WO2024160647A1

WO2024160647A1 - Device and method for processing a workpiece

Info

Publication number: WO2024160647A1
Application number: PCT/EP2024/051768
Authority: WO
Inventors: Daniel FLAMM; Jonas Kleiner; Jonas Mayer; Malte Kumkar; Daniel Grossmann
Original assignee: Trumpf Laser Gmbh; Trumpf Laser- Und Systemtechnik Gmbh
Priority date: 2023-01-30
Filing date: 2024-01-25
Publication date: 2024-08-08

Abstract

The invention relates to a device and a method for processing a workpiece (4), in particular for impressing a surface functionalization, using laser pulses (100) of a laser beam (10), comprising a laser (1), a hologram (2), and an optical imaging system (3), wherein the laser (1), in particular a short pulse laser or an ultrashort pulse laser, is designed to provide the laser beam (10) with the laser pulses (100) to the hologram (2), and the hologram (2) is designed to receive the laser beam (10), convert the laser beam (10) into a plurality of sub-laser beams (12), and bring same into interference and forward same to the optical imaging system (3). The optical imaging system (3) is designed to receive the sub-laser beams (12) of hologram (2) and focus the sub-laser beams onto a focal plane on or in the workpiece (4) as a processing beam (14), and the workpiece (40) is supplied with the processing beam (14) and is thus processed. The hologram (2) is additionally designed to impress a regular intensity distribution (I) onto the processing beam (14) on the focal plane.

Description

Device and method for machining a workpiece

Technical area

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

State of the art

It is known that during laser material processing, material can be removed from a workpiece by vaporizing or condensing the material within the focus zone of a laser beam through a strong light-matter interaction. The structures created in this way can be, for example, line-, point- or plate-shaped depressions. If such structures are introduced in a regular manner onto or into the surface of the workpiece, this can functionalize the surface of the workpiece. In particular, this can influence the optical or tribological properties of the workpiece surface.

The optical arrangements used to introduce regular structures are often implemented as interferometers, whereby a laser beam emitted by a laser is split into at least two partial beams and these partial laser beams are directed onto the surface of the workpiece in an interfering manner using a focusing element to form a structure.

EP 3466598 B1 discloses a laser optical arrangement for laser interference processing.

EP 3735332 B1 discloses an optical arrangement for direct laser interference structuring.

The devices for processing a workpiece must always ensure that the interference conditions are met for the partial laser beams. The optical path length differences of the partial laser beams in pulsed laser operation must be smaller than the temporal coherence length of the pulses used. For short laser pulses with pulse durations of less than 10Ops, the path length differences must therefore be less than 30mm, according to L = c * dT, where c is the speed of light and dT is the pulse duration. For ultrashort laser pulses with pulse durations in the In the range of 100fs, path length differences of 30|jm result. If the path length of the different partial laser beams is larger, then the laser pulses in the individual partial laser beams cannot interfere with each other, because the laser pulses are not simultaneously in a place where they could interfere. For interferometer-based devices, such an adjustment of the path lengths is very complex, which is why long laser pulses with a pulse duration of more than 100ps often have to be used.

Description of the invention

Based on the known prior art, it is an object of the present invention to provide an improved device for machining a workpiece, as well as a corresponding method.

The object is achieved by a device for machining a workpiece with the features of claim 1. Advantageous further developments emerge from the subclaims, the description and the figures.

Accordingly, a device for processing a workpiece, in particular for imparting surface functionalization, by means of laser pulses of a laser beam is proposed, comprising a laser, a hologram and an imaging optics. The laser, in particular a short-pulse laser or an ultra-short-pulse laser, is designed to provide the laser beam with the laser pulses to the hologram. The hologram is designed to receive the laser beam, convert the laser beam into a plurality of partial laser beams and cause them to interfere and pass them on to the imaging optics. The imaging optics are designed to receive the partial laser beams and focus them as a processing beam in a focal plane on or in the workpiece, wherein the workpiece is exposed to the processing beam and is thereby processed. According to the invention, the hologram is further designed to impart a regular intensity distribution to the processing beam in the focal plane, preferably a high-frequency, periodic intensity distribution.

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

Instead of individual laser pulses, the laser can also provide laser bursts, with each

Burst involves the emission of several laser pulses. For a certain time interval, the Emitting the laser pulses very closely, at intervals of a few picoseconds to nanoseconds, one after the other. The laser bursts can be GHz bursts in particular, where 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, whereby the time interval between the laser pulses can be between 10ns and 50ns. A burst can also comprise between 30 and 300 laser pulses, whereby the time interval between the laser pulses can be between 100ps and 1000ps.

The repetition rate of the laser pulses and/or the 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, for example, more than 1000 pulses per second or more than 10,000 pulses per second are emitted by the laser.

The pulse energy of the laser pulses can be greater than 1 pJ, for example 2pJ or 2mJ.

The diameter of the laser beam provided by the laser can be larger than 0.1 mm, for example 1 mm or 15 mm.

The laser beam of the laser first passes through the hologram. Such a hologram is designed to modulate the laser beam. In particular, this can mean that the phase of the laser beam is modulated and the laser beam is converted into a large number of partial laser beams, whereby each partial laser beam can have 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.

The partial laser beams begin to interfere with each other after the hologram and, through a periodic continuation of the phase manipulation, form a regular interference pattern that can form in the near field immediately after the hologram.

Because all partial laser beams are generated by the same hologram, the differences in the path lengths of the partial laser beams are not a problem. The pulses that run in the partial laser beams can therefore easily interfere with each other, regardless of the pulse length.

The partial laser beams are introduced into or onto the material through the imaging optics, thereby providing a processing beam. The energy of the processing beam is absorbed or partially absorbed in the material, for example through linear interactions or non-linear interactions, in particular through multiphoton processes. The focus of the partial laser beams that form the processing beam can be on or in the workpiece in the direction of beam propagation. The focus is on the workpiece if the focal plane coincides exactly with the surface of the workpiece. The focus is in the workpiece if the focal plane is above or below the surface in the direction of beam propagation, while the surface is still being processed. In particular, the focus position can be within ten times the Rayleigh length from the surface.

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.

In particular, the term "focus" can generally be understood as a targeted increase in intensity, whereby the laser energy converges in at least one "focus zone". In the case of several focus zones, these are preferably located in one focal plane.

In the following, the term "focus" is used independently of the beam shape actually used and the methods for bringing about an intensity increase. Focusing can also influence the location of the at least one focus zone along the beam propagation direction. For example, the at least one focus zone can be quasi point-shaped and have a Gaussian intensity cross-section, as provided by a Gaussian laser beam. The at least one focus zone can also be linear or rectangular, or have the shape of an Airy distribution. Furthermore, other more complex beam shapes are also possible, the focus position of which extends in three dimensions, such as a multi-spot profile of Gaussian laser beams and/or non-Gaussian intensity distributions.

Due to the energy of the processing beam absorbed in the material in the at least one focus zone, the material heats up according to the intensity distribution of the processing beam and/or changes into a temporary plasma state due to the electromagnetic interaction of the processing beam with the material.

In addition to linear absorption processes, non-linear absorption processes can also be used, which are made accessible by using high laser energies or laser intensities. The material is modified by the processing beam, particularly in the at least one focus zone, since the intensity of the laser beam is greatest there. In particular, this can result in part of the material being released from the composite of the workpiece material, for example by melting or evaporating. This means that there are no significant differences in the interaction between the processing beam and the material to be processed. For the material of the workpiece to be machined, known machining processes are possible, such as laser drilling, percussion drilling, laser ablation, blasting or compaction.

The modifications to the workpiece by the processing beam are called material modifications. A material modification can be created with a laser pulse or a laser burst. Such a material modification is caused by the evaporation of the workpiece material on the surface by the irradiated laser intensity. The material of the workpiece is evaporated in particular where the intensity of the processing beam exceeds a critical, material-specific processing threshold. Accordingly, the form and shape of the processing beam, in particular the intensity distribution of the processing beam in the focal plane, are crucial for the form and shape of the material modification.

Before hitting the hologram, the laser beam has, for example, a Gaussian beam profile or a super-Gaussian profile. In particular, the laser beam can also have a super-Gaussian-like profile with raised edges or a ring profile.

A certain spatial area is formed around the focus zone in which the laser energy is above the critical processing threshold. In other words, in the intensity distribution of the processing beam in the focus there is an iso-intensity area within which the material can be vaporized. This iso-intensity area thus determines the form and shape 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, so that an essentially rectangular cross-section of the material modification results in the plane perpendicular to the material surface. For example, such a material modification can also have a uniform depth.

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 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, quartz glass, or an aluminosilicate glass.

The hologram is designed to impose a regular intensity distribution on the incoming laser beam in the focal plane as a processing beam. A regular intensity distribution enables the workpiece to be processed in a regular manner. The regular intensity distribution generated by the hologram in the focal plane enables particularly homogeneous and regular material modifications to be produced using a particularly simple optical concept, even without classic interferometer structures. In particular, there is no need to bring spatially separated partial laser beams into alignment and interference within their coherence time, as the hologram already provides the interference pattern.

The hologram can be designed to modulate the phase of the partial laser beams.

A modulation of the phase can in particular mean a regular or periodic change in the phase of the laser beam. This can result in a regular intensity distribution in the focal plane.

Such regular intensity distributions can, for example, consist of local intensity maxima distributed on a grid. Furthermore, the local intensity maxima can have a line geometry or a hexagonal geometry or a circular or elliptical geometry.

A grid describes the regular arrangement of the local intensity maxima. Typically, a grid can be described by specifying a unit cell. For example, the grid can have a cubic unit cell in which the local intensity maxima lie on the corners of a square. However, each local intensity maximum can have the shape of a line, a hexagon, an ellipse or another geometric figure.

The hologram can be a reflective or transmissive hologram. In other words, the hologram can be designed to transmit the laser beam in transmission or in reflection from the laser to the imaging optics. For example, the hologram can transmit the incident laser beam so that the laser beam propagates through the hologram and is modulated in the process. For example, the laser beam can be modulated on the hologram so that the laser beam does not penetrate the hologram but is reflected by it. For example, the hologram can be a mirror that is not flat but has a regular pattern.

The hologram can have a phase pattern, in particular a binary phase pattern, which is designed to impart a location-dependent phase difference to the incoming laser beam.

The number of different phase shifts that can be generated with the hologram is determined by the so-called phase quantization of the hologram. With a phase quantization of 2, the hologram has 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 hologram of four, four different phase shifts can be generated, for example 0°, 90°, 180°, 270°. However, it is also possible for the hologram to enable, for example, 8 or 16 different phase shifts between the partial laser beams.

For example, a first modulation region of the hologram can have a first material thickness and a second modulation region can have a second material thickness. If the hologram 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, partial laser beams adjacent to the modulation regions have a phase difference of 180°.

However, it is also possible for the laser beam to be transmitted through a hologram of different thicknesses, with the modulation areas of different thicknesses providing optical path lengths of different lengths. If the optical path lengths differ by half a wavelength, the partial laser beams have a phase difference of 180°.

The phase pattern of the hologram can be expressed in one or two dimensions.

A phase pattern in one dimension produces a regular phase pattern in one direction in the focal plane. A phase pattern in two dimensions produces a regular phase pattern in two different directions in the focal plane. For example, a one-dimensional phase pattern can look like zebra stripes.

For example, a two-dimensional phase pattern can look like a checkerboard pattern or like concentric rings.

The regular phase modulation can be realized by periodically continuing the phase modulation of a phase unit cell. In other words, the phase pattern is created by a periodic continuation of a phase unit cell.

This phase unit cell can be continued on a Cartesian grid or a hexagonal grid, for example. Furthermore, one-dimensional Cartesian periodic continuations are also possible, for example line grids. Periodic continuations in the radial direction are also conceivable.

The phase modulation of a phase unit cell of the hologram can have the function of a lens, for example an asphere, a sphere or an axicon in a convex or concave design. The phase modulation can have a period of a sinusoidal oscillation or a rectangular oscillation or a sawtooth oscillation. Furthermore, any phase modulation of a unit cell is conceivable.

In other words, each phase unit cell provides the optical function of an asphere through phase modulation. The various “aspheres” or phase unit cells are arranged on a grid.

A periodic continuation of a phase unit cell can therefore also mean that the phase unit cells are placed next to one another in one or two dimensions. For example, the phase unit cell can have the function of a lens. By periodically continuing such a unit cell, one arrives at an array of lenses that lie, for example, on the corners of a rectangle or a triangle.

The size of a phase unit cell can, for example, be between 0.01 mm and 5 mm. The size can indicate the maximum extension of the unit cell.

The hologram can be a spatial light modulator or a diffractive optical element. In addition, the hologram can be realized as a freeform optic or component, where the height profile of a unit cell is produced as a continuous profile.

Furthermore, the hologram can be a so-called geometric phase hologram, in which the phase of the light is modulated depending on the polarization state. Such geometric phase holograms can be written via fs-induced nanostructures in quartz glass, see, for example, Kim, Jihwan, et al. "Fabrication of ideal geometric-phase holograms with arbitrary wavefronts." Optica 2.11 (2015): 958-964.

A spatial light modulator can be, for example, a nanograting or a hybrid element, which can impose a defined phase distribution on the laser beam through their inherent structure or design. For example, a light modulator can also be a spatial light modulator whose cells or pixels influence the laser beam through adjustable birefringent properties. The spatial light modulator can also be a digital micromirror device.

A diffractive optical element is designed, similar to a light modulator, to influence the incident laser beam in two spatial dimensions in one or more properties. In contrast to 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, whereby the laser beam takes on the desired beam shape through diffraction.

The device can have a feed device. A feed device can be designed to move the laser beam, in particular the processing beam, and the workpiece relative to one another with a feed, wherein the feed device preferably comprises a scanner device and/or an axis device, wherein the scanner device preferably comprises an AOM (acoustic optic modulator) and/or a galvano scanner and/or a polygon scanner.

Movable relative to one another means that the processing beam can be moved translationally relative to a stationary workpiece and the workpiece can be moved relative to the processing beam, or both the workpiece and the processing beam move. This means that the regular intensity distribution of the processing beam can be placed at different locations on the workpiece in order to introduce laser pulses. The laser pulses lie in particular on 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 workpiece surface.

For example, the processing beam can be moved along with a feed while the laser pulses are emitted into or onto the workpiece, so that the They can be arranged in regular intensity distributions or even overlapped to enable uniform and flat processing of the workpiece.

The axis device can be used, for example, to move the workpiece mechanically, while a scanner device moves the processing beam over the workpiece. In particular, the axis device can be an XYZ table with stepper motor control. However, the axis device can also be designed with piezo adjustments in order 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.

In an acousto-optical deflector, an alternating voltage is applied to a piezo 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 as 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 is thereby at least partially deflected at an angle to its original beam propagation direction. The grating constant of the diffraction grating and thus the deflection angle depend, among other things, on the wavelength of the acoustic wave and thus on the frequency of the applied alternating voltage.

Electro-optical deflectors are based on prisms made of electro-optical crystals. Applying a voltage changes the refractive index of the electro-optical crystal, so that the path of the laser beam through the prism changes. The spatial statistical distribution with an electro-optical and/or acousto-optical deflector can be carried out at a clock rate of over 1 MHz. Accordingly, several million repositionings of the laser pulse can take place per second. In particular, the electro-optical and/or acoustic deflectors can be used to reposition the laser pulses with individual pulse precision, so that each individual laser pulse is introduced at a different location in the material.

In a galvano scanner, a rotating mirror is used to reposition the laser beam with high accuracy and repeatability. In particular, 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.

The feed device makes it possible in particular to change the position of the processing beam relative to the workpiece, so that successively emitted laser pulses process the workpiece at different locations. Accordingly, the The processing beam covers the entire surface of the workpiece and thus carries out surface material processing.

The imaging 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 hologram, 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 which corresponds to the sum of the focal lengths of the first lens and the second lens.

Overall, positioning the components in this way makes it possible to create a so-called 4f optic. This makes it possible to transfer the modulated light of the hologram, in particular possible location and angle deviations of the laser beam, into a corresponding imaging plane. This can, for example, make it possible to enlarge or reduce the regular intensity distribution, so that a larger or smaller area of the workpiece can be processed in the focal plane. In particular, by reducing the regular intensity distribution, the laser power can be concentrated on a smaller area, so that material processing is also possible with low-power laser systems. For example, the first and second lenses can have an aperture ratio of f100.

The focusing optics can comprise a cylindrical lens that is designed to generate a line-shaped, regular intensity distribution on the workpiece. In particular, the first lens of the focusing optics can be a cylindrical lens that is designed to generate an intensity-modulated, line-shaped, regular intensity distribution on the workpiece.

Because the focusing optics include a cylindrical lens, the regular intensity distribution of the laser beam in the focal plane can be stretched in one direction. For example, the cylindrical lens has an aperture ratio of f200 (focal length f=200mm) in one direction, while it has no focal length in a direction perpendicular to this. In particular, the cylindrical line can generate a linear, regular intensity distribution in the focal plane. This also means that the energy of the laser beam is only distributed in one dimension, so that a high power density or a high intensity is provided in the focal plane.

This makes it possible to achieve appropriate material processing even with low-power laser systems. The imaging optics can have a reduction factor M with which the regular intensity distribution in the focal plane is imaged. The reduction factor can be between 1.1 and 40.

In particular, the reduction factor of the imaging optics can be used to create a focal plane with a particularly high intensity in or on the workpiece.

The device can have a beam shaping device. A beam shaping device can be designed to impose a beam shape on the laser beam, in particular to impose a flat-top beam shape, wherein the beam shaping device is preferably arranged in front of the hologram.

This means that, for example, each partial laser beam can be given a corresponding beam shape.

A beam shaping optic can be, for example, a commercially available Pi-Shaper, which imposes a flat-top beam shape on the laser beam. In comparison to a Gaussian laser beam, a flat-top laser beam has a homogeneous intensity in the beam cross-section, which drops rapidly after the beam diameter is reached. 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.

A flat-top laser beam provides a particularly simple beam shape. For example, flat-top laser beams can be used particularly easily to create several 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.

The device can have a first telescope that is designed to adjust the beam diameter of the laser beam on the beam shaping device. In particular, the diameter of the shaped laser beam can thereby be adjusted.

The device can have a second telescope that is designed to adjust the beam diameter of the laser beam on the hologram. This makes it possible to adjust the size of the regular intensity distribution on the workpiece in addition to the imaging optics.

In general, surface structuring can change the optical properties of the material, such as color or gloss, transmittance, Absorption level or reflection level. It is also possible that the surface structuring changes the tribological properties, i.e. properties relating to wear, friction or lubrication of surfaces. It is possible that the surface texturing changes the liquid-repellent properties of the surface or the anti-fog properties of the workpiece.

Surface texturing can change the haptic properties of the workpiece.

Other properties that can be improved or at least changed include surface hardness, weather resistance, corrosion protection, chemical resistance, etc. For example, the chemical reactivity of the workpiece can also be changed, in particular increased. For example, roughened surfaces and the associated increase in the surface area of the workpiece can enable more efficient reactions in batteries.

The main advantage of the described device for surface texturing of workpieces is that the typically used interferometer optics, which require a lot of effort for beam splitting, path length adjustment and beam merging, are replaced by a much simpler optics concept. The interference pattern required for processing is realized by using the hologram in the beam path, behind which the said interference pattern is directly generated by the periodic phase modulation. A classic beam splitting, as described for example in EP 3735332 B1, i.e. a complete separation of the partial laser beams including the necessary path length adjustment to comply with the interference condition, for example by means of so-called "delay stages", is not necessary.

Another advantage concerns the directly proportional scaling of the processing speed, in this case the processed area per time interval. The spatial illumination of the hologram, i.e. the diameter of the raw beam or the beam-shaped laser beam, determines the diameter of the regular intensity distribution of the surface structured on the workpiece by the interference pattern without feed.

A telescope with variable or stationary magnification can be used in front of the hologram. Another way to adjust the diameter of the interference pattern on the workpiece is to choose the magnification factor, i.e. the ratio of the focal lengths of the lenses that make up the 4f setup mentioned above.

The diameter of the interference pattern on the workpiece can be between 0.05mm and 100mm.

In the case of forming an intensity-modulated line focus, the line length on the workpiece can be between 0.2 mm and 1000 mm.

The device is particularly suitable for illuminating large areas simultaneously with the intensity pattern. In conjunction with a feed device, for example, large area rates can also be achieved.

The above object is further achieved by a method for machining a workpiece with the features of claim 12. Advantageous further developments of the method emerge from the subclaims as well as the present description and the figures.

Accordingly, a method for processing a workpiece, in particular for imparting surface 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 guided through a hologram, wherein the laser beam is converted into a plurality of partial laser beams and these interfere with one another, wherein the partial laser beams are focused as a processing beam with imaging optics in a focal plane on or in the workpiece, wherein the workpiece is exposed to the processing beam and is thereby processed. According to the invention, a regular intensity distribution is impressed on the processing beam by the hologram in the focal plane.

The workpiece and the processing beam can be moved relative to each other along a feed trajectory. This makes it possible to process larger areas of the workpiece surface.

The regular intensity distributions of different, especially successive laser pulses can overlap. In this sense, the material modifications that are created on or in the workpiece can also overlap.

By overlapping the regular intensity distributions, a continuous machined surface of the workpiece can be formed. This has the particular advantage that regular patterns, which for example result from a uniform offset of the machining beam with the feed rate between two laser pulses can be avoided.

In particular, flat sections of the workpiece can be machined. It is also possible to machine the entire surface of the workpiece.

In particular, the regular intensity distributions can cover a surface-wide section of the workpiece. A surface-wide section means that a contiguous area with the extent of at least two regular intensity distributions has been processed, while full-surface processing of the surface of the workpiece means processing at least the side facing the processing beam. This enables particularly simple surface-wide processing of the material.

The size of the regular intensity distribution of the processing beam in the focal plane can be determined by the size of the illumination of the hologram. This enables particularly simple and flexible control of the material processing.

Short description of the characters

Preferred further embodiments of the invention are explained in more detail by the following description of the figures.

Figure 1 is a schematic representation of the device of an embodiment;

Figures 2A, B, C are schematic representations of the operation of a beam shaping device;

Figures 3A, B, C, D, E show schematic representations of different holograms and corresponding regular intensity distributions after passing through the imaging optics;

Figure 3F schematic representation of a regular intensity distribution in different focal planes;

Figure 4 is a schematic representation of the regular intensity distribution after passing through the imaging optics when a cylindrical lens is used as the first lens; and

Figure 5 is a schematic representation of the method according to the invention. Detailed description of preferred embodiments

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

Figure 1 shows an embodiment of the proposed device.

The device has a laser 1 which provides a laser beam 10. This laser beam 10 is received by a hologram 2, converted into a plurality of partial laser beams and then caused to interfere. This interference pattern is then imaged as a processing beam 14 by an imaging optics 3 in the focal plane on or in a workpiece 4.

The intensity distribution of the processing beam 12 in the focal plane is a regular focus distribution I. As a result, regularly arranged material modifications are generated in the focal plane on or in the workpiece 4, which provide a functionalization of the surface of the workpiece 4.

In the embodiment shown, the device additionally has a beam shaping device 6 for the laser beam 10. The laser beam 10 is guided through the beam shaping device 6 and thereby shaped. For example, the laser beam 10 of the laser 1 is thereby converted into a flat-top-shaped laser beam with a rectangular or elliptical geometry. The beam shaping device can be implemented as a field mapper, e.g. by a so-called pi-shaper, see 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 the embodiment shown, an imaging optics 3 is provided, which is, for example, a 4f imaging optics. The imaging optics 3 comprises a first lens 30 and a second lens 32. The first lens 30 is at a distance of the first focal length f1 of the first lens 30 from the hologram 2, while the second lens 32 is at a distance of the sum of the two focal lengths f1 and f2 of both lenses 30, 32 from the first lens 30. The focal plane is then located approximately at a distance f2 in the beam propagation direction behind the second lens 32. Through this so-called 4f imaging in the focal plane, the modulated laser beam of the hologram can be enlarged or reduced. It is also possible for the first lens 32 to be designed as a cylindrical lens in order to image the interference pattern in only one dimension. This makes it particularly easy to generate interference-modulated line foci in order to apply them to the workpiece.

In a further embodiment of the device, it is possible for it to comprise a scanner which is designed as a galvano scanner or as an AOM (not shown). The second lens 32 typically performs an angle-to-location transformation of the laser beam 10, so that two partial laser beams 12 running at different angles in front of the second lens 32 are imaged behind the second lens 32 in two different locations in the focal plane. Accordingly, it is particularly advantageous to position the scanner which deflects the laser beam at a distance of the second focal length f2 in front of the second lens (not shown). The angular deflection by the scanner is thus translated into a location deflection in the focal plane.

In the embodiment shown, the device additionally has a first telescope 7 in front of the beam shaping device 6 and a second telescope 7' after the beam shaping device 6.

The first telescope 7 can be designed to adjust the beam diameter of the incident laser beam on the beam shaping device 6. By adjusting the beam diameter of the laser beam 10 that hits the beam shaping device 6, the size of the intensity distribution of the outgoing laser beam can be adjusted particularly easily.

The second telescope 7' can be set up to adjust the size of the illuminated area on the hologram 2. This makes it possible, in particular, to adjust the size of the regular intensity distribution on the workpiece 4 in addition to the imaging optics 3. The second telescope 7' can, for example, be designed as a simple telescope with two lenses according to Galileo, or as a flexible telescope with three lenses and thus with variable magnification and divergence adjustment.

Figure 2A shows schematically the functioning of a flat-top beam former 6. The laser beam 10 running on the optical axis, which hits the beam forming device 6, has a first diameter, which relates, for example, to the drop in intensity to 1/e ^A 2 of the intensity maximum of the laser beam 10 or to its beam diameter, which was determined using the method of second moments, see ISO11146 1/2/3. In the beam forming device 6, the laser beam 10 can be reshaped by 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 can be separated from the optical axis, so that although there is a lower maximum intensity on the optical axis, there is a uniform intensity profile over a larger area. The partial laser beams can then be parallelized again, whereby the outgoing flattop laser beam 10' is formed. The diameter of the outgoing flattop laser beam 10' can have a larger or smaller or the same diameter as the incident Gaussian laser beam 10.

Depending on the beam diameter of the incident 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 2B, the incident laser beam 10 has a larger diameter than in Figure 2A. As a result, edge elevations form on the intensity profile of the outgoing flat-top laser beam 10' after the beam shaping device 6.

In Figure 2C, the incident laser beam 10 has a smaller diameter than in Figure 2A. As a result, the outgoing flattop laser beam 10' has a lower edge steepness.

Figures 3A, B, C, D, E show the phase modulations of the holograms 2 and the corresponding intensity distributions I with which the workpiece 4 can be exposed.

The hologram 2 in Figure 3A has phase unit cells that are arranged on a Cartesian grid. The phase modulation of a phase unit cell has a lens-like shape. Immediately behind the hologram 2, an intensity distribution I is formed, which is imaged onto the workpiece 4 by the imaging optics 3. As can be seen in the detailed section, the intensity distribution is firstly regular and secondly the intensity distribution has intensity maxima that are also arranged along a Cartesian grid.

Figure 3B shows a similar situation as in Figure 3A. Here, the distance between the unit cells is increased with lens-like modulation. Consequently, the resulting intensity pattern shows local intensity maxima with larger distances.

Figure 3C shows phase unit cells that are periodically continued in one dimension and whose phase modulation has a one-dimensional dependence. Here, a sine function is realized in the x-direction. The resulting intensity distribution I has local intensity maxima in the form of lines. Figure 3D shows a hexagonal array of phase unit cells with lens-like phase modulation. The resulting intensity pattern exhibits local intensity maxima at a hexagonal array.

Figure 3E also shows a hexagonal arrangement of unit cells with lens-like phase modulation. The resulting regular intensity distribution exhibits local intensity maxima at a hexagonal arrangement.

Figure 3F shows another effect that occurs with the proposed device. It shows a regular intensity distribution as in Figure 3E, but at different propagation distances. Different propagation distances result in a different z-distance between the imaging optics and the workpiece. The basic structure - i.e. the arrangement of the intensity maxima - of the regular intensity distribution is retained at different propagation distances. However, the shape of the local intensity maxima changes. For example, at all propagation distances z1 to z4, the local intensity maxima are arranged on a rhombic grid.

However, by changing the focus position, the shape of the local intensity maxima can be adjusted and thus different surface modifications can be introduced onto the workpiece 4.

Figure 4 shows the regular intensity distribution when a cylindrical lens is used as the first lens 30 of the imaging optics 3. The hologram 2 used was that of Figure 3C. The cylindrical lens 30 produces a linear intensity distribution that has regularly arranged maxima along its long axis.

Figure 5A shows a corresponding method for processing a workpiece. Laser pulses 100 are emitted with a laser 1, which form a laser beam 10. The laser beam 10 is guided through a hologram 2 and is focused as a processing beam 14, for example reduced in size, onto or into the surface of the workpiece 4 using imaging optics 3. The processing beam 14 strikes the workpiece 4 in the focal plane, thereby processing it. The intensity distribution of the processing beam 14 has regularly arranged local intensity maxima, so that the surface of the workpiece 4 can be functionalized, for example.

The workpiece 4 can be displaced relative to the processing beam 14 along a trajectory 50 using a feed device 5, so that the regular intensity distribution I of the processing beam 14 covers the entire surface or part of the surface of the workpiece 4 successively. The machining of the workpiece 4 can be carried out by overlapping material modifications. This means in particular that a first laser pulse with a regular intensity distribution I is introduced into the workpiece at a first location X1, while a second laser pulse with the regular intensity distribution I is introduced at a second location X2 of the workpiece.

Figure 5B shows that the regular intensity distributions I introduced one after the other can overlap in order to process the workpiece as evenly as possible. In particular, the individual material modifications near the edge that are generated by the intensity distributions introduced one after the other overlap. With a repetition rate of 10 kHz of the laser 1 and a diameter of the regular intensity distribution of 1 mm, the feed rate can be up to 10 m/s, for example, so that the surface of a workpiece 4 can be processed very quickly.

Where applicable, all individual features shown in the embodiments can be combined and/or exchanged without departing from the scope of the invention.

List of reference symbols

1 lasers

10 Laser beam

12 Partial laser beam 14 Processing beam

100 laser pulses

2 Hologram

3 Imaging optics

4 Workpiece 5 Feed device

50 Trajectory

6 Beam shaping device

7 Telescope

Claims

Expectations

1 . Device for processing a workpiece (4), in particular for imparting a surface functionalization, by means of laser pulses (100) of a laser beam (10), comprising a laser (1), a hologram (2) and an imaging optics (3), wherein the laser (1), in particular a short-pulse laser or an ultra-short-pulse laser, is designed to provide the laser beam (10) with the laser pulses (100) to the hologram (2), wherein the hologram (2) is designed to receive the laser beam (10), to convert the laser beam (10) into a plurality of partial laser beams (12) and to cause them to interfere and to pass them on to the imaging optics (3), and wherein the imaging optics (3) is designed to receive the partial laser beams (12) of the hologram (2) and to focus them as a processing beam (14) in a focal plane on or in the workpiece (4), wherein the workpiece (40) is provided with the processing beam (14) and is processed thereby, characterized in that the hologram (2) is further configured to impart a regular intensity distribution (I) to the processing beam (14) in the focal plane.

2. Device according to one of the preceding claims, characterized in that the hologram (2) is further configured to modulate the phase of the partial laser beams (12).

3. Device according to one of the preceding claims, characterized in that the regular intensity distribution (I) has a line geometry and/or a hexagonal geometry and/or a circular geometry and/or an elliptical geometry.

4. Device according to one of the preceding claims, characterized in that the hologram (2) is a reflective or transmissive hologram.

5. Device according to one of the preceding claims, characterized in that the hologram (2) has a phase pattern (20), in particular a binary phase pattern, wherein the phase pattern (20) is designed to impart a location-dependent phase difference to the laser beam (10).

6. Device according to claim 5, characterized in that the phase pattern (20) is created by a periodic continuation of a phase unit cell (200).

7. Device according to claim 5 or 6, characterized in that the size of a phase unit cell (200) is between 0.01 mm and 5 mm.

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

9. Device according to one of the preceding claims, characterized by a feed device which is designed to move the processing beam (14) and the workpiece (4) relative to one another with a feed (V), wherein the feed device preferably comprises an axis device and/or a scanner device, wherein the scanner device preferably comprises an acousto-optical modulator and/or a galvo scanner and/or a polygon scanner.

10. Device according to one of the preceding claims, characterized in that the imaging optics (3) have at least a first lens (30) with a first focal length (f1) and a second lens (32) with a second focal length (f2), wherein the first lens (30) is arranged at a distance of the first focal length (f1) from the hologram (2), wherein the second lens (32) is arranged at a distance of the second focal length (f2) 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 (f1, f2) of the first lens (30) and the second lens (32), wherein the imaging optics (3) preferably have a reduction factor M between 1.1 and 40.

11. 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 hologram (2).

12. Device according to claim 11, characterized by a first telescope (7) which is designed to adjust the beam diameter of the laser beam (1) to the beam shaping device (6)

13. Device according to one of the preceding claims, characterized by a second telescope (7') which is adapted to adjust the beam diameter of the laser beam (1) on the hologram (2).

14. Method for processing a workpiece (4), in particular for imparting a surface functionalization, by means of laser pulses (100) of a laser beam (10) of a laser (1), in particular a short-pulse laser or an ultra-short-pulse laser, wherein the laser beam (10) is guided through a hologram (2) and is converted by the hologram (2) into a plurality of partial laser beams (12) and these interfere with one another, wherein the partial laser beams (12) are focused with an imaging optics (3) as a processing beam (14) in a focal plane on or in the workpiece (4), wherein the workpiece (4) is exposed to the processing beam (14) and is thereby processed, characterized in that a regular intensity distribution is impressed on the processing beam (14) by the hologram (2) in the focal plane.

15. Method according to claim 14, characterized in that the processing beam (14) and the workpiece (4) are displaced relative to one another by means of a feed device (5).

16. Method according to claim 14 or 15, characterized in that the machining of the workpiece (4) is carried out by overlapping regular intensity distributions (I) of the machining beam (14).

17. Method according to one of claims 14 to 16, characterized in that the size of the intensity distribution (I) in the focal plane is determined by the size of the illumination of the hologram (2).