DEVICE AND METHOD FOR LASER INTERFERENCE STRUCTURING OF SUBSTRATES WITH PERIODIC POINT STRUCTURES FOR ANTI-REFLECTION PROPERTIES

Description

Technical field

[0001] The present invention relates to the field of substrate structuring, in particular a device and a method for structuring the surfaces and the interior of a transparent substrate by means of laser interference structuring. Furthermore, the present invention relates to a structured substrate—for example, planar substrates, in particular so-called antireflection glazing—with antireflection properties, comprising a periodic dot structure. State of the art

[0002] Methods for treating surfaces are known from the prior art, which can modify the surface of transparent substrates, especially glass, but also solid polymers, in such a way as to reduce the substrate's reflectivity. Typical methods for this purpose involve applying an additional material to the surface of the substrate to be antireflectively treated (so-called structure- or layer-building methods), whereby the refractive index of the different materials varies.

[0003] For example, US patent 8,557,877 B2 describes a possible layer-by-layer coating process. In this process, a coating solution is created from at least two chemical starting materials, its pH is then reduced, and it is optionally diluted with another solution before the coating is applied to the desired substrate. This type of coating process uses various chemical substances, often with low environmental compatibility, and their disposal and handling are costly and complex.

[0004] This type of process is based on a reduction in reflectance through destructive interference. The refractive index of the coating material must be matched to the substrate being coated and the medium in front of the substrate (usually air). Since not every coating material can be processed in the same way, different processes are required for coating different substrate materials.

[0005] US patent 10,459,125 B2 describes a method for chemically generating a so-called moth-eye structure on a substrate by applying a polymer film to the substrate. This type of structure is modeled on the principle of the moth's eye, on whose surface regularly arranged nanostructures are found, the dimensions of which are smaller than the wavelength of the incident light. This creates a layer with a graded refractive index at the interface between the medium in front of the substrate and the substrate itself, which significantly reduces reflection.

[0006] A film produced in this way can be used regardless of the substrate being coated, since the reduction in reflection does not depend on the refractive index of the material used for the coating. However, the coating method is still based on chemical substances with the disadvantages already mentioned above.

[0007] Additionally, a coating produced in this way is susceptible to mechanical stress (abrasion, impacts, etc.) and therefore ages quickly. After some time, the coating often detaches from the substrate and / or loses its anti-reflective properties.

[0008] In WO 2019 / 166836 A1, a method for producing an antireflection structure is described in which the surface of a substrate is treated with a laser to impart antireflection properties. A focused laser beam modifies the substrate material, thereby generating a nanostructure through self-organization processes that utilize laser-induced periodic surface structures (LIPSS). By appropriately selecting the laser fluence and superimposing the beam focal points on the substrate surface, a quasi-periodically repeating pattern can be generated. This results in an antireflection surface. No chemicals are required, and a wide range of substrate materials can be treated in this way.

[0009] However, this process is sequential and, due to the underlying self-organization process of LIPSS, time-consuming. Generating a large-area nanostructure in a single step is not possible, as LIPSS only develop through repeated processing of adjacent surface areas. Furthermore, the regularity of the structure depends on the specific process and environmental conditions, so variations in the surface condition (slight material differences, microscopic contamination) can lead to altered results.

[0010] EP 2 431 120 A1 discloses a method for the direct structuring of a thin film, in which periodic structures can be generated in thin metal films using interfering laser beams. In this process, several pulsed laser beams are directed onto the thin film, interfering within an interference region, such that the material of the thin film is vaporized in the high-intensity areas. The method is characterized by the fact that the resulting structure can be modified by adjusting the intensity of the laser beams or by shifting the film in the z-direction (i.e., towards or away from the incident laser beams). Additional optical elements are used to generate a phase difference between the laser beams, which influences the interference pattern.The incoming laser beams are focused onto the surface of the thin film by a focusing element and thereby reduced in size, resulting in areas of high intensity where the material of the thin film is vaporized.

[0011] This process requires a way to modify the intensity of the incident laser beams. This can be achieved either by specifying a particular laser radiation source or by using a unit to control the laser beam intensity. The intensity must be adjusted according to the vaporization threshold of the thin film material. This means that different laser radiation sources must be used for different materials, or an additional element for intensity control is required. Moving the optical elements does not allow for control of the resulting interference pattern. Furthermore, when processing materials with a high vaporization threshold, damage to the optical elements in the laser beam path is a possibility.

[0012] US Patent 2004 / 0227927 A1 discloses an interferometer device designed to generate an interference pattern with variable periodicity at a focal point. The device comprises a movable beam splitter and a movable reflector, which split an incident beam into two laser partial beams and deflect at least one of the laser partial beams. The periodicity can be varied by moving the beam splitter and the reflector. The movement of the beam splitter and the reflector is effected by a motorized platform.

[0013] This device has a complex and wear-prone design, as beam shaping to influence the periodicity of the generated interference pattern can only be achieved by moving two optical elements: the beam splitter and the reflector. Furthermore, the distance between the beam splitter and the reflector is fixed, and their arrangement on a motorized platform is space-consuming.

[0014] Methods for direct laser interference patterning are known from scientific publications ("Microfabrication and Surface Functionalization of Soda Lime Glass through Direct Laser Interference Patterning", Soldera et al., Nanomaterials 2021). However, these methods require complex reconfiguration and realignment of more than one optical element in the beam path to control the generated structures. In industrial applications with a high throughput of substrates to be patterned, with varying requirements for the desired feature sizes, this necessitates regular movement and adjustment of the optical elements in the beam path. This makes the process less flexible and, moreover, exposes the optical elements to greater wear and tear and a greater risk of damage with each application due to the constant readjustment.

[0015] Furthermore, the minimum structural dimensions achievable through direct laser interference structuring are limited to the micrometer range. The minimum achievable dimensions reported in publications are in a range that is sometimes significantly larger than the wavelength of radiation from the visible spectrum. An antireflection structure produced in this way may exhibit undesirable diffraction patterns for particularly short-wavelength light and is unsuitable for suppressing reflection in these wavelength ranges or for ensuring the transmission of incident light rays from the entire visible spectrum.

[0016] Another publication (“Improving throughput and microstructure uniformity in Direct Laser Interference Patterning utilizing top-hat shaped beams”, EI-Khoury et al., Research Square 2021) discloses the use of laser beams with Gaussian and top-hat profiles in an optical setup to generate an interference pattern on a substrate. The optical setup comprises a laser radiation source, a first deflection element, a beam shaping element, a beam splitter element, a second deflection element, and a focusing element. The periodicity of the interference pattern can be adjusted by moving the optical elements relative to each other, in particular by moving the second deflection element in the beam path of the laser (partial) beams.

[0017] Generating the interference pattern requires a large number of optical elements, resulting in a complex and wear-prone setup. Furthermore, the achievable structural periods are limited to a minimum of 6.7 µm.

[0018] Furthermore, a method for generating hierarchical microtextures using laser-patterned stamps is known ("Hierarchical Microtextures Embossed on PET from Laser-Patterned Stamps", Bouchard et al., Materials 2021), in which the laser-patterned stamp is created using Direct Laser Writing (DLW) and Direct Laser Interference Patterning (DLIP). A fixed optical arrangement was used, which generates a defined feature size of 3.1 µm for the interference patterning. The interference patterning thus generated, with dimensions in the low micrometer range, is superimposed on a laser patterning generated by Direct Laser Writing. In this process, a laser beam is directed onto the material to create a patterning of the substrate, in particular a cone-shaped patterning, in the region of maximum intensity.The diameter of the structure is typically around 110 µm, and thus a multiple of the structure periods generated by interference structuring. The structure created in the substrate by the superposition of the two structures is called a hierarchical structure.

[0019] However, the specified method is not suitable for producing an antireflection coating on a planar substrate, as the structuring process consists of several process steps (successive structuring first using DLW, then DLIP), and the minimum achievable structure dimensions using the same setup are limited to the specified dimensions (3.1 µm). Therefore, the device shown and the described method are not suitable for producing a uniform antireflection structure within a single structuring step and with variable structure sizes that exhibit antireflection properties for electromagnetic waves across the entire visible light spectrum.

[0020] US patent 2001 / 035991 A1 discloses an interference lithography system with which an incident laser beam can be split into more than two sections ("partial beams") and with which a three-dimensional surface structure can be created in a thin photoresist layer, wherein this surface structure can be configured as cylindrical or cup-shaped holes. However, the patent does not disclose that such structured substrates exhibit antireflection properties or how such structures must be designed to generate antireflection properties.

[0021] EP 2 596 899 B1 discloses a device and a method for interference structuring of planar samples. The device comprises a focusing arrangement that focuses a laser beam into the sample volume. The laser beam can also be focused in a further spatial direction that is not parallel to the first spatial direction. The device includes a beam splitter and spreader, which is positioned in the beam path only after the focusing arrangement and which spreads the laser beam. The beam splitter and spreader consists solely of a beam splitter that is only capable of spreading a laser beam into two partial beams. Solution

[0022] The present invention provides a structured substrate according to claim 1 and a laser interference structuring device according to claim 7. Furthermore, a method according to claim 12 is provided. The claimed invention also relates to the use of a structured substrate according to claim 18.

[0023] Further advantageous features can be found in the description and the dependent claims. General advantages

[0024] An advantage of the device defined herein is that, through this device and the method achievable with its aid, the structuring of substrates, particularly the creation of structures with antireflective properties, can be achieved without the use of chemicals and their costly disposal. Furthermore, the purification of the substrates can also be dispensed with.

[0025] Furthermore, a wide variety of substrates, preferably planar and / or transparent substrates, especially transparent materials, can be processed with the device. Since the process is not dependent on the refractive index or the adhesion of specific coating materials to the substrate, this method is more flexible than conventional chemical processes.

[0026] Compared to WO 2019 / 166836 A1, the processing time using this method is significantly shorter, as the periodicity of the structures is ensured by the interference of the incident, at least three, preferably at least four, partial beams within an interference region, and not by more time-consuming self-organization processes. Furthermore, an advantage over conventional methods is that the shape (structural design; geometry) of the generated micro / nanostructures can be controlled. The geometry of the structures can be controlled by adjusting the number of interfering (partial) beams, their polarization, and the process parameters, thereby allowing for targeted influence on the antireflection properties.

[0027] Furthermore, the stability of the periodic dot structure thus created should be mentioned, which is more durable compared to conventional coatings, as it cannot detach from the substrate to be coated over time and the material stress caused by use.

[0028] If the structuring is carried out in volume, i.e., within the substrate, preferably a planar and / or transparent substrate, particularly in the transparent material, the resulting structuring (i.e., the periodic dot structure of the structured substrate) is less sensitive to impacts and abrasion than conventional coatings. The inventors have found that structuring (also referred to herein as texturing) within the material (i.e., below the surface) does not necessarily produce antireflective properties. However, texturing within the material is of interest for other applications, such as product protection, optical data storage, decoration, etc.

[0029] A particular advantage is that, due to the apparatus design and the arrangement of the optical component disclosed herein, substrates can be structured with very high structuring rates of up to 0.9 m² / min, particularly in the range of 0.01 to 0.9 m² / min, especially preferably in the range of 0.05 to 0.9 m² / min, and most preferably in the range of 0.1 to 0.9 m² / min. This is ensured by the fact that the area in which the at least three partial beams are superimposed can be expanded by a preferred selection of optical elements, thereby enabling a large area to be irradiated in a single processing step. In contrast to methods known to those skilled in the art, such as direct laser writing, no strong focusing is necessary to generate high-resolution features.

[0030] Such a setup advantageously allows for the rapid scanning of a substrate surface, enabling a high structuring rate of up to 3 m² / min, particularly in the range of 0.05 to 2 m² / min, especially preferably in the range of 0.1 to 1 m² / min, and most preferably in the range of 0.1 to 0.9 m² / min. The exact structuring rate depends primarily on the available laser power. Therefore, even higher structuring rates will be achievable with future technologies that offer higher laser power. Detailed description

[0031] The device according to the invention describes a setup for laser interference structuring of substrates, e.g. planar and / or transparent substrates, to produce a structured substrate, comprising a periodic dot structurein the micro- or sub-micrometer range, especially for the production of a so-called anti-reflective glazing on the substrate or in the volume (i.e. within) this substrate.

[0032] This is a laser interference structuring device for the direct laser interference structuring of a substrate - examples of which are planar and / or transparent substrates - comprising a laser radiation source (1) for emitting a laser beam, a beam splitter element (2) arranged in the beam path (3) of the laser beam, a focusing element (4) arranged such that the partial beams pass through it in such a way that the partial beams can be interfered with on the surface or in the volume of a substrate, preferably a planar and / or transparent substrate (5) in an interference region, wherein the beam splitter (2) is freely movable along its optical axis in the beam path (3), and wherein the beam splitter (2) is configured to divide the incident laser beam emitted by the laser radiation source (1) into at least 3 partial beams, particularly preferably at least 4, in particular 4 to 8, i.e. 4, 5, 6, 7, or 8 partial beams.

[0033] Particularly preferably, the beam splitter (2) is configured such that it divides the incident laser beam into an even multiple, i.e. 4, 6 or 8 partial beams, most preferably 4 partial beams.

[0034] Alternatively or additionally, a beam splitter (2) can be provided such that it comprises a first beam splitter and at least one further beam splitter downstream of the first beam splitter, wherein the first beam splitter divides the incident laser beam into at least 2 partial beams and the further beam splitter is arranged in at least one beam path of a partial beam and divides this partial beam into at least 2 partial beams as it passes through.

[0035] For laser interference structuring of the substrate (5), preferably a planar and / or transparent substrate, the laser beam emitted by the laser radiation source is split into at least 3, preferably at least 4 partial beams by the beam splitter element (2). Only two-beam interference (i.e., structuring by interference of two partial beams) is known from the prior art. However, such two-beam interference only produces line structures on the substrate.

[0036] Subsequently, the partial beams are deflected by the focusing element (4) so ​​that they interfere on the surface or inside a substrate (5), preferably a planar and / or transparent substrate, in an interference area, also called an interference pixel.

[0037] This allows the creation of a two-dimensional, periodic dot pattern with dimensions in the micro- and sub-micrometer range, the structure period of which can be freely adjusted by shifting the beam splitter element (2) along its optical axis. Planar processing of a substrate (5), preferably a planar and / or transparent substrate, is possible. substrate

[0038] For the purposes of the invention, the term "substrate" refers to a substrate whose surface extends in several spatial directions. A substrate, preferably a planar and / or transparent substrate, can be a planar substrate or a curved substrate, for example, a parabolic substrate. For the purposes of the invention, "planar" further means that the extent of a substrate, preferably a planar and / or transparent substrate, for example, a planar substrate, in the x and y directions, or the extent of a curved substrate along its radius of curvature, is greater than the extent of the area in which the at least three partial beams interfere with each other.

[0039] In a preferred embodiment, the substrate is a substrate whose extent in the x and y directions, or whose extent along a radius of curvature, is less than or equal to the extent of the region in which the at least three partial beams interfere with each other. Homogeneous structuring of the substrate is possible in a single processing step (during one laser pulse).

[0040] In a particularly preferred embodiment, the substrate is a planar substrate whose extent in the x and y directions, or whose extent along a radius of curvature, is greater than the extent of the area in which the at least three partial beams interfere with each other. By moving the substrate in the x and y planes, a planar, homogeneous structuring of the substrate is possible in several processing steps (with several laser pulses). The movement of the substrate can be achieved by rotation or translation, or by a superposition of rotation and translation.

[0041] For the purposes of the invention, the term substrate includes a solid material with a reflective surface. Examples of such materials are metals, polymers, ceramics, and glasses.

[0042] With regard to the substrates that can be processed by applying the laser interference structuring method according to the invention with a periodic dot structure defined therein, in particular with antireflective properties, there is a wide selection of transparent and translucent as well as opaque materials within the scope of the present invention.

[0043] In a particularly preferred embodiment, the planar substrate comprises a transparent material.

[0044] In general, the transparent material exhibits high transmittance for visible light, although this varies depending on the application. The transmittance of the transparent material is not less than 70%, preferably not less than 80%, and even more preferably not less than 90%, without any deviation in the spectrum within the visible light range (wavelength 380 nm to 780 nm).

[0045] The geometry of the substrate can be variable; for example, planar substrates can have curves or surface irregularities, and / or non-planar substrates such as tubes or fibers can be used.

[0046] Preferably, the substrate is a flat and / or transparent material.

[0047] The substrate can be designed as a flexible and / or bendable substrate, such as a flexible glass film, (artificial) leather, a metal foil, a thin sheet of metal or a plastic film, as is used, for example, in solar films or displays.

[0048] In a particularly preferred embodiment, the planar substrate comprises a transparent material; preferably, the substrate consists of a transparent material. A material or substrate is transparent within the meaning of the present invention if it exhibits high transmittance for at least a portion of the electromagnetic radiation spectrum between 1 nm and 1 m. Such portions include, for example, electromagnetic radiation in the visible light range from 380 nm to 780 nm, or in a range that also includes infrared light, from 780 nm to 5,000 nm, or in a region of infrared light (thermal radiation), or in a region of microwave radiation, in particular radar beams in the wavelength range from 1 mm to 10 m, or any other portion adapted to the desired application, in particular to the wavelength of the laser source.Such a sub-region preferably has a width of at least 10% or 50% of the wavelength that forms the lower boundary of the sub-region. High transmittance in a sub-region, as defined by the invention, is a transmittance of at least 50%, or preferably at least 70%, or particularly preferably at least 80% or at least 90% for each wavelength in the sub-region, i.e., for the entire spectrum in the sub-region. A transparent substrate can also be defined as a substrate that selectively exhibits high transmittance for certain wavelength ranges in the visible light range; for example, the substrate has high transmittance for electromagnetic radiation with wavelengths in the range of 500 nm to 800 nm. The transmittance can vary across the wavelength range being transmitted, for example...The transmittance must be at least 70% for wavelengths in the range of 380 nm to 500 nm, and at least 90% in the range of 500 nm to 750 nm. For example, the substrate transmits radiation with wavelengths from 380 nm to 780 nm. It exhibits particularly high transmittance, e.g., a transmittance of 90%, at wavelengths from 450 nm to 690 nm; the transmittance at wavelengths below and above this range is, for example, 70%.

[0049] Furthermore, the light transmittance of a transparent material offers the advantage that laser interference processing of a plane within the volume / inside of the substrate is possible.

[0050] For the purposes of the present invention, a transparent material comprises transparent materials, in particular glass (e.g., borosilicate glasses, quartz glasses, alkali-alkaline earth silicate glasses (e.g., soda-lime glass), aluminosilicate glasses, metallic glasses), but also solid polymers (e.g., polycarbonates, such as Makrolon® and Apec®; polycarbonate blends, such as Makroblend® and Bayblen®; polymethyl methacrylate, such as Plexiglas®; polyester; polyethylene terephthalate, polypropylene, polyethylene) as well as transparent ceramics (e.g., spinel ceramics, such as Mg-Al spinel, ALON, aluminum oxide, yttrium aluminum garnet, yttrium oxide, or zirconium oxide) or mixtures thereof. Polycarbonates include homopolycarbonates, copolycarbonates, and thermoplastic polyester carbonates.

[0051] According to a particularly preferred embodiment, the transparent material consists of a glass (as defined herein) or a solid polymer (as defined herein).

[0052] The silicate framework of glass preferably provides a transmission window for wavelengths in the range between 170 nm and 5,000 nm, i.e., a wavelength range that includes visible light in the range from 380 nm to 780 nm and infrared radiation.

[0053] Alternatively, the substrate, preferably a planar and / or transparent substrate, can also comprise an opaque material. Structuring the opaque material creates a periodic dot pattern on its surface in the micro- or sub-micrometer range, as defined herein. As a result, a structure with antireflection properties can be created on an opaque material, whereby the original roughness of the surface of the opaque substrate (i.e., before the application of the structuring according to the invention) remains unchanged or almost unchanged in the macroscopic range, effectively reducing the reflection of an otherwise reflective surface of an opaque material, e.g., a metal surface. Particularly suitable opaque materials include metals (e.g., silicon, aluminum, copper, gold) and metallic alloys (e.g.,Steel, brass), ceramic materials (e.g., zirconium oxide, titanium dioxide, zirconia), and polymers (PEEK, polyetheretherketones; polyfluorinated hydrocarbons, such as Teflon), as well as combinations thereof. For example, such a structured substrate is suitable as a negative mold for the indirect application or creation of structures on another substrate. The structured substrate can, for instance, be used as a "stamp" to create a structure inverse to the one created on the substrate on any number of other substrates. Furthermore, such a structured substrate exhibits increased diffraction of electromagnetic radiation, meaning that the structuring of the substrate reduces its spectral reflection.Due to the structural dimensions, scattering processes occur at these structures, which are introduced by interference structuring at the level of the substrate, especially at one of its surfaces. Point-like structure / interference pattern / anti-reflective glazing

[0054] The present invention also comprises a structured substrate (5) with antireflection properties, wherein the structured substrate has a periodic dot structure encompasses the micro- or sub-micrometer range, with the periodic dot structure consisting of inverse Conesis formed, and wherein the inverse cones are periodically arranged at a distance relative to their respective saddle point or center of height (circular base) in the range of 50 nm to 50 µm, preferably in the range of 50 nm to 20 µm, particularly preferably in the range of 100 nm to 4 µm, more preferably in the range of 100 nm to 2 µm, even more preferably in the range of 200 nm to 1.5 µm, and most preferably in the range of 300 nm to 800 nm.

[0055] In the context of this invention, the term "inverted cones" refers to structures with a circular, elliptical, triangular, or substantially rectangular base, particularly a circular base, which taper conically into the substrate in the vertical direction and have a rounded conical tip at their saddle point. The inverted cones are formed during the structuring process, i.e., when a laser pulse strikes the substrate as a result of a high-intensity region. Ideally, the areas between the inverted cones on or within the substrate remain essentially unstructured due to destructive interference, resulting in zero intensity. Consequently, focusing the laser (partial) beams on or within the substrate creates the negative of what the intensity distribution dictates.The described form of inverted cones refers to point structures arranged on the surface of the substrate. An arrangement of the point structures in or along a plane within the volume results in a symmetrical shape. For the purposes of the invention, point structures generated within a volume by means of laser interference structuring are also referred to as inverted cones.

[0056] Cones with an elliptical base can be generated, for example, by tilting the substrate relative to the angle of incidence of the focused laser beam(s), by tilting the interference volume (i.e., volumetric pixel, voxel; the angle at which the partial beams are focused on the surface or in the volume of the substrate so that they interfere in an interference region) relative to the substrate, e.g., by tilting the apparatus relative to the substrate, or by a combination of these methods. According to a preferred embodiment, cones with an elliptical base are generated by tilting the substrate relative to the angle of incidence of the focused laser beam(s).

[0057] The period of the structure is designated as Λ in accordance with the invention. It generally depends on the wavelength of the interfering laser (partial) beams, the angle of incidence of the interfering laser (partial) beams, and the number of interfering laser (partial) beams.

[0058] A structured substrate with antireflection properties, here referred to as an antireflection glazing, describes, according to the invention, a substrate, preferably a planar and / or transparent substrate, with a periodic dot structure with structure sizes in the micro- and submicrometer range, i.e., in the range of 50 nm to 50 µm. These antireflection properties arise when the dimensions of the generated structure, i.e., the structure period and the dimensions of the individual cones, are in ranges smaller than the wavelength of visible light.

[0059] In physics, reflection refers to the bouncing back of an electromagnetic wave at the interface of materials with different refractive indices. The angle of reflection and the angle of transmission of light in transparent substrates can generally be calculated using Snell's law of refraction. n 1 sinδ 1 = n 2 sinδ 2 calculated where n 1 and n 2 specify the refractive index of air and the substrate, and δ 1 and δ 2 respectively specify the angles of the incident and reflected rays.

[0060] Due to the periodic dot structure on the surface or within the volume of the substrate, preferably a planar and / or transparent substrate, the refractive index of the substrate changes in such a way that a gradual refractive index results. This means that light with wavelengths greater than the structure period Λ of the periodic dot structure is transmitted more widely. Light with wavelengths less than or equal to the periodic dot structure is diffracted at the surface.

[0061] In the context of the invention, antireflection properties refer to periodic point structures whose dimensions lie within the range of the incident electromagnetic wave, such that the incident wave is deflected away from the observer in such a way that no reflection is perceived as "disturbing". Additionally, the term antireflection properties, as used in the invention, also encompasses the fact that the refractive index at the boundary between the first medium, for example, air, and the substrate, preferably a planar and / or transparent substrate, is gradual, so that there is no clear transition from one medium to the other for the incident electromagnetic wave, and the incident electromagnetic wave is transmitted more effectively.

[0062] For the purposes of the invention, a structured substrate with antireflection properties also describes a substrate which comprises a periodic dot structure, wherein the periodic dot structure consists of superimposed structures, wherein at least one structure has dimensions in the submicrometer range, and wherein at least one structure is formed from inverted cones (as defined herein), which can be generated in particular by interfering laser beams.

[0063] For example, the periodic dot structure, in particular the periodic dot structure consisting of superimposed structures when using interfering laser beams, can be optimally adapted to the requirements of the respective application by appropriately designing the parameters (selection of the laser radiation source, arrangement of the optical elements, pulse duration and intensity, number of laser pulses which hit an interference pixel).

[0064] For example, a structure with antireflection properties generated in this way is a periodic dot structure composed of inverted cones with mean dimensions in the micrometer range, in particular with a mean spacing of 1 µm to 50 µm relative to their respective saddle point or height center. A further structure is superimposed on this periodic dot structure, wherein the mean dimension of the superimposed structure preferably has dimensions in the range of the laser wavelength λ, or λ / 2, in particular from 100 nm to 1000 nm, preferably from 100 nm to 800 nm, and most preferably from 100 nm to 600 nm, and more particularly from 100 nm to 400 nm. For the purposes of the invention, such a structure is also referred to as a hierarchical structure.

[0065] In particular, the superimposed structure has a quasi-periodic wave structure, wherein the material on the surface of the substrate in the region of the superimposed structure has a sequence of wave crests and wave troughs whose periodicity is in the submicrometer range, particularly preferably in the range of 100 nm to 1000 nm, preferably in the range of 100 nm to 800 nm, particularly preferably 100 nm to 600 nm, and especially 100 nm to 400 nm.

[0066] The wave structure is formed during the structuring process, i.e., when a laser pulse strikes the substrate to be structured, as a result of the appearance of a high-intensity region. The structuring occurs through a self-organization process, which is stimulated by the at least partial melting of the substrate material by a laser pulse in a high-intensity region. In particular, the wave structure is generated by utilizing laser-induced periodic surface structures (LIPSS), where the appearance of these surface structures is coupled to the generation of periodic point structures by means of interfering laser beams.

[0067] Alternatively, the wave structure superimposed on the inventive point structure of inverted cones with average dimensions in the micrometer range can also be applied by subsequently applying a further interference pixel to the surface of the (pre-structured) substrate, wherein the structures generated with the further interference pixel have a structure period relative to the cones formed by the further interference pixel, on average in the range of 100 nm to 1,000 nm, preferably in the range of 100 nm to 800 nm, particularly preferably 100 nm to 600 nm, e.g. in the range of 200 nm to 500 nm, and especially in the range of 100 nm to 400 nm.

[0068] Advantageously, this allows for the planar structuring of a substrate, e.g., with antireflection properties, using interfering laser beams and utilizing laser-induced periodic surface structures, without incurring long processing times or a large number of successively executable process steps. The invention thus enables the simultaneous generation of hierarchical structures, which can be used in technical applications both for substrates with antireflection properties and for self-cleaning, hydrophobic or superhydrophobic, as well as hydrophilic or superhydrophilic substrates with anti-icing and / or anti-fogging properties.

[0069] According to a preferred embodiment of the present invention, the application of an interference pixel (or the interference volume that generates the interference pixel on or in the substrate), e.g., a first, a second, and / or a third interference pixel, to the surface or volume of the substrate is carried out by means of laser interference structuring by irradiating the substrate with several laser (partial) beams at an angle to the surface of the substrate of 45° to 90° (perpendicular), preferably at an angle of 60° to 90°, particularly preferably at an angle of 75° to 90°, e.g., in each case in an angular range of / to 76°, 77°, 78°, 79°, 80°, 81°, 82°, 83°, 84°, 85°, 86°, 87°, 88°, 89°, 90°, each with respect to the optical axis of the Substrates. It is particularly preferred that an interference pixel is applied to the surface of a substrate essentially perpendicular to a normal to the surface, i.e. at an angle of 90° ± 1°. Interference area, or interference pixel

[0070] The device according to the invention is designed to a periodic dot structureThe aim is to generate a periodic dot pattern on a substrate in the micro- or sub-micrometer range, whereby the periodic dot structure can be produced by laser beams interfering within an interference region. This interference region is characterized by alternating radiation intensity maxima and minima occurring within its spatial extent. These maxima and minima occur with periodic, i.e., repeating, regularity and thus form an interference pattern that can be transferred to the substrate. The interference region within which this pattern is recognizable is also called an interference pixel. The extent of the interference pixel is typically circular, but other geometric dimensions, e.g., elliptical or linear, are also conceivable. The interference region within which the interference pattern is recognizable is physically determined by the intensity threshold of the substrate being processed.The intensity threshold refers to the energy at which the substrate material interacts with the incident laser beams, causing a change within the material, such as melting or ablation. With a laser radiation source exhibiting a Gaussian radiation profile, the energy of the interfering laser beams at the maxima of the interference pattern decreases towards the edge of the interference region. Consequently, the interference pixel deposited on the substrate is smaller than the interference region itself, with the precise size determined by the properties of the laser radiation source and the substrate.

[0071] The term interference pixel, e.g. first, second, third and / or further interference pixel, thus refers, within the meaning of the present invention, to a periodic pattern or grid of at least three inverse cones, preferably at least seven inverse cones, most preferably at least 19 inverse cones on the surface of a substrate, which form within an interference pixel (cf. Fig. 6 Preferably, the periodic pattern or grid is generated by superimposing at least three, particularly preferably at least four, laser (partial) beams as a result of focusing (bundling) these laser (partial) beams onto the surface or into the interior of the substrate, whereby the partial beams interfere constructively and destructively on the surface or in the interior of the substrate.

[0072] According to a preferred embodiment of the present invention, the structured substrate comprises not merely a single interference pixel of one type, e.g., a first interference pixel, a second interference pixel, and / or a third interference pixel, but rather several interference pixels of one type, e.g., several first interference pixels and / or several second interference pixels, each arranged independently of one another within a plane in at least one spatial direction (x and / or y orientation), particularly preferably in two spatial directions (planar), adjacent to one another and repetitively offset from one another. For example, it can be provided that, in a first step, at least several first interference pixels within a plane are applied to a plane on a surface or in the volume of the substrate to be structured, arranged adjacent to one another and repetitively offset from one another in at least one spatial direction (see, e.g., [reference]). Fig. 6) and in a second step, several second interference pixels are superimposed on these several first interference pixels within a plane, adjacent to each other in at least the same spatial direction and repetitively offset from one another. However, it is also possible that these several first interference pixels and several second interference pixels are applied to the plane alternately, i.e., one first interference pixel, then a second interference pixel, and then the process repeats.

[0073] By arranging multiple first interference pixels and multiple second interference pixels, specific properties, particularly antireflection properties, can be selectively applied over a large area, especially across a plane of the substrate defined by its surface, or within the substrate's volume. Such structuring with multiple first interference pixels and multiple second interference pixels can be achieved, for example, by scanning the substrate with a polygon scanner.

[0074] Preferably, the periodic dot structures within a type of interference pixel exhibit a coefficient of variation (a value resulting from dividing the standard deviation by the mean value) of the cone cross-section of 15% or less, more preferably 10% or less, and even more preferably 5% or less. This also allows for better detectability of the substrate structured according to the invention compared to conventional methods for structuring / coating substrates (e.g., etching, particle blasting, polymer coating), in which the deviations are larger due to the process and the structure period to be generated is less accurately reproduced. Laser radiation source (1)

[0075] The device according to the invention comprises a laser radiation source (1) that emits a laser beam. The radiation profile of the emitted laser beam corresponds either to a Gaussian profile or to a top-hat profile, particularly preferably to a top-hat profile. The top-hat profile is helpful for structuring or covering a substrate surface to be structured more homogeneously and, if necessary, for enabling a faster structuring rate.

[0076] In a particularly preferred embodiment, the laser radiation source (1) is a source that generates a pulsed laser beam. The pulse width of the pulsed laser radiation source is, for example, in the range of 10 femtoseconds to 100 nanoseconds, in particular 50 femtoseconds to 10 nanoseconds, and most preferably 50 femtoseconds to less than 100 picoseconds.

[0077] Unless explicitly stated otherwise, the term laser beam or partial beam does not refer to an idealized beam of geometric optics, but to a real light beam, such as a laser beam that does not have an infinitesimally small, but rather an extended beam cross-section (Gaussian distribution profile or an intrinsic top-hat beam).

[0078] A top-hat profile or top-hat intensity distribution refers to an intensity distribution that can be described essentially by a rectangular function (rect(x)) with respect to at least one direction. Real intensity distributions that exhibit deviations from a rectangular function in the percentage range or that have sloped edges are also referred to as top-hat distributions or top-hat profiles. Methods and devices for generating a top-hat profile are well known to those skilled in the art and are described, for example, in EP 2 663 892. Optical elements for transforming the intensity profile of a laser beam are also already known.For example, diffractive and / or refractive optics can be used to transform laser beams with a Gaussian intensity profile into laser beams that exhibit a top-hat intensity profile in one or more defined planes, such as a Gauss-to-Top Hat Focus Beam Shaper from TOPAG Lasertechnik GmbH, see e.g. DE102010005774A1. Such laser beams with top-hat intensity profiles are particularly attractive for laser material processing, especially when using laser pulses shorter than 50 ps, ​​as the essentially constant energy and power density allows for particularly good and reproducible processing results.

[0079] The laser radiation source (1) contained in the device according to the invention can have an intensity of 0.01 to 5 J / cm², particularly preferably 0.1 to 2 J / cm², and most preferably 0.1 to 0.5 J / cm². The intensity of the laser radiation source can be flexibly selected within a range according to the device. The beam diameter is irrelevant for generating the interference pattern on the substrate, preferably a planar and / or transparent substrate. Due to the preferred arrangement of the optical elements in the laser beam path, no unit for controlling the intensity of the laser beam is necessary.

[0080] The laser radiation source is preferably configured to emit wavelengths in the range of 200 nm to 15 µm (e.g., CO₂ lasers in the range of 10.6 µm), and most preferably in the range of 266 nm to 1064 nm. Suitable laser radiation sources include, for example, UV laser beam sources, laser beam sources (155 to 355 nm) emitting green light (532 nm), diode lasers (typically 800 to 1000 nm), or laser beam sources emitting radiation in the near-infrared (typically 1064 nm), particularly with a wavelength in the range of 200 to 650 nm. Lasers suitable for microprocessing are known to those skilled in the art and include, for example, HeNe lasers, HeAg lasers (approx. 224 nm), NeCu lasers (approx. 249 nm), Nd:YAG lasers (approx. 355 nm), YAG lasers (approx. 532 nm), and InGaN lasers (approx. 532 nm).

[0081] In a further embodiment, the device according to the invention comprises at least one further laser radiation source, which is configured to generate a laser beam that interferes with the laser beam of the first laser radiation source, or with the laser beam of the first laser radiation source divided into partial beams, in an interference region. The further laser radiation source has the same properties as described above, which may be the same as or different from those of the first laser radiation source. Optical elements

[0082] The present invention comprises a plurality of optical elements. These elements are primarily prisms and lenses.

[0083] These lenses can be refractive or diffractive. Spherical, aspherical, or cylindrical lenses can be used. In a preferred embodiment, cylindrical lenses are employed. This makes it possible to compress the overlapping regions of the partial beams (also referred to herein as interference pixels) in one spatial direction and stretch them in another. If the lenses are not spherical / aspherical but cylindrical, this has the advantage that the beams can be deformed simultaneously. This allows the processing spot (i.e., the interference pattern generated on the substrate) to be deformed from a point into a line containing the interference pattern. With sufficient laser energy, this line can be in the range of 10–15 mm long (and approximately 100 µm thick).

[0084] Furthermore, spatial light modulators (SLMs) can be used for beam shaping. Those skilled in the art are aware of the use of SLMs for spatially modulating the phase or intensity, or the phase and intensity, of an incident light beam. The application of liquid crystal on silicon (LCoS) SLMs for beam splitting is described in the literature and is also conceivable in the device according to the invention. In addition, SLMs can also be used to focus the partial beams onto the substrate. Such an SLM can be controlled optically, electronically, or acoustically.

[0085] All optical elements described below are arranged in the beam path (3) of the laser. For the purposes of the invention, the beam path of the laser refers to the path of both the laser beam emitted by the laser radiation source and the path of the partial beams split by a beam splitter element. However, the optical axis of the beam path (3) is understood to be the optical axis of the laser beam emitted by the laser radiation source (1). Unless otherwise stated, all optical elements are arranged perpendicular to the optical axis of the beam path (3). Beam splitter element (2)

[0086] In the beam path (3) of the laser, downstream of the laser radiation source (1), there is a beam splitter element (2). The beam splitter element (2) can be a diffractive or a refractive beam splitter element. Diffractive beam splitter elements are also referred to simply as diffractive optical elements (DOEs). For the purposes of the invention, a diffractive beam splitter element is an optical element that contains micro- or nanostructures, preferably microstructures, which split an input beam into different beams according to the different diffraction orders. For the purposes of the invention, a refractive beam splitter element is a beam splitter element in which the beams are split due to differences in refractive index at surfaces, these surfaces being typically transparent optical elements, such as a prism or a double prism.Preferably, the beam splitter element (2) is a diffractive optical beam splitter element.

[0087] In a preferred embodiment, the beam splitter element is a single optical element, in particular a diffractive or refractive optical element, which is designed such that the division of the incident laser beam is based on the optical properties of the beam splitter element. This advantageously ensures that, compared to a multi-part beam splitter element consisting of several optical elements (e.g., mirrors, prisms, etc.), a simpler optical design can be implemented. The desired beam division can be achieved without the need for calibration or adjustment of the arrangement of multiple optical elements relative to each other. Furthermore, the mobility of the beam splitter element within the beam path is easy to implement, as only the movement of a single optical element is required.Furthermore, the use of a one-piece beam splitter element results in fewer components that are prone to wear and tear and may need to be replaced.

[0088] According to one possible embodiment, the beam splitter is designed as a polarizing beam splitter, in which one of the resulting beams has a different polarization than the other, or as a non-polarizing beam splitter, in which the polarization plays no role in the division of the beam.

[0089] In a preferred embodiment, the beam splitter element (2) divides the emitted laser beam into at least 3, preferably at least 4, in particular 4 to 8, i.e. 4, 5, 6, 7, or 8 partial beams.

[0090] In a further embodiment, the beam splitter element (2) divides the emitted laser beam into at least 2, preferably at least 3 to 4, in particular 4 to 10, i.e. 4, 5, 6, 7, 8, 9 or 10 partial beams.

[0091] The beam splitter element (2) is freely movable along its optical axis. That is, it can be moved towards or away from the laser radiation source along its optical axis. The movement of the beam splitter element (2) changes the spread of the at least three partial beams, causing them to strike a focusing element at different distances from one another. This allows the angle θ at which the partial beams strike the substrate (5), preferably a planar and / or transparent substrate, to be changed. Thus, when four partial beams are superimposed, a seamless change in the structure period Λ is achieved. Λ = λ 2 sinθ where λ is the wavelength of the emitted laser beam.

[0092] According to a preferred embodiment of the present invention, the beam splitter element is designed as a rotating element. This advantageously allows the polarization of the partial beams to be modified.

[0093] Particularly preferably the angle θ at which the partial rays strike the substrate (5), preferably a planar and / or transparent substrate, is 0.1° to 89.9°, preferably 5° to 85°, particularly preferably 10° to 60°, most preferably 15° to 45°.

[0094] The angle θ also depends on the distances between the optical elements, in particular the distance of the optical elements to the beam splitter element, and especially the distance of the focusing element to the beam splitter element. Depending on the desired structure period to be generated on or in the planar and / or transparent substrate, the position of the beam splitter element can be adjusted or calculated so that the desired structure period is achievable. The position of the optical elements encompassed by the device, in particular the position of the focusing element, is taken into account in relation to the beam splitter element in such a way that the position of the beam splitter element can be adjusted accordingly for larger or smaller distances between the optical elements.

[0095] To generate a structured substrate with antireflection properties, it has proven particularly advantageous to set a distance of 10 to 300 nm between the beam splitter element (2) and the deflection element (7).

[0096] According to one embodiment, point-like structures having small structure periods, preferably on average in the range of 100 nm to 1,000 nm (or as further defined herein), can be generated directly by applying an interference pattern, wherein the distance between the beam splitter element (2) and the deflection element (7) is large, e.g. in the range of 40 mm to 200 mm, in particular 80 mm to 150 mm.

[0097] According to a further embodiment, point-like structures exhibiting small structure periods, preferably on average in the range of 100 nm to 1,000 nm (or as further defined herein), can be generated by a self-organizing process of the LIPSS, wherein the distance between the beam splitter element (2) and the deflection element (7) is small, e.g., in the range of 1 mm to 100 mm, in particular 50 mm to 75 mm, and most preferably 10 mm to 50 mm. This allows an interference pattern with large structure periods to be generated by directly applying an interference pattern, overlaid with the point structure in the submicrometer range (as defined herein).

[0098] According to a preferred embodiment of the invention, the device also includes a measuring device, in particular a measuring device which operates by means of a laser or an optical sensor, which is configured to measure the position of the beam splitter element and optionally the distance of the beam splitter element to the other optical elements, in particular to the position of the focusing element.

[0099] Furthermore, the device according to the invention can comprise a control unit connected to the measuring device via a signal, which is in particular connected to a computing unit in such a way that the measured position of the beam splitter element is comparable to a first predetermined reference value, wherein the control unit is programmed such that, if the distance of the beam splitter element to the other optical elements, in particular to the position of the focusing element and / or the deflecting element (7), is greater or less than the first predetermined reference value, then a control signal is generated via the control unit with which at least one position of an optical element, in particular the beam splitter element (2), is changed in such a way, in particular the beam splitter element (2) in relation to the deflecting element (7), that the desired structure period is generated on the substrate.

[0100] In this context, the process for producing a substrate with a dot structure in the micro- or submicrometer range may also include the following steps, particularly after step (a): (i) Measuring the position of the beam splitter element (2) and, optionally, the distance of the beam splitter element to the other optical elements or to at least one of the other optical elements, in particular to the position of the focusing element (4) and / or the deflecting element (7), (ii) comparing the measured position of the beam splitter element with a first predetermined reference value, and (iii) if the measured distance of the beam splitter element to the other optical elements or to at least one of the other optical elements, in particular to the position of the focusing element (4) and / or the deflecting element (7), is greater or less than the first predetermined reference value: changing the position of the optical element, in particular the beam splitter element (2) such that (in particular in relation to the other optical elements, especially preferably the beam splitter element (2) in relation to the deflecting element (7)).that the desired structural period is generated on the substrate.

[0101] The division of the laser beam in the beam splitter element (2) can be achieved by either a partially reflective beam splitter element, for example a semi-transparent mirror, or a transmissive beam splitter element, for example a dichroic prism.

[0102] In a preferred embodiment, further beam splitter elements are arranged downstream of the beam splitter element (2) in the laser beam path. These beam splitter elements are arranged such that they divide each of the at least three partial beams into at least two further partial beams. This allows a higher number of partial beams to be generated, which are directed onto the substrate, preferably a planar and / or transparent substrate, so that they interfere on the surface or within the substrate. This allows the structure period of the interference pattern to be adjusted. Focusing element (4)

[0103] Furthermore, a focusing element (4) is arranged downstream of the beam splitter element (2) in the beam path (3) of the laser. The focusing element (4) is configured such that the partial beams pass through it in such a way that they interfere on the surface or inside a substrate (5) to be structured within an interference region. The focusing element (4) focuses the at least three partial beams in one spatial direction without focusing the at least three partial beams in the spatial direction perpendicular to it. For example, the focusing element (4) can be a focusing optical lens. For the purposes of the invention, focusing means bundling the at least three partial beams on the surface or inside a substrate, preferably a planar and / or transparent substrate.

[0104] The focusing element (4) can be freely movable in the beam path (3). According to a preferred embodiment of the present invention, the focusing element (4) is fixed in the beam path or along the optical axis.

[0105] It is understood that the optical elements defined herein, for example for beam splitting and for aligning the partial beams towards a substrate to be structured accordingly, can be arranged in a common housing.

[0106] In a preferred embodiment, the focusing element (4) is a spherical lens. The spherical lens is configured such that the incident at least three partial beams pass through it in such a way that they interfere on the surface or in the interior of the substrate (5) to be structured, preferably a planar and / or transparent substrate, within an interference region. The width of the interference region is preferably 1 to 600 µm, particularly preferably 10 to 400 µm, and most preferably 20 to 200 µm. This allows a high structuring rate, for example as defined herein, to be achieved.

[0107] In a particularly preferred embodiment, the focusing element (4) is a cylindrical lens. The cylindrical lens is configured such that the area in which the at least three partial beams overlap on the surface or within the substrate (5), preferably a planar and / or transparent substrate, is stretched in one spatial direction. This causes the area of ​​the substrate on which the interference pattern can be generated to assume an elliptical shape. The major semi-axis of this ellipse can have a length of 20 µm to 15 mm. This increases the area that can be patterned in a single irradiation. First deflection element (7)

[0108] In a particularly preferred embodiment, a deflecting element (7) is arranged upstream of the focusing element (4) and downstream of the beam splitter element (2), preferably in the beam path (3) of the laser. This deflecting element (7) is used to widen the distances between the at least three partial beams and can thus also change the angle at which the partial beams strike the substrate (5), preferably a planar and / or transparent substrate. It is configured to increase the divergence of the at least three partial beams and thus move the area in which the at least three partial beams interfere away from the laser radiation source (1) along the optical axis of the beam path (3).

[0109] In the context of the invention, widening the distances between the at least three partial beams means that the angle of the respective partial beams to the optical axis of the laser beam emitted by the laser radiation source (1) increases.

[0110] The widening and resulting deflection of the partial beams has the advantage that the partial beams can be more tightly focused by the focusing element (4). This results in a higher intensity in the area where the at least three partial beams interfere on the surface or inside the substrate (5), preferably a planar and / or transparent substrate.

[0111] By selecting a suitable deflection element, a unit for controlling the intensity of the laser beam can be dispensed with. In a preferred embodiment of the device, a deflection element (7) is used which, by widening the at least three partial beams, allows the focusing of the at least three partial beams on the substrate (5) by means of a focusing element (4), whereby the intensity of the interference points on the surface or in the interior of the substrate, preferably a planar and / or transparent substrate, can be achieved without additional adjustment of the intensity of the laser radiation source (1). This has the advantage that even low-intensity laser radiation sources (power per unit area) can be used to structure the substrate and generate the periodic point structure, thereby protecting the optical elements from wear. Further deflection element (6)

[0112] Furthermore, it can be provided that a further deflecting element (6) is arranged downstream of the beam splitter element (3) in the beam path (3) of the laser radiation source (1), which deflects the partial beams such that they run essentially parallel to each other after exiting the further deflecting element (6). This allows the device to be configured such that the processing point, i.e., the point at which the at least three partial beams interfere on the surface or inside the substrate, preferably a planar and / or transparent substrate, remains constant when the beam splitter element is moved along its optical axis in the laser beam path.In this document, the term "essentially parallel" is understood to mean an angular offset of between +15° and -15°, particularly between +10° and -10°, and most preferably between +5° and -5° between the two partial beams, but especially of course a very small angular offset, i.e., +1° to -1°. Ideally, the angular offset is 0°, although slight deviations due to manufacturing tolerances of the optical elements are possible.

[0113] The further deflecting element (6) can be a conventional refractive lens. Alternatively, the further deflecting element (6) can also be designed as a diffractive lens (e.g., a Fresnel lens). Diffractive lenses have the advantage of being significantly thinner and lighter, which simplifies miniaturization of the device disclosed herein.

[0114] By appropriately selecting the refractive indices of the optical elements (4), (6), and (7), the distances between the optical elements and the substrate, as well as the structure period Λ, can be adjusted. All optical elements, with the exception of the beam splitter element (2), can preferably be fixed within the beam path (3) of the laser. This particularly preferred embodiment therefore offers the advantage that only one element, namely the beam splitter element (2), needs to be moved to adjust the interference range or the interference angle. This eliminates setup steps, such as calibrating the device to the desired structure period. Furthermore, a fixed setting, i.e., preferably with all optical elements fixed within the beam path (3) of the laser, prevents wear on the optical elements. Polarization element (8)

[0115] In a further embodiment, a polarization element (8) is located behind the deflecting element, particularly preferably in a setup with two deflecting elements (6), (7) behind the further deflecting element (6), and in front of the focusing element (4) in at least one of the beam paths of the at least 3 partial beams. The polarization elements can modify the polarization of the partial beams relative to each other. This allows the resulting interference pattern, which the at least 3 partial beams project onto the surface or in the volume of a substrate, preferably a planar and / or transparent substrate, to be modified.By arranging a polarization element (8) in at least one of the beam paths of the partial beams, preferably not in every beam path of the partial beams, preferably in a beam path up to (n-1) beam paths, where n is the number of partial beams generated in the application process, the polarization plane of at least one partial beam in the beam path can advantageously be rotated and thus the pattern of an interference pixel in the plane of the substrate can be "disturbed".

[0116] In particular, the interfering partial beams can therefore be unpolarized, linearly polarized, circularly polarized, elliptically polarized, radially polarized, or azimuthally polarized. Optical element for beam shaping

[0117] In a further embodiment, the laser radiation source (1) has a radiation profile corresponding to a Gaussian profile, as described above. In such an embodiment, a further optical element for beam shaping can be located behind the laser radiation source (1) and in front of the beam splitter element (2). This element serves to adapt the radiation profile of the laser radiation source to a top-hat profile.

[0118] The device according to the invention can also include an optical element with a concave parabolic or planar reflective surface, wherein the optical element is, for example, rotatable about at least one axis or displaceable along the beam path (3). This may eliminate the need for an additional focusing element (4) or a further deflecting element (6) positioned in the beam path (3). For example, this optical element can direct laser beams or partial laser beams onto the surface of the focusing element (4) or another focusing optical element before the beams reach the substrate to be structured in order to form structural elements.

[0119] Alternatively, for example, at least one optical element with a concave parabolic or planar reflective surface can be provided, which is designed to be rotatable about at least one axis or displaceable along the beam path (3), wherein this optical element is positioned downstream of the first deflecting element (7) and the further deflecting element (6) in the beam path. In this way, for example, the partial beams in the beam path can be deflected (deflection mirror) or focused in the beam path in such a way that the substrate to be structured can be positioned in a fixed position during processing (so-called focusing mirror or galvo mirror (laser scanner) (9)).

[0120] Another conceivable embodiment includes a polygon scanner. In this configuration, at least one optical element comprises a periodically rotating prism, preferably a periodically rotating mirror prism, in particular a polygon mirror or polygon wheel, and a focusing element (4) arranged downstream of the periodically rotating prism in the beam path. The focusing element is configured such that the partial beams pass through it in such a way that the partial beams interfere on the surface or inside a substrate (5) to be structured in an interference region. In a preferred embodiment, the optical element further comprises at least one additional deflecting element, for example, a reflective deflecting element for deflecting the partial beams in the beam path. The at least one additional deflecting element can be arranged upstream and / or downstream of the periodically rotating prism in the beam path.At least one further deflection element is positioned upstream of the focusing element in the beam path.

[0121] Such a setup advantageously allows for the rapid scanning of a substrate surface, enabling a high structuring rate of up to 3 m² / min, particularly in the range of 0.05 to 2 m² / min, especially preferably in the range of 0.1 to 1 m² / min, and most preferably in the range of 0.1 to 0.9 m² / min. The exact structuring rate depends primarily on the available laser power. Therefore, even higher structuring rates will be achievable with future technologies that offer higher laser power. Holding device for the substrate

[0122] In a further embodiment, the substrate (5), preferably a planar and / or transparent substrate, is movable in the xy-plane. By moving the substrate (5), preferably a planar and / or transparent substrate, in the xy-plane, planar processing by means of laser interference structuring can be achieved. In each processing step (i.e., the laser pulse that strikes the substrate to be structured), an interference pixel (as defined herein) is generated, which has a size D depending on the angle of incidence and the intensity distribution of the laser beam, as well as the focusing properties of the optical elements. The distance between the different interference pixels, the pixel density Pd, is determined by the repetition rate of the laser radiation source (1) and the movement of the substrate relative to the focusing point of the optical elements, i.e., the point at which the interference region is generated on the surface or in the interior of the substrate.If the pixel density Pd is smaller than the size of the interference pixels D, then a flat, homogeneous processing is possible.

[0123] By moving the substrate in relation to the focal point (which generates the interference pixel) in combination with pulsed laser (partial) beams, a planar, optionally homogeneous and periodic, point structure can be generated on the surface or inside a substrate, preferably a planar and / or transparent substrate.

[0124] As an alternative to moving the substrate relative to the focusing point, the focusing point can also be moved across the sample or substrate (e.g., using scanner-based methods).

[0125] Moving the substrate to be structured, preferably a planar and / or transparent substrate, within the laser beam can be comparatively complex and slow due to the relatively large masses involved. It is therefore advantageous to keep the substrate, preferably a planar and / or transparent substrate, stationary during processing and to achieve planar structuring of the substrate by focusing the partial beams onto the surface or volume of the substrate through manipulation of the laser beams with optical elements (focusing mirrors or galvo mirrors (laser scanners)) in the beam direction. Since the masses involved are relatively small, this can be achieved with significantly less effort and much faster. Preferably, the substrate is stationary during the process. Proceedings

[0126] The present invention also includes a method for producing a substrate, preferably a planar and / or transparent substrate, with a periodic dot structure in the micro or submicrometer range by means of laser interference structuring.

[0127] According to the invention, the method for producing a structured substrate, preferably a planar and / or transparent substrate, with a periodic dot structure in the micro- or sub-micrometer range by means of laser interference structuring comprises the following steps: A substrate (5), preferably a planar and / or transparent substrate, is provided, which is located on a holding device. A laser beam is emitted from a laser radiation source (1). The laser beam is split by a beam splitter element (2) and at least three, particularly preferably four, partial beams. The partial beams strike a focusing element (4), which focuses (bundles) the at least three, particularly preferably four, partial beams on the surface or in the interior of the substrate (5), preferably a planar and / or transparent substrate, such that the partial beams interfere constructively and destructively on the surface or in the interior of the substrate.Thus, a periodic dot pattern in the micro- or sub-micrometer range is generated on the surface or in the interior of the substrate (5), preferably a planar and / or transparent substrate, by laser interference processing. The method is characterized in that the at least three partial beams are superimposed in such a way as to create a 2D pattern.

[0128] According to a further embodiment of the invention, the laser beam is divided into at least two partial beams by the beam splitter element. The partial beams strike a focusing element (4), which focuses (bundles) the at least three, particularly preferably four, partial beams on the surface or within the substrate (5), preferably a planar and / or transparent substrate, so that the partial beams interfere constructively and destructively on the surface or within the substrate. Thus, a periodic dot pattern in the micro- or sub-micrometer range is generated on the surface or within the substrate (5), preferably a planar and / or transparent substrate, by laser interference processing. The method is characterized in that the at least three partial beams are superimposed in such a way that a 1D pattern, in particular a line pattern, is created.

[0129] The point structures thus generated are formed in the form of periodically arranged, inverse cones, wherein the distance between the vertices (i.e., the center of height or centers of the elevations) is on average in the range of 50 nm to 50 µm, preferably in the range of 50 nm to 20 µm, particularly preferably in the range of 100 nm to 4 µm, more preferably in the range of 100 nm to 2 µm, even more preferably in the range of 200 nm to 1.5 µm, and most preferably in the range of 300 nm to 800 nm.

[0130] The inventors of the present invention have further discovered that, in addition to periodicity, the structure depth (i.e., the depth of the inverted cones, measured from their saddle point of the depression to the vertex) or profile depth also influences the antireflection properties (as defined herein). For example, the structure depth or profile depth of the inverted cones (protrusions and depressions) is, on average, in the range of 5 nm to 500 nm, preferably in the range of 5 nm to 300 nm, most preferably in the range of 5 nm to 100 nm, and even more preferably in the range of 5 nm to 75 nm. The structure depth of the inverted cones of an interference pixel is generally described by the mean structure depth (d50), which, within an interference pixel, defines the 50% of cones with a specific structure depth smaller or larger than the specified value for the structure depth.

[0131] According to a preferred embodiment of the present invention, the inverse cones have a structural depth in the range of 5 nm to 200 nm, particularly preferably in the range of 5 nm to 150 nm, and most preferably 10 nm to 100 nm.

[0132] A device for producing a structured substrate (5), preferably a planar and / or transparent substrate, is preferably used, comprising two deflection elements (6), (7). The deflection elements (6), (7) are arranged in the beam path (3) of the laser between the beam splitter element (2) and the focusing element (4). The deflection elements (6), (7) serve to widen the diffraction angle of the at least three, particularly preferably four, partial beams by interfering on the surface or inside the substrate (5), preferably a planar and / or transparent substrate. By adjusting the distances between the optical elements, it can be ensured that only the beam splitter element (2) needs to be movable along its optical axis to change the structure period. This facilitates easier adjustment processes during processing.

[0133] In a particularly preferred embodiment, a transparent material is provided as a planar substrate. Due to the light transmission of the transparent material, laser interference processing is possible, preferably with an embodiment of the aforementioned device inside the substrate.

[0134] In a preferred embodiment, a device for producing a structured substrate, preferably a planar and / or transparent substrate, is used, which employs a pulsed laser radiation source (1). In a particularly preferred embodiment, a device for producing a structured substrate, preferably a planar and / or transparent substrate, is used, which has a holding device for the substrate that is freely movable in the xy-plane, perpendicular to the beam path (3) of the laser beam emitted by the laser radiation source (1).

[0135] The pixel density Pd, i.e. the distance at which an interference pixel with width D can be applied to the substrate, preferably a planar and / or transparent substrate, can be adjusted via the frequency of the laser radiation source (1), f, and the speed of movement of the holding device, v: Pd = v f

[0136] If the width of the interference pixel, D, is greater than the pixel density Pd, then neighboring interference pixels overlap in a region. This region is known to those skilled in the art as pulse overlap, OV. It can be calculated as: OV = D − Pd D

[0137] In a preferred embodiment of the process for producing a structured substrate, preferably a planar and / or transparent substrate, Pd is smaller than D. The resulting pulse overlap OV leads to multiple irradiations of the substrate, preferably a planar and / or transparent substrate. This preferably avoids the formation of non-textured areas.

[0138] In a particularly preferred embodiment of the process for producing a structured substrate, preferably a planar and / or transparent substrate, the same interference pixels are irradiated multiple times. This makes it possible to increase the depth of the resulting microstructures.

[0139] The advantage of a structured substrate produced by such a method, preferably a planar and / or transparent substrate, is the high regularity of the generated periodic dot structures with structural dimensions in the micro- or sub-micrometer range. A periodic dot structure produced in this way with dimensions in the micro- or sub-micrometer range preferably has a coefficient of variation (a value resulting from dividing the standard deviation by the mean value) of the cone cross-section of 15% or less, more preferably 10% or less, and even more preferably 5% or less.

[0140] In particular, multiple irradiations of a substrate are suitable for the fabrication of hierarchical structures. Multiple irradiations of the same interference pixel cause at least partial melting of the substrate material. During the structuring process, i.e., upon impact of a laser pulse, a wave structure forms as a result of the occurrence of a high-intensity region. This structuring, and especially the wave structure, develops through a self-organizing process. Specifically, the wave structure is superimposed on a periodic dot pattern in the micro- or sub-micrometer range, which can be generated using laser interference structuring. Thus, a hierarchical structure can be created in a substrate in a single process step.According to a preferred embodiment of the invention, multiple irradiations, preferably 2 to 400, more particularly 20 to 300, and especially preferably 50 to 200, of the same interference pixel on the substrate are carried out, whereby a wave structure (as defined herein) is formed, in particular a periodic dot structure composed of superimposed structures, wherein at least one structure has dimensions in the submicrometer range, in particular a quasi-periodic wave structure, and wherein at least one structure is formed from inverted cones. The time offset between the individual pulses is particularly preferably in the range of the pulse duration of the laser pulse, preferably in the range of 1 fs to 100 ns, particularly preferably in the range of 10 fs to 10 ns, and most preferably in the range of 10 fs to 15 ps.

[0141] A hierarchical structure is defined as a structure in which a first structure with dimensions in the micro- or sub-micrometer range, corresponding to an interference pattern, is superimposed by a further structure with dimensions smaller than those of the first structure, formed through a self-organizing process. Preferably, the dimensions of the further structure formed through a self-organizing process are in the range of 1% to 30% of the dimensions of the first structure, which corresponds to an interference pattern.

[0142] Hierarchical structures have numerous technical applications, such as the production of substrates with hydrophobic or superhydrophobic as well as hydrophilic or superhydrophilic surfaces, and substrates with anti-icing or anti-fogging properties, in addition to the aforementioned substrates with antireflection properties. A method for producing such hierarchical structures, as described herein, advantageously allows for the precise adjustment of the process parameters for the structure dimensions by selecting a suitable laser radiation source and correspondingly shifting the beam splitter element within the laser beam path.

[0143] In addition, the method defined herein makes it possible to provide a substrate with hierarchical structures using the same device and in the same process step, whereas conventional processes proceed successively, i.e., they are not able to simultaneously create a first structure with dimensions in the micro- or sub-micrometer range, which corresponds to an interference pattern, and a further structure, which is formed by a self-organization process.

[0144] Moving the substrate to be structured, preferably a planar and / or transparent substrate, within the laser beam is comparatively complex and slow due to the relatively large masses involved. It is therefore advantageous to keep the substrate, preferably a planar and / or transparent substrate, stationary during processing and to achieve planar structuring of the substrate by focusing the partial beams onto the surface or volume of the substrate through manipulation of the laser beams with optical elements (focusing mirrors or galvo mirrors (laser scanners)) in the beam direction. Since the masses involved are relatively small, this can be achieved with significantly less effort and much faster. Preferably, the substrate is stationary during the process.

[0145] Of course, the planar structuring of the substrate is also fundamentally possible by shifting the substrate in the laser beam.

[0146] The periodic structures in the micro- and / or nanometer range produced by the method and apparatus disclosed herein give the structured substrate antireflection properties. This is ensured by the fact that light incident on the substrate is reflected less or at such a shallow angle that it does not appear "disturbing" when viewing the material surface normally.

[0147] The invention therefore also encompasses a structured substrate with antireflection properties comprising a periodic dot structure in the micro- or submicrometer range, wherein the periodic dot structure is formed from inverted cones, the inverted cones being periodically arranged with a distance relative to their saddle point or center point in the range of 50 nm to 50 µm, preferably in the range of 50 nm to 20 µm, particularly preferably in the range of 100 nm to 4 µm, more preferably in the range of 100 nm to 2 µm, even more preferably in the range of 200 nm to 1.5 µm, more preferably in the range of 100 nm to 1,000 nm, and most preferably in the range of 300 nm to 800 nm to each other.

[0148] According to a preferred embodiment of the invention, the structured substrate is obtained by processing with a method as defined herein.

[0149] The present invention also relates to a method for producing a substrate with a periodic dot structure in the micro- or sub-micrometer range by means of laser interference structuring, in particular by a method disclosed herein, comprising the following steps: a) Applying a first pulse to the surface of a substrate (5), preferably by a device as defined herein, which generates a first interference pixel on the surface of the substrate (5) or in the substrate (5), b) Applying a second pulse to the surface of a substrate (5), preferably by a device as defined herein, which generates a second interference pixel on the surface of the substrate (5) or in the substrate (5), wherein the first and the second interference pixel each independently comprise a periodic dot structure with dimensions in the micro- and sub-micrometer range, characterized in that the offset between the second interference pixel and the first interference pixel is in the range of 10% ≤ x ≤ 50% of the interference period.

[0150] This makes it particularly advantageous to create a structure on the substrate, especially on a transparent substrate, that has anti-glare properties.

[0151] In the context of the invention, glare refers to the reflection of light from a light source (e.g., the sun) on a transparent substrate, such as a window or a screen, which can make it difficult to see what is happening on the screen.

[0152] These glare effects can be reduced by using an anti-glare treatment on the surfaces (typically achieved through coatings in the prior art). An anti-glare structure scatters incident light at the surface, thus significantly reducing reflections.

[0153] According to a preferred embodiment of the invention, the period of the dot structure of the first interference pixel and the period of the second interference pixel are identical.

[0154] Furthermore, it can be provided that after step b) a third pulse is applied to the surface of a substrate (5), preferably by a device as defined herein, wherein the third interference pixel comprises a periodic dot structure with dimensions in the micro- and submicrometer range, wherein the third pulse generates a third interference pixel on the surface of the substrate (5) or in the substrate (5), wherein the third interference pixel has an offset relative to the second interference pixel in the range of 10% ≤ x ≤ 50% of the interference period,

[0155] Method according to claim 17 or 18, wherein the offset of the interference period is uniform in at least one spatial direction. Structured substrate

[0156] The inventors have discovered that substrates structured primarily by a device or method disclosed herein exhibit pronounced antireflection properties. The present invention therefore also relates to a structured substrate with antireflection properties, as defined herein, comprising a periodic dot structure in the micro- or submicrometer range, wherein the periodic dot structure is formed, in particular, from an inverted cone structure (hereinafter also referred to as inverted cones), wherein the inverted cones are periodically spaced at intervals relative to their saddle point or center point in the range of 50 nm to 50 µm, preferably in the range of 50 nm to 20 µm, particularly preferably in the range of 100 nm to 4 µm, more preferably in the range of 100 nm to 2 µm, even more preferably in the range of 200 nm to 1.5 µm, and more preferably in the range of 100 nm to 1.000 nm is particularly preferred in the range of 300 nm to 800 nm.

[0157] The resulting periodic dot structure has the property that, depending on its structural dimensions, incident electromagnetic radiation with wavelengths in the range of 10 nm to 1 mm is increasingly transmitted or diffracted by the periodic structures, resulting in reduced reflection at the substrate surface. If the period of the generated periodic dot structure is close to the wavelength of the incident electromagnetic wave, it is diffracted at the substrate surface. If the period of the generated periodic dot structure is smaller than the wavelength of the incident electromagnetic wave, it is transmitted.

[0158] The periodic dot structure is preferably designed such that the structured substrate transmits electromagnetic radiation with a wavelength greater than 550 nm for a periodic dot structure of less than 1,000 nm, more preferably greater than 500 nm for a periodic dot structure of less than 750 nm, and most preferably greater than 450 nm for a periodic dot structure of less than 600 nm. Depending on the structure depth of the inverted cones, wavelengths in the red and / or yellow light spectrum, the green light spectrum, and even the blue light spectrum can thus be transmitted into the substrate.

[0159] The refractive index of the structured substrate is gradual due to the generated periodic point structure. It decreases with increasing height of the structure, so that no clear air-medium interface exists. This results in increased transmission of incident electromagnetic waves with a wavelength greater than the structure period of the generated point structure, and diffraction of incident electromagnetic waves with a wavelength on the order of the structure period of the generated point structure.

[0160] Due to the very small structural dimensions that can be produced, the device and method disclosed herein for producing an antireflection structure are also suitable for producing surfaces with hydrophobic and / or superhydrophobic as well as hydrophilic and / or superhydrophilic properties.

[0161] Hydrophobic properties depend on both the chemical and surface properties, particularly the surface roughness, of a substrate. The inventors have now surprisingly discovered that, by incorporating structures in the micrometer and submicrometer range, especially superimposed structures (as defined herein), the inventive process yields substrate surfaces that exhibit superhydrophobic and self-cleaning properties, particularly hydrophobic substrates. Substrates with superhydrophobic properties are especially preferred if they have a hierarchical surface structure.Hierarchical surface structuring, as used here, refers to a surface with regular structures on it, measuring in the micrometer range, which in turn exhibit their own surface structures with submicrometer dimensions. Such hierarchical structuring can lead to high surface roughness.

[0162] The inventors have also discovered that substrates structured primarily by a device or method disclosed herein exhibit pronounced hydrophobic properties on their surface. Using the device and method disclosed herein for generating antireflection structures with dimensions in the micro- and submicrometer range, it is also possible to structure a substrate to create a surface texture, in particular a surface roughness, that results in the substrate exhibiting hydrophobic or superhydrophobic properties. Hydrophobic material properties can be generated by creating a structure with dimensions in the micro- and / or submicrometer range using direct laser interference structuring.In a preferred embodiment, a structure with micrometer-scale dimensions is first generated on the surface. Then, by moving the beam splitter element in the laser beam path, a structure with submicrometer-scale dimensions is generated on the surface of the first structure, preferably by multiple irradiations of the substrate. The hierarchical structure thus generated has hydrophobic or superhydrophobic properties.

[0163] To create a substrate with hydrophobic properties, it is also conceivable to create only a structure with dimensions in the micro- or sub-micrometer range without moving the beam splitter element in an intermediate step.

[0164] Advantageously, substrates with hydrophobic and / or superhydrophobic properties can be produced using the same method and based on the same device in a technically straightforward manner by generating a periodic dot structure in the micro- or sub-micrometer range and / or a periodic dot structure with a hierarchical structure in the micro- and sub-micrometer range. By moving the beam splitter element, at least two, but also any number of additional, structuring elements can be created on the substrate surface without further modification of the setup, e.g., without exchanging optical elements or moving the substrate. This increases both the precision in the alignment of the structures and the speed of the process compared to conventional methods or devices.

[0165] The inventors have established a correlation between the surface properties of a substrate and ice formation on its surface. Specifically, so-called anti-icing properties can be generated if the surface structure of a substrate is sufficiently small. Research results have shown that a substrate with superhydrophobic properties can also exhibit anti-icing properties.

[0166] For the purposes of the invention, anti-icing properties mean that no or very little water freezes on the surface of a substrate, this property being attributable to the surface texture, in particular the surface roughness.

[0167] Such a substrate can be advantageously used in the aerospace industry, in wind turbines, in the field of automotive components or also in telecommunications and antenna technology to protect exposed components from icing.

[0168] The inventors have further discovered that substrates structured primarily by a device or method disclosed herein exhibit pronounced hydrophilic properties on their surface. Using the device and method disclosed herein for generating antireflection structures with dimensions in the micro- and submicrometer range, it is also possible to structure a substrate to create a surface texture, in particular a surface roughness, which results in the substrate exhibiting hydrophilic or superhydrophilic properties.

[0169] Hydrophilic material properties can be generated by creating a structure with dimensions in the micrometer and / or submicrometer range using direct laser interference structuring. In a preferred embodiment, a structure with dimensions in the micrometer range is first created on the surface. Subsequently, by moving the beam splitter element in the laser beam path, a structure with dimensions in the submicrometer range is generated on the surface of the first structure, preferably by multiple irradiations of the substrate. The hierarchical structure thus created has hydrophilic or superhydrophilic properties.

[0170] To create a substrate with hydrophilic properties, it is also conceivable to create only a structure with dimensions in the micro- or sub-micrometer range without moving the beam splitter element in an intermediate step.

[0171] Advantageously, substrates with hydrophilic and / or superhydrophilic properties can be produced using the same method and based on the same device in a technically straightforward manner by generating a periodic dot structure in the micro- or sub-micrometer range and / or a periodic dot structure with a hierarchical structure in the micro- and sub-micrometer range. By moving the beam splitter element, at least two, but also any number of additional, structuring elements can be created on the substrate surface without further modification of the setup, e.g., without replacing optical elements or moving the substrate. This increases both the precision in the alignment of the structures and the speed of the process compared to conventional methods or devices.

[0172] The inventors have established a correlation between the surface properties of a substrate and the formation of condensation, particularly in the form of fog or mist, on its surface. Specifically, so-called anti-fogging properties can be generated if the surface structure of a substrate is sufficiently small. Research results have shown that a substrate with superhydrophilic properties can also exhibit anti-fogging properties.

[0173] For the purposes of the invention, anti-fogging properties mean that no or very little water condenses on the surface of a substrate in the form of droplets, this property being attributable to the surface texture, in particular the surface roughness.

[0174] Such a substrate can be advantageously used in the aerospace industry, in the field of automotive components or also in telecommunications and antenna technology to protect exposed components from fogging.

[0175] In one embodiment of the invention, the method and the apparatus disclosed herein are suitable for producing a substrate comprising a periodic dot structure in the micro- or sub-micrometer range, generated by laser interference structuring, and characterized by antireflection properties. For the purposes of the invention, antireflection properties refer to the increased transmission or diffraction of incident electromagnetic radiation with wavelengths in the visible light range, particularly with wavelengths in the range of 400 nm to 700 nm. The substrate is characterized in that the periodic dot structure it comprises preferably has dimensions in the sub-micrometer range, and particularly preferably in the nanometer range.The dimensions of the periodic dot structure are particularly favored in the range of the wavelength of electromagnetic radiation in the visible light range. The dimensions of the periodic dot structure are preferably in the range of 630 nm to 700 nm for transmitting or diffracting red light, in the range of 590 nm to 630 nm for transmitting or diffracting red and orange light, in the range of 560 nm to 590 nm for transmitting or diffracting red, orange, and yellow light, in the range of 500 nm to 560 nm for transmitting or diffracting red, orange, yellow, and green light, in the range of 475 nm to 500 nm for transmitting or diffracting red, orange, yellow, green, and turquoise light, in the range of 450 nm to 475 nm for transmitting or diffracting red, orange, yellow, green, turquoise, and blue light, and in the range of 425 nm to 450 nm for transmission, orDiffraction of red, orange, yellow, green, turquoise, blue, and indigo light in the range of 400 nm to 425 nm for transmission, or diffraction of red, orange, yellow, green, turquoise, blue, indigo, and violet light. Thus, the antireflection properties of the substrate can be controlled by changing the dimensions of the periodic dot structure.

[0176] In one embodiment of the invention, the method and the apparatus disclosed herein are suitable for producing a substrate comprising a periodic dot structure in the micro- or sub-micrometer range, generated by laser interference structuring, and characterized by antireflection properties. For the purposes of the invention, antireflection properties refer to the increased transmission or diffraction of incident electromagnetic radiation with wavelengths in the non-visible light range, particularly in the infrared range, or thermal radiation, particularly with wavelengths in the range of 780 nm to 1 mm. The substrate is characterized by the fact that the periodic dot structure it comprises preferably has dimensions in the micrometer range. Advantageously, the thermal transmission of the substrate can be adjusted by changing the dimensions of the periodic dot structure.

[0177] In one embodiment of the invention, the method and apparatus disclosed herein are suitable for producing a substrate comprising a periodic dot structure in the micro- or sub-micrometer range, generated by laser interference structuring, and characterized by antireflection properties. For the purposes of the invention, antireflection properties refer to the increased transmission or diffraction of incident electromagnetic radiation with wavelengths in the non-visible light range, particularly in the ultraviolet (IV) radiation range, especially with wavelengths in the range of 100 nm to 380 nm. The substrate is characterized by the fact that the periodic dot structure it comprises preferably has dimensions in the nanometer range. A substrate structured in this way is advantageously usable in areas where protection against UV radiation is necessary.

[0178] In a further embodiment of the invention, the method and the apparatus disclosed herein are suitable for producing a substrate that has hierarchical structures generated by laser interference structuring through multiple irradiations of the same interference pixel, and which are characterized by hydrophobic or superhydrophobic properties. These hydrophobic or superhydrophobic properties are due to the fact that structures with dimensions in the micro- or submicrometer range, in particular hierarchical structures with dimensions in the micro- and submicrometer range, alter the contact angle of liquids on the substrate in such a way that it becomes larger. A larger contact angle results in liquids that come into contact with the surface not wetting it well and instead beading up and rolling off. A substrate treated in this way exhibits self-cleaning and water-repellent properties.Particularly suitable materials for such a structured substrate are those materials which already have hydrophobic properties, e.g. metal or polymer surfaces.

[0179] In a further embodiment of the invention, the method and the apparatus disclosed herein are suitable for producing a substrate that has hierarchical structures generated by laser interference structuring through multiple irradiations of the same interference pixel. These structures exhibit anti-icing properties, i.e., properties that prevent the formation of ice layers. The anti-icing properties are based on the fact that structures with dimensions in the micro- or sub-micrometer range, in particular hierarchical structures with dimensions in the micro- and sub-micrometer range, alter the contact angle of liquids on the substrate in such a way that it becomes larger. The structured substrate thus exhibits hydrophobic or superhydrophobic properties. A larger contact angle means that liquids striking the surface do not wet it well and instead bead up and roll off.This also makes it more difficult for ice layers to form on the surface. Particularly suitable materials for such a structured substrate are those that already possess hydrophobic properties, such as metal or polymer surfaces.

[0180] In a further embodiment of the invention, the method and the apparatus disclosed herein are suitable for producing a substrate that has hierarchical structures generated by laser interference structuring through multiple irradiations of the same interference pixel, and which are characterized by hydrophilic or superhydrophilic properties. These hydrophilic or superhydrophilic properties are due to the fact that structures with dimensions in the micro- or submicrometer range, in particular hierarchical structures with dimensions in the micro- and submicrometer range, alter the contact angle of liquids on substrates such that it becomes smaller. A smaller contact angle results in liquids striking the surface wetting it very well and preventing droplet formation.Instead, a uniform wetting is achieved, which does not impair the transparency of the substrate. Particularly suitable materials for such a structured substrate are those that already exhibit hydrophilic properties, e.g., glass surfaces.

[0181] In a further embodiment of the invention, the method and the apparatus disclosed herein are suitable for producing a substrate that has hierarchical structures generated by laser interference structuring through multiple irradiations of the same interference pixel. These structures are characterized by anti-fogging properties. The anti-fogging properties are based on the fact that structures with dimensions in the micro- or sub-micrometer range, in particular hierarchical structures with dimensions in the micro- and sub-micrometer range, alter the contact angle of liquids on the substrate in such a way that it becomes smaller. The structured substrate thus exhibits hydrophilic or superhydrophilic properties. A smaller contact angle results in liquids hitting the surface wetting it very well, and no droplet formation occurs.Instead, a uniform wetting is achieved, which does not impair the transparency of the substrate. Particularly suitable materials for such a structured substrate are those that already exhibit hydrophilic properties, e.g., glass surfaces. Such a structured substrate can be advantageously used in the automotive, aerospace, and aviation industries, as well as more generally in glazing applications in building technology.

[0182] In one embodiment of the invention, the method and the apparatus disclosed herein are suitable for producing a substrate comprising a periodic dot structure in the micro- or sub-micrometer range, generated by laser interference structuring, which exhibits increased surface roughness. The increased surface roughness is based on the fact that the surface texture is altered by the periodic dot structure in the micro- or sub-micrometer range introduced into the substrate, in particular on the fact that the surface of the substrate has elevations and depressions due to the introduced periodic dot structure.In particular, increased surface roughness can be achieved by structuring a substrate with hierarchical structures in the micro- and sub-micrometer range using laser interference structuring with multiple irradiations of the same interference pixel, as described herein. A substrate treated in this way is advantageously suited for use in manufacturing, for example, to increase static and / or kinetic friction between technical components, or in medical technology to enhance cell adhesion to a foreign surface.

[0183] In one embodiment of the invention, the method and the apparatus disclosed herein are suitable for producing a substrate comprising a periodic dot structure in the micro- or sub-micrometer range, generated by laser interference structuring, which has an increased surface area compared to an unstructured substrate with the same external dimensions. The periodic dot structure in the micro- or sub-micrometer range contributes to the surface area of ​​the substrate increasing proportionally to the density of the interference areas per interference pixel.In particular, an increased surface area compared to an unstructured substrate with the same external dimensions can be achieved by structuring a substrate with hierarchical structures in the micro- and sub-micrometer range using the method and device described herein, through laser interference structuring by multiple irradiations of the same interference pixel. A substrate processed in this way is advantageously suited for use in technical applications requiring high heat transfer, as the increased surface area provides a greater heat exchange capacity compared to an unstructured substrate with the same external dimensions.Furthermore, a substrate treated in this way can be used in electrical connection technology to reduce contact resistance, since the increased surface area allows for more contact points between the materials to be connected compared to an unstructured substrate with the same external dimensions. In addition, such a structured substrate can be used in battery technology, particularly for structuring the anode and cathode, since the increased surface area provides greater capacity for the exchange of charge carriers between the electrode metals compared to an unstructured substrate with the same external dimensions.

[0184] Furthermore, the method and apparatus disclosed herein are suitable for producing a substrate comprising a periodic dot structure with dimensions in the micrometer or submicrometer range, which exhibits antibacterial (antiseptic) properties. In a preferred embodiment, the periodic dot structure has dimensions that are significantly larger, at least 10% to 30% larger, than the bacteria deposited on it. This isolates the bacteria deposited on the surface and thus renders them harmless. In a particularly preferred embodiment, the periodic dot structure has dimensions that are significantly smaller, at least 10% to 30% smaller, than the bacteria deposited on it. This prevents the bacteria from adhering to the surface, thus keeping the surface sterile.

[0185] A structured substrate produced by the method and apparatus disclosed herein is further suitable for further processing by means of a coating process, wherein the substrate can receive a physical and / or chemical coating. Such a coating can enhance the properties of the structured substrate, for example, its antireflective properties and / or hydrophilic and / or hydrophobic properties. Possible methods include applying a chemical spray coating and / or a coating by chemical vapor deposition and / or sputtering and / or sol-gel processes.

[0186] According to a preferred embodiment of the present invention, the structured substrate comprises a dot structure formed from a first and a second interference pixel, wherein the first and the second interference pixel each independently comprise a periodic dot structure with dimensions in the micro- and sub-micrometer range, wherein the first interference pixel and the second interference pixel are superimposed such that the offset between the second interference pixel and the first interference pixel is in the range of 10% ≤ x ≤ 50%, particularly in the range of 20% ≤ x < 50%, and most preferably in the range of 25% ≤ x ≤ 45% of the interference period. Particularly advantageously, this allows a structuring with anti-glare properties to be created on the substrate, especially on a transparent substrate, particularly with the dot structure dimensions defined herein (regardless of their application).

[0187] According to a preferred embodiment of the invention, the periodic dot structure is designed such that at least a third interference pixel is superimposed on the first and second interference pixels in such a way that the offset between the third interference pixel and the second interference pixel is in the range of 10% ≤ x ≤ 50%, in particular in the range of 20% ≤ x < 50%, and most preferably in the range of 25% ≤ x ≤ 45% of the interference period. Use of the structured substrate

[0188] The structured substrate with antireflective properties defined herein is used, for example, in photovoltaic systems, where the incorporation of antireflective properties can significantly increase the efficiency of these systems. A major challenge in the field of photovoltaic systems lies in the substantial losses due to the reflection of sunlight. On average, reflections cause 40% energy / power losses per system. The efficiency of photovoltaic systems must therefore be continuously improved. One of the most promising approaches is the reduction of reflection using antireflective coatings and / or surface texturing. The application of the method disclosed herein simplifies, accelerates, and improves the surface treatment.

[0189] Furthermore, it is known that monitors and screens are often placed in fixed locations and are therefore susceptible to unfavorable lighting conditions, which can lead to viewing problems for the user. While there are ways to minimize this effect, these approaches are not widely used because they tend to alleviate the symptoms rather than solve the underlying problem. The structured substrate with anti-reflective properties defined herein is ideally suited, for example, for application or integration within the display area, such as in the form of anti-reflective glazing for monitors, screens, and displays.

[0190] Another area of ​​application lies in the field of antireflection within optical fibers, which enables higher transmission rates and minimizes back reflections. The method disclosed herein is therefore ideally suited for structuring optical fibers, so that the structured optical fiber thus provides a further application example for a structured substrate with antireflection properties defined herein. The present invention therefore also encompasses the use of a structured substrate defined herein as a component of optical fibers.

[0191] Furthermore, the inventors have discovered that the method defined herein is suitable for structuring window panes (as another example of anti-reflective glazing). The structured substrates disclosed herein can thus be used, for example, as anti-reflective glazing or as a film on building facades, preferably flat and / or transparent substrates, as heat-insulating glazing, which can be used, for example, to protect against concentrated solar radiation through curved building facades and to improve the thermal insulation of buildings.

[0192] Furthermore, reducing reflection in microscopes and telescopes can increase the contrast of the images recorded, thereby increasing the efficiency and usability of these optical devices. The present invention therefore also encompasses the use of a structured substrate defined herein as an optical element with a periodic dot structure in the micro- or sub-micrometer range in optical devices such as microscopes and telescopes, for which beam guidance, beam shaping, beam focusing, and / or beam focusing are essential.

[0193] It is also advantageous to use the structured substrate defined herein as a negative mold (so-called master) within an embossing process for the indirect application or creation of structures on another substrate. This is relevant, for example, in roll-to-roll processes where structures are transferred from a so-called master (usually a metal such as nickel) to a polymer film (e.g., PET) in a continuous process using a hot or UV embossing process. Thus, the inverse structures can be produced on other substrates in high throughput as periodic dot structures in the micro- or sub-micrometer range.

[0194] The device and method according to the invention also offer the possibility of producing a substrate with hydrophobic or superhydrophobic properties over a large area without significant technical effort. Such a structured substrate has a wide range of applications in areas where the self-cleaning properties of hydrophobic and / or superhydrophobic substrates are desirable, e.g., in the field of automotive components, displays, or glazing, but also in the aerospace and antenna technology sectors.

[0195] The device and method according to the invention also offer the possibility of producing a substrate with hydrophilic or superhydrophilic properties over a large area without significant technical effort. Such a structured substrate has a wide range of applications in areas where the homogeneous wetting properties of hydrophilic and / or superhydrophilic substrates are desired, e.g., in the field of automotive components, displays, or glazing, but also in the aerospace and antenna technology sectors.

[0196] Furthermore, the inventive method and the inventive device also offer the possibility of producing a structured substrate which is suitable for further processing, for example a chemical and / or physical treatment, in particular for coating by means of a chemical spray coating and / or to increase and / or modify the resulting antireflection properties and / or hydrophobic or superhydrophobic and / or hydrophilic or superhydrophilic properties of the substrate.

[0197] According to a preferred embodiment of the present invention, the method disclosed herein is suitable for structuring a substrate surface such that it exhibits anti-glare properties. Structured substrates with a dot structure are particularly suitable for this purpose, the latter being formed – as defined herein – from a first and a second interference pixel, wherein the first and the second interference pixel each independently comprise a periodic dot structure with dimensions in the micro- and sub-micrometer range, and wherein the first interference pixel and the second interference pixel are superimposed such that the offset between the second interference pixel and the first interference pixel is in the range of 10% ≤ x ≤ 50%, particularly in the range of 20% ≤ x < 50%, and most preferably in the range of 25% ≤ x ≤ 45% of the interference period. Reference symbol list

[0198] 1 Laser radiation source 2 Beam splitter element 3 Beam path 4 Focusing element 5 Substrate 6 Further deflection element 7 Deflection element 8 Polarizing element 9 Focusing mirror or galvo mirror 31 Optical axis 91 Polygon wheel Examples of implementation

[0199] The present invention is explained in more detail with reference to the following figures and embodiments, without limiting the invention to these. In particular, the features shown in the individual figures and described in relation to the respective example are not limited to the respective individual example.

[0200] This shows Fig. 1: a schematic perspective view of a device according to the invention. Fig. 2: a schematic perspective view of a device according to the invention, which includes a deflecting element (6) for parallelizing the partial beams. Fig. 3:a schematic perspective view of a device according to the invention, which includes a deflecting element (7) for widening the angle of the partial beams to the optical axis of the beam path (3). Fig. 4A: a schematic perspective view of a device according to the invention, which includes optical elements (6) with a planar, reflective surface that deflects the partial beams onto the focusing element (4). Fig. 4B: a schematic perspective view of a device according to the invention, which includes a galvo mirror (9) as an optical element for beam shaping, which allows a fixed positioning of the substrate to be structured during the structuring process. Fig. 5:A schematic perspective view of a device according to the invention, wherein the device includes a polarization element (8) which shifts the phase relationship of the partial beams relative to each other, wherein a) the beam splitter element (2) is positioned in the beam path (3) close to the laser radiation source (1). b) the beam splitter element (2) is positioned in the beam path (3) close to the deflection element (7). Fig. 6: a schematic view of the interference pixels with width D that result on the surface or inside the substrate, and the distribution of the individual interference pixels on the surface or inside the substrate, wherein the interference pixels are shifted relative to each other with pixel density Pd. Fig. 7:a schematic perspective view of the structured substrate (5) with the generated periodic point structures, consisting of inverse cones, with dimensions in the micro- and submicrometer range, and symbolically the transmission of incident electromagnetic waves with wavelengths larger than the structure period of the generated structures, as well as the diffraction of incident electromagnetic waves with wavelengths in the range or smaller of the generated structures. Fig. 8: a schematic perspective view of a device according to the invention, which includes as an optical element a galvo mirror (9) with a planar, reflective surface which deflects the partial rays onto the focusing element (4) and a polygon wheel (91). Fig. 9: A graphical representation of the diffraction angle of incident light versus the wavelength of the incident light for structured substrates with three different structure widths. Fig. 10:a schematic perspective view of the structured substrate (5) with the generated periodic point structures, consisting of inverted cones, with dimensions in the micrometer range, overlaid with a periodic wave structure in the submicrometer range.

[0201] Fig. 1 Figure 1 visualizes the device according to the invention in a first embodiment, comprising a laser radiation source (1) for emitting a laser beam. A beam splitter element (2), which is movably arranged in the beam path (3) of the laser beam downstream of the laser radiation source (1), is located in the beam path (3). A focusing element (4) is located in the beam path (3) of the laser beam downstream of the beam splitter element (2). A holding device, on which a substrate (5), preferably a planar and / or transparent substrate, is mounted, is located in the beam path (3) of the laser beam downstream of the focusing element (4).

[0202] In this embodiment, the laser radiation source (1) emits a pulsed laser beam. The laser radiation source is a UV laser with a wavelength of 355 nm and a pulse duration of 12 ps. In this embodiment, the radiation profile of the laser radiation source corresponds to a top-hat profile.

[0203] In this embodiment, the beam splitter element (2) corresponds to a diffractive beam splitter element. A diffractive beam splitter element, in this context, is one that contains micro- or nanostructures. The beam splitter element (2) divides the laser beam into four partial beams.

[0204] In this embodiment, the focusing element (4) corresponds to a refractive, spherical lens that directs the essentially parallel partial beams onto the substrate (5), preferably a planar and / or transparent substrate, such that they interfere there in an interference region. In this configuration, the interference angle is 27.2°, resulting in a structure period of 550 nm for the periodic dot structure at the same polarization state.

[0205] According to this embodiment, the planar substrate is irradiated once, resulting in a processing time of 12 ps per structural unit, i.e., per interference pixel.

[0206] The substrate (5), preferably a planar and / or transparent substrate, is a glass, specifically a quartz glass, which is mounted on a holding device so that it is movable in the xy-plane, perpendicular to the beam path of the laser beam emitted by the laser radiation source (1).

[0207] Fig. 2 In another embodiment, the device is visualized as shown in Fig. 1 described, additionally comprising a deflecting element (6) which is located in the beam path (3) of the laser after the beam splitter element (2) and the focusing element (4).

[0208] In this embodiment, the deflecting element is a conventional, refractive, convex lens. The partial beams strike the deflecting element (6) in such a way that, after passing through the deflecting element, they are essentially parallel to each other. This allows the point at which the partial beams interfere on the surface or inside the substrate to be adjusted.

[0209] Fig. 3 In another embodiment, a device based on the one described in the following is visualized. Fig. 1 and Fig. 2 The setup shown. In addition, this setup includes a further deflecting element (7), which is arranged in the beam path (3) of the laser between the beam splitter element (2) and the deflecting element (6).

[0210] In this embodiment, the further deflecting element (7) is a conventional, refractive, concave lens. The partial beams strike the further deflecting element in such a way that their angle to the optical axis of the beam path is widened. This allows the interference angle at which the partial beams interfere on the surface or inside the substrate, preferably a planar and / or transparent substrate, to be changed.

[0211] In this embodiment, all optical elements except the beam splitter element (2) are fixed along the optical axis of the beam path (3). The interference angle of the partial beams on the substrate is adjusted by shifting the beam splitter element (2) along the optical axis of the beam path.

[0212] Fig. 4A Another embodiment shows a device as shown in Fig. 3, comprising the optical elements (6) with a planar, reflective surface, which are arranged to deflect the partial rays onto the focusing element (4).

[0213] In this embodiment, the at least three partial beams are directed onto the substrate at a preferred angle by shifting the optical elements (6). This allows for the use of a deflecting element in the form of a lens (reference numeral (6) in Fig. 3 ) can be dispensed with.

[0214] Fig. 5 In another embodiment, a device as shown in Fig. 3 , additionally comprising one polarization element (8) per partial beam, which are arranged in the beam path (3) of the laser beam between the deflecting element (6) and the focusing element (4).

[0215] The polarization element is arranged in such a way that it changes the polarization of the individual partial beams relative to each other, resulting in a change in the interference pattern.

[0216] This design is shown in two different configurations. In Fig. 5 a) The beam splitter element (2) is positioned close to the laser radiation source (1) in the beam path (3). Fig. 5 b) The beam splitter element (2) is positioned close to the deflecting element (7) in the beam path (3). In this way, the interference pattern of the interfering partial beams on the surface of the substrate (5) can be continuously adjusted without having to move the other optical elements in the setup or the substrate.

[0217] Additionally, it would also be conceivable that the arrangement includes an additional optical element for beam shaping, which is located downstream in the beam path (3) of the laser beam from the laser radiation source (1). In this configuration, the radiation profile of the laser radiation source corresponds to a Gaussian profile. The optical element for beam shaping converts this profile into a top-hat profile.

[0218] Fig. 6 contains a schematic view of the interference pixels with width D that result on the surface or inside the substrate, and the distribution of the individual interference pixels on the surface or inside the substrate, wherein the interference pixels are shifted relative to each other with pixel density Pd.

[0219] In this embodiment, the pixel density Pd is smaller than the width of an interference pixel, D. This allows a planar homogeneous periodic dot structure to be generated on the surface or inside a substrate, preferably a planar and / or transparent substrate, by moving the substrate (5) using a pulsed laser beam.

[0220] Fig. 7 The structured substrate (5) produced by the inventive method is visualized with the generated periodic point structures, consisting of inverted cones, with dimensions in the micro- and sub-micrometer range. The transmission of incident electromagnetic waves with wavelengths greater than the structure period of the generated structures, as well as the diffraction of incident electromagnetic waves with wavelengths in the range of or smaller than those of the generated structures, is also symbolically illustrated.

[0221] Fig. 8Another embodiment shows a device as shown in Fig. 4B , comprising the optical element (91) with a planar, reflective surface, which is a polygonal wheel configured to rotate about a defined axis. The incident partial beams are deflected such that they strike a galvo mirror (9), which directs the beams onto the substrate via a focusing element (4). The rotation of the polygonal wheel causes the point at which the beams are focused on the substrate to move along a line during the exposure process. The partial beams thus scan the substrate, resulting in an increased processing speed.

[0222] Fig. 9This graphic illustrates the transmission and diffraction properties of a structured substrate as a function of the structure size. It shows the diffraction angle of light as a function of its wavelength for structures with three different structure sizes. If the wavelength of the incident light is larger than the structure size, the light is transmitted completely. At wavelengths at or below the structure size, diffraction occurs. The diffraction angles can be read from the graphic.

[0223] Fig. 10The structured substrate (5) produced by the inventive method is visualized with the generated periodic dot structures, consisting of inverted cones, with dimensions in the micrometer range. Superimposed on this periodic dot structure in the micrometer range is a periodic wave structure in the submicrometer range, which can also be produced in a single production step by the inventive method described herein.

Claims

1. Patterned substrate (5) with anti-reflective properties comprising a periodic dot structure in the micro- or sub-micrometer range, wherein the periodic dot structure is formed of inverse cones, wherein the cones are arranged periodically with a distance from one another in the range of 50 nm to 50 µm wherein a further structure is superimposed on the periodic dot structure, wherein the superimposed structure has a quasi-periodic wave structure, wherein the material on the surface of the substrate in the region of the superimposed structure has a sequence of wave crests and wave troughs, the periodicity of which is in the range of 100 nm to 1000 nm.

2. Patterned substrate according to claim 1, wherein the periodic dot structure is formed such that the structured substrate transmits electromagnetic radiation with a wavelength of more than 550 nm, preferably of more than 500 nm, particularly preferably of more than 450 nm.

3. Patterned substrate according to claim 1 or 2, comprising a periodic dot structure in the micro- or submicrometer range, wherein a periodic wave structure is superimposed on the periodic dot structure, wherein the wave crests are arranged with a spacing in the range from 20 nm to 5 µm.

4. Patterned substrate according to one of the claims 1 to 3, wherein the patterned substrate comprises a dot structure formed of a first and a second interference pixel, wherein the first and the second interference pixel each independently comprise a periodic dot structure having dimensions in the micro- and / or sub-micrometer range, wherein the first interference pixel and the second interference pixel are arranged superimposed to each other such that the offset between the second interference pixel and the first interference pixel is in the range of 10% ≤ x ≤ 50% of the interference period.

5. Patterned substrate according to any one of the claims 1 to 4, wherein the patterned substrate comprises a transparent material, and wherein the transparent material is selected from the group comprising glass, solid polymers, transparent ceramics or mixtures thereof.

6. Patterned substrate according to any one of the claims 1 to 5, wherein the refractive index of the patterned substrate is gradual.

7. Laser interference patterning apparatus for direct laser interference patterning of a substrate for producing a patterned substrate according to any one of the claims 1 to 6, comprising - a laser radiation source (1) for emitting a laser beam, - a beam splitter element (2) arranged in the optical path (3) of the laser beam, - a focusing element (4) which is arranged in succession of the beam splitter element in the optical path of the laser and configured so that the sub-beams pass through it in such a way that the sub-beams are interfereable on the surface or in the volume of a substrate (5) in an interference region, characterized in that the beam splitter (2) is freely movable along its optical axis in the optical path (3), the beam splitter (2) is set up to split the incident laser beam emitted by the laser radiation source (1) into at least three sub-beams, wherein a first deflecting element (7) is arranged in succession of the beam splitter element (2) in the optical path (3) of the laser radiation source (1), which is configured so that the at least three sub-beams are widened when passing through the deflecting element (7).

8. Apparatus according to claim 7, wherein a further deflecting element (6) is arranged in succession to the laser radiation source (1) and the beam splitter element (2) in the optical path (3), which is configured so that it deflects the sub-beams in such a way that they run essentially parallel to one another after emerging from the further deflecting element (6).

9. Apparatus according to claim 7 or 8, wherein the deflecting element (7) is a concave lens.

10. Apparatus according to claim 8 or 9, wherein the further deflecting element (6) is a convex lens.

11. Apparatus according to any one of the claims 7 to 10, wherein the laser radiation source is a pulsed laser radiation source with pulse widths in the range from 10 nanoseconds to 10 femtoseconds.

12. Method for producing a substrate with a periodic dot structure in the micro- or submicrometer range by means of laser interference patterning, in particular for producing a patterned substrate according to any one of the claims 1 to 6, comprising the following steps: a) providing a substrate (5), preferably comprising a transparent material, b) emitting a laser beam from a laser radiation source (1), c) splitting the laser beam by means of a beam splitter element (2) into at least three sub-beams, d) focusing the sub-beams onto the surface or within the volume of the substrate (5), so that the sub-beams interfere constructively and destructively on the surface or within the volume of the substrate, characterized in that the at least three sub-beams are superimposed on the substrate by the focusing such that a periodic dot structure in the micro- or sub-micrometer range is generated on the surface or in the volume of the substrate, wherein the periodic dot structure is formed of inverse cones, wherein the inverse cones are arranged periodically at a distance from one another in the range from 50 nm to 50 µm, wherein a further structure is superimposed on the periodic dot structure, wherein the superimposed structure has a quasi-periodic wave structure, wherein the material on the surface of the substrate in the region of the superimposed structure has a sequence of wave crests and wave troughs, the periodicity of which is in the range of 100 nm to 1000 nm.

13. Method according to claim 12, wherein the structure period of the generated periodic dot structure of the substrate (5) is steplessly adjustable in the micro- or submicrometer range by moving the beam splitter element (2) along its optical axis in the optical path (3).

14. Method according to claim 12 or 13, wherein the substrate (5) comprises a transparent material and the sub-beams interfere inside the transparent material.

15. Method according to any one of the claims 12 to 14, comprising the following steps: a) applying a first pulse on the surface of a substrate (5), which generates a first interference pixel on the surface of the substrate (5) or within the substrate (5), b) applying a second pulse to the surface of a substrate (5), which generates a second interference pixel on the surface of the substrate (5) or within the substrate (5), wherein the first and second interference pixels each independently comprise a periodic dot structure with dimensions in the micro- and submicrometer range, characterized in that the offset between the second interference pixel and the first interference pixel is in the range of 10% ≤ x ≤ 50% of the interference period.

16. Method according to claim 15, wherein after step b) a third pulse is applied on the surface of a substrate (5), wherein the third interference pixel comprises a periodic dot structure with dimensions in the micro- and submicrometer range, wherein the third pulse generates a third interference pixel on the surface of the substrate (5) or in the substrate (5), wherein the third interference pixel has an offset in the range of 10% ≤ x ≤ 50% of the interference period with respect to the second interference pixel.

17. Method according to claim 15, wherein the offset of the interference period is uniform in at least one spatial direction.

18. Use of the patterned substrate according to claim 1 in photovoltaic systems.

19. Use of the patterned substrate according to any one of the claims 1 to 6 as anti-reflective glazing of monitors, screens and displays.

20. Use of the patterned substrate according to any one of the claims 1 to 6 in glass fibers.

21. Use of the patterned substrate according to any one of the claims 1 to 6 as a negative mold for indirectly applying or creating patterns on another substrate.