Device and method for processing a workpiece

Abstract

The invention relates to a device for processing a workpiece (4), in particular for impressing an antiglare functionalization, using laser pulses (100) of a laser (1), comprising a laser (1), in particular a short pulse laser or an ultrashort pulse laser, which is designed to provide a laser beam (10) with laser pulses (100), at least one diffusing disc (2) which is designed to diffuse the laser beam (10), and at least one optical focusing system (3) which is designed to focus the laser beam (10) onto a focal zone (120) on the focal plane (12) on the workpiece (4), wherein the workpiece (4) is supplied with the laser beam (10) and is thus processed, and the diffusing disc (2) is designed to impress a locally randomized intensity distribution onto the laser beam (10) on the focal plane (12).

Description

[0001] Device and method for machining a workpiece

[0002] Technical area

[0003] The present invention relates to a device and a method for machining a workpiece.

[0004] State of the art

[0005] It is known that laser material processing can remove material from a workpiece by vaporizing or condensing the material within the focus 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.

[0006] However, when processing a material with a pulsed laser, regular structures often arise, especially regularly arranged dimples, for example, due to a oscillation 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 appearance of the processed material.

[0007] EP3735332B1, for example, discloses an optical arrangement for direct laser interference structuring, in which a laser beam emitted by a laser beam source is split into two partial beams and these partial beams are directed onto the surface of a component in an interfering manner by means of a focusing optical element to form a structuring.

[0008] Description of the invention Starting from the known prior art, it is an object of the present invention to provide an improved device for processing a material, as well as a corresponding method.

[0009] 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.

[0010] Accordingly, a device for processing a workpiece, in particular for applying an anti-glare functionalization, using laser pulses of a laser is proposed, comprising a laser, in particular a short-pulse laser or an ultrashort-pulse laser, which is configured to provide a laser beam with laser pulses, at least one diffusion disk configured to scatter the laser beam, and at least one focusing optic 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 processed. According to the invention, the diffusion disk is configured to impart a spatially randomized intensity distribution to the laser beam in the focal plane.

[0011] The material of the workpiece can, for example, be a polymer or a plastic. The material to be processed can also be a semiconductor, for example an elemental 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, whereby each layer can be 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.

[0012] 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 300 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.

[0013] Instead of individual laser pulses, the laser can also provide laser bursts, with each burst comprising the emission of several laser pulses. For a specific time interval, the laser pulses can be emitted very closely one after the other, at intervals of a few picoseconds to nanoseconds. The laser bursts can in particular be GHz bursts, in which the sequence of consecutive 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.

[0014] 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 can emit, for example, more than 1,000 pulses per second or more than 10,000 pulses per second.

[0015] The pulse energy of the laser pulses can be greater than 1 pJ, for example 2 pJ.

[0016] The diameter of the laser beam provided by the laser can be larger than 0.1 mm, for example 1 mm or 5 mm.

[0017] 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.

[0018] The incoming laser beam first passes through the diffusion disk. Such a diffusion disk is designed 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.

[0019] 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 can be 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.

[0020] 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 independently 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.

[0021] 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 are 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 the intensity of the laser beam is greatest there. In particular, this can achieve the separation of part of the material from the composite material of the workpiece, for example, by melting or vaporizing.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.

[0022] The interaction of the laser pulses with the workpiece material to be processed creates corresponding material modifications on the workpiece surface. In particular, a material modification can be created using a laser pulse or a laser burst.

[0023] Such material modification occurs through the evaporation of the workpiece material at the surface due to the incident laser intensity. The workpiece material is evaporated particularly where the intensity of the laser beam exceeds a critical, material-specific processing threshold. Accordingly, the shape and form of the laser beam, in particular the intensity distribution of the laser beam in the focal plane, are crucial for the shape and form of the material modification. Without a diffuser, for example, the laser beam 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 isointensity area in the intensity distribution of the laser beam at the focus within which the material can be evaporated.The shape and form of the material modification thus arise from this isointensity surface. 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 an essentially 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 scattering disk in the beam path of the device, the laser beam is randomly scattered, creating a spatially randomized intensity distribution in the focal plane. Accordingly, the laser beam hitting the scattering disk is scattered into a multitude 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 a largest and smallest propagation angle of the partial laser beams is predetermined by the shape and form of the scattering disk. This imparts a random or statistical component to the intensity profile in the focal plane, which has spatially randomly distributed intensity peaks or intensity valleys, each of which leads to particularly strong or particularly weak material processing.In particular, such scattering can impart a speckle pattern to 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.

[0025] By introducing such inhomogeneous material modifications using a spatially randomized intensity distribution on the material's surface, 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.

[0026] For example, the type and shape of the material modifications, as well as their distribution 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.

[0027] 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 across a spatial region, allowing the energy of the incident light beam to be detected within a range of angles of reflection.

[0028] The at least one diffusing disc can be configured to scatter the laser beam in transmission or in reflection.

[0029] For example, the diffuser can transmit the incident laser beam, causing the laser beam to propagate through the diffuser and be scattered in the process. For example, the laser beam can be scattered by the 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.

[0030] The 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.

[0031] The diffusion disk has scattering regions that locally influence or do not influence the phase of the incident laser beam. The various scattering regions are randomly distributed on the diffusion disk, so that the scattering of the laser beam depends on the point of impact on the diffusion disk. For example, a first partial laser beam can exhibit a phase shift from a second partial laser beam after scattering at a first scattering region. Such a phase shift makes it possible to deflect the partial laser beams from their original propagation direction.

[0032] The number of different phase shifts that can be generated with the diffusion disk 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°, 90°, 180°, 270°. However, it is also possible for the diffusion disk to enable, for example, 8 or 16 different phase shifts between the partial laser beams.

[0033] For example, a first scattering region can have a first material thickness, and a second scattering region can have a second material thickness. If the scattering disk is reflective, the first and second thicknesses 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°.

[0034] 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°.

[0035] If the lens has a binary pattern, this can mean that the lens provides only two different optical path lengths. The pattern can be distributed over the geometric extent of the lens, so that the lens, for example, has statistically distributed regions of a first thickness and a second thickness.

[0036] If the diffuser disc has a binary pattern in two dimensions, this can mean that the diffuser has randomly distributed scattering regions in both height and width. However, if the diffuser disc only has a binary pattern in one dimension, this can mean that the diffuser only has randomly distributed scattering regions in height or width. For example, the binary pattern then corresponds to a striped pattern. In particular, the spatial frequency of the spatially randomized intensity distribution can be adjusted via the size of the scattering regions of the diffuser disc. The spatial frequency can be understood as the inverse of the period length of the scattering regions. If, for example, the diffuser disc has small rectangular scattering regions, this leads to a high spatial frequency of the spatially randomized intensity distribution and thus to a particularly inhomogeneous intensity distribution.

[0037] For example, the edge length of the pixels can be larger than 1 pm, for example 20pm or 100pm.

[0038] The diffuser can be a spatial light modulator or a diffractive optical element.

[0039] A spatial light modulator can, for example, be a nanograting or a hybrid element, which, through their inherent structure or design, can impose a defined phase distribution on 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.

[0040] 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.

[0041] At least two diffusion disks can be provided and scatter the laser beam one after the other, wherein a first diffusion disk can be moved relative to a second diffusion disk, in particular rotated or shifted.

[0042] By rotating or shifting the beam, the point of incidence of the laser beam on the diffusion disk can be changed. Due to the altered scattering properties at the different points of incidence, 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.

[0043] For example, the second scattering disc can be rotated, then the scattered

[0044] Laser beams of two consecutive pulses are directed to different positions on the rotated diffusion disk, so that the intensity distribution of the first laser pulse in the focal plane differs from the intensity distribution of the second laser pulse.

[0045] However, it is also possible that the first diffusion disc is rotated, causing the laser pulses to hit different scattering areas of the first diffusion disc. However, the second diffusion disc always receives different intensity distributions.

[0046] However, the first and second diffusion disks can also be rotated, for example, at different rotation frequencies. This allows the intensity distributions in the focal plane to be further randomized. In particular, the diffusion disks can also be rotated against each other, i.e., in opposite directions.

[0047] However, it is also possible for the second diffusion disc to be shifted laterally relative to the first, i.e., perpendicular to the beam propagation direction. It is also possible for the first disc to be shifted laterally relative to the second disc. It is also possible for the first and second diffusion discs to be shifted laterally relative to each other.

[0048] The diffusers can also be moved in an oscillating manner, for example, using a piezoelectric actuator to which an alternating voltage is applied. The alternating voltage causes the piezoelectric actuator to expand periodically according to the alternating voltage frequency, resulting in an oscillating displacement of the diffuser. For example, the alternating voltage can have a frequency of more than 100 Hz, preferably more than 1 kHz. The amplitude of the movement can be, for example, 10 μm, 10 μm, or 1 mm, or a value in between.

[0049] This has the advantage that, for example, statically designed diffusion disks with a fixed binary pattern, which essentially scatter the laser beam equally, can generate different randomized intensity distributions in the focal plane. This makes it possible to avoid periodic, recurring patterns in the material modifications, thus enabling particularly high-quality material processing.

[0050] A particular advantage is that the double scattering can achieve a large difference in the local randomization of the intensity distribution by a small rotation or displacement of a scattering disc.

[0051] A 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 and / or an axis device, wherein the scanner device preferably comprises an AOM and / or a galvano scanner and / or a polygon scanner.

[0052] Relatively displaceable means that both the laser beam can be moved translationally relative to a stationary material and the material can be moved relative to the laser beam, or there is a movement of both the material and the laser beam.

[0053] 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.

[0054] 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.

[0055] The feed device may preferably comprise an axis device and / or a scanner device.

[0056] For example, the axis device can be used to move the material mechanically, while a scanner device moves the laser beam over the material. 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. The scanner device can, in particular, be a galvano scanner. However, the feed device can also be a roll-to-roll device.

[0057] In an acousto-optical deflector, an alternating voltage is applied to a piezoelectric crystal in an optically adjacent material to generate an acoustic wave that periodically modulates the refractive index of the material. The wave can propagate through the optical material, for example, as a propagating wave or a wave packet, or it can be in the form of a standing wave. The periodic modulation of the refractive index creates a diffraction grating for an incident laser beam. An incident laser beam is diffracted by the diffraction grating and thereby deflected at least partially at an angle to its original beam propagation direction. The grating constant of the diffraction grating, and thus the deflection angle, depends, among other things, on the wavelength of the acoustic wave and thus on the frequency of the applied alternating voltage.

[0058] Electro-optical deflectors are based on prisms made of electro-optical crystals. Applying a voltage changes the refractive index of the electro-optical crystal, altering the path of the laser beam through the prism.

[0059] Spatial statistical distribution using an electro-optical and / or acousto-optical deflector can be achieved at a clock rate of over 1 MHz. Accordingly, several million repositionings of the laser pulse can be achieved per second. In particular, the electro-optical and / or acoustic deflectors can achieve single-pulse precision repositioning of the laser pulses, ensuring that each individual laser pulse is applied to a different location in the material.

[0060] In a galvano scanner, the laser beam is repositioned with high precision and repeatability using a rotating mirror. 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, which are preferably orthogonal to each other.

[0061] The feed mechanism 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-to-surface material processing.

[0062] The material modifications created on the workpiece can overlap.

[0063] 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.

[0064] In particular, this allows for machining flat sections of the workpiece. It is also possible to machine the entire surface of the workpiece.

[0065] A flat section here means that a contiguous area extending across at least two focus zones has been machined, while full-surface machining of the workpiece surface means machining at least the side facing the laser beam. The focusing optics can have at least a first lens with a first focal length and a second lens with a second focal length, wherein the first lens is arranged at a distance of the first focal length from the diffuser, wherein the second lens is arranged at a distance of the second focal length from the workpiece, and wherein the first lens and the second lens are arranged at a distance from one another that corresponds to the sum of the focal lengths of the first lens and the second lens.

[0066] Overall, such positioning of the components creates a so-called 4f optic, which makes it possible to transfer the scattered light from the diffusion discs, in particular any possible spatial and angular deviations of the laser beam, into a corresponding scattering plane. This can, for example, enlarge or reduce the focal zone, so that a larger or smaller area of ​​the workpiece can be processed in the focal plane. In particular, by reducing the focal zone, the laser power can be concentrated on a smaller area, enabling material processing even with low-power laser systems. For example, the first and second lenses can have an aperture ratio of f100.

[0067] The focusing optics may comprise a cylindrical lens configured to create a linear focus zone on the workpiece. In particular, the first lens of the focusing optics may be a cylindrical lens configured to create a linear focus zone on the workpiece.

[0068] By including a cylindrical lens in the focusing optics, the focus zone of the laser beam in the focal plane can be stretched in one direction. For example, the cylindrical lens has an aperture ratio of f / 200 in one direction, while it has no focal length in a direction perpendicular to this. In particular, the cylindrical lens can create a linear focus zone in the focal plane. This also distributes the energy of the laser beam across only one dimension, providing a high power density or high intensity in the focal plane.

[0069] This makes it possible to achieve appropriate material processing even with low-power laser systems.

[0070] A beam-shaping device can be configured to impart a beam shape to the laser beam, in particular a flat-top beam shape. The beam-shaping device is preferably arranged in front of the first diffusion disk. The beam-shaping device can generate the flat-top beam shape in an elliptical, circular, or rectangular geometry, in particular a square one.

[0071] Beam-shaping optics can, for example, be a commercially available pi-shaper, which imposes a flat-top beam shape on 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.

[0072] 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.

[0073] The above-mentioned object is further achieved by a method for processing a material having the features of claim 10. Advantageous developments of the method emerge from the subclaims as well as the present description and the figures.

[0074] Accordingly, a method for machining a workpiece, in particular for applying an anti-glare functionalization, using laser pulses from a laser, in particular a short-pulse laser or ultrashort-pulse laser, is proposed. The laser beam is scattered by the laser pulses from at least one diffusion disk. The scattered laser beam is focused by focusing optics into a focus zone in a focal plane in or on the workpiece. The workpiece is exposed to the laser beam and thus machined. According to the invention, a spatially randomized intensity distribution is impressed on the laser beam in the focus zone by the diffusion disk.

[0075] At least two scattering discs can be moved relative to each other, whereby the spatially randomized intensity distribution undergoes a correspondingly randomized change.

[0076] The workpiece and the laser beam can be moved relative to each other along a feed trajectory.

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

[0078] The focus zones can cover a large portion of the workpiece, making it particularly easy to process the material over a large area.

[0079] A further aspect of the invention relates to a workpiece with an anti-glare functionalization produced by the method.

[0080] The functionalized surface of the workpiece can be designed by the described method in such a way that it reduces the direct reflection of light from the workpiece.

[0081] Direct reflection, for example, is zero-order diffraction at the surface of the component. Direct reflection is suppressed if, at the angle of reflection according to Snell's law of refraction, less than 90%, preferably less than 70%, and particularly preferably less than 50%, of the incident light is reflected.

[0082] The sparkle of the surface with the anti-glare functionalization can be less than 5%.

[0083] Sparkle describes an optical effect that manifests as a glittering or sparkling effect on a transparent component when light is reflected from the surface of the component or transmitted through it. The appearance depends heavily on the chosen angle of incidence of the light and the angle of observation. Sparkle is thus a measure of irregular fluctuations in intensity and color.

[0084] The sparkle can, for example, be quantified as the intensity modulation of the light by the sparkle, in particular the intensity increase or decrease in intensity with uniform illumination.

[0085] Anti-glare functionalization can suppress such sparkle and homogenize transmission and reflection.

[0086] The Distinctness of Image can be more than 70%.

[0087] The Distinctness of Image (DOI) describes image sharpness and quantifies the deviation from theoretical light propagation due to light scattering by the material modifications. A high DOI, in particular, means high image sharpness. The scattering of light by the dimples influences both the transmission and reflection of light at or through the surface. A low DOI results in significant light scattering, while a high DOI results in minimal light scattering, thus enabling high image sharpness. Therefore, the DOI scales inversely with the scattering or diffusion.

[0088] Diffusion can exceed 22%. Diffusion is a measure of the scattering strength of the material. In particular, diffusion also depends on the shape and nature of the individual material modifications, so diffusion can be adjusted via the laser beam shape and the size and depth of the material modifications.

[0089] The transparent component can be a cover or protective part of a smart device.

[0090] In particular, so-called smart devices could be electronic devices that are touch-sensitive and can be controlled by finger gestures, for example smartwatches, smartphones, tablets, but also image display devices in cars, etc. In general, screens and displays are included in smart devices.

[0091] However, it may also be the case that the transparent component is arranged on the back of a smart device and gives the back a particularly high-quality and non-slip surface finish due to its matte surface and its roughness due to the material modifications.

[0092] Short description of the characters

[0093] Preferred further embodiments of the invention are explained in more detail in the following description of the figures. In the figures:

[0094] Figures 1A, B, C, D are schematic representations of the device of a first embodiment;

[0095] Figures 2A, B, C, D are schematic representations of the device of a second embodiment;

[0096] Figures 3A, B, C are schematic representations of the operation of a beam shaping device;

[0097] Figures 4A, B, C, D, E are schematic representations of the device of a third embodiment;

[0098] Figures 5A, B, C are schematic representations of the scattering plates;

[0099] Figures 6A, B, C show further schematic representations of the scattering plates; and

[0100] Figures 7A, B show a schematic representation of the method according to the invention.

[0101] Detailed description of preferred embodiments

[0102] Preferred embodiments are described below with reference to the figures. Identical, similar, or equivalent elements in the different figures are provided with identical reference numerals, and a repeated description of these elements is partially omitted to avoid redundancies.

[0103] Figure 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 scattering disk 2, 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. A focusing optics 3, here consisting of a first 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 coincides, for example, with the surface 40 of the workpiece 4.The focused and 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.

[0104] The alignment of the focal plane 12 with the surface 40 of the workpiece 4 is achieved, for example, by means of an axis system (not shown), by which a distance between the focusing optics 3 and the surface 40 can be adjusted. By varying the distance, a desired intensity can be set in the local maxima of the focus zone 120 on the surface 40.

[0105] Figure 1B schematically shows a 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 generate no 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.

[0106] Such spatially randomized intensity distributions are shown in Figures 1 C, D. Figure 1 C shows an intensity distribution of the laser beam 10 in the focal plane 12 during a first pass through the diffuser plate 2 at a first point of incidence, and Figure 1 D shows a different intensity distribution during another pass at a second point of incidence through the diffuser plate 2. The intensity distributions are different from one another and thus produce different material modifications on the surface 40 of the workpiece 4. In order to produce the different spatially randomized intensity distributions in the focal plane 12, the diffuser plate 2 can be rotated or displaced, for example, using an adjustment mechanism 2, so that the point of incidence of the laser beam 10 on the diffuser plate 2 can be adjusted.

[0107] 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.

[0108] Figure 2A shows a further embodiment of the device according to the invention. In contrast to Figure 1A, the laser beam 10 is shaped by a beam-shaping device 6. For example, a so-called flat-top beam is formed from a Gaussian laser beam, so that the envelope of the intensity distribution in the focus zone 12 is evened out (see Figure 2C).

[0109] 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'. To further randomize the scattering of the laser beam 10, the first and second scattering plates 2, 2' can be displaced and / or rotated relative to one another using the associated adjustment mechanisms 20, 20', as explained in detail below. 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.

[0110] The scattered laser beam 10 is directed onto the focusing optics 3, which comprises a first lens 30 and a second lens 32. The first lens 30 is spaced from the diffusion plate 2' at a distance equal to the first focal length f1, while the second lens 32 is spaced from each other at a distance equal to the sum of the first focal length f1 and the second focal length f2. The focal plane 12 is then located at a distance f2 in the beam propagation direction behind the second lens 32, which coincides with the surface 40 of the workpiece 4. The so-called 4f imaging into the focal plane 12 allows the scattered light from the diffusion plate to be imaged in an enlarged or reduced size.

[0111] It is also possible for the device to comprise a scanner 50 configured as a galvano scanner or as an AOM. The second lens 32 typically performs an angle-to-location transformation of the laser beam 10, so that a laser beam 10 deflected in front of the second lens 32 is imaged behind the second lens 32 at a different location in the focal plane 12. Accordingly, it is particularly advantageous to position the scanner 50, which deflects the laser beam 10, at a distance of the second focal length f2 in front of the second lens 32. The angular deflection by the scanner is thus translated into a spatial deflection in the focal plane 12.

[0112] 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.

[0113] Figure 2C shows the envelope of the intensity distributions from Figures 1C (dashed) and 2B (solid) 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.

[0114] Figure 2D shows a further intensity distribution that is generated when the first diffusion disk 2 is rotated or shifted relative to the second diffusion disk 2'. Since the first diffusion disk scatters the laser beam 10 differently in the shifted or rotated position, a different locally randomized intensity profile results in the focal plane 12. This avoids repetitive randomized intensity distributions on the surface 40 of the workpiece 4. In Figures 2B, 2D, the diameter of the focus zone is approximately 1 mm, so that the laser power is distributed over an area of ​​approximately 0.8 mm 2 is distributed.

[0115] Figure 3A shows schematically the operation of a flat-top beam former 6. The laser beam 10 running on the optical axis, which strikes the beam forming device 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 while there is a lower maximum intensity on the optical axis, a uniform intensity distribution is present over a larger area. The partial laser beams can then be parallelized again, forming the flat-top laser beam 10'. The diameter of the flat-top laser beam can be larger than the Gaussian laser beam.

[0116] 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 Figure 3B, the incoming laser beam 10 has a larger diameter than in Figure 3A. As a result, edge peaks form on the intensity profile of the flat-top laser beam after the beam shaping device 6. In Figure 3C, the incoming laser beam 10 has a smaller diameter than in Figure 3A. As a result, the flat-top laser beam 10' has a lower edge steepness.

[0117] Figure 4A shows another embodiment of the device. In contrast to Figure 2A, the first lens 30 of the focusing device 3 is a cylindrical lens. A cylindrical lens focuses the laser beam 10 in only one direction. Accordingly, the area exposed to the laser power is smaller than the area exposed in Figure 2A. The power is thus distributed over a smaller area, and the intensity in the focal plane is increased. This also enables material processing with lower-power laser systems.

[0118] In addition, Figure 4A additionally shows a first telescope 60 in front of the beam-shaping device 6 and a second telescope 62 after the beam-shaping device 6. Such a configuration is, of course, also possible in Figure 2A.

[0119] The first telescope 62 can be configured to adjust the beam diameter of the incident laser beam 10 to the beam-shaping device 6. As shown in Figures 3A, B, and C, the intensity distribution of the outgoing laser beam can be adjusted by adjusting the beam diameter in front of the beam-shaping device 6.

[0120] The second telescope 62 can be configured to adjust the size of the illuminated area on the diffuser 2. This allows, in particular, the size of the focal zone 120 on the workpiece to be adjusted in addition to the focusing optics 3. The second telescope 62 can be designed, for example, as a simple telescope with two lenses according to Galilean principles, or as a flexible telescope with three lenses and thus with variable magnification and divergence adjustment.

[0121] Figures 4B and 4C show the diffusion plates 2 and 2', which are designed as phase plates. In particular, the phase plates have a one-dimensional binary pattern, whereby the laser beam 10 is also scattered in only one direction. However, it is also possible for both phase plates or just one of the two phase plates to have a two-dimensional pattern, as shown in Figure 1B.

[0122] Figures 4D and 4E show the intensity profiles in the focal plane 12, as generated with a device according to Figure 4A. Figures 4D and 4E show two different intensity profiles as they can be generated after rotation or displacement of the diffusion discs 2, 2'. In Figures 4D and 4E, the focal zone through the cylindrical lens is only about 2 mm wide and 30 pm high. This reduces the laser power to an area of ​​only about 0.06 mm. 2The power density, or fluence, of the cylindrical lens used in the focal zone is therefore more than 10 times greater than in Figures 2B and D.

[0123] To randomize the intensity distribution of the scattered laser beam 10 in the focal plane 12 particularly easily, the first and second diffusion disks 2, 2' can, for example, be rotated relative to each other, as shown in Figure 5A. In particular, both diffusion disks 2, 2' can be rotated at different rotation frequencies. It is also possible for only one of the two diffusion disks 2, 2' to be rotated.

[0124] It is also possible for the device to have three scattering discs 2, 2', 2", as shown in Figure 5B. All three scattering discs can also be moved parallel to each other along different axes to achieve further randomization. In particular, the scattering discs can be oscillated back and forth along the different axes, preferably at different frequencies.

[0125] It is also possible to move one lens and rotate another lens (not shown).

[0126] Figure 5C shows another possible embodiment in which both diffusion plates 2, 2' are reflective. For example, the laser beam 10 strikes the first diffusion plate 2 at an angle and is then reflected onto the diffusion plate 2', thereby scattering it. This process is repeated several times until the scattered laser beam 10 is scattered by the second diffusion plate 2' in the direction of the focusing device 3. The first or the second or both diffusion plates can have an adjustment mechanism 20 so that the laser beam 10 strikes the respective diffusion plate 2, 2' at different locations, thus further randomizing the intensity distribution in the focal plane 12.

[0127] Figure 6A shows a further embodiment for further randomizing the intensity distributions. The incident laser beam 10 is deflected by a first scanner 50 and guided through a first lens, a first diffusion plate 2, a second diffusion plate 2', and a second lens before the scattered laser beam is deflected again by another scanner 50'. The first scanner 50 can direct the laser beam 10 to different areas on the diffusion plates 2, 2', and the second scanner 50', which can be synchronized with the first scanner 50, can compensate for the spatial offset caused by the deflection.

[0128] Figure 6B shows that the second half of the beam path of Figure 6A can also be replaced by a mirror 52, which is arranged, for example, behind the first diffusing disk 2.

[0129] However, it is also possible, as shown in Figure 6C, that only one scanner 50 is arranged in front of the diffusion plate 2, and then a telescope consisting of two lenses images the scattered laser beam 10.

[0130] Figure 7A shows a corresponding method for machining a workpiece 4. Laser pulses 100 are emitted by a laser 1, forming a laser beam 10. The laser beam 10 is scattered by at least one diffusion disk 2 and 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.

[0131] The workpiece 4 is moved by a feed device 5 so that the focus zone 120 of the laser beam 10 successively covers 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.

[0132] If the different focal planes 12, 12' are to have different randomized intensity distributions, the diffusion disks 2, 2' of the device can be rotated or shifted relative to one another. This ensures that 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. Figure 7B shows that the different focal zones 120, 120' of the laser pulses 100, 100', which are introduced one after the other with the temporal pulse spacing t0, can overlap in order to process the workpiece 4 as extensively as possible. Between the laser pulses 100, 100', the scattering of the laser beam 10 can be changed by a corresponding relative movement of the diffusion disks 2, 2' in order to achieve inhomogeneous material processing.

[0133] With a laser repetition rate of 10 kHz and a focus zone diameter of 1 mm, the feed rate can be up to 10 m / s, so that the surface of a workpiece can be machined very quickly.

[0134] Where applicable, all individual features presented in the embodiments may be combined and / or exchanged without departing from the scope of the invention.

[0135]

[0136] 1 laser

[0137] 10 laser beam

[0138] 12 focal plane

[0139] 120 focus zone

[0140] 100 laser pulses

[0141] 102 partial laser beams

[0142] 2 diffuser

[0143] 20 Adjustment mechanism

[0144] 3 Focusing optics

[0145] 30 first lens

[0146] 32 second lens

[0147] 4 Workpiece

[0148] 40 Workpiece surface

[0149] 5 Feed device

[0150] 50 scanner device

[0151] 52 axle system

[0152] 6 beam ifo rmung device

[0153] 60 first telescope

[0154] 62 second telescope

[0155] V feed

Claims

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 configured to provide a laser beam (10) with laser pulses (100), at least one diffusing disc (2) which is configured to scatter the laser beam (10), at least one focusing optics (3) which is configured 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 machined, characterized in that the diffusing disc (2) is configured to impart a locally randomized intensity distribution to the laser beam (10) in the focus plane (12).

2. Device according to claim 1, characterized in that the at least one diffusing disc (2) is designed to scatter the laser beam (10) in transmission or in reflection.

3. Device according to one of the preceding claims, characterized in that the 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.

4. Device according to one of the preceding claims, characterized in that the diffusing screen (2) is a spatial light modulator or a diffractive optical element.

5. Device according to one of the preceding claims, characterized by at least two scattering discs (2, 2') which scatter the laser beam (10) one after the other, wherein a first scattering disc (2) can be moved, in particular rotated or displaced, relative to a second scattering disc (2').

6. Device according to one of the preceding claims, characterized by 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) and / or an axis system (52), wherein the scanner device preferably comprises an AOM and / or a galvano scanner and / or a polygon scanner.

7. Device according to one of the preceding claims, characterized in that the focusing optics (3) have at least a first lens (30) with a first focal length and a second lens (32) with a second focal length, wherein the first lens (30) is arranged at a distance of the first focal length from the diffuser (2), wherein the second lens (32) is arranged at a distance of the second focal length from the workpiece (4), and wherein the first lens (30) and the second lens (32) are arranged at a distance from one another which corresponds to the sum of the focal lengths of the first lens (30) and the second lens (32).

8. Device according to one of the preceding claims, characterized in that the focusing optics (3) comprises a cylindrical lens which is designed to produce a linear focus zone (120) on the workpiece (4).

9. Device according to one of the preceding claims, characterized by a beam-shaping device (6) which is designed to impart a beam shape to the laser beam (10), in particular to impart a flat-top beam shape, wherein the beam-shaping device (6) is preferably arranged in front of the first diffusing disc (2).

10. Method for machining a workpiece (4), in particular for applying 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 at least one diffusion plate (2), 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 machined, characterized in that a locally randomized intensity distribution is impressed on the laser beam (10) in the focal plane (12) by the diffusing disc (2). 11 . Method according to claim 10, characterized in that at least two scattering discs (2, 2') are moved relative to each other, wherein the locally randomized Intensity distribution undergoes a correspondingly randomized change.

12. Method according to one of claims 10 or 11, characterized in that the workpiece (4) and the laser beam (10) are displaced relative to each other along a feed trajectory.

13. Method according to one of claims 10 to 12, characterized in that the Focus zone (120) of different, in particular successive laser pulses (100) overlap.

14. Method according to one of claims 10 to 13, characterized in that the focus zones (120) cover a planar section of the workpiece (4).

15. Workpiece (4) with an anti-glare functionalization produced by the method according to one of claims 10 to 14, wherein the direct reflection of light at the workpiece is less than 50% and / or the sparkle of the surface with the anti-glare functionalization is less than 5% and / or the distinctness of image is more than 70% and / or the diffusion is more than 22%.

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