Method for producing recesses on surface of transparent material

Abstract

The invention relates to a method for producing recesses (2) on a surface of a transparent material (1) by means of laser pulses of a short-pulse laser, in which method at least one recess (2) is produced by means of a single laser pulse (300) or a single laser pulse train.

Description

Technical Field

[0001] The present invention relates to producing dimples on the surface of a transparent material. Background Art

[0002] It is well known that during laser processing, material can be removed from a component by vaporizing the material due to the intense light-matter interaction in the focal zone of the laser beam. The resulting structural depression is called a recess.

[0003] It is also known that by means of the successive interaction of the same material area with at least two laser pulses, so-called laser-induced periodic surface structures can also be produced. English: laser-induced periodic surface structures, hereinafter referred to as LIPSS).

[0004] In this respect, recesses and LIPSS are suitable for the functionalization of component surfaces, wherein the visual properties, wetting properties and tribological properties can be influenced in particular.

[0005] A method for producing a structured surface on a substrate is known from DE 10 2017 006 358 A1, in which surface structures having dimensions in the submicrometer range are produced by treatment with an intense pulsed laser beam.

[0006] A method for machining a sliding component is known from EP 3 270 016 B1, wherein the sliding component has a pair of sliding parts, and the sliding component has a plurality of recessed parts formed by irradiation with ultrashort pulse laser light generated by an ultrashort pulse laser oscillator.

[0007] A method for making a glass surface oleophobic / hydrophobic is known from US 2018 / 0118612 A1, in which a femtosecond UV excimer laser is applied to the glass surface to vaporize parts of the glass surface and form nanostructures in the glass surface without significantly reducing the optical clarity of the glass surface. Summary of the invention

[0008] Based on the known prior art, the object of the present invention is to provide an improved method.

[0009] This object is achieved by a method having the features of claim 1. Advantageous developments emerge from the dependent claims, the description and the drawings.

[0010] It is therefore proposed to produce depressions in the surface of the transparent material by means of laser pulses of a short-pulse laser, wherein at least one depression is produced by means of a single laser pulse or a train of single laser pulses.

[0011] The transparent material of the component can be a material such as 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. Exemplarily, the material can be a silicon wafer. In particular, the material can be a layer system, wherein each layer can be selected from the group of metals, polymers, plastics or semiconductors. In particular, the material can also be a glass, for example sapphire or quartz glass.

[0012] "Transparent" may mean that the material is optically transparent, i.e., transparent to wavelengths visible to the human eye. For example, the material may transmit more than 80%, or more than 85%, or more than 90%, or more than 95%, or more than 99% of visible light. However, "transparent" may also mean that the material is transparent to the wavelength of the processing laser.

[0013] A short-pulse laser provides laser pulses of a laser beam, wherein the individual laser pulses form a laser beam in a beam propagation direction.

[0014] The pulse duration of the laser pulses may be between 300 fs and 10 ps or between 100 ps and 100 ns.

[0015] In the range between 300 fs and 10 ps, ​​LIPSS can be produced particularly easily, while pulse durations between 100 ps and 100 ns are particularly suitable for producing recesses using UV lasers.

[0016] The wavelength of the laser pulses may be between 300 nm and 3000 nm, preferably between 900 nm and 2200 nm.

[0017] This enables the selection of a laser wavelength at which the material is transparent, allowing the indentations and LIPSS to be introduced into the material through nonlinear interactions. Additionally, the short pulse duration prevents unnecessary heating of the material, which counteracts the formation of LIPSS.

[0018] Instead of individual laser pulses, the laser can also provide laser pulse trains, wherein each pulse train (burst) comprises the emission of a plurality of laser pulses. In this case, for a specific time interval, the laser pulses can be emitted very closely one after another at intervals of a few picoseconds to a few nanoseconds. In particular, the laser pulse train can be a GHz pulse train, wherein the sequence of continuous laser pulses of the respective pulse train occurs in the GHz range.

[0019] For example, a pulse train may contain 2 to 10 laser pulses, wherein the time interval between the laser pulses may be between 10 ns and 50 ns.

[0020] However, the pulse train may also contain 30 to 300 laser pulses, wherein the time interval between the laser pulses may be between 100 ps and 1000 ps.

[0021] For example, the length of the laser pulse can be between 100ps and 100ns, in particular between 1ns and 20ns, wherein the wavelength can be between 300nm and 550nm, in particular 355nm, wherein the repetition frequency of the laser pulse can be between 10kHz and 100kHz, in particular between 10kHz and 50kHz, wherein the laser pulse can have an energy between 60μJ and 300μJ, and 1 to 4 pulses can be emitted at each point.

[0022] For example, the length of the laser pulse can be between 200fs and 1000fs, in particular between 300fs and 450fs, wherein the wavelength can be between 900nm and 2300nm, in particular 1030nm, wherein the repetition frequency of the laser pulse can be between 10kHz and 400kHz, wherein the laser pulses are emitted in laser pulse trains, wherein each laser pulse train can contain 2 to 4 laser pulses, wherein the laser pulse train can have an energy between 100μJ and 400μJ, and the numerical aperture can be between 0.01 and 0.2, in particular 0.08.

[0023] In particular, the laser pulses of a laser pulse train act together on the material via a rapid pulse sequence.

[0024] The laser pulses are introduced into the material, wherein the energy of the laser beam is at least partially absorbed in the material, for example by nonlinear interactions, in particular by multiphoton processes.

[0025] Here, the focal point of the laser beam can be located above the surface of the material to be processed in the beam propagation direction, or below the surface in the volume of the material to be processed. The focal position can also be located exactly on the surface of the material to be processed. In particular, the focal position can be within ten times the Rayleigh length from the surface, wherein the Rayleigh length is the distance along the optical axis that the laser beam needs to travel from the beam waist or focus until its cross-sectional area doubles.

[0026] In particular, the term "focus" can generally be understood as a targeted increase in intensity, wherein the laser energy is concentrated in a "focal region". In particular, the term "focus" is therefore used below without taking into account the actual beam shape used and the method used to cause the intensity increase. By "focusing", it is also possible to influence the position of the intensity increase along the beam propagation direction. For example, the intensity increase can be almost point-shaped and the focal region can have a Gaussian-shaped intensity cross-section, as provided by a Gaussian laser beam. The intensity increase can also be linear, wherein a Bessel-type focal region is generated around the focal position, as can be provided by a non-diffracting beam. In addition, other more complex beam shapes are also possible, whose focal position extends in three dimensions, such as a multi-point profile of a Gaussian laser beam and / or a non-Gaussian intensity distribution.

[0027] Due to the energy absorbed from the laser beam, the material heats up, depending on the intensity distribution of the laser, and / or is transformed into a temporary plasma state due to the electromagnetic interaction between the laser and the material. In particular, in addition to linear absorption processes, nonlinear absorption processes can also be used, which become achievable by using high laser energies or laser intensities. The material is thus modified in particular at the focus of the laser, since this is where the intensity of the laser beam is greatest. In particular, this can achieve that parts of the material can be released from the material composite, the material for example melting or being evaporated. Thus, with regard to the interaction between the laser and the material to be processed, processing processes known per se are possible, these methods being known, for example, as laser drilling, percussion drilling or laser ablation.

[0028] By the interaction of a single laser pulse or a single laser pulse train with the material to be processed, at least one recess is produced in the surface of the transparent material.

[0029] The recess is produced by vaporizing the material on the surface due to the intensity of the irradiating laser. In particular, the material is vaporized when the intensity of the laser beam exceeds a critical, material-specific processing threshold. Therefore, the shape and form of the laser beam, in particular the beam profile, is crucial for the shape and form of the recess.

[0030] In the simplest case, the laser beam is a Gaussian laser beam with a Gaussian beam profile. There is a certain spatial region around the focus in which the laser energy is above a critical threshold. That is, there is an isointensity surface in the intensity distribution of the laser beam in the focus, within which the material can be vaporized. The shape and form of the recess is generated by this isointensity surface.

[0031] In particular, the recess can thus have an annular, oval or angular, in particular square or rounded cross section in the plane of the material surface, wherein the recess has a depth that increases from the edge to the center. In particular, the cross section of the recess in a plane perpendicular to the surface can also be annular or circular.

[0032] By introducing recesses on the surface of the material, the optical properties of the material can be determined, for example, by scattering light guided through the transparent material at the recesses, so that the material appears diffuse and / or matte. In particular, the recesses on the surface of the material can suppress reflections on the material.

[0033] For example, at least two laser pulses of a laser pulse train can overlap spatially, thereby generating so-called LIPSS. This occurs when an excited plasma state exists in the first recess, and a second laser pulse of the laser pulse train can interact with the first recess so that the heated material orients itself along the electric field of the second laser pulse.

[0034] The combination of recesses and LIPSS can be used to create complex functionalities on the surface of transparent materials.

[0035] For example, the tactile feel or the roughness can be adjusted by the type and shape of the recesses and their distribution on the surface of the material. However, it is also possible to adjust the scattering of light and thus the optical properties of the material.

[0036] However, further functionalization of the surface can be achieved, for example, by the size of the LIPSS. For example, the LIPSS can be used to adjust the wetting properties of the surface, since the LIPSS changes the contact angle between the liquid and the material. In addition, the tribological properties of the material can also be changed and, for example, the sliding properties of the material can be adjusted.

[0037] The combination of recesses and LIPSS enables the surface of transparent materials to be functionalized both optically and mechanically.

[0038] In particular, recesses and LIPSS can be produced particularly efficiently by means of the method.

[0039] Additionally, the laser light may have a linear polarization, for example the polarization degree of the laser beam may be higher than 80%, preferably higher than 95%.

[0040] Due to the high linear polarization, LIPSS can be generated particularly easily in recesses.

[0041] However, the laser beam can also be circularly or elliptically polarized and only produce the recesses.

[0042] The average emitted laser power at the laser output can be between 30 W and 1000 W, preferably between 30 W and 300 W.

[0043] Due to the high average power, for example, a plurality of partial laser beams can be formed from a single laser beam, wherein each partial laser beam can produce its own recess. In particular, this makes it possible to work at high feed rates so that the energy of the laser beam can be distributed over a large area.

[0044] The specified power range also corresponds to commercially available short-pulse lasers, so that the costs of the method can be kept low.

[0045] In a preferred embodiment of the method, the laser pulse duration is between 300 fs and 10 ps at a wavelength between 900 nm and 1200 nm, or between 100 ps and 100 ns at a wavelength between 300 nm and 520 nm, wherein at least one recess is generated by means of a laser pulse train, wherein the laser pulse train comprises 2 to 10 laser pulses and the time interval between the laser pulses is between 10 ns and 50 ns, wherein the polarization degree of the laser light is preferably higher than 80%, and wherein the average emitted laser power at the laser output is preferably between 30 W and 1000 W.

[0046] In another preferred embodiment of the method, the laser pulse duration is between 300 fs and 10 ps or between 100 ps and 100 ns, wherein at least one recess is generated by means of a laser pulse train, wherein the laser pulse train comprises 30 to 300 laser pulses and the time interval between the laser pulses is between 100 ps and 1000 ps, ​​wherein the polarization degree of the laser light is preferably higher than 80%, and wherein the average emitted laser power at the laser output is preferably between 30 W and 1000 W.

[0047] In a particularly preferred embodiment of the method, the laser pulse duration is between 300 fs and 10 ps, ​​wherein at least one recess is generated by means of a laser pulse train, and the laser pulse train comprises 2 to 10 laser pulses, wherein the time interval between the laser pulses is between 10 ns and 50 ns, and the polarization degree of the laser light is higher than 95%, and the average emitted laser power at the laser output is between 30 W and 300 W.

[0048] The photon energy of the laser pulse or laser pulse train is less than the band gap of the material.

[0049] The band gap is the energy distance between the valence band and the energy band of a material, wherein the electrical and optical properties are essentially determined by the size of the band gap.

[0050] If the energy of the laser's photons is less than the band gap, the photons cannot be absorbed by the solid and the material therefore becomes transparent to the laser's wavelength.

[0051] For example, the band gap in quartz glass may be about 9 eV, making light absorption possible only at photon energies above 9 eV. The band gap corresponds to a wavelength of about 137 nm, making quartz glass transparent to lower energy, ie, longer wavelength photons.

[0052] The recess can have a depth between 100 nm and 2000 nm, preferably between 200 nm and 1000 nm.

[0053] This makes it particularly advantageous to adjust the roughness of the surface, wherein excessive weakening of the material can be avoided.

[0054] The recess can have a diameter between 3 μm and 30 μm, preferably between 3 μm and 10 μm.

[0055] This allows the diameter to be adjusted particularly advantageously to the microstructure desired for functionalization.

[0056] The size of the recess may vary from 5% to 80% of the diameter.

[0057] For example, the size variation may be 50% and the diameter of the recess may be 20 μm. The recesses on the surface may then have a diameter between 10 μm and 30 μm.

[0058] LIPSS may have a periodicity between 40 nm and 1000 nm, preferably between 50 nm and 300 nm.

[0059] The periodicity is determined by the distance between two adjacent peaks or valleys in the profile of the LIPSS. The periodicity makes it particularly advantageous to adjust the functionalization of the surface. For example, for the medical field, the LIPSS can have a periodicity of 100 nm, so that the surface is rendered particularly hydrophilic. This means that a surface treated in this way can be used particularly advantageously in endoscopes or laryngoscopes, for example, so that the appropriately treated surface has the effect of repelling liquids and thus enables a clear view of the inside of the body when used, for example, inside the body. In particular, such a functionalized surface is particularly suitable for use in medical devices that enable optical access to the inside of the body.

[0060] In a particularly preferred embodiment, the recesses have a diameter of between 13 μm and 20 μm, wherein the laser-induced periodic surface structure has a periodicity of between 650 nm and 1000 nm.

[0061] The roughness of the transparent part may be between 0.05 μm and 1.5 μm.

[0062] This can produce a particularly high-quality tactile impression of the surface.

[0063] Surface roughness can be defined as the peak-to-valley value, i.e., the distance from the highest protrusion to the lowest depression. However, roughness can also be defined as the standard deviation of the depth of the valleys.

[0064] The surface filling of the surface by means of the recesses can be between 20% and 95%.

[0065] The surface filling of the surface is given by the area ratio of the surface processed by the recesses to the total surface of the transparent material. The surface filling can be adjusted according to the desired roughness or functionalization.

[0066] In particular, when machining a surface, it is also possible to do so continuously or in multiple passes. Recesses are introduced in the embodiment of the present invention, wherein the surface coverage increases continuously while the deformation or smearing of the recesses decreases.

[0067] In particular, at least two recesses can overlap spatially.

[0068] “Overlapping spatially” can mean that the recesses touch at the edges or that the recesses lie partially on top of one another, ie there is a surface intersection of the recesses.

[0069] LIPSS may cover less than 90% of the concavities.

[0070] For example, LIPSS may be located in the center of a recess. For example, a recess may have a diameter of 10 μm, while LIPSS is only present in the surface region with a diameter of 9 μm.

[0071] However, two recesses may also overlap and form a LIPSS only in the spatial overlap.

[0072] The laser beam and the material can be displaced relative to each other by means of a feed device.

[0073] "Displaceable relative to each other" means that not only the laser beam can be displaced translationally relative to the stationary material, but also the material can be displaced relative to the laser beam, or both the material and the laser beam can be moved.

[0074] In particular, this allows the focus of the laser beam to be placed at different locations on the material for the introduction of the laser pulses. For example, the laser spots can be randomly distributed in the material around a feed track, wherein the feed track can be straight or curved. This allows, for example, the laser beam to move with the feed when the laser pulses are emitted into or onto the material.

[0075] The feed device may preferably comprise an axis device and / or a scanner device.

[0076] For example, the axis device can be used to mechanically move the material, while the scanner device is used to move the laser beam over the material. In particular, the axis device can be an XYZ stage with stepper motor control. However, in order to achieve the fastest possible adjustment, the axis device can also be designed with piezoelectric adjustment. In particular, the scanner device can be a galvanometer scanner.

[0077] Processing optics can be used to focus the laser beam onto the surface of the material.

[0078] The processing optics can in particular be a lens or an objective or a telescope. In particular, the processing optics can be arranged behind the optional beam shaping device and in front of the transparent material surface in the beam propagation direction.

[0079] The recesses may be randomly arranged on the surface of the transparent material.

[0080] A random arrangement may occur if the spatial distances between the recesses have random sizes. The spatial distances result from the minimum distance from recess edge to recess edge or the center distance.

[0081] In particular, the spatial frequency distribution of the recesses is derived, for example, from the spatial distribution of the recesses, including their size, by Fourier transformation. The more irregular the distance between the recesses, the greater the bandwidth of the spatial frequency distribution, and the more diffusely the incident beam is reflected by the transparent material.

[0082] In particular, "random arrangement" may mean that the recesses are randomly distributed in the spatial frequency space. By displaying the positions of the recesses in the spatial frequency domain, potential spatial directions along which reflected or transmitted light interference may occur may also be identified in order to optimize the arrangement.

[0083] “Random distribution” may also mean that the spatial distribution of the recesses follows a random distribution, such as a uniform distribution, a Gaussian distribution, a triangular distribution, or other statistical distribution of the recesses on the surface of the transparent material.

[0084] The laser beam can be shaped by means of a beam shaping device into a multi-focus distribution and the surface can be impinged with the multi-focus distribution and thus a plurality of depressions can be produced using a single laser pulse or a single laser pulse train.

[0085] A multifocal distribution is a spatial distribution of individual focal regions, so-called single foci. A multifocal distribution comprises at least two single foci, whereby the single foci are spatially separated from one another. However, the single foci can all lie in one focal plane, so that the single foci are all present in one plane along the beam propagation direction of the laser beam, but have different coordinates on the surface of the transparent material.

[0086] The multi-focal distribution can be provided by a beam shaping device, whereby an incident laser beam can be converted into a plurality of partial laser beams, which are directed to different single focal points. Beam shaping comprises the design of a multi-focal distribution. However, beam shaping can also comprise the design of a single focal point, such as the formation of a Gaussian laser beam or a non-diffracting laser beam.

[0087] For example, the laser may emit 10 mJ of energy per pulse train. For example, the pulse energy for forming the recesses may be 20 μJ, so that about 500 recesses may be produced per pulse train. A typical repetition rate is 30 kHz, which corresponds to an average power of 300 W.

[0088] However, a single pulse can also have an energy of 1 mJ and can also be split by the beam shaping device into 50 partial laser beams, each with an energy of 20 μJ. Each partial laser beam can then be transferred to a single laser focus on the surface of the material, so that each partial laser beam of a single pulse generates a recess.

[0089] In particular, the multifocal point distribution can have an intensity gradient, in particular the individual focal points of the multifocal point distribution can at least partially have different intensities.

[0090] In particular, different laser focuses may have different laser energies. Since the laser energy determines the size of the concave portion via the isointensity surface, concave portions of different sizes may be generated by different distributions of energy in the laser focus.

[0091] The beam shaping device may be an acousto-optic deflector and / or a microlens array and / or a diffractive optical element.

[0092] Diffractive optical elements are configured to affect an incident laser beam in one or more properties in two spatial dimensions. Typically, a diffractive optical element is a specially designed diffraction grating, wherein an incident laser beam is changed into a desired beam shape by diffraction.

[0093] In an acousto-optic 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 as a wave packet or in the form of a standing wave. By periodically modulating the refractive index, a diffraction grating is realized for an incident laser beam. The incident laser beam diffracts at the diffraction grating and is therefore at least partially deflected at an angle to its original beam propagation direction. The grating constant of the diffraction grating and therefore the deflection angle depends on, among other things, the wavelength of the acoustic wave and therefore on the frequency of the applied alternating voltage. Exemplarily, a deflection in the x-direction and the y-direction can therefore be generated by a combination of two acousto-optic deflectors in a deflector unit.

[0094] The acousto-optic deflector may in particular be a polarization-dependent acousto-optic deflector and may therefore be particularly suitable for high performance.For example, the acousto-optic deflector unit may be a quartz-based deflector unit.

[0095] The microlens array comprises an arrangement of a plurality of microlenses. In this case, the microlenses are small lenses, in particular lenses having a typical distance ("pitch") from lens center to lens center of 0.1 mm to 10 mm, preferably 1 mm, wherein each individual lens of the arrangement can have the effect of a normal macro lens. The plurality of microlens arrays is used to generate an angular spectrum from an (at least substantially) collimated input laser beam, whereby a large number of partial laser beams are generated by interference and diffraction effects, depending on the distance between the microlens arrays. A variable variation of the interference pattern results in a variation of the number of partial laser beams. BRIEF DESCRIPTION OF THE DRAWINGS

[0096] The preferred further embodiments of the present invention are described in more detail by the following description of the accompanying drawings. In the accompanying drawings:

[0097] Figure 1 A schematic structure for producing a recess is shown;

[0098] Figure 2A , Figure 2B , Figure 2C and Figure 2D A schematic representation of a multifocal distribution is shown;

[0099] Figure 3 showing a microscope image of a transparent material having randomly arranged recesses; and

[0100] Figure 4 Confocal microscopy images of a transparent material with randomly arranged recesses are shown. DETAILED DESCRIPTION

[0101] Preferred exemplary embodiments are described below with reference to the accompanying drawings. In this case, in different figures, identical, similar or elements having the same effect are provided with the same reference numerals, and repeated description of these elements is omitted in some instances to avoid redundancy.

[0102] Figure 1 A device according to the invention for producing a recess 2 is schematically shown. The device has a laser 3 which generates laser pulses 300 which propagate in a laser beam 30 and are focused by processing optics 5 onto the surface of a transparent material 1 .

[0103] The laser pulses 300 can then generate recesses 2 and LIPSS on the surface of the transparent material.

[0104] The feed device 4 can move the transparent material 1 and the laser beam 30 relative to each other, so that the laser beam 30 is moved along the feed path by the feed. For example, the feed device 4 is designed as a scanner device, with which the laser beam 30 is periodically moved over the material 1.

[0105] For example, during the advancement of the feeding device 4, the laser pulse 300 of the laser 3 can be triggered by a random generator so that randomly distributed recesses 2 (not shown) are generated on the surface of the transparent material 1. However, the feeding device 4 can also spontaneously reposition the laser beam 30 using a random generator to generate randomly distributed recesses 2 (not shown) on the surface of the transparent material 1. In particular, both the feeding device 4 and the pulse triggering of the laser 3 can be triggered by such a random generator so that the distribution of the recesses 2 on the surface of the transparent material 1 is as random as possible (not shown).

[0106] Generally, the laser pulses 300 of the laser 3 can also be triggered regularly during the feeding of the feeding device 4 .

[0107] Furthermore, a beam shaping device 7 can be arranged in the beam path, which can impart a multi-focus distribution 70 to the laser beam 30 , so that a large number of single focuses are generated on the surface of the transparent material 1 by the processing optics.

[0108] To produce recesses 2, the average emitted laser power at the laser output may be between 30W and 1000W, preferably between 30W and 300W, so that as many recesses 2 as possible can be produced per second with the laser beam. In addition, the laser pulse duration may be between 300fs and 10ps or between 100ps and 100ns.

[0109] In particular, at these average laser powers, a plurality of recesses 2 can be produced by means of a single laser pulse 300 or a single laser pulse train, as is shown in FIG. 2 .

[0110] For example, Figure 2A It is shown that a single laser pulse 300 can be shaped into a multi-focus distribution 70 by the beam shaping device 7. Then, 300 different recesses 2 can be generated from a single laser pulse. However, all laser pulses 300 of a laser pulse train, here labeled A, B, ..., F, can also be directed to all single focuses. However, the beam shaping device 7 can also perform a rapid repositioning of the laser beam 30, so that one or more laser pulses 300 of the laser pulse train are arranged at different positions on the surface of the transparent material 1, such as Figure 2B shown.

[0111] However, if Figure 2CAs shown, the multi-focus distribution 70 can also have an intensity gradient. Each single focus has a different intensity, so that the introduced recesses 2 have different sizes. In addition, the random arrangement of the recesses 2 can also be achieved by the multi-focus distribution 70.

[0112] However, if Figure 2D As shown, the successively repositioned laser pulses 300 of a laser pulse train can also have different intensities. In this case, the recesses 2 can then also have different sizes.

[0113] Figure 3 A microscope image of a transparent material 1 is shown, the surface of which is covered with recesses 2. The so-called recesses 2 are impressed on the surface of the transparent material 1 by corresponding laser pulses 300 of a laser 3, for example by two laser pulses 300 of a laser pulse train. The recesses 2 appear as circular to oval ablation defects in the surface of the transparent material 1. In particular, each recess 2 can be produced individually by two laser pulses of a laser pulse train.

[0114] The transparent material 1 may be, for example, sapphire or quartz glass.

[0115] like Figure 3 As can be seen in FIG. 1 , the recesses 2 can be randomly arranged on the surface of the transparent material, wherein the recesses 2 can also partially overlap or be adjacent to each other. By applying the recesses 2 in an irregular pattern to the surface of the transparent material 1, in particular, direct reflection of the incident beam can be suppressed, because the incident beam is refracted by the recesses 2 into a plurality of partial beams and reflected out.

[0116] Figure 4 The same transparent material 1 is shown in a confocal microscope image of a dimensioned image of FIG. The recess 2 has a depth between 100 nm and 2000 nm, for example 500 nm. The recess 2 also has a diameter between 3 μm and 25 μm, for example 20 μm. The recess 2 also has a size variation of between 5% and 80%, for example 10%, of the diameter. In addition, the area of ​​the surface filled by the recess 2 is between 20% and 95%, for example 30%.

[0117] For example, the transparent material 1 can be arranged on the display panel of the smart device so that the transparent material 1 serves as a protective layer or a cover layer. In particular, due to the roughness of the transparent material 1, the tactile quality can also be adjusted by the size of the recesses. In addition, the random arrangement of the recesses 2 and / or the size of the recesses that is smaller than the pixel size can prevent the formation of a moire effect (not shown).

[0118] To the extent applicable, all the individual features presented in the embodiments may be combined with one another and / or interchanged without departing from the scope of the invention.

[0119] Reference numerals list

[0120] 1. Transparent Materials

[0121] 2 concavity

[0122] 3 Laser

[0123] 30 Laser Beam

[0124] 300 laser pulses

[0125] 4 Feeding device

[0126] 5 Processing optical devices

[0127] 7 Beam shaping device

Claims

1. A method for producing a recess (2) on a surface of a transparent material (1) by means of laser pulses (300) of a short-pulse laser (3), It is characterized in that At least one recess (2) is produced by means of a single laser pulse (300) or a single laser pulse train.

2. The method according to claim 1, characterized in that: The laser pulse duration is between 300 fs and 10 ps or between 100 ps and 100 ns.

3. The method according to claim 1 or 2, characterized in that: The at least one recess (2) is produced by means of a laser pulse train, wherein the laser pulse train comprises 2 to 10 laser pulses and the time intervals between the laser pulses are between 10 ns and 50 ns.

4. The method according to claim 1 or 2, characterized in that: The at least one recess (2) is produced by means of a laser pulse train, wherein the laser pulse train comprises 30 to 300 laser pulses and the time intervals between the laser pulses are between 100 ps and 1000 ps.

5. The method according to any one of the preceding claims, characterized in that At least two laser pulses of the laser pulse train overlap spatially, wherein a laser-induced periodic surface structure is generated.

6. The method according to any one of the preceding claims, characterized in that The polarization degree of the laser (3) is higher than 80%, preferably higher than 95%.

7. The method according to any one of the preceding claims, characterized in that The average emitted laser power at the laser output is between 30W and 1000W, preferably between 30W and 300W.

8. The method according to any one of the preceding claims, characterized in that The photon energy of the laser pulse or laser pulse train is less than the band gap of the material.

9. The method according to any one of the preceding claims, characterized in that The laser beam (30) and the transparent material (1) can be displaced relative to each other by means of a feed device (4).

10. The method according to any one of the preceding claims, characterized in that A laser beam (30) is focused onto the surface of the transparent material (1) by means of processing optics (5).

11. The method according to any one of the preceding claims, characterized in that The recesses (2) are randomly positioned on the surface of the transparent material (1).

12. The method according to any one of the preceding claims, characterized in that The laser beam (30) is shaped into a multi-focus distribution by means of a beam shaping device (7), and the surface is impinged with the multi-focus distribution, thereby generating a plurality of recesses (1) by means of a single laser pulse or a single laser pulse train.

13. The method according to any one of the preceding claims, characterized in that The multifocal point distribution has an intensity gradient, in particular, single focal points in the multifocal point distribution have at least partially different intensities.

14. The method according to any one of the preceding claims, characterized in that The beam shaping device (7) is an acousto-optic deflector and / or a microlens array and / or a diffractive optical element.

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