Device and method for machining a workpiece

Abstract

The present invention relates to a device and a method for processing a workpiece (4), in particular for applying an anti-glare functionalization, by means of laser pulses (100) of a laser (1), comprising a laser (1), in particular a short-pulse laser or an ultrashort-pulse laser, which is configured to provide a laser beam (10) with laser pulses (100), a first diffusing disc (2) and a second diffusing disc (2'), each configured to scatter the laser beam (10) and to impose a spatially randomized intensity distribution on the laser beam (10) in the focal plane (12), wherein the first diffusing disc (2) and the second diffusing disc (2') scatter the laser beam (10) one after the other, at least one focusing optics (3) configured to focus the laser beam (10) into a focal zone (120) in the focal plane (12) on the workpiece (4),wherein the workpiece (4) is impinged upon by the laser beam (10) and is processed thereby, a feed device (5) which is configured to move the laser beam (10) and the workpiece (4) relative to one another at a feed rate (V), wherein the feed device comprises a scanner device (50) with a first scanner element (500) and a second scanner element (502), wherein a movement of the scanner elements (500, 502) generates a feed rate, wherein the second scanner element (502) comprises the second diffusion plate (2'), wherein the movement of the scanner elements modifies the local randomized intensity distribution.

Description

Technical area

[0001] The present invention relates to a device and a method for machining a workpiece. State of the art

[0002] It is known that laser material processing can remove material from a workpiece by vaporizing or condensing the material within the focal zone of the laser beam through a strong light-matter interaction. The resulting structures are called dimples. Dimples are suitable for functionalizing the surfaces of components, particularly influencing optical and tribological properties.

[0003] However, when processing a material with a pulsed laser, regular structures often arise, particularly regularly arranged dimples, for example, due to a beat between the repetition rate of the laser system and other process parameters such as the feed rate and the number of repetitive material passes. Such regular structures can, for example, lead to interference effects when viewed, which disrupt the visual impression of the processed material.

[0004] US 2017 / 0368638 A1 concerns the processing of materials using high-power lasers with shapeable beams and / or variable beam polarizations. Description of the invention

[0005] Based on the known prior art, it is an object of the present invention to provide an improved device for processing a material and a corresponding method.

[0006] The object is achieved by a device for processing a material having the features of claim 1. Advantageous further developments emerge from the subclaims, the description and the figures.

[0007] Accordingly, a device for machining a workpiece, in particular for applying an anti-glare functionalization, by means of laser pulses of a laser is proposed, comprising a laser, in particular a short-pulse laser or an ultra-short-pulse laser, which is configured to provide a laser beam with laser pulses, a first diffusion disk and a second diffusion disk, each configured to scatter the laser beam and to impose a spatially randomized intensity distribution on the laser beam in the focal plane, wherein the first diffusion disk and the second diffusion disk scatter the laser beam one after the other, at least one focusing optics configured to focus the laser beam into a focus zone in the focal plane on the workpiece, wherein the workpiece is exposed to the laser beam and is thereby machined, a feed device configured toto move the laser beam and the workpiece relative to each other with a feed, wherein the feed device comprises a scanner device with a first scanner element and a second scanner element, wherein a movement of the scanner elements generates a feed. According to the invention, the second scanner element is designed as a second diffusion disc, wherein the movement of the scanner elements modifies the local randomized intensity distribution.

[0008] The material of the workpiece can be, for example, a polymer or a plastic. The material can also be a semiconductor, for example an elementary semiconductor such as silicon or germanium, or a III-V semiconductor such as gallium arsenide, or an organic semiconductor or any other type of semiconductor. For example, the material can be a silicon wafer. However, it is also possible for the material to comprise any metal, for example aluminum, magnesium, titanium, iron, or a steel alloy. In particular, the material can be a layer system, with each layer being selected from the group of any metals, polymers, plastics, or semiconductors. In particular, the material can also be a glass, for example sapphire or quartz glass.

[0009] The laser provides the laser pulses of the laser beam, with the individual laser pulses forming the laser beam in the beam propagation direction. The pulse duration of the laser pulses can be between 100 fs and 100 ps. The wavelength of the laser pulses can be between 300 nm and 3000 nm, preferably between 900 nm and 2200 nm.

[0010] Instead of individual laser pulses, the laser can also provide laser bursts, with each burst comprising the emission of several laser pulses. In this case, the laser pulses can be emitted very closely one after the other for a certain time interval, at intervals of a few picoseconds to nanoseconds. The laser bursts can in particular be GHz bursts, in which the sequence of successive laser pulses of the respective burst takes place in the GHz range. A burst can, for example, comprise between 2 and 20 laser pulses, preferably between 2 and 10 laser pulses, with the time interval between the laser pulses being between 10 ns and 50 ns. However, a burst can also comprise between 30 and 300 laser pulses, with the time interval between the laser pulses being between 100 ps and 1000 ps.

[0011] The repetition rate of the laser pulses and / or laser bursts can be greater than 1 kHz, preferably greater than 10 kHz. For example, the repetition rate can also be 100 kHz or more. Accordingly, the laser emits, for example, more than 1,000 pulses per second or more than 10,000 pulses per second.

[0012] The pulse energy of the laser pulses can be greater than 1µJ, for example 2µJ.

[0013] The diameter of the laser beam provided by the laser can be larger than 0.1 mm, for example 1 mm or 5 mm.

[0014] The laser pulses are introduced into the material after passing through the further device, whereby the energy of the laser beam is at least partially absorbed in the material, for example by nonlinear interactions, in particular by multiphoton processes.

[0015] The incoming laser beam first passes through the first diffusion disk and then through the second diffusion disk. Such a diffusion disk is configured to scatter the laser beam. In particular, this can mean that the laser beam is converted into a plurality of partial laser beams, each partial laser beam having its own propagation direction and / or its own intensity and / or its own phase front. In particular, the beam propagation direction of the partial laser beams can differ from that of the incoming laser beam.

[0016] The scattering of the laser beam depends on both the point of impact on the first diffusion disc and the point of impact on the second diffusion disc.

[0017] The multitude of partial laser beams are superimposed in a focus zone in the focal plane by focusing optics, for example, a 2f optic. The focus of the scattered laser beam can be on the workpiece in the beam propagation direction. The focus is on the workpiece when the focal plane coincides exactly with the surface of the workpiece, or it is above or below the surface in the beam propagation direction, while the surface is still being processed. In particular, the focus position can be within ten times the Rayleigh length from the surface, where the Rayleigh length is the distance along the optical axis that a laser beam needs until its cross-sectional area doubles, starting from the beam waist or focus.

[0018] In particular, the term "focus" can generally be understood as a targeted intensity increase, whereby the laser energy converges into a "focus zone." Therefore, the term "focus" is used below regardless of the actual beam shape used and the methods used to achieve an intensity increase. Focusing can also influence the location of the focus zone along the beam propagation direction. For example, the focus zone can be quasi-point-shaped and have a Gaussian intensity cross-section, as provided by a Gaussian laser beam. However, the focus zone can also be linear or rectangular, or have the shape of an Airy distribution.Furthermore, other more complex beam shapes are possible, whose focus position extends in three dimensions, such as a multi-spot profile of Gaussian laser beams and / or non-Gaussian intensity distributions.

[0019] Due to the absorbed energy of the laser beam in the focus zone, the material heats up according to the intensity distribution of the laser in the focus zone and / or enters a temporary plasma state due to the electromagnetic interaction of the laser with the material. In particular, in addition to linear absorption processes, nonlinear absorption processes can also be used, which become accessible through the use of high laser energies or laser intensities. The material is therefore modified particularly in the focus zone of the laser, since this is where the intensity of the laser beam is greatest. In particular, this can achieve the effect of separating part of the material from the composite material of the workpiece, for example, by melting or vaporizing it.This allows for known machining processes with regard to the interaction between the laser beam and the material of the workpiece to be machined, such as laser drilling, percussion drilling, laser ablation, blasting or compaction.

[0020] The interaction of the laser pulses with the material of the workpiece to be processed creates corresponding material modifications on the surface of the workpiece.

[0021] In particular, a material modification can be created using a laser pulse or a laser burst.

[0022] Such material modification occurs through the vaporization of the workpiece material at the surface due to the incident laser intensity. The workpiece material is vaporized particularly where the laser beam intensity exceeds a critical, material-specific processing threshold. Accordingly, the shape and form of the laser beam, particularly the intensity distribution of the laser beam in the focal plane, are crucial for the shape and form of the material modification.

[0023] Without a diffusion screen, for example, the laser beam only has a Gaussian beam profile. A certain spatial region is formed around the focal point in which the laser energy lies above the critical processing threshold. In other words, there is an iso-intensity surface in the intensity distribution of the laser beam at the focus within which the material can be vaporized. This iso-intensity surface thus determines the shape and form of the material modification. In particular, the material modifications can then have a round or elliptical cross-section in the plane of the material surface, with the material modifications having an increasing depth from the edge to the center. In particular, the cross-section of the material modifications in the plane perpendicular to the surface can also be round or rounded.However, it is also possible for the material modification to have an elliptical or circular cross-section in the plane of the material surface, but with a steep edge slope, resulting in a substantially rectangular cross-section of the material modification in the plane perpendicular to the material surface. For example, such a material modification can also have a uniform depth.

[0024] However, with the first and second diffusion plates in the beam path of the device, the laser beam is scattered randomly, creating a spatially randomized intensity distribution in the focal plane. Accordingly, the laser beam striking the first diffusion plate is scattered into a plurality of partial laser beams whose intensities and propagation angles are randomly distributed or statistically distributed, for example, normally distributed or Gaussian distributed. The intensities and propagation angles can also be band-limited and statistically distributed, so that the largest and smallest propagation angles of the partial laser beams are determined by the shape and form of the diffusion plate.

[0025] Scattering occurs again when the partial laser beams generated by the first diffusion disc hit the second diffusion disc and are scattered there. The scattering at the second diffusion disc depends on where the laser beam hits the second diffusion disc after the first scattering.

[0026] This imposes a doubly random or statistical component on the intensity profile in the focal plane, featuring spatially randomly distributed intensity peaks or valleys, each of which leads to particularly strong or weak material processing. In particular, such scattering can imprint a type of speckle pattern on the laser beam in the focal plane, as defined, for example, in Goodman's "Speckle phenomena in optics: theory and applications," Roberts and Company Publishers, 2007. This spatially randomized intensity distribution allows the material to be processed inhomogeneously, thus avoiding regular and / or smooth processing structures in the individual material modifications.

[0027] By introducing such inhomogeneous material modifications using a spatially randomized intensity distribution on the surface of the material, the optical properties of the material can be determined, for example, by scattering light guided through a transparent material at such a material modification, thus making the material appear diffuse and / or matte. In particular, such material modifications on the surface of the workpiece material can reduce reflection from the material.

[0028] For example, the type and shape of the material modifications, as well as the distribution of the material modifications on the surface of the component, can be used to adjust the haptics or roughness. It is also possible to adjust the light scattering and thus the optical properties of the material.

[0029] In particular, the material modifications can be used to create anti-glare functionalization. Anti-glare functionalization can then consist of an incident light beam being reflected from the surface not only at the angle of reflection according to Snell's law of refraction. It can also be the case that the incident light beam is reflected or scattered away from the surface at other angles. In particular, this directs the incident light beam in different spatial directions, preventing a sharp reflection from occurring, in the sense that the entire energy of the incident light beam can be detected at a specific angle of reflection. Rather, the energy of the incident light is distributed over a spatial region, allowing the energy of the incident light beam to be detected within a range of angles of reflection.

[0030] The feed device can be configured to move the laser beam and the workpiece relative to each other with a feed, wherein the feed device comprises a scanner device with a first scanner element and a second scanner element, wherein a movement of the scanner elements generates a feed.

[0031] Relatively displaceable means that both the laser beam can be displaced translationally relative to a stationary material and the material can be displaced relative to the laser beam, or there is a movement of both the material and the laser beam.

[0032] This allows the laser beam's focus zone to be positioned at various locations on the material to introduce laser pulses. The laser pulses are positioned along the so-called feed trajectory. For example, the feed trajectory can be straight or curved. In particular, the local feed direction is always the y-direction, while the z-axis is parallel to the surface normal and the x-axis is perpendicular to the y-axis and parallel to the material surface.

[0033] For example, the laser beam can be moved along with a feed while the laser pulses are emitted into or onto the material, so that the different focus zones can be arranged next to each other or even overlap to enable uniform and flat processing of the workpiece.

[0034] The feed mechanism thus makes it possible, in particular, to change the position of the laser relative to the workpiece, allowing successive laser pulses to process the workpiece at different locations. Accordingly, the laser beam can cover the entire surface of the workpiece, thus performing surface material processing.

[0035] The scanner elements of the scanner device can be configured to shift the laser beam along different axes on the workpiece. For example, the first scanner element can generate a shift in the x-direction, while the second scanner element generates a shift in the y-direction. By superimposing both shifts, the laser beam can be shifted in the xy-plane using the scanner elements.

[0036] According to the invention, the second scanner element is designed as a second diffusion disk. Accordingly, by generating a feed, the spatially randomized intensity distribution can also be modified, since the second diffusion disk already provides scattering depending on the incidence location of the light scattered by the first diffusion disk.

[0037] The term “comprises the scattering element” can mean that the second scanner element itself has a beam deflection effect and a scattering effect, i.e. the second scanner element and the second scattering element are formed as a single piece. For example, the second scanner element can have a coating that has a corresponding scattering and deflecting effect. However, it can also be the case that the second scattering element and the second scanning element are designed merely as a functional unit, i.e., the second scattering disc is arranged directly behind the scanner element. In particular, the second scattering disc and the second scanning element can either be mechanically connected, so that a movement of the second scanner element entails a movement of the second scattering disc. However, it can also be the case that the second scanner element can be moved independently of the second scattering disc.

[0038] By moving the second scanner element, the point of incidence of the laser beam scattered by the first diffusion disk on the second diffusion disk can be changed. Due to the changed scattering properties at the different impact locations, a first laser pulse can exhibit a first spatially randomized intensity distribution, while a second laser pulse can exhibit a second spatially randomized intensity distribution, with the intensity distributions being different. This makes it possible, in particular, to avoid periodic, recurring patterns in the material modifications, thus enabling particularly high-quality material processing.

[0039] A particular advantage is that due to the double scattering on the first and second diffusion disc, a small change in the second scanner element can already achieve a large difference in the local randomization of the intensity distribution.

[0040] In particular, by using the scanner device as a scattering device, a separate second scattering device can be dispensed with.

[0041] By using the scanning motion to randomize the intensity distribution, the device is also suitable for applying anti-glare functionalizations with particularly high laser energies. For example, the state of the art requires rapid repositioning of the laser beam for a randomized intensity distribution. However, high laser powers require thick optical elements, which are associated with high inertia. By randomizing the intensity distribution within the scanner device, which can exhibit low dynamics, optical elements suitable for high laser powers can also be used.

[0042] The first scanner element can be arranged before or after the first diffusion disc.

[0043] If the first scanner element is positioned after the first diffusion disk, the laser's point of incidence on the first diffusion disk is not shifted by a scanner element, so that no variable randomization of the intensity distribution is performed at the first diffusion disk. However, the scattered laser beam is shifted by the first scanner element, so that the point of incidence of the scattered laser beam on the second diffusion disk changes, and thus, a variable randomization of the intensity distribution is achieved by advancing the first and second scanner elements.

[0044] If the first scanner element is arranged in front of the first diffusion disc, a variable randomized scattering is already achieved due to the different impact locations on the first diffusion disc.

[0045] The first scanner element can also include the first diffusion screen in the sense described above. This allows, in particular, the first and second scanner elements to be designed identically. This results in the same technical advantages as described above.

[0046] At least one diffusion plate can be configured to diffuse the laser beam in transmission or reflection. In particular, both diffusion plates can also be configured to transmit or reflect the laser beam.

[0047] For example, a diffuser can transmit the incident laser beam, causing the laser beam to propagate through the diffuser and be scattered. For example, the laser beam can be scattered by a diffuser, causing the laser beam to reflect off the diffuser rather than pass through it. For example, the diffuser can be a mirror that is not flat but has an irregular pattern.

[0048] At least one diffusion plate can have a phase pattern, in particular a binary phase pattern, which is designed to impart a location-dependent phase difference to the laser beam, in particular the phase pattern can be expressed in one or two dimensions.

[0049] The diffusion disks have scattering regions that locally influence or do not influence the phase of the incident laser beam. The various scattering regions are randomly distributed across the diffusion disks, so that the scattering of the laser beam depends on the point of impact on the respective diffusion disk. For example, a first partial laser beam, after scattering at the first diffusion disk, can exhibit a phase shift from a second partial laser beam at a first scattering region. Such a phase shift makes it possible to deflect the partial laser beams from their original propagation direction.

[0050] The number of different phase shifts that can be generated with the diffusion disks is determined by the so-called phase quantization of the diffusion disk. With a phase quantization of 2, the diffusion disk exhibits a binary phase pattern. With a binary phase pattern, only two phase shifts can be generated between the partial laser beams, for example, 0° and 180°. With a phase quantization of the diffusion disk of four, four different phase shifts can be generated, for example, 0°, 45°, 90°, 180°. However, it is also possible for the diffusion disk to enable, for example, 8 or 16 different phase shifts between the partial laser beams.

[0051] For example, a first scattering region of the diffusion plate can have a first material thickness, and a second scattering region can have a second material thickness. If the diffusion plate is reflective, the first thickness and the second thickness can be selected such that the path difference of the reflected partial laser beams corresponds to half the wavelength. Accordingly, adjacent partial laser beams at the scattering regions have a phase difference of 180°.

[0052] However, it is also possible for the laser beam to be transmitted through a diffusion disk with diffusion zones of different thicknesses, with the different thicknesses providing different optical path lengths. If the optical path lengths differ by half a wavelength, the partial laser beams exhibit a phase difference of 180°.

[0053] If the diffuser has a binary pattern, this can mean that the diffuser provides only two different optical path lengths. The pattern can be distributed over the geometric extent of the diffuser, so that the diffuser, for example, has statistically distributed regions of a first thickness and a second thickness.

[0054] If a lens exhibits a binary pattern in two dimensions, this may mean that the lens has randomly distributed scattering areas in both height and width. However, if a lens exhibits a binary pattern in only one dimension, this may mean that the lens only has randomly distributed scattering areas in either height or width. For example, the binary pattern would then correspond to a striped pattern.

[0055] In particular, the spatial frequency of the spatially randomized intensity distribution can be adjusted by adjusting the size of the scattering areas of the respective scattering disk. The spatial frequency can be understood as the inverse of the period length of the scattering areas. For example, if the scattering disk has small rectangular scattering areas, this leads to a large spatial frequency of the spatially randomized intensity distribution and thus to a particularly inhomogeneous intensity distribution.

[0056] For example, the edge length of the pixels can be larger than 1µm, for example 20µm or 100µm.

[0057] The diffuser can be a spatial light modulator or a diffractive optical element.

[0058] A spatial light modulator can, for example, be a nanograting or a hybrid element, which, due to their inherent structure or design, can impart a defined phase distribution to the laser beam. However, a light modulator can also be a spatial light modulator whose cells or pixels influence the laser beam through adjustable birefringent properties. Accordingly, a spatial light modulator can be implemented, for example, as an LCD (liquid crystal display).

[0059] A diffractive optical element, similar to a light modulator, is designed to influence one or more properties of the incident laser beam in two spatial dimensions. Unlike an LCD-based spatial light modulator, a diffractive optical element is a fixed component that can be used to produce exactly one beam shape from the incident laser beam. Typically, a diffractive optical element is a specially shaped diffraction grating, where the laser beam assumes the desired beam shape through diffraction.

[0060] The diffractive optical element can be designed as a geometric phase hologram, in which the diffractive effect exhibits a polarization dependence, see Kim et al., "Fabrication of ideal geometric-phase holograms with arbitrary wavefronts," Optica 2, 958-964 (2015). Furthermore, the geometric phase hologram can be designed as a switchable element, in particular as a binary switchable element.

[0061] The feed device may comprise an axis device.

[0062] The axis device can, for example, be used to move the material mechanically. In particular, the axis device can be an XYZ table with stepper motor control. However, the axis device can also be designed with piezo actuators to achieve the fastest possible adjustment.

[0063] For example, a rough adjustment of the workpiece can be achieved with the axis device, while the scanner device scans the workpiece relative to it along the feed trajectory

[0064] The scanner device may comprise a galvano scanner and / or a polygon scanner.

[0065] In a galvano scanner, the laser beam is repositioned with high accuracy and repeatability. Specifically, a one-dimensional galvano scanner deflects the laser beam in only one direction, while a two-dimensional galvano scanner deflects the laser beam in two different directions, preferably orthogonal to each other.

[0066] In a polygon scanner, the laser beam is directed onto a rotating, polygonal mirror, which periodically deflects the laser beam onto the workpiece. The polygonal mirror consists of various facets, each of which can contain its own diffusion disc.

[0067] These components enable material processing with particularly high laser energies, as they move comparatively slowly and can therefore also support heavy, high-performance components.

[0068] The focusing optics can also include a diffuser. In particular, the side facing the workpiece can include a diffuser or be designed as a diffuser. This allows the intensity distribution on the workpiece to be further randomized.

[0069] A beam shaping device can be configured to impart a beam shape to the laser beam, in particular to impart a flat-top beam shape, wherein the beam shaping device is preferably arranged in front of the scanner device.

[0070] Beam-shaping optics can, for example, be a commercially available pi-shaper, which imparts a flat-top beam shape to the laser beam. Compared to a Gaussian laser beam, a flat-top laser beam has a homogeneous intensity across the beam cross-section, which drops rapidly after reaching the beam diameter. In a sense, the flat-top laser beam has a largely rectangular intensity profile, while the intensity profile of a Gaussian laser beam has a Gaussian intensity profile.

[0071] A flat-top laser beam provides a particularly simple beam shape. For example, flat-top laser beams make it particularly easy to create multiple adjacent material modifications that adjoin one another or partially overlap, since the intensity variations at the edge of a Gaussian laser beam do not need to be compensated.

[0072] An aperture can also be placed in the beam path. This aperture makes it possible to narrow the beam profile. This allows a beam profile with a desired length and radial intensity distribution to be generated.

[0073] This makes it possible to create a homogeneous modified surface where the transitions are not visible when material modifications are introduced adjacent to each other.

[0074] The above-mentioned object is further achieved by a method for processing a material having the features of claim 11. Advantageous developments of the method emerge from the subclaims as well as the present description and the figures.

[0075] Accordingly, a method for machining a workpiece, in particular for applying an anti-glare functionalization, by means of laser pulses of a laser, in particular a short-pulse laser or ultra-short-pulse laser, is proposed, wherein the laser beam is scattered with the laser pulses by a first scattering disk and a second scattering disk and a locally randomized intensity distribution is impressed on the laser beam in the focal plane by the scattering disks, wherein the workpiece and the laser beam are displaced relative to one another along a feed trajectory, wherein the feed is generated by a movement of a first scanner element and a second scanner element of a scanner device, wherein the scattered laser beam is focused by focusing optics into a focus zone in a focal plane on the workpiece, wherein the workpiece is exposed to the laser beam and is thereby machined.According to the invention, the second scanner element is designed as a second diffusion disk, wherein the spatially randomized intensity distribution is modified by the relative movement of the scanner elements.

[0076] The first scanner element may be arranged before or after the first diffusion disc and / or the first scanner element may comprise the first diffusion disc.

[0077] The focus zone of different, especially successive laser pulses, can overlap.

[0078] By overlapping the material modifications, a continuous machined surface of the workpiece can be created. This has the particular advantage of avoiding regular patterns that result, for example, from a uniform offset of the laser beam with the feed rate between two laser pulses.

[0079] In particular, the focus zones can cover a flat section of the workpiece and process it. It is also possible to process the entire surface of the workpiece.

[0080] A flat section means that a contiguous area of ​​at least two focal zones has been machined, while full-surface machining of the workpiece surface means machining at least the side facing the laser beam. Short description of the characters

[0081] Preferred further embodiments of the invention are explained in more detail by the following description of the figures. In the figures: Fig. 1A, B, C, D, E, F are schematic representations of the device of a first embodiment; Fig. 2A, B, C, D are schematic representations of the device of a second embodiment; Fig. 3A, B, C schematic representations of the operation of a beam shaping device; Fig. 4 schematic representations of the device of a third embodiment; Fig. 5 schematic representations of a scanner device; and Fig. 6A, B a schematic representation of the method according to the invention. Detailed description of preferred embodiments

[0082] Preferred embodiments are described below with reference to the figures. Identical, similar, or equivalent elements in the various figures are provided with identical reference numerals, and a repeated description of these elements is partially omitted to avoid redundancies.

[0083] In Fig. 1A schematically shows a device according to a first embodiment. The device comprises a laser 1, in particular a short-pulse laser or an ultrashort-pulse laser, which provides laser pulses 100 that form the laser beam 10. The laser beam 10 passes through a first scattering disk 2 and then through a second scattering disk 2', each of which scatters the laser beam 10 and thereby forms a plurality of partial laser beams whose intensity and propagation direction are randomized by the scattering. The partial laser beams scattered onto the second scattering disk 2' are randomized again there. A focusing optics 3, here consisting of a lens 30, focuses the scattered laser beam 10 or the plurality of partial laser beams into a focus zone 120 in the focus plane 12, which, for example, coincides with the surface 40 of the workpiece 4.The focused and doubly scattered laser beam 10 accordingly has a locally randomized intensity distribution in the focal plane 12, so that the surface 40 of the workpiece 4 is inhomogeneously exposed in the focal zone 120 and thereby an inhomogeneous material modification is generated.

[0084] In Fig. 1B schematically shows a first diffusion plate 2. The diffusion plate has various scattering regions, which are arranged, for example, on a grid, for example in a shape reminiscent of rectangular pixels. The white scattering regions do not generate a phase shift, while the black scattering regions generate a phase shift of 180° compared to the white scattering regions. Due to the randomized scattering regions, i.e. the random arrangement of scattering regions that generate a phase shift or no phase shift, the laser beam 10 transmitted through the diffusion plate 2 can be imprinted with a randomized intensity distribution in the focal plane 12. The second diffusion plate 2' is shaped accordingly, but has different randomized scattering regions.

[0085] The device of the Fig. 1A generated spatially randomized intensity distributions are in Fig. 1C, D. Fig. 1C shows an intensity distribution of the laser beam 10 in the focal plane 12 after a first pass at a first point of impact through the diffusion plate 2 and Fig. 1D shows a different intensity distribution during a different pass at a second impact location through the diffusion plate 2. The intensity distributions are different from each other and thus produce different material modifications on the surface 40 of the workpiece 4.

[0086] The intensity distribution exhibits a kind of coarse structure based on the shape of the pixel-shaped scattering areas. For example, diffraction at the rectangular pixels creates a sinc 2 -shaped envelope, which is superimposed by a randomized intensity curve. The randomized intensity curve reflects the influence of the various scattering regions on the laser beam 10.

[0087] According to the invention, the plurality of scattered partial laser beams is directed onto a second scattering disk 2' and scattered there again. Since the scattering with the second scattering disk 2' also depends on the point of incidence of the partial laser beams, the already randomized intensity distribution is randomized again.

[0088] The device of Fig. 1A also has a feed device 5, which has a scanner device 50 with a first scanner element 500 and a second scanner element 502. The scanner device 50 can be designed to deflect the laser beam 10 and to move the laser beam along a feed trajectory on the workpiece 4. For this purpose, the laser beam 10 strikes the first scanner element 500, where the laser beam 10 is deflected, for example, in a first direction. The laser beam 10 then strikes the second scanner element 502, where the laser beam 10 is then deflected along a second direction. The point of impact of the laser beam on the second scanner element 502 depends in particular on the deflection and the point of impact of the laser beam on the first scanner element 500.

[0089] According to the invention, the first scanner element 500 comprises a first diffusion plate 2, and the second scanner element 502 comprises a second diffusion plate 2'. Accordingly, a movement of the first scanner element 500 and the second scanner element 502 not only causes the laser beam 10 to be displaced along a feed trajectory across the workpiece 4, but also causes spatially randomized intensity distributions to be introduced into the workpiece 4 during the feed. The feed along the workpiece surface 40 is thus automatically linked to a spatially randomized intensity distribution, without the need for further means to randomize the intensity distribution.

[0090] In Fig. 1E, F alternative embodiments of the first scanner element 500 and the first diffusion plate 2 are shown. In contrast to Fig. 1A, the first scanner element 500 does not include the diffusion plate 2, but the diffusion plate 2 is spatially separated from the first scanner element 500.

[0091] In Fig. 1E, the diffusion screen 2 is arranged in front of the scanner element 500 in the beam propagation direction. The scanner element 500 receives an already scattered laser beam. The scattered laser beam 10 is therefore guided by the scanner element 500 to the second scanner element (not shown) and scattered there again.

[0092] In Fig. 1F, the diffusion plate 2 is arranged after the scanner element 500 in the beam propagation direction. The scanner element 500 therefore directs the unscattered laser beam 10 to different impact locations on the diffusion plate 2, so that a different scattering of the laser beam is achieved there depending on the impact location. Subsequently, the scattered laser beam is also directed to the second scanner element (not shown) and scattered there again. Fig. 1E, F, a double randomization of the intensity distribution also takes place.

[0093] Fig. Figure 2A shows a further embodiment of the device according to the invention. In contrast to Fig. 1A, the laser beam 10 is additionally shaped by a beam shaping device 6. For example, a so-called flat-top beam is formed from a Gaussian laser beam of the laser, so that the envelope of the intensity distribution in the focus zone 12 is evened out, see Fig. 2B.

[0094] The device also has two scattering plates 2, 2', through which the laser beam 10 passes one after the other. The laser beam 10 scattered by the first scattering plate 2 is scattered again by the second scattering plate 2'. As a result, the various laser pulses 100 of the laser 1 experience different scattering, whereby laser pulses introduced one after the other into the material of the workpiece 4 also produce differently shaped material modifications.

[0095] In Fig. Figure 2B shows a first intensity profile of the scattered laser beam 10 in the focal plane 12. The intensity profile of the flat-top laser beam 10 provides uniform illumination of a certain area, with the intensity distribution being sharply defined toward the edge of the area. The double scattering process creates a spatially randomized intensity profile in the area, reminiscent of laser speckles. The spatially randomized intensity distribution exhibits, for example, more than 100 local intensity maxima, which lead to a highly inhomogeneous and irregular material modification.

[0096] In Fig. 2C is the envelope of the intensity distributions from Fig. 1C (dashed) and 2B (solid) are shown in comparison. It is clearly visible that the sinc 2-shaped intensity curve in a Gaussian raw beam concentrates a large part of the intensity on a small spatial area, while with a flattop laser beam, surface processing of the workpiece 4 is significantly simplified.

[0097] In Fig. 2D shows a further intensity distribution that is generated when the first diffusion plate 2 is displaced relative to the second diffusion plate 2' during the scanning process. Since the first diffusion plate 2 and the second diffusion plate 2' scatter the laser beam 10 differently in the displaced position, a different spatially randomized intensity distribution results in the focal plane 12. This avoids repetitive randomized intensity distributions on the surface 40 of the workpiece 4. Fig. 2B, Fig. 2D, the diameter of the focus zone is about 1 mm, so that the power of the laser is focused on an area of ​​about 0.8 mm 2 is distributed.

[0098] Fig. Figure 3A shows schematically the operation of a flat-top beam former 6. The laser beam 10 traveling on the optical axis, which strikes the beam former 6, has a first diameter, which relates, for example, to the drop in intensity to 1 / e 2of the intensity maximum of the laser beam 10. In the beam-shaping device 6, the laser beam 10 can be reshaped using a combination of phase plates, spherical lenses, and aspherical lenses. For example, the partial laser beams that form the intensity maximum of the incoming laser beam 10 can be distributed away from the optical axis, so that although there is a lower maximum intensity on the optical axis, a uniform intensity profile is present over a larger area. The partial laser beams can then be parallelized again, thereby forming the flat-top laser beam 10'. The diameter of the flat-top laser beam can have a larger diameter than the Gaussian laser beam.

[0099] Depending on the beam diameter of the incoming laser beam 10, different beam shapes can be generated using the same beam shaping device 6. See, for example, Laskin et al. “Variable beam shaping with using the same field mapping refractive beam shaper.” Laser Resonators, Microresonators, and Beam Control XIV. Vol. 8236. SPIE, 2012. In Fig. 3B, the incident laser beam 10 has a larger diameter than in Fig. 3A. This results in edge peaks forming on the intensity profile of the flattop laser beam after the beam shaping device 6. In Fig. 3C, the incident laser beam 10 has a smaller diameter than in Fig. 3A. As a result, the flattop laser beam 10' has a lower edge steepness.

[0100] In Fig. 4 shows a further embodiment of the device. In contrast to Fig. 2A, a further 2" diffusion plate is arranged behind the focusing optics 30. The further 2" diffusion plate allows further randomization of the intensity distribution in the focus zone 120.

[0101] In Fig. 5 shows a further possible embodiment in which both scanner elements 500, 502 comprise diffusion disks 2, 2' that are reflective. For example, the laser beam 10 strikes the first diffusion disk 2 at an angle and is then reflected onto the diffusion disk 2', thereby being scattered. This process can be repeated several times until the scattered laser beam 10 is scattered by the second diffusion disk 2' in the direction of the focusing device 3. Both diffusion disks 2, 2' are designed as scanner elements 500, 502, so that when traversing the feed trajectory, the laser beam 10 strikes the respective diffusion disk 2, 2' at different locations, thus further randomizing the intensity distribution in the focal plane 12.

[0102] In Fig. 6A shows a corresponding method for machining a workpiece 4. Laser pulses 100 are emitted by a laser 1, forming a laser beam 10. A scanner device 50 of the feed device 5 guides the laser beam 10 over the surface of the workpiece 4 along a feed trajectory. For this purpose, the laser beam 10 is deflected by the scanner elements 500 and 502 and scattered at each of the scanner elements 500, 502, which are designed as scattering elements 2, 2'. The laser beam 10 is then focused onto the surface 40 of the workpiece 4 using focusing optics 3. The laser beam 10 impinges on the workpiece 4 in the focal plane 12, thereby machining it. The intensity distribution of the laser beam is locally randomized in the focal plane 12, so that the surface 40 of the workpiece 4 can, for example, be functionalized, in particular provided with an anti-glare functionalization.

[0103] The workpiece 4 can additionally be displaced using an axis device 504, so that the focus zone 120 of the laser beam 10 successively sweeps the entire surface 40 or a portion of the surface 40 of the workpiece 4. The focus zones 120 of the various laser pulses 100 can overlap. This means, in particular, that a first laser pulse 100 is introduced into a first focus zone 120 at a first location x in the material of the workpiece 4, while a second laser pulse 100' is introduced into a second focus zone 120' at a second location x' in the material of the workpiece 4.

[0104] By moving the scanner elements 500, 502 relative to each other for the feed, different randomized intensity distributions are generated in the different focus zones 120, 120'. Thus, even with a uniform feed, no uniform material modifications are generated on the surface 40 of the workpiece 4, thus avoiding the formation of disturbing interference or diffraction patterns when viewing the surface.

[0105] In Fig.Figure 6B shows that the different focus zones 120, 120' of the laser pulses 100, 100', introduced one after the other with a pulse spacing t0, can overlap in order to perform the most extensive processing of the workpiece 4 possible. Between the laser pulses 100, 100', the scattering of the laser beam 10 can be changed by a corresponding relative movement of the scattering disks 2, 2' in order to achieve inhomogeneous material processing. For example, the feed rate between the laser pulses can be between 10 µm and 30 µm.

[0106] Where applicable, all individual features shown in the embodiments may be combined and / or exchanged with one another without departing from the scope of the invention. List of reference symbols 1 laser 10 laser beam 12 focal plane 120 focus zone 100 laser pulses 102 partial laser beams 2 first diffuser 2' second lens 3 Focusing optics 30 first lens 4 Workpiece 40 Workpiece surface 5 Feed device 50 scanner device 500 first scanner element 502 second scanner element 52 axle system 6 Beam shaping device V feed QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 2017 / 0368638 A1

[0004] Cited non-patent literature

[0000] Goodman „Speckle phenomena in optics: theory and applications“, Roberts and Company Publishers, 2007

[0026] Kim et al., „Fabrication of ideal geometric-phase holograms with arbitrary wavefronts,“ Optica 2, 958-964 (2015

[0060] Laskin et al. „Variable beam shaping with using the same field mapping refractive beam shaper.“ Laser Resonators, Microresonators, and Beam Control XIV. Vol. 8236. SPIE, 2012

[0099]

Claims

[1] Device for machining a workpiece (4), in particular for applying an anti-glare functionalization, by means of laser pulses (100) of a laser (1), comprising a laser (1), in particular a short-pulse laser or an ultra-short-pulse laser, which is designed to provide a laser beam (10) with laser pulses (100), a first diffusing disc (2) and a second diffusing disc (2'), each designed to scatter the laser beam (10) and to impose a locally randomized intensity distribution on the laser beam (10) in the focal plane (12), wherein the first diffusing disc (2) scatters the laser beam (10) and the second diffusing disc (2') scatters the scattered laser beam (10), at least one focusing optics (3) which is designed to focus the laser beam (10) into a focus zone (120) in the focus plane (12) on the workpiece (4), wherein the workpiece (4) is exposed to the laser beam (10) and is thereby processed, a feed device (5) which is designed to move the laser beam (10) and the workpiece (4) relative to one another with a feed (V), wherein the feed device comprises a scanner device (50) with a first scanner element (500) and a second scanner element (502), wherein a movement of the scanner elements (500, 502) generates a feed, and the second scanner element (502) comprises the second diffusion disc (2'), where the movement of the scanner elements modifies the local randomized intensity distribution. [2] Device according to claim 1, characterized bythat the first scanner element (500) is arranged before or after the first diffusion disc (2) and / or the first scanner element (500) comprises the first diffusion disc (2). [3] Device according to claim 1 characterized by that at least one diffusing disc (2, 2') is designed to scatter the laser beam (10) in transmission or in reflection. [4] Device according to one of the preceding claims, characterized by that at least one diffusion plate (2) has a phase pattern, in particular a binary phase pattern, which is designed to impose a location-dependent phase difference on the laser beam (10), in particular wherein the phase pattern is pronounced in one or two dimensions. [5] Device according to one of the preceding claims characterized by that the diffusing disc (2) is a spatial light modulator or a diffractive optical element. [6] Device according to one of the preceding claims, characterized bythat the feed device (5) comprises an axis system (52). [7] Device according to one of the preceding claims, characterized by that the scanner device comprises a galvano scanner and / or a polygon scanner. [8] Device according to one of the preceding claims, characterized by that the focusing optics (3) comprises a further diffusion disc. [9] Device according to one of the preceding claims, characterized by a beam shaping device (6) which is designed to impose a beam shape on the laser beam (10), in particular to impose a flat-top beam shape. [10] Device according to claim 9, characterized by that the beam shaping device (6) is arranged in front of the scanner device (50) in the beam propagation direction. [11] Method for machining a workpiece (4), in particular for imprinting an anti-glare functionalization, by means of laser pulses (100) of a laser (1), in particular a short-pulse laser or ultra-short-pulse laser, wherein the laser beam (10) is scattered with the laser pulses by a first diffusion disk and a second diffusion disk and a locally randomized intensity distribution is impressed on the laser beam (10) in the focal plane (12) by the diffusion disks (2), wherein the workpiece (4) and the laser beam (10) are displaced relative to each other along a feed trajectory, wherein the feed is generated by a movement of a first scanner element (500) and a second scanner element (502) of a scanner device (50), wherein the scattered laser beam is focused by a focusing optics (3) into a focus zone (120) in a focus plane (12) on the workpiece (4), wherein the workpiece (4) is exposed to the laser beam (10) and is thereby processed, and wherein the second scanner element is designed as a second diffusion disk, wherein the spatially randomized intensity distribution is modified by the relative movement of the scanner elements. [12] Method according to claim 11, characterized by that the first scanner element (500) is arranged before or after the first diffusion disc (2) and / or the first scanner element (500) comprises the first diffusion disc (2). [13] Method according to one of claims 11 or 12, characterized by that the focus zone (120) of different, in particular successive laser pulses (100) overlap. [14] Method according to one of claims 11 to 13, characterized bythat the focus zones (120) cover a surface section of the workpiece (4).

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