) of the input laser beam (108), and a focusing optics (118) for focusing partial beams (116) coupled out of the beam-splitting element (106), wherein, by focusing the partial beams (116), a plurality of focusing elements (120) are formed for laser processing of the workpiece (104), characterized in that the phase imprinting is effected by means of the beam-splitting element (106) in such a way that at least two of the formed focusing elements (120) have a different intensity (I).

15. The apparatus according to claim 14, characterized in that the splitting of the input laser beam (108) by means of the beam-splitting element (106) is effected by phase manipulation and, in particular, exclusively by phase manipulation of a phase of the input laser beam (108).