DE102021117204A1 - Device and method for laser interference structuring of transparent substrates with periodic point structures for anti-reflection properties - Google Patents

Abstract

The present invention relates to the field of structuring substrates with periodic point structures in the micrometer or submicrometer range, in particular a device and a method for structuring surfaces and the interior of a transparent substrate by means of laser interference structuring. The structuring produced in this way with periodic point structures in the micrometer or submicrometer range is distinguished by a pronounced anti-reflection property. In addition, the present invention relates to a structured substrate with antireflection properties, which includes a periodic point structure.

Description

technical field

The present invention relates to the field of structuring substrates, in particular a device and a method for structuring surfaces and the interior of a transparent substrate by means of laser interference structuring. In addition, the present invention relates to a structured substrate--flat substrates, in particular so-called anti-reflection glazing are mentioned here by way of example--with anti-reflection properties, which comprises a periodic point structure.

State of the art

Methods for treating surfaces are known from the prior art, with which the surface of transparent substrates, in particular glass, but also solid polymers, can be modified in such a way that the reflection of the substrate can be reduced. For this purpose, typical methods apply an additional material to the surface of the substrate to be anti-reflective (so-called structure or layer-building methods), with the refractive index of the different materials being different.

In US8557877B2 a possible layer-building process is explained, for example. A coating solution is created from at least two chemical starting materials, the pH of which is then reduced and then optionally diluted with another solution before the coating is applied to the desired substrate. In this type of coating process, various chemical substances are used, which are often of low environmental compatibility, and the disposal and handling of which is cost-intensive and complex.

This type of method is based on a reduction in reflectivity through destructive interference. The refractive index of the material used for the coating must be matched to the substrate to be coated and the medium in front of the substrate (usually air). Since not every coating material can be processed in the same way, such a method requires the use of different processes for coating different substrate materials.

In US10459125B2 a method is therefore described in which a so-called moth-eye structure is chemically generated on a substrate by applying a polymer film to the substrate. This type of structure is based on the principle of the moth's eye, on the surface of which are regularly arranged nanostructures whose dimensions are smaller than the wavelength of the light that strikes them. 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.

A film produced in this way can be used independently of the substrate to be 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.

In addition, a coating produced in this way is susceptible to mechanical stress (abrasion, impacts, etc.) and ages accordingly quickly. Therefore, over time, the coating often delaminates from the substrate and/or loses its anti-reflective properties.

In WO 2019/166836 A1 a method for producing an anti-reflection structure is explained, in which the surface of a substrate is processed by means of a laser in such a way that it receives anti-reflection properties. The substrate material is modified with a focused laser beam and a nanostructure is thereby generated by self-organization processes using laser-induced periodic surface structures (LIPSS). A quasi-periodically repeating structuring can be generated by the suitable selection of laser fluence and superimposition of the beam focal points on the substrate surface. An antireflection surface is thus obtained. No chemicals are required and a wide range of substrate materials can be processed in this way.

However, this method works successively and is time-consuming due to the underlying self-organization process of the LIPSS. A two-dimensional nanostructure production in one step is not possible, since the LIPSS are only formed by repeated processing of nearby surface areas. In addition, the regularity of the structure depends on the specific process and environmental conditions, so that deviations in the surface condition (slightly different material, microscopic contamination) can lead to changed results.

In EP2431120A1 discloses a method for direct structuring of a thin film in which periodic structures can be created in thin metal films by means of interfering laser beams. In this case, several pulsed laser beams are directed onto the thin film, interfering in an interference area so that the material of the thin film is vaporized in the high-intensity areas. The method is characterized in that the resulting structure can be changed by adjusting the intensity of the laser beams or by shifting the film in the z-direction (i.e. in the direction of the incident laser beams or away from them). A phase difference between the laser beams is generated via additional optical elements, which influence the interference pattern. The incident 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 thin film material is vaporized.

This method requires a way to modify the intensity of the incident laser beams. This can be done either by specifying a specific laser radiation source or by using a unit to control the intensity of the laser beam. The intensity needs to be adjusted depending on the evaporation threshold of the thin film material. This means that different laser radiation sources must be used for different materials, or an additional element is required for intensity control. Shifting the optical elements does not allow the resulting interference pattern to be controlled. When processing materials with a high evaporation threshold, damage to the optical elements in the laser beam path is also conceivable.

task

It is therefore the object of the present invention to provide a device and a method with which a direct structuring of surfaces, for example transparent and/or flat surfaces, can be produced without the use of environmentally harmful chemicals, which gives the material anti-reflective properties.

In addition, it is an object of the present invention to produce a structuring that is as robust as possible and that does not lose its effectiveness as a result of the transparent substrate being stressed. In addition, the structuring of flat samples should be feasible within a short time.

A further object of the invention is to provide a method for structuring by means of laser interference, which is independent of the intensity of the laser radiation source. The method should be set up in such a way that the optical elements are not damaged even at high intensities on the substrate to be structured.

solution

The present invention provides a device which enables the structuring of substrates, for example flat and/or transparent substrates, by means of laser interference structuring. This device can be used to produce periodic point structures with dimensions in the micrometer and submicrometer range on the surface or inside transparent substrates, which give the substrate anti-reflection properties (increased transmission).

• - eine Laserstrahlungsquelle (1) zum Emittieren eines Laserstrahls,
• - ein Strahlteilerelement (2), das im Strahlengang (3) des Laserstrahls angeordnet ist,
• - ein Fokussierelement (4), das derart eingerichtet ist, dass dieses die Teilstrahlen derart durchlaufen, dass die Teilstrahlen auf der Oberfläche oder im Volumen eines Substrats, bevorzugt flächigen und/oder transparenten Substrats (5) in einem Interferenzbereich interferierbar sind,

wobei der Strahlteiler (2) entlang seiner optischen Achse im Strahlengang (3) frei beweglich ist, und wobei der Strahlteiler (2) dazu eingerichtet ist, den einfallenden Laserstrahl, der von der Laserstrahlungsquelle (1) ausgesandt wird, in zumindest 3, vorzugsweise zumindest 4 Teilstrahlen, insbesondere 4 bis 8, also 4, 5, 6, 7, oder 8 Teilstrahlen, aufzuteilen.The present objects are achieved according to the invention by means of a laser interference structuring device for direct laser interference structuring of a substrate--flat and/or transparent substrates are to be mentioned here by way of example--according to claim 1, comprising

• - a laser radiation source (1) for emitting a laser beam,
• - a beam splitter element (2) which is arranged in the beam path (3) of the laser beam,
• - a focusing element (4), which is set up in such a way 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 flat 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 set up to split the incident laser beam, which is emitted by the laser radiation source (1), into at least 3, preferably at least 4 sub-beams, in particular 4 to 8, ie 4, 5, 6, 7, or 8 sub-beams to split.

The beam splitter (2) is particularly preferably set up in such a way that it splits the incident laser beam into an even multiple, i.e. 4, 6 or 8 partial beams, very particularly preferably 4 partial beams.

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

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

The partial beams are then deflected by the focusing element (4) in such a way that they interfere in an interference region on the surface or inside a substrate (5), preferably a flat and/or transparent substrate.

As a result, a two-dimensional, periodic point structure with dimensions in the micrometer and submicrometer range can be produced, the structure period of which can be freely adjusted by shifting the beam splitter element (2) along its optical axis. A flat processing of a substrate (5), preferably a flat and/or transparent substrate, is possible.

Further advantageous embodiments can be found in the description and the dependent claims.

General Benefits

An advantage of the device defined herein is that this device and the method that can be implemented with its help in the structuring of substrates, in particular in the production of a structure with anti-reflection properties, the use of chemicals and their complex disposal can be dispensed with. In addition, the purification of the substrates can thus also be dispensed with.

Furthermore, a large number of substrates, preferably flat and/or transparent substrates, in particular 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 process is more flexible than traditional chemical processes.

Compared to WO 2019/166836 A1 the processing time is significantly shorter with this method, since the periodicity of the structures is ensured by the interference of the incident, at least 3, preferably at least 4 partial beams in an interference area, and does not come about through more time-consuming self-organization processes. In addition, compared to conventional methods, it is advantageous that the shape (structural configuration; geometry) of the micro-/nanostructures produced can be controlled. The geometry of the structures can be controlled by the number of interfering (partial) beams, their polarization and the setting of the process parameters, thereby specifically influencing the anti-reflection properties.

Furthermore, the stability of the periodic point structure produced in this way should be mentioned, which is more stable than conventional coatings, since it cannot become detached from the substrate to be coated over time and the material stress caused by use.

If the structuring is carried out in the volume, i.e. inside the substrate, preferably a flat and/or transparent substrate, in particular in the transparent material, the resulting structuring (i.e. the periodic point structure of the structured substrate) is less sensitive to impact and abrasion than conventional coatings. The inventors have found that patterning (also referred to herein as texturing) inside the material (i.e. below the surface) does not necessarily produce anti-reflective properties. However, the texturing inside the material is interesting for other areas of application, such as product protection, optical data storage, decoration, etc.

It is of particular advantage that the construction of the device disclosed herein or the arrangement of the optical component means that substrates with very high structuring rates of up to 0.9 m ² /min, in particular in the range from 0.01 to 0.9 m ² / min, particularly preferably in the range from 0.05 to 0.9 m ² /min, very particularly preferably in the range from 0.1 to 0.9 m ² /min. This is ensured by the fact that the area in which the at least three partial beams are superimposed can be widened by a preferred selection of optical elements, as a result of which a large area can be irradiated in one processing step. In contrast to methods known to those skilled in the art, such as direct laser writing, no strong focusing is necessary to produce high-resolution features.

Detailed description

The device according to the invention describes a structure for laser interference structuring of substrates, for example flat and/or transparent substrates, for producing a structured substrate, comprising a periodic cal point structure in the micro or submicrometer range, in particular for the production of a so-called. Anti-reflection glazing on the substrate or in the volume (ie inside) of this substrate.

substrate

For the purposes of the invention, the term substrate refers to a substrate whose surface extends in several spatial directions. A substrate, preferably a flat and/or transparent substrate, can be a planar substrate or a curved substrate, for example a parabolic substrate. For the purposes of the invention, flat is also to be understood as meaning that the extent of a substrate, preferably flat and/or transparent substrate, for example a planar substrate, in the x and y direction, 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.

In a preferred configuration, the substrate is a substrate whose extent in the x and y direction, or whose extent along a radius of curvature, is less than or equal to the extent of the area in which the at least three partial beams interfere with one another. A homogeneous structuring of the substrate is possible in one processing step (during a laser pulse).

In a particularly preferred embodiment, the substrate is a flat substrate whose extent in the x and y direction, 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 one another. By moving the substrate in the x and y plane, a two-dimensional, homogeneous structuring of the substrate is possible in several processing steps (with several laser pulses).

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.

With regard to the substrates that can be processed by applying the laser interference structuring method according to the invention with a periodic point structure with anti-reflection properties, there is a wide selection of transparent and translucent but also non-transparent materials within the scope of the present invention.

In a particularly preferred embodiment, the flat substrate comprises a transparent material.

In general, the transparent material has a high visible light transmittance, but it varies depending on the application. The transmittance of the transparent material is not less than 70%, preferably not less than 80%, more preferably not less than 90% with no deviation in spectrum in the visible light region (wavelength 380 nm to 780 nm).

For the purposes of the present invention, a transparent material includes transparent materials, in particular glass (e.g. borosilicate glasses, quartz glasses, alkali-earth-alkaline 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) and 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 are homopolycarbonates, copolycarbonates and thermoplastic polyester carbonates.

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

As an alternative to this, the substrate, preferably a flat and/or transparent substrate, can also comprise a non-transparent material. By structuring the opaque material, a periodic point structure in the micrometer or submicrometer range is generated on the surface of the opaque material. As a result, a structure with anti-reflection properties can be produced on an opaque material, with the original roughness of the surface of the opaque substrate (i.e. before the structuring according to the invention) remaining unchanged or almost unchanged in the macroscopic range, effectively reducing the reflection of an otherwise reflective surface of a non-transparent material, e.g. a metal surface is induced. Metals (e.g. silicon, aluminium, copper, gold), metallic alloys (e.g. steel, brass), ceramic materials (e.g. zirconium oxide, titanium dioxide, zirconium dioxide) and polymers (PEEK, polyetheretherketone; polyfluorinated hydrocarbons such as Teflon) are particularly suitable as opaque materials. as well as combinations thereof.

Punctual structure/interference pattern/anti-reflection glazing

The present invention also includes a structured substrate (5) with anti-reflection properties, the structured substrate comprising a periodic point structure in the micrometer or submicron range, the periodic point structure being formed from inverse cones, and the inverse cones being periodically spaced apart are arranged on their respective saddle point or midpoint (circular base area) in the range of 50 nm to 50 µm to each other.

In the context of this invention, the term inverse peg refers to structures with a circular base area, which taper conically into the substrate in the vertical direction and have a rounded cone tip at their saddle point. The inverse cones are formed during the structuring process, i.e. when a laser pulse strikes as a result of the impact of a high-intensity area on the substrate to be structured, with the areas between the inverse cones on or within the substrate ideally being formed by destructive interference whose intensity is zero in the Essentially remain unstructured. Consequently, by focusing the partial laser beams on or within the substrate, the negative of what is specified by the intensity distribution is formed.

The period of the structure is referred to as Λ for the purposes of the invention. It depends on the wavelength of the interfering laser beams, the angle of incidence of the interfering laser beams and the number of interfering laser beams.

A structured substrate with anti-reflection properties, here called anti-reflection glazing, describes a substrate, preferably flat and/or transparent substrate, with a periodic point structure with structure widths in the micrometer and submicrometer range, i.e. in the range from 50 nm to 50 μm. These antireflection properties come about when the dimensions of the structure produced, i.e. the structure period and dimensions of the individual cones, are in the ranges smaller than the wavelength of visible light.

berechnet, wobei n₁ und n₂ den Brechungsindex von Luft und dem Substrat angeben und δ₁ und δ₂ jeweils die Winkel des einfallenden und reflektierten Strahls angeben.In physics, reflection is the reflection of an electromagnetic wave at an interface between 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 $$n_{1}sin{\delta }_1=n_{2}sin{\delta }_2$$

calculated, where n ₁ and n ₂ denote the refractive index of air and the substrate and δ ₁ and δ ₂ denote the angles of the incident and reflected beam, respectively.

Due to the periodic point structure on the surface or in the volume of the substrate, preferably a flat and/or transparent substrate, the refractive index of the substrate changes in such a way that a gradual refractive index results. As a result, light with wavelengths greater than the structure period Λ of the periodic point structure is increasingly transmitted. Light with wavelengths shorter than or equal to the periodic point structure is diffracted at the surface.

For the purposes of the invention, anti-reflection properties refer to periodic point structures whose dimensions are in the range of the incident electromagnetic wave, so that the incident wave is deflected away by the viewer in such a way that no reflection is perceived as “disturbing”. In addition, the term anti-reflection properties within the meaning of the invention also includes that the refractive index is gradual at the boundary between the first medium, for example air, and the substrate, preferably flat and / or transparent substrate, so that there is no clear transition for the incident electromagnetic wave is present from one medium to another and the incident electromagnetic wave is increasingly transmitted.

laser radiation source (1)

The device according to the invention consists of a laser radiation source (1) which 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 a top-hat profile. The top-hat profile is helpful for structuring or covering a surface of a substrate that is to be structured more homogeneously.

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 from 10 nanoseconds to 10 femtoseconds, in particular 1 to 200 picoseconds, very particularly preferably 1 to 20 picoseconds.

Unless expressly stated otherwise, laser beam or partial beam does not mean an idealized beam of geometric optics, but a real light beam, such as a laser beam that does not have an infinitesimally small, but an extended beam cross-section (Gaussian distribution profile).

Top-hat profile or top-hat intensity distribution means an intensity distribution that can be described, at least with regard to one direction, essentially by a rectangular function (rect (x)). In this case, real intensity distributions which have deviations from a rectangular function in the percentage range or sloped flanks 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. Likewise, optical elements for transforming the intensity profile of a laser beam are already known. For example, using diffractive and/or refractive optics, laser beams with a Gaussian intensity profile can be transformed into laser beams which have a top-hat-shaped 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-shaped intensity profiles are particularly attractive for laser material processing, especially when using laser pulses that are shorter than 50 ps, since particularly good and reproducible processing results can be achieved with the essentially constant energy or power density .

The laser radiation source (1) contained in the device according to the invention can have an intensity of 0.01 to 5 J/cm ² , particularly preferably 0.1 to 2 J/cm ² , very particularly preferably 0.1 to 0.5 J/cm ² . With the device according to the invention, the intensity of the laser radiation source can be flexibly selected in a range. The beam diameter plays no role in generating the interference pattern on the substrate, preferably a flat and/or transparent substrate. Due to the preferred arrangement of the optical elements in the beam path of the laser, no unit for checking the intensity of the laser beam is required.

UV laser beam sources, laser beam sources (155 to 355 nm) that emit green light (532 nm), diode lasers (typically 800 to 1000 nm) or laser beam sources that emit radiation in the near infrared (typically 1064 nm), in particular with a wavelength in the range of 200 to 650 nm wavelength. Lasers suitable for microprocessing are known to those skilled in the art and include, for example, HeNe lasers, HeAg lasers (ca. 224 nm), NeCu lasers (ca. 249 nm), Nd:YAG lasers (ca. 355 nm).

optical elements

The present invention includes a number of optical elements. These elements are prisms and lenses.

These lenses can be refractive or diffractive. Spherical, aspherical or cylindrical lenses can be used. In a preferred embodiment, cylindrical lenses are used. This makes it possible to compress the overlapping areas of the partial beams (herein also referred to as interference pixels) in one spatial direction and to stretch them in another. If the lenses are not spherical/aspherical, but cylindrical, this has the advantage that the rays can be deformed at the same time. This allows the processing spot (i.e. the interference pattern created on the substrate) to be deformed from a point to a line containing the interference pattern. With sufficient energy from the laser, this line can be up to 10-15 mm long (and about 100 µm thick).

Furthermore, Spatial Light Modulators (SLM) can be used for beam shaping. It is known to those skilled in the art to use SLMs to spatially modulate the phase, or the intensity, or both the phase and intensity, of an incident light beam. The use of Liquid Crystal on Silicon (LCoS)-SLM 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 on the substrate. Such an SLM can be controlled optically, electronically or acoustically.

All of the optical elements explained below are arranged in the beam path (3) of the laser. For the purposes of the invention, the beam path of the laser designates the course of both the laser beam emitted by the laser radiation source and the course of the partial beams divided by a beam splitter element. However, the optical axis of the laser beam emitted by the laser radiation source (1) is understood to be the optical axis of the beam path (3). Unless otherwise explained, all optical elements are arranged perpendicularly to the optical axis of the beam path (3).

beam splitter element (2)

A beam splitter element (2) is located in the beam path (3) of the laser, behind the laser radiation source (1). The beam splitter element (2) can be a diffractive or a refractive beam splitter element. For the purposes of the invention, a diffractive beam splitter element refers to an optical element that contains microstructures or nanostructures. a refrac tive beam splitter element referred to in the context of the invention, a transparent optical element such. B. a prism.

The beam splitter element (2) splits the emitted laser beam into at least 3, preferably at least 4, in particular 4 to 8, ie 4, 5, 6, 7 or 8 partial beams.

wobei λ die Wellenlänge des emittierten Laserstrahls ist.The beam splitter element (2) can move freely 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 widening of the at least 3 partial beams, so that they impinge on a focusing element at different distances from one another. As a result, the angle θ at which the partial beams impinge on the substrate (5), preferably a flat and/or transparent substrate, can be changed. Thus, when four partial beams are superimposed, the structure period Λ changes seamlessly $$\mathrm{\Lambda }=\frac{\lambda }{\sqrt{2}sin\theta }$$

where λ is the wavelength of the emitted laser beam.

The laser beam can be subdivided in the beam splitter element (2) both by a partially reflective beam splitter element, for example a semitransparent mirror, and by a transmissive beam splitter element, for example a dichroic prism.

In a preferred embodiment, the beam splitter element (2) is followed by further beam splitter elements in the beam path of the laser. These beam splitter elements are arranged in such a way that they split each of the at least three partial beams into at least two further partial beams. As a result, a higher number of partial beams can be generated, which are directed onto the substrate, preferably a flat and/or transparent substrate, so that they interfere on the surface or inside the substrate. This allows the structure period of the interference pattern to be adjusted.

focusing element (4)

Furthermore, a focusing element (4) is arranged in the beam path (3) of the laser, downstream of the beam splitter element (2), which is set up in such a way that the partial beams pass through it in such a way that the partial beams are on the surface or inside a substrate (5 ) interfere in an interference area. 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 thereto. For example, the focusing element (4) can be a focusing optical lens. Within the meaning of the invention, focusing is understood as meaning the bundling of the at least three partial beams on the surface or in the interior of a substrate, preferably a flat and/or transparent substrate.

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.

It goes without saying that the optical elements defined herein, for example for beam splitting and for aligning the partial beams in the direction of a substrate to be correspondingly structured, can be arranged in a common housing.

In a preferred embodiment, the focusing element (4) is a spherical lens. The spherical lens is set up in such a way that the incident at least three partial beams pass through them in such a way that they interfere in an interference region on the surface or inside the substrate (5) to be structured, preferably a flat and/or transparent substrate. The width of the interference range is preferably 1 to 600 μm, particularly preferably 10 to 400 μm, very particularly preferably 20 to 200 μm. In this way, a high structuring rate, for example as defined herein, can be set at the same time.

In a particularly preferred embodiment, the focusing element (4) is a cylindrical lens. The cylindrical lens is set up in such a way that the area in which the at least three partial beams overlap on the surface or inside the substrate (5), preferably a flat and/or transparent substrate, is stretched in one spatial direction. As a result, the area of the substrate on which the interference pattern can be generated assumes an elliptical shape. The semimajor axis of this ellipse can reach a length of 20 µm to 15 mm. This increases the area that can be structured in one irradiation.

First deflection element (7)

In a particularly preferred embodiment, a deflection element (7) is located in front of the focusing element (4) and after the beam splitter element (2), which is preferably arranged in the beam path (3) of the laser. This deflection element (7) is used to widen the distances between the at least three partial beams used and can thus also change the angle at which the partial beams impinge on the substrate (5), preferably a flat and/or transparent substrate. It is set up in such a way that it increases the divergence of the at least three partial beams and thus moves the area in which the at least three partial beams interfere along the optical axis of the beam path (3) away from the laser radiation source (1).

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.

The widening and the resulting deflection of the partial beams has the advantage that the partial beams can be bundled more strongly by the focusing element (4). This results in a higher intensity in the area in which the at least three partial beams interfere on the surface or in the interior of the substrate (5), preferably a flat and/or transparent substrate.

A unit for controlling the intensity of the laser beam can be dispensed with by suitably selecting the deflection element. In a preferred embodiment of the device, a deflection element (7) is used which, by expanding the at least three partial beams, allows the at least three partial beams to be focused on the substrate (5) by means of a focusing element (4), the intensity of the interference points on the surface or inside the substrate, preferably a flat and/or transparent substrate, without additional adjustment of the intensity of the laser radiation source (1). This has the advantage that laser radiation sources with low intensity (power per area) can also be used to structure the substrate while generating the periodic point structure, as a result of which the optical elements are protected from wear.

Additional deflection element (6)

Provision can also be made for a further deflection element (6) to be arranged downstream of the beam splitter element (3) in the beam path (3) of the laser radiation source (1), which deflects the partial beams in such a way that, after exiting the further deflection element (6), they Substantially parallel to each other. As a result, the device can be set up in such a way that the processing point, i.e. the point at which the at least three partial beams on the surface or in the interior of the substrate, preferably a flat and/or transparent substrate, interfere when the beam splitter element is displaced in the beam path of the laser along its optical axis remains constant.

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

The distances between the optical elements and the substrate, as well as the structure period Λ, can be set by suitably selecting the refractive indices of the optical elements (4), (6) and (7). 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), has to be moved to adjust the interference range or the interference angle. This saves work steps when setting up the device, such as calibrating the device to the desired structure period. Furthermore, a fixed setting, i.e. with preferably all optical elements within the beam path (3) of the laser being fixed, prevents the optical elements from wearing out.

polarizing element (8)

In a further embodiment, one is located behind the deflection element, particularly preferably in a structure with two deflection elements (6), (7) behind the further deflection element (6) and in front of the focusing element (4) in each of the beam paths of the at least 3 partial beams polarization element (8). The polarization elements can modify the polarization of the partial beams relative to one another. As a result, the resulting interference pattern, which the at least 3 partial beams image on the surface or in the volume of a substrate, preferably a flat and/or transparent substrate, can be modified.

Optical element for beam shaping

In a further embodiment, the laser radiation source (1) has a radiation profile that corresponds to a Gaussian profile, as described above. In such an embodiment, another 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.

An optical element with a concave, parabolic or planar reflecting surface can also be provided in the device according to the invention, the optical element being designed to be rotatable about at least one axis or displaceable along the beam path (3). As a result, an additional focusing element (4) or a further deflection element (6) positioned in the beam path (3) can be dispensed with. For example, this optical element can be used to direct laser beams or partial laser beams onto the surface of the focusing element (4) or another focusing optical element before the beams for forming structural elements reach the substrate to be structured.

Alternatively, for example, at least one optical element with a concave, parabolic or planar reflecting surface can be provided, which is designed to be rotatable about at least one axis or displaceable along the beam path (3), for example, with this optical element being assigned to the first deflection element (7) and the other Deflection element (6) is positioned downstream in the beam path. For example, the partial beams can be deflected in the beam path (deflection mirror) or focused in the beam path in such a way that the substrate to be structured can be stationary during processing (so-called focusing mirror or galvo mirror (laser scanner) (9)).

Holding device for the substrate

In a further embodiment, the substrate (5), preferably a flat and/or transparent substrate, can be moved in the xy plane. By moving the substrate (5), preferably a flat and/or transparent substrate, in the xy plane, flat processing can be ensured by means of laser interference structuring. In each processing step (i.e. laser pulse that hits the substrate to be structured), a so-called interference pixel 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). If the pixel density Pd is smaller than the size of the interference pixels D, a two-dimensional, homogeneous processing is possible.

procedure

The present invention also includes a method for producing a substrate, preferably a flat and/or transparent substrate, with a periodic point structure in the micrometer or submicrometer range by means of laser interference structuring.

• Es wird ein Substrat (5), bevorzugt flächiges und/oder transparentes Substrat, bereitgestellt, welches sich auf einer Haltevorrichtung befindet. Von einer Laserstrahlungsquelle (1) wird ein Laserstrahl emittiert. Der Laserstrahl wird durch ein Strahlteilerelement (2) und zumindest drei, besonders bevorzugt vier Teilstrahlen geteilt. Die Teilstrahlen treffen auf ein Fokussierelement (4) auf, welches die zumindest drei, besonders bevorzugt vier Teilstrahlen auf der Oberfläche oder im Inneren des Substrats (5), bevorzugt flächigen und/oder transparenten Substrats, fokussiert (bündelt), sodass die Teilstrahlen auf der Oberfläche oder im Inneren des Substrats konstruktiv und destruktiv interferieren. Somit wird eine periodische Punktstruktur im Mikro- oder Submikrometerbereich auf der Oberfläche oder im Inneren des Substrats (5), bevorzugt flächigen und/oder transparenten Substrats, durch Laserinterferenzbearbeitung erzeugt. Das Verfahren ist dadurch gekennzeichnet, dass die zumindest drei Teilstrahlen so überlagert werden, dass ein 2D-Muster entsteht.

According to the invention, the method for producing a structured substrate, preferably a flat and/or transparent substrate, with a periodic point structure in the micrometer or submicrometer range by means of laser interference structuring, comprises the following steps:

• A substrate (5), preferably a flat 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 divided by a beam splitter element (2) and at least three, particularly preferably four, partial beams. The partial beams impinge on a focusing element (4), which focuses (bundles) the at least three, particularly preferably four, partial beams on the surface or inside the substrate (5), preferably a flat and/or transparent substrate, so that the partial beams on the Interfere constructively and destructively on the surface or inside the substrate. A periodic point structure in the micrometer or submicrometer range is thus produced on the surface or inside the substrate (5), preferably a flat 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 2D pattern is created.

The point structures produced in this way are in the form of periodically arranged, inverse cones, with the distance between the vertices (i.e. midpoint of height or centers of the elevations) being on average in the range from 50 nm to 50 µm, preferably in the range from 50 nm to 20 μm are arranged, more preferably in the range from 100 nm to 1000 nm, particularly preferably in the range from 100 nm to 600 nm.

The inventors of the present invention have also found that, in addition to the periodicity, the structure depth (i.e. the depth of the inverse cones, measured from the saddle point of the recess to the apex) has an influence on the antireflection properties (as defined herein). For example, the structural depth or profile depth of the inverse cones (elevations and depressions) is on average in the range from 5 nm to 100 nm, preferably in the range from 5 nm to 75 nm.

According to a preferred embodiment of the present invention, the inverse pegs have a structure depth in the range from 5 nm to 200 nm, particularly preferably in the range from 5 nm to 150 nm, very particularly preferably 10 nm to 100 nm.

A device for producing a structured substrate (5), preferably a flat and/or transparent substrate, is preferably used, which comprises 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) are used 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 flat and/or transparent substrate. Adjusting the distances between the optical elements can ensure that only the beam splitter element (2) has to be movable along its optical axis in order to change the structure period. This enables easier adjustment processes during machining.

In a particularly preferred embodiment, a transparent material is provided as the planar substrate. Due to the transparency of the transparent material, laser interference processing is possible, preferably with an embodiment of the above-mentioned device inside the substrate.

In a preferred embodiment, a device for producing a structured substrate, preferably a flat and/or transparent substrate, is used, which uses a pulsed laser radiation source (1). In a particularly preferred embodiment, a device for producing a structured substrate, preferably a flat and/or transparent substrate, is used, which has a holding device for the substrate that is in the xy plane, perpendicular to the beam path (3) of the laser radiation source (1) emitted laser beam can move freely.

Ist die Weite des Interferenzpixels, D, größer als die Pixeldichte Pd, so überlagern sich benachbarte Interferenzpixel in einem Bereich. Dieser Bereich ist dem Fachmann als Pulsüberlapp, OV, bekannt. Er kann berechnet werden zu: $$OV=\raisebox{1ex}{$\left(D-Pd\right)$}\!\left/ \!\raisebox{-1ex}{$D$}\right.$$

In einer bevorzugten Ausgestaltung ist bei dem Verfahren zur Herstellung eines strukturierten Substrats, bevorzugt flächigen und/oder transparenten Substrats, Pd kleiner als D. Der dadurch entstehende Pulsüberlapp OV führt zu einer Mehrfachbestrahlung des Substrats, bevorzugt flächigen und/oder transparenten Substrats. Bevorzugt können so nicht-texturierte Flächen vermieden werden.Via the frequency of the laser radiation source (1), f, and the speed of movement of the holding device, v, the pixel density Pd, i.e. the distance at which an interference pixel with the width D on the substrate, preferably flat and/or transparent substrate, can be applied, set to: $$P\mathrm{i.e}=\raisebox{1ex}{$v$}\!\left/ \!\raisebox{-1ex}{$ƒ$}\right.$$

If the width of the interference pixel, D, is greater than the pixel density Pd, neighboring interference pixels overlap in one area. This range is known to those skilled in the art as pulse overlap, OV. It can be calculated to: $$OV=\raisebox{1ex}{$\left(D-P\mathrm{i.e}\right)$}\!\left/ \!\raisebox{-1ex}{$D$}\right.$$

In a preferred embodiment, in the method for producing a structured substrate, preferably a flat and/or transparent substrate, Pd is less than D. The resulting pulse overlap OV leads to multiple irradiation of the substrate, preferably a flat and/or transparent substrate. In this way, non-textured surfaces can preferably be avoided.

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

The advantage of a structured substrate produced by such a method, preferably a flat and/or transparent substrate, is the high level of regularity of the periodic point structures produced with structure dimensions in the micrometer or submicrometer range. A periodic point structure thus produced with dimensions in the micron or submicron range preferably has a coefficient of variation (a value obtained by dividing the standard deviation by the average value) of the pin cross-section of 15% or less, more preferably 10% or less, even more preferably 5% or less.

Shifting the substrate to be structured, preferably a flat and/or transparent substrate, in the laser beam is comparatively complex and slow due to the relatively large masses being moved. It is therefore advantageous to provide the substrate, preferably a flat and/or transparent substrate, in a stationary manner during processing and to implement the flat structuring of the substrate by focusing the partial beams on the surface or the volume of the substrate by manipulating the partial laser beams with optical elements ( Focusing mirror or galvo mirror (laser scanner)) is effected in the beam direction. Since the masses moved are relatively small, this can be done with far less effort and much faster. Preferably, the substrate is stationary during the process.

The planar structuring of the substrate is, of course, basically also possible by shifting the substrate in the laser beam.

By the periodic generated by the method and apparatus disclosed herein The substrate structured in this way has antireflection properties in the micrometer and/or nanometer range. This is ensured by the fact that light that hits the substrate is reflected less or is reflected at such a shallow angle that it is not "disturbing" when the material surface is viewed normally.

The invention therefore also covers a structured substrate with anti-reflection properties, which comprises a periodic point structure in the micrometer or submicrometer range, the periodic point structure being formed from inverse cones, the inverse cones being periodically spaced at a distance relative to their saddle point or center point Are arranged in the range from 50 nm to 50 μm, preferably in the range from 50 nm to 20 μm, more preferably in the range from 100 nm to 1000 nm, particularly preferably in the range from 100 nm to 600 nm.

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

Structured substrate

The inventors have found that substrates that have been structured primarily by a device disclosed herein or a method disclosed herein are characterized by pronounced anti-reflection properties. The present invention therefore also relates to a structured substrate with anti-reflection properties, as defined herein, which has a periodic point structure in Micrometer or submicrometer range, the periodic point structure being formed in particular from an inverse peg structure (herein also referred to as inverse pegs), the inverse pegs being spaced periodically at a distance in relation to their saddle point or midpoint in the range of 50 nm to 50 µm, are preferably arranged in the range from 50 nm to 20 μm, more preferably in the range from 100 nm to 1000 nm, particularly preferably in the range from 100 nm to 600 nm.

The periodic point structure produced in this way has the property that, depending on its structural dimensions, incoming electromagnetic radiation with wavelengths in the range from 10 nm to 1 mm can be increasingly transmitted or diffracted by the periodic structures, resulting in reduced reflection at the surface of the substrate. If the period of the periodic point structures produced is in the range of the wavelength of the incident electromagnetic wave, then this is diffracted at the surface of the substrate. If the period of the generated periodic point structure is smaller than the wavelength of the incident electromagnetic wave, then this is transmitted.

The periodic point structure is preferably designed in such a way that the structured substrate completely absorbs electromagnetic radiation with a wavelength of more than 550 nm in the case of a periodic point structure of less than 1,000 nm, preferably more than 500 nm in the case of a periodic point structure of less than 750 nm particularly preferably transmitted with a periodic point structure of less than 600 nm of more than 450 nm. Depending on the structural depth of the inverse cones, wavelengths in particular in the red and/or yellow light spectrum, in the green light spectrum up to the blue light spectrum can thus be transmitted into the substrate.

The refractive index of the structured substrate is gradual due to the periodic point structure produced. It decreases with the height of the structure, so no clear air-medium transition exists. This results in increased transmission of incident electromagnetic waves with a wavelength greater than the structure period of the point structure produced, and diffraction of incident electromagnetic waves with a wavelength in the range of the structure period of the point structure produced.

Use of the structured substrate

The structured substrate with anti-reflection properties defined herein is used, for example, in photovoltaic systems, it being possible to significantly increase the efficiency of these photovoltaic systems by introducing anti-reflective properties. A major challenge in the field of photovoltaic systems lies in the large losses due to the reflection of the sun's rays. On average, reflections cause 40% energy/power losses per system. The efficiency of photovoltaic systems must be constantly improved accordingly. One of the most promising approaches is the reduction of reflection with the help of anti-reflective coatings and/or texturing of the surface. The use of the method disclosed herein simplifies, accelerates and improves the treatment of the surfaces.

It is also well known that monitors and screens are often placed in fixed locations and are therefore susceptible to unfavorable incidences of light, leading to viewing problems for the viewer. Although there are fundamental ways of minimizing this effect, these approaches are not widely used, as they tend to alleviate the symptoms rather than solve the problem in concrete terms. The patterned substrate with antireflection egg defined herein properties is ideal, for example, for application or integration in the display area, e.g. in the form of anti-reflection glazing for monitors, screens and displays.

Another area of application opens up in the area of anti-reflection coating within glass fibers, which ensures higher transmission rates and minimizes back reflections. The method disclosed herein is therefore ideally suited for structuring glass fibers, so that the glass fiber structured in this way offers a further application example for a structured substrate defined herein with anti-reflection properties. The present invention therefore also includes the use of a structured substrate as defined herein as a component of glass fibers.

In addition, the inventors have found that the method defined herein is suitable for structuring window panes (as another example of anti-reflection glazing). For example, the structured substrates disclosed herein can be used in the form of anti-reflection glazing or as a film on house facades, preferably flat and/or transparent substrates, as heat-insulating glazing, which is used, for example, to protect against concentrated solar radiation through curved house facades and for better thermal insulation of buildings can.

In addition, reducing the reflection in microscopes and telescopes can increase the contrast of the images recorded with them, thereby increasing the efficiency and use of these optical devices. The present invention therefore also includes the use of a structured substrate defined herein as an optical element with a periodic point structure in the micrometer or submicrometer range in optical devices, such as microscopes and telescopes, for which beam guidance, beam shaping, beam bundling and/or beam focusing are essential.

It is also expedient to use the structured substrate defined herein as a negative mold (so-called master), for example within an embossing process for the indirect application or production of structures on another substrate. For example, this is relevant for roll-to-roll processes in which structures are transferred from a so-called master (usually 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 in high throughput as periodic point structures in the micrometer or submicrometer range on other substrates.

Reference List

1

laser radiation source

2

beam splitter element

3

beam path

4

focusing element

5

substrate

6

another deflection element

7

deflection element

8th

polarizing element

9

Focusing mirror or galvo mirror

exemplary embodiments

The present invention is explained in more detail on the basis of the following figures and exemplary embodiments, without restricting the invention to these. In particular, features shown in the individual figures and described for the respective example are not limited to the respective individual example.

character list

• 1 : a schematic perspective view of a device according to the invention.
• 2 : a schematic perspective view of a device according to the invention, which contains a deflection element (6) for making the partial beams parallel.
• 3 : a schematic perspective view of a device according to the invention, which contains a deflection element (7) for widening the angle of the partial beams to the optical axis of the beam path (3).
• 4A : a schematic perspective view of a device according to the invention, which contains optical elements (6) with a planar, reflecting surface, which deflect the partial beams onto the focusing element (4).
• 4B : a schematic perspective view of a device according to the invention, which comprises a galvo mirror (9) as an optical element for beam shaping, which allows stationary positioning of the substrate to be structured during the structuring process.
• 5 : a schematic perspective view of a device according to the invention, wherein the device contains a polarization element (8) which shifts the phase profile of the partial beams relative to one another, wherein
  1. a) the beam splitter element (2) is positioned in the beam path (3) close to the laser radiation source (1).
  2. b) the beam splitter element (2) is positioned in the beam path (3) close to the deflection element (7).
• 6 : a schematic view of the resulting interference pixels with width D on the surface or inside the substrate, and the distribution of the individual interference pixels on the surface or inside the substrate, the interference pixels being mutually shifted with the pixel density Pd.
• 7 : a schematic perspective view of the structured substrate (5) with the generated periodic point structures, consisting of inverse cones, with dimensions in the micrometer and submicrometer range, and symbolically the transmission of incident electromagnetic waves with wavelengths longer than the structure period of the structures generated, as well as the Diffraction of incident electromagnetic waves with wavelengths in the range or smaller of the created structures.

1 visualizes in a first embodiment the device according to the invention, comprising a laser radiation source (1) for emitting a laser beam. Arranged in the beam path (3) of the laser beam behind the laser radiation source (1), there is a beam splitter element (2) which is movably arranged in the beam path (3). A focusing element (4) is arranged in the beam path (3) of the laser beam behind the beam splitter element (2). Arranged in the beam path (3) of the laser beam behind the focusing element (4), there is a holding device on which a substrate (5), preferably a flat and/or transparent substrate, is mounted.

In this configuration, 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.

In this exemplary embodiment, the beam splitter element (2) corresponds to a diffractive beam splitter element. A diffractive beam splitter element here is a beam splitter element that contains microstructures or nanostructures. The beam splitter element (2) divides the laser beam into 4 partial beams.

In this exemplary embodiment, the focusing element (4) corresponds to a refractive, spherical lens, which directs the partial beams running essentially parallel to one another onto the substrate (5), preferably a flat and/or transparent substrate, such that they interfere there in an interference region. In this configuration, the interference angle corresponds to 27.2°, which results in a structure period of 550 nm for the periodic point structure with the same polarization state.

According to this exemplary embodiment, the planar substrate is irradiated once, so that a processing time per structural unit, i. H. per interference pixel, of 12 ps.

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

2 visualized in a further embodiment, the device as in 1 described, additionally comprising a deflection element (6), which is located in the beam path (3) of the laser after the beam splitter element (2) and the focusing element (4).

In this embodiment, the deflection element is a conventional, refractive, convex lens. The partial beams impinge on the deflection element (6) in such a way that, after passing through the deflection element, they run essentially parallel to one another. This allows the point at which the partial beams interfere on the surface or inside the substrate to be set.

3 visualizes in a further embodiment a device based on the in 1 and 2 structure shown. In addition, this structure includes a further deflection element (7), which is arranged in the beam path (3) of the laser between the beam splitter element (2) and the deflection element (6).

In this embodiment, the further deflection element (7) is a conventional, refractive, concave lens. The partial beams impinge on the further deflection element in such a way that their angle to the optical axis of the beam path is widened. As a result, the interference angle with which the partial beams interfere on the surface or inside the substrate, preferably a flat and/or transparent substrate, can be changed.

In this embodiment, all optical elements apart from 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 a shift of the beam part lerelements (2) set along the optical axis of the beam path.

4A shows a device as in FIG 3 , comprising the optical elements (6) with a planar, reflective surface, which are set up in such a way that they deflect the partial beams onto the focusing element (4).

In this configuration, the at least three partial beams are directed onto the substrate at a preferred angle by displacing the optical elements (6). As a result, a deflection element in the form of a lens (reference number (6) in 3 ) can be waived.

5 visualized in a further embodiment, a device as in 3 , Additionally comprising one polarization element (8) per partial beam, which are arranged in the beam path (3) of the laser beam between the deflection element (6) and the focusing element (4).

The polarization element is arranged in such a way that it changes the polarization of the individual partial beams relative to one another in such a way that the interference pattern changes.

This embodiment is shown in two different configurations. In 5 a) the beam splitter element (2) is positioned in the beam path (3) close to the laser radiation source (1). In 5b) the beam splitter element (2) is positioned in the beam path (3) close to the deflection element (7). 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 structure or the substrate.

In addition, it would also be conceivable for the arrangement to contain an additional optical element for beam shaping, which is arranged downstream of the laser radiation source (1) in the beam path (3) of the laser beam. In this configuration, the radiation profile of the laser radiation source corresponds to a Gaussian profile. The beam-shaping optical element converts this profile into a top-hat profile.

6 contains a schematic view of the resulting interference pixels with width D on the surface or inside the substrate, and the distribution of the individual interference pixels on the surface or inside the substrate, the interference pixels being mutually shifted with pixel density Pd.

In this configuration, the pixel density Pd is smaller than the width of an interference pixel, D. As a result, by moving the substrate (5) using a pulsed laser beam, a planar, homogeneous, periodic point structure can be created on the surface or inside a substrate, preferably a planar and/or transparent substrate , be generated.

7 visualizes the structured substrate (5) produced by the method according to the invention with the periodic point structures produced, consisting of inverse pegs, with dimensions in the micrometer and submicrometer range. In addition, the transmission of incident electromagnetic waves with wavelengths greater than the structure period of the structures produced, as well as the diffraction of incident electromagnetic waves with wavelengths in the range or smaller of the structures produced, are symbolically illustrated.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• US 8557877 B2 [0003]
• US10459125B2 [0005]
• WO 2019166836 A1 [0008, 0025]
• EP 2431120 A1 [0010]
• DE 102010005774 A1 [0050]

Claims (24)

Laser interference structuring device for direct laser interference structuring of a substrate, comprising - a laser radiation source (1) for emitting a laser beam, - a beam splitter element (2) which is arranged in the beam path (3) of the laser beam, - a focusing element (4) which is set up in such a way that the partial beams pass through in such a way that the partial beams can be interfered with 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 beam path (3), the beam splitter (2) is set up to split the incident laser beam, which is emitted by the laser radiation source (1), into at least 3 partial beams. device after claim 1 A first deflection element (7) is arranged downstream of the beam splitter element (2) in the beam path (3) of the laser radiation source (1) and is set up in such a way that the at least three partial beams are widened as they pass through the deflection element (7). device after claim 1 or 2 , wherein a further deflection element (6) is arranged in the beam path (3) downstream of the laser radiation source (1) and the beam splitter element (2), which is set up in such a way that it deflects the partial beams in such a way that, after exiting the further deflection element (6 ) run essentially parallel to each other. Device according to one of Claims 1 until 3 , wherein the beam splitter element (2) is a diffractive beam splitter element or a refractive beam splitter element. Device according to one of claims 2 until 4 , wherein the deflection element (7) is a concave lens. Device according to one of claims 3 until 5 , wherein the further deflection element (6) is a convex lens. Apparatus according to any preceding claim, wherein the focusing element (4) is a convex lens. Device according to one of the preceding claims, wherein the device comprises at least one polarization element (8) which is arranged in the beam path between the deflection element and the focusing element. Device according to one of the preceding claims, in which the laser radiation source is a pulsed laser radiation source with pulse widths in the range from 10 nanoseconds to 10 femtoseconds. Device according to one of the preceding claims, in which the radiation profile of the laser beam emitted by the laser radiation source corresponds to a Gaussian profile or a top-hat profile. Device according to one of the preceding claims, wherein a further optical element which can be used for beam shaping is located in front of the beam splitter element. Device according to one of the preceding claims, wherein the device comprises a holding device on which the substrate is mounted and which is movable in the xy plane perpendicular to the beam path (3) of the laser beam emitted by the laser radiation source (1). A device according to any one of the preceding claims, wherein the substrate comprises a transparent material. Method for producing a substrate with a periodic point structure in the micrometer or submicrometer range by means of laser interference structuring, 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 ) dividing the laser beam by a beam splitter element (2) into at least three partial beams, d) focusing the partial beams onto the surface or within the volume of the substrate (5), so that the partial beams interfere constructively and destructively on the surface or within the volume of the substrate, characterized in that the at least three partial beams are superimposed on the substrate by focusing in such a way that a periodic point structure in the micrometer or submicrometer range is generated on the surface or in the volume of the substrate, the periodic point structure being formed from inverse cones, wherein the inverse pins are arranged periodically with a distance in the range of 50 nm to 50 microns to each other. procedure after Claim 14 , where the structure period is the generated periodic point Structure of the substrate (5) in the micro or submicron range by moving the beam splitter element (2) along its optical axis in the beam path (3) is continuously adjustable. procedure after Claim 14 or 15 , wherein the substrate (5) comprises a transparent material and the partial beams interfere inside the transparent material. Structured substrate with antireflection properties, comprising a periodic point structure in the micron or submicron range, where the periodic point structure is formed from inverse cones, the pegs being periodically spaced in the range 50 nm to 50 µm. Structured substrate after Claim 17 , wherein the periodic point structure is formed in such a way that the structured substrate transmits electromagnetic radiation with a wavelength of more than 550 nm, preferably more than 500 nm, very particularly preferably more than 450 nm. Structured substrate after Claim 17 , wherein the structured substrate comprises a transparent material, and wherein the transparent material is selected from the group consisting of glass, solid polymers, transparent ceramics or mixtures thereof. Structured substrate according to one of claims 17 until 19 , where the refractive index of the structured substrate is gradual. Use of the structured substrate according to one of claims 17 until 20 in photovoltaic systems. Use of the structured substrate according to one of claims 17 until 20 as anti-reflection glazing for monitors, screens and displays. Use of the structured substrate according to one of claims 17 until 20 in glass fibers. Use of the structured substrate according to one of claims 17 until 20 as a negative mold for indirect application or creation of structures on another substrate.

Images