METHOD FOR PRODUCEING A LIGHT DEFECTION STRUCTURE, USE OF A SUBSTRATE WITH SUCH A LIGHT DEFECTION STRUCTURE, AND LIGHT DEFECTION UNIT WITH SUCH A LIGHT DEFECTION STRUCTURE

Description

[0001] The invention relates to a method for producing a light deflection structure, and a light deflection unit with such a light deflection structure according to the preamble of claims 1 and 8 (see e.g. EP 2 965 852 A1), and a use of a substrate with such a light deflection structure, see claim 7

[0002] Such a light deflection structure comprises periodic material modifications, in particular refractive index modifications or scattering disturbances, for example vacancies or damages, in the volume or on the surface of a substrate, wherein these material modifications influence properties of light transmitted by the substrate.

[0003] Periodic material modifications have so far been used primarily to influence the polarization properties of transmitted light. However, there is often a need for light-deflecting structures that exhibit a predetermined intensity and / or orientation of light deflection. For example, in a laser disk, desired laser light generated by stimulated emissions should be coupled out in a specific, well-defined direction, while unwanted, spontaneously emitted light should be radiated over the widest possible solid angle range. In other components, such as solar cells, there is a need to capture incident light wherever possible and retain it within the component, thus preventing it from being deflected out of the component.

[0004] WO 2019158910 A1 (state of the art according to Article 54(3) EPC), for example, discloses an optical element for modifying an incident laser beam propagating through the optical element from an input surface to an output surface via a geometric phase birefringence effect. The optical element comprises a substrate made of a transparent amorphous material and a structural modification in a volume. The structural modification includes a plurality of randomly positioned nanostructures, each nanostructure having a flattened spherical shape with an elliptical cross-section in a plane parallel to the input surface.

[0005] The present invention is based on the object of creating a method for producing a light deflection structure that enables targeted light deflection to at least a certain extent. Furthermore, the object of the invention is to specify the use of a substrate with such a light deflection structure and to create a light deflection unit with such a light deflection structure.

[0006] The object is achieved by providing the present technical teaching, in particular the teaching of independent claims 1, 7, and 8, as well as the embodiments disclosed in the dependent claims and the description.

[0007] The object is achieved in particular (see claim 1) by providing a method for producing a light deflection structure, wherein a substrate material of a substrate is irradiated with at least one pulsed laser beam, and wherein the substrate material is transparent or partially transparent to the pulsed laser radiation used to produce the light deflection structure, the method comprising the following steps: a) a first plurality of interaction regions is generated along a first path with spatial overlap of the interaction regions. b) a second plurality of interaction regions is generated with spatial overlap of the interaction regions along a second path, wherein the second path is offset from the first path and spatially overlaps the first path.Optionally, c) a further plurality of interaction regions is generated, with spatial overlap of the further interaction regions along a further path offset from the previously used paths and with spatial overlap with the immediately previously used path. Optionally, d) step c) is performed multiple times to obtain a predetermined number of paths, in particular until the predetermined number of paths is obtained.

[0008] Interaction regions - type II modifications of the substrate material are generated, wherein the type II modifications result from self-organizing effects through multiple irradiation of the same location. At least one process parameter is changed from path to path during production in order to generate a predetermined diffractive or scattering deflection geometry, wherein the process parameter is selected from a group consisting of: a spectrum, a pulse energy, a fluence, a temporal pulse width, a temporal pulse shape, a spatial pulse shape, beam dynamics, a polarization, in particular polarization direction, a pulse repetition rate, a micropulse repetition rate, a focus size, a focus cross-sectional shape, and a focus profile, a feed rate of a laser spot per unit time relative to the substrate (7), a pulse number per laser spot, and an overlap of immediately adjacent interaction regions (9) with one another.According to the invention, this means that the at least one process parameter is varied from path to path in such a way that the predetermined deflection geometry is generated. Using the method, it is possible to create a light deflection structure that has a defined, predetermined deflection characteristic for specific wavelengths of light transmitted through the substrate material.

[0009] An interaction region is understood here, in particular, to be a spatial region in which the at least one laser beam interacts with the substrate material. An interaction is understood, in particular, to mean that the substrate material undergoes a permanent material change due to the laser beam in the interaction region, i.e., a permanent material change under normal conditions—in particular at 1013 mbar and 25 °C. The interaction region is therefore a spatial region in which the energy density or power density of the laser beam is higher than a modification threshold of the substrate material for permanent material changes.A spatial overlap of the interaction regions is understood here in particular to mean that at least immediately adjacent interaction regions overlap with one another—along a path or at least in immediately adjacent paths—so that, in particular, the laser radiation in a second interaction region, which overlaps with a first interaction region, interacts with the material modification generated in the first interaction region or with the laser radiation in the first interaction region. The material modification or laser radiation in the first interaction region influences the effect of the laser radiation in the second interaction region; conversely, the laser radiation in the second interaction region preferably influences the material modification or laser radiation in the first interaction region.

[0010] The substrate material is transparent or partially transparent. In particular, the substrate material is transparent or partially transparent to the pulsed laser radiation used to produce the light deflection structure. In particular, the substrate material is transparent or partially transparent both to the pulsed laser radiation used to produce the light deflection structure and to at least one target wavelength of light that is intended to be deflected by the produced light deflection structure. Transparency is understood, in particular, to mean that a transmission of radiation of a specific wavelength in the substrate material for cw radiation is more than 80%, preferably more than 85%, preferably more than 90%.

[0011] According to the invention, the at least one process parameter is selected from a group consisting of: a spectrum of the laser beam, a pulse energy of the laser beam, a fluence of the laser beam, a temporal pulse width of the laser beam, a temporal pulse shape of the laser beam, a spatial pulse shape of the laser beam, a beam dynamics of the laser beam, a polarization, in particular a polarization direction of the laser beam, a pulse repetition rate of the laser beam, a micropulse repetition rate of the laser beam, a focus size, in particular a focus diameter or laser spot diameter of the laser beam, a focus cross-sectional shape of the laser beam, a focus profile of the laser beam, a feed rate of a laser spot of the at least one laser beam per unit time relative to the substrate, a pulse number per laser spot or per unit length, and an overlap of immediately adjacent interaction regions with one another.

[0012] A temporal pulse shape of a laser beam is understood, in particular, to be the shape of an envelope of the temporal intensity profile of a laser pulse. In contrast, a beam dynamics of a laser beam is understood to be a temporal structure of the intensity profile within a pulse, thus essentially a temporal microstructure of the laser pulse. This includes, in particular, whether the laser pulse has a continuous temporal pulse shape or consists of a burst or a plurality of bursts and is thus designed as a pulse train.

[0013] A pulse repetition rate is understood in particular as a macropulse repetition rate, i.e., a repetition rate of the individual laser pulses or pulse trains. In contrast, a micropulse repetition rate is understood as a repetition rate of the individual micropulses or bursts within a laser pulse or pulse train.

[0014] A focus size is understood to be, in particular, a spot size of the laser beam, in particular a characteristic extension or length of the laser spot in a plane perpendicular to the propagation direction, or an area of ​​the laser spot in the plane. In the case of a Gaussian beam, the laser spot—or spot for short—is defined as twice the beam waist radius R, which results from the peak wavelength λ divided by the sum of the number π and the numerical aperture NA of the laser system (R = λ / (π*NA)).

[0015] A focus cross-sectional shape refers, in particular, to the cross-sectional shape of the laser spot. A focus profile refers, in particular, to the profile of the laser spot, particularly in the focal plane. A profile is, in particular, a spatial intensity profile, i.e., in particular, the intensity profile in the focal plane or on the spot surface.

[0016] To achieve Type II modifications—for example, self-organizing nanostructures, nanolattices, or periodically arranged destruction—the number of pulses per laser spot must be greater than 1. The number of pulses per laser spot is calculated by multiplying the spot size by the pulse repetition rate divided by the feed rate. The pulse rate per laser spot therefore ultimately corresponds to a number of pulses per unit length, whereby this number of pulses per unit length must be selected such that more than one pulse is applied over the length of the laser spot in the feed direction.

[0017] If the interaction regions are not generated sequentially but simultaneously, the number of pulses per laser spot or the number of pulses per unit length corresponds in particular to the overlap of immediately adjacent interaction regions.

[0018] According to the invention, it is provided that a diffractive or scattering deflection geometry is created. For a diffractive deflection geometry, a period of the light deflection structure is preferably selected that is greater than or approximately equal to a wavelength at which the deflection structure is intended to act. The deflection structure then exhibits a diffractive effect for this wavelength. Alternatively, a scattering deflection geometry is created. For this purpose, the period of the light deflection structure is preferably selected to be smaller than the wavelength at which the light deflection structure is intended to act. The substrate then represents an effective medium with a refractive difference, which leads to anisotropic scattering of light of the intended wavelength.

[0019] Deflection is therefore generally understood to mean a change in the direction of propagation of light, whereby the term "deflection" includes in particular diffraction or scattering.

[0020] In particular, the light deflection structure proposed here enables localized light deflection.

[0021] It is possible for the method to be carried out with exactly one pulsed laser beam, in particular with one pulsed laser beam per interaction region or with a pulsed laser beam suitably distributed among the various interaction regions. In this case, it is preferably ensured by suitable focusing that the fluence, i.e., in particular, the energy surface density, in the interaction regions is greater than the modification threshold of the substrate material.

[0022] Alternatively, it is also possible to use a plurality of pulsed laser beams, in particular two pulsed laser beams per interaction region, for example, by causing the pulsed laser beams to overlap in the respective interaction region. The fluence is then precisely above the modification threshold where the laser beams overlap, whereby the individual laser beams do not, on their own, provide a fluence above the modification threshold.

[0023] A plurality of laser beams can also be generated by appropriately splitting a pulsed laser beam generated by a laser source into a plurality of sub-laser beams. This is also referred to as multiplexing.

[0024] The light deflection structure is preferably created in the substrate material, i.e., in a volume of the substrate material. In particular, a three-dimensional light deflection structure is preferably created in the volume of the substrate material. Accordingly, the various paths are preferably not arranged merely along a plane in the substrate material, but rather are distributed three-dimensionally within the volume.

[0025] Alternatively or additionally, it is possible for the light deflection structure to be created on the surface of the substrate material. The individual paths then run at least partially or completely along the surface of the substrate.

[0026] The substrate material used is preferably a silicate-containing material, in particular silicate, fused silica, or borosilicate. In particular, the substrate can be a glass, in particular quartz glass, in particular borosilicate glass. However, it is also possible for the substrate to be a polymer, a ceramic, a semiconductor, in particular comprising Si and / or GaAs, or a crystal.

[0027] The fact that two paths spatially overlap means in particular that the interaction areas of the two paths spatially overlap.

[0028] That a path is offset from another path means in particular that the path, in particular a center of gravity or center line of the path, is spaced perpendicularly from a center of gravity or center line of the other path.

[0029] According to the invention, Type II modifications are understood to be material modifications of the substrate material that result from self-organizing effects upon repeated irradiation of the same spot—hence the spatial overlap of the interaction regions and paths. In particular, the previously irradiated spot optically interacts with the laser beam upon repeated irradiation of the same spot; preferably, the previously irradiated spot acts as a grating. This results in the formation of anisotropic structures that, due to their anisotropy, exhibit a directional deflection effect. A Type II modification is characterized in particular by the fact that the effective refractive index varies laterally. The modification thus behaves, in particular, like a uniaxial optical crystal.The generation of Type II modifications therefore means, in particular, that at least one process parameter, in particular a beam parameter of the at least one laser beam and / or at least one arrangement parameter of an arrangement of the interaction regions, is selected such that Type II modifications are formed. The generation of the Type II modifications is based, in particular, on an optical effect, not on a thermal effect.

[0030] The fact that at least one process parameter is changed from path to path means in particular that different values ​​are selected for at least one process parameter for at least two paths. In particular, a value or a setting for at least one process parameter is preferably changed between the creation of a previous path and the creation of a next path. It is possible for more than one process parameter to be changed, or for all process parameters to be changed. An embodiment of the method is also possible in which all process parameters are kept constant for a plurality of paths, wherein at least one process parameter is changed for at least one further path or a plurality of further paths. It is therefore also possible in particular for paths to be generated in groups with constant process parameters, wherein at least one process parameter is changed between different groups of paths.Preferably, however, at least one process parameter is selected for each path differently than for an immediately adjacent, particularly previously used and / or subsequently generated, path. It is possible for the same process parameter or the same plurality of process parameters to be varied from path to path. It is also possible for different process parameters to be varied from path to path.

[0031] A predetermined deflection geometry is understood in particular to mean that the light deflection structure is spatially and geometrically designed in such a way that light of a specific wavelength with a defined intensity is deflected into a defined solid angle range.

[0032] The first plurality, the second plurality and the at least one further plurality may be different numbers, but it is also possible that at least two of these pluralities represent the same number.

[0033] According to a further development of the invention, the pulsed laser beam has a temporal pulse width of at least 100 fs to at most 5 ps. The pulsed laser beam thus comprises, in particular, ultrashort laser pulses.

[0034] According to a further development of the invention, an induced grating period of the light deflection structure is modulated by changing the at least one process parameter. This generates a so-called chirp in the light deflection structure, resulting in a broad deflection and / or scattering angle distribution. Such chirped structures with a variable period, in particular gratings, can be produced with constant or variable orientation.

[0035] According to a further development of the invention, a plurality of nanolattice layers are formed one after the other in the substrate. This can enhance the deflection effect.

[0036] According to a further development of the invention, the at least one process parameter is changed within at least one path selected from the first path, the second path, and optionally a further path according to one of steps c) and d) in order to generate the predetermined deflection geometry. Thus, the light deflection structure can be modified even more finely. In particular, the induced grating period of the light deflection structure can be changed, in particular modulated, within a path.In particular, 2D-adapted structures can be created, wherein within a path, in particular, the grating period is changed, in particular by means of variable pulse energy and / or variable advance of a laser spot of the at least one laser beam per unit time relative to the substrate, and furthermore, the grating period is changed in the same or a different way from path to path, resulting in a two-dimensionally chirped grating that deflects or scatters light components with different angles of incidence at the same exit angle, or - depending on the application - vice versa. Likewise, the diffraction response can be made to continuously increase or decrease, in particular by changing a process parameter, in particular the pulse repetition rate, along a path in such a way that grating formation is inhibited, whereby the efficiency of the grating, which is chirped in particular from path to path, changes along the advance.

[0037] Alternatively, the at least one process parameter is preferably kept constant within each path and varies only from path to path. In particular, all process parameters within the same path are preferably kept constant. According to a further development of the invention, at least one of the paths, selected from the first path, the second path, and optionally a further path according to one of steps c) and d), runs along a straight line. This represents a particularly simple embodiment of the method.

[0038] Alternatively or additionally, it is possible for at least one of the paths selected from the first path, the second path, and optionally a further path according to one of steps c) and d) to have a finite curvature, at least in some regions. The path can also be curved entirely. This allows for even more flexible and precisely tuned light deflection structures and deflection geometries to be created. The fact that the curvature is finite means that it is greater than zero, i.e., it does not vanish. The curvature can be constant along the path or vary at least in certain sections.

[0039] The at least one process parameter is selected, in particular, from at least one beam parameter of the at least one laser beam and at least one arrangement parameter of the arrangement of the interaction regions. An arrangement parameter relates, in particular, to the spatial-geometric arrangement of the interaction regions or the generation of the spatial-geometric arrangement of the interaction regions. As will be explained below, the various interaction regions can be generated simultaneously or sequentially, wherein they can be generated sequentially, in particular, by displacing a focus region or laser spot of the at least one laser beam relative to the substrate. In this latter case, the arrangement parameter is, in particular, a displacement parameter of the relative displacement of the laser beam relative to the substrate.

[0040] Where reference is made here and below to a relative displacement, or even merely a displacement of the laser beam relative to the substrate, this should in no way be understood as limiting the laser beam to being displaced while the substrate is held in a fixed position. Rather, it is possible for the laser beam to be held in a fixed position while the substrate is displaced. It is also possible for both the laser beam and the substrate to be displaced. A particularly preferred embodiment, however, because it is particularly simple to implement, is for the substrate to be held in a fixed position while the laser beam is displaced.

[0041] According to a further development of the invention, it is provided that the wavelength, in particular peak wavelength, of the laser beam is at least 200 nm to at most 5000 nm.

[0042] Alternatively or additionally, the pulse repetition rate is preferably from at least 1 Hz to at most 5 MHz, preferably to at most 4 MHz, preferably to at most 3 MHz, preferably to at most 2 MHz, preferably to at most 1 MHz.

[0043] Alternatively or additionally, the micropulse repetition rate is preferably from at least 1 MHz to at most 50 GHz.

[0044] Alternatively or additionally, the temporal pulse width is preferably from at least 100 fs to at most 5 ps.

[0045] Alternatively or additionally, the fluence is preferably more than 0.01 J / cm 2 , in particular for glass, in particular fused silica, as substrate, preferably more than 0.1 J / cm 2 , preferably more than 1 J / cm 2 . The modification threshold in the volume of the substrate material is typically more than 0.1 J / cm 2 , optionally also more than 1 J / cm 2 . At the surface of the substrate material, in contrast, the modification threshold is reduced and is typically more than 0.01 J / cm 2 , optionally also more than 0.1 J / cm 2 . The fluence used is preferably selected to be greater than the respectively relevant value for the modification threshold.

[0046] Alternatively or additionally, it is provided that the feed rate of the laser spot per unit of time relative to the substrate is preferably from at least 0.01 mm / s to at most 1000 mm / s, preferably up to at most 500 mm / s.

[0047] Alternatively or additionally, it is provided that the number of pulses per unit length is preferably greater than one pulse per µm (1 / µm), whereby here too the term "pulse" includes a pulse train.

[0048] According to a further development of the invention, the interaction regions are generated simultaneously at least along one path selected from the first path, the second path, and optionally a further path according to one of steps c) and d). This can be done in particular by means of a spatiotemporally shaped excitation beam and / or by means of a phase mask.

[0049] Alternatively, the interaction regions are generated at least along one path selected from the first path, the second path, and optionally a further path according to one of steps c) and d), preferably sequentially, in particular by shifting a focus region or laser spot of the at least one laser beam relative to the substrate. The light deflection structure is then written into the substrate in a point-by-point manner, in particular by scanning the laser beam.

[0050] Preferably, the interaction regions along all paths are generated simultaneously or sequentially.

[0051] Preferably, steps a) to d) are performed either simultaneously or sequentially. It is therefore particularly possible for steps a) to d) to be performed simultaneously, in particular by means of a spatiotemporally shaped excitation beam and / or by means of a phase mask. It is also possible for a plurality of laser beams to be simultaneously shifted along the paths, offset from one another, in particular at least one laser beam per path. In the case of simultaneously performed steps, the term "previously used path" in step c) refers to the previously mentioned paths, which, however, are generated simultaneously with the respective additional path. In this respect, the term "multiple execution" in step d) also refers to simply generating a plurality of additional paths.

[0052] The focus area or laser spot can be shifted relative to the substrate perpendicular to the laser beam's propagation direction and / or parallel to the laser beam's propagation direction. The only important thing is that the area of ​​the laser beam in which a permanent material modification is achieved is shifted relative to the substrate.

[0053] According to a further development of the invention, a predetermined temporal shape is imposed on individual pulses of the at least one laser beam. By temporally shaping the laser beam or the laser pulses, in particular individual pulses, the resulting light deflection structure can be further influenced.

[0054] According to a further development of the invention, the substrate is heated at least in regions after step b) in order to modify the generated type II modifications. In particular, the substrate is heated at least in regions such that the generated type II modifications are modified in a predetermined manner. By such subsequent heating of the substrate, defects can be healed and, for example, optical properties of the induced periodic material modifications can be modified. The fact that the substrate is heated at least in regions after step b) includes the substrate being optionally heated after step c) or after step d). In particular, the substrate is heated accordingly at the end of the manufacturing process, i.e., after all interaction regions have been generated.

[0055] The substrate is preferably heated to a temperature T for which the following applies: 0,5 T g < T < 1,2 T g , where T g is the transition temperature of the substrate. The transition temperature is, in particular, the temperature at which the viscosity of the substrate is 10 12 < Pas.

[0056] The object is also achieved, see claim 7, by providing a use of a substrate with a light deflection structure, wherein the light deflection structure is produced in a method according to the invention or in one of the previously described embodiments of the method, wherein the substrate is used as an optical fiber, as a laser disk, as a glass display or as a solar cell.The substrate consists of a material that is transparent or partially transparent to the pulsed laser radiation used to create the light deflection structure, with a first row of spatially overlapping interaction regions and a second row of spatially overlapping interaction regions, whereby type II modifications of the substrate material are created. The type II modifications result from a self-organizing effect by repeatedly irradiating the same spot, and whereby a diffractive deflection geometry or a scattering deflection geometry is created. This results in the advantages described in connection with the light deflection structure in a particular way.

[0057] Particularly when the substrate is used as a laser disk, the light deflection structure can be used to couple desired, stimulated, and amplified laser light out of the laser disk in a defined direction. Alternatively, the light deflection structure can be provided to couple unwanted, spontaneously emitted and amplified light out of the laser disk in a way that is as broadly scattered as possible, particularly at different wavelength-dependent angles, thus reducing the thermal stress on surrounding areas caused by such spontaneous emissions.

[0058] If the substrate is used as a solar cell, the light deflection structure can particularly help to keep light entering the solar cell within it and thus increase the efficiency and yield of the solar cell.

[0059] The object is finally also achieved, see claim 8, by providing a light deflection unit comprising a substrate with a light deflection structure produced using a method according to the invention or using one of the previously described embodiments of the method. The substrate consists of a material that is transparent or partially transparent to the pulsed laser radiation used to produce the light deflection structure, with a first row of spatially overlapping interaction regions, and with a second row of spatially overlapping interaction regions, wherein type II modifications of the substrate material are generated, wherein the type II modifications result from a self-organizing effect by repeatedly irradiating the same location, and wherein a diffractive deflection geometry or a scattering deflection geometry is generated.In connection with the light deflection unit, the advantages already described above arise in particular.

[0060] The task is explained in more detail below using the drawing. It shows: Figure 1 shows a schematic representation of two embodiments of a light deflection structure, Figure 2 shows an example of the dependence of a period of a light deflection structure produced in a specific substrate material on the pulse number per laser spot, and Figure 3 shows an example of the dependence of the period of a light deflection structure produced in a specific substrate material on the wavelength of the laser radiation used for production.

[0061] Fig. 1shows at a) a schematic representation of a first embodiment of a light deflection unit 1 with a first embodiment of a light deflection structure 3, which is produced in a substrate material 5 of a substrate 7 by means of at least one pulsed laser beam, in particular in a method comprising the following steps: A first plurality of interaction regions 9 are generated, of which only two are schematically marked and provided with the corresponding reference numerals for the sake of clarity. The interaction regions 9 are generated along a first path P1 with spatial overlap - step a).

[0062] The light deflection structure 3 is produced in particular as a nano-lattice, the lattice webs of which are Figure 1 are illustrated by black lines.

[0063] In step b), a second plurality of interaction regions 9 is generated with spatial overlap of the interaction regions 9 along a second path P2, wherein the second path P2 is offset from the first path P1, but spatially overlaps with the first path P1, which is illustrated here by overlapping curly brackets. This means, in particular, that the interaction regions of the second plurality of interaction regions 9 arranged along the second path P2 overlap with the interaction regions 9 of the first plurality of interaction regions 9 arranged along the first path P1.

[0064] Optionally, a further plurality of interaction regions 9 is generated with spatial overlap of the further interaction regions 9 along a further path PN offset from the previously used paths P1, P2 and with spatial overlap with the immediately previously used path PN-1. Specifically, a third plurality of interaction regions 9 is generated with spatial overlap along a third path P3, which is offset from the first path P1 and the second path P2, but overlaps with the second path P2 - step c).

[0065] This step c) can - step d) - be executed several times until a predetermined number of paths is obtained.

[0066] As part of the process, type II modifications are created in the substrate material 5.

[0067] At least one process parameter is varied from path to path to generate a predetermined deflection geometry. It is also possible for at least one process parameter to be varied during the generation of at least one path—within the path—to generate the predetermined deflection geometry.

[0068] According to the invention, the deflection geometry is a diffractive deflection geometry or a scattering deflection geometry.

[0069] In the embodiment shown here, paths P1, P2, and P3 run along straight lines. However, it is also possible for at least one of the paths to run along a curved curve, in particular along a circular arc. Different geometries for different paths are also possible.

[0070] The at least one process parameter is preferably selected from a group consisting of: a spectrum of the laser beam, a pulse energy of the laser beam, a fluence of the laser beam, a temporal pulse width of the laser beam, a temporal pulse shape of the laser beam, a spatial pulse shape of the laser beam, a beam dynamics of the laser beam, a polarization, in particular polarization direction, of the laser beam, a pulse repetition rate, a micropulse repetition rate, a focus size or laser spot size, in particular focus diameter or laser spot diameter, a focus cross-sectional shape or laser spot cross-sectional shape, a focus profile or laser spot profile, a feed rate of a laser spot per unit time relative to the substrate 7, a pulse number per laser spot or a pulse number per unit length on the substrate 7, and an overlap of immediately adjacent interaction regions 9 with one another.

[0071] In the embodiment shown here, the polarization direction - shown schematically here by double arrows DP - is changed as a process parameter from path to path.

[0072] The interaction regions 9 are preferably generated at least along one path simultaneously or sequentially, in particular by shifting a focus region or laser spot of the at least one laser beam relative to the substrate 7.

[0073] The different paths can also be covered simultaneously by a plurality of laser beams offset from one another, wherein in particular at least one laser beam is used for each path.

[0074] Preferably, a predetermined temporal shape is impressed on individual pulses of the at least one laser beam.

[0075] Preferably, after step b), in particular after the generation of all interaction regions 9 along all paths P1, P2, PN, the substrate 7 is heated at least in regions in order to change the type II modifications generated.

[0076] The light deflection structure 3 is preferably used as an optical fiber, as a laser disc, as a glass display or as a solar cell.

[0077] Overall, the invention is based on the idea that the generation of periodic material modifications, in particular refractive index modifications, in the volume and / or on the surface of (partially) transparent materials using ultrashort laser pulses allows the properties of the transmitted light to be influenced and deflected in a targeted manner. Geometric or structural properties of the induced modifications (e.g., period, refractive index contrast) and thus the strength and orientation of the deflection can be controlled using inscription parameters and / or inscription laser parameters, beam shaping, and / or beam dynamics.

[0078] When ultrashort laser pulses from an inscription laser are focused into the volume of a substrate, such as quartz glass, the high intensity at the focus leads to nonlinear absorption processes, which induce material modifications. Inscription can be performed pointwise and / or simultaneously at multiple locations, particularly using a spatiotemporally shaped excitation beam and / or a phase mask.

[0079] The structures can be used to deflect light into a specific angular range, either diffractingly or based on inherent scattering. The orientation of the deflection can be controlled by the period of the grating, which is defined by laser parameters such as the wavelength of the inscription laser. The strength of the diffraction efficiency can be controlled by various concepts such as laser pulse energy, feed rate, and / or beam dynamics, particularly temporally, for example, through laser bursts and / or beam shaping.

[0080] Depending on the substrate material, the induced nanostructures can exhibit widely varying structural properties. In glasses, in particular, nanolattices are formed from microscopic holes with anisotropic shapes and dimensions of a few hundred nanometers in length and at least ten nanometers in thickness. Irradiation with light, for example, in the visual spectral range, results in a scattering cone due to the anisotropic structure, which is aligned according to the grating orientation – always parallel to the polarization of the inscription laser and thus, in particular, perpendicular to the grating bars of the nanolattice. Within the framework of the technical teaching presented here, this targeted scattering can also be used to deflect the incident light.

[0081] If such laser-induced nanolattices are inscribed closely to one another, especially overlapping, the newly inscribed lattice coherently aligns itself with the orientation of the existing lattice. This creates a self-organizing structure. This allows for the creation of regions with, for example, continuously changing nanolattice orientations – see Figure 1a ) - and thus light can be deflected or scattered over a wide angular spectrum.

[0082] Figure 1b ) shows a further embodiment of a light deflection unit 1 with a further embodiment of a light deflection structure 3.

[0083] Identical and functionally identical elements are provided with the same reference symbols in all figures, so that reference is made to the preceding description in each case.

[0084] In this further embodiment, the induced grating period is modulated by varying at least one process parameter within the individual paths. In particular, a so-called chirp is generated, resulting in a broad deflection or scattering angle distribution. This can be achieved, for example, by varying process parameters such as feed rate, pulse overlap, and / or wavelength of the inscribed laser beam. Such chirped gratings can be produced with constant or variable alignment. Furthermore, multiple nanograting layers arranged one behind the other can enhance the deflection effect.

[0085] Specifically, the process parameter here is the feed rate of the laser spot per unit of time relative to the substrate 7, i.e. the displacement speed of the laser beam, which is changed within the individual paths in order to modulate the grating period. An acceleration is schematically indicated by an arrow. v̇ of the laser beam within the individual paths. Of course, the displacement speed of the laser beam along a path can also be reduced.

[0086] Within the framework of the technical teaching presented here, the periodic modifications are tailored to the desired deflection geometry. This means, in particular, that the lattice webs of the nanogratings can exhibit any angle to the material surface, depending on the application. In particular, the geometry of the inscribed periodic modifications is tailored to the desired application, whereby concepts such as beam dynamics, beam shaping, and multi-beam processing (multiplexing) can be used to create extended modification regions in the material.

[0087] By subsequently heating the manufactured light deflection structure 3, defects can be healed and, for example, optical properties of the induced periodic material modifications can be changed.

[0088] Various approaches are conceivable for inscribing periodic material modifications: Firstly, ultrashort laser pulses can be focused into the volume of the substrate 7 using a microscope objective, and extended areas can be structured by scanning the substrate 7 and / or the laser spot. Furthermore, the modification or absorption area can be modified by beam-shaping elements in the processing head, such as diffractive optical elements, spatial light modulators, or acousto-optical deflectors. The latter can also occur highly dynamically during processing. Digital optics or scanners with acousto-optical deflectors can be used, in particular. The temporal absorption dynamics can be modified by short pulse trains, especially bursts.

[0089] Preferably, in a first step, the dependencies of the periodic material modifications to be generated on the various process parameters for a substrate material 5 to be processed are defined and stored as a table in a program. Subsequently, a specific diffraction or scattering or grating period can be specified, and the control parameters for the processing can be derived from the table.

[0090] Fig. 2 shows, as an example, such a dependence of the periodic material modifications to be created on a process parameter, specifically the dependence of the period of the resulting nanograting on the pulse rate per laser spot. The period of the material modification is determined in particular by λ / 2n, i.e., by the wavelength λ of the laser beam used divided by twice the refractive index n of the substrate material 5.

[0091] Fig. 3shows, as an example, the dependence of the period of the generated material modifications on the wavelength λ of the inscription laser.

Claims

1. A method for producing a light deflection structure (3), wherein a substrate material (5) of a substrate (7) is irradiated with at least one pulsed laser beam and wherein the substrate material (5) is transparent or partially transparent for the pulsed laser radiation used to produce the light deflection structure, comprising the following steps: a) generating a first plurality of interaction regions (9), in each of which the at least one laser beam interacts with the substrate material (5), along a first path (P1) with spatial overlap of the interaction regions (9); characterized in that the method includes the following steps: b) generating a second plurality of interaction regions (9) with spatial overlap of the interaction regions (9) along a second path (P2) offset from the first path with spatial overlap to the first path (P1); c) optionally generating a further plurality of interaction regions (9) with spatial overlap of the further interaction regions (9) along a further path (PN) offset from the previously used paths (P1, P2) and with spatial overlap with the immediately previously used path (PN-1); d) optionally executing step c) several times to obtain a predetermined number of paths (P1, P2, PN), wherein - type II modifications of the substrate material (5) are produced, the type II modifications resulting from self-organizing effects due to multiple irradiation of a same location, wherein - at least one process parameter is changed from path (P1, P2, PN) to path (P1, P2, PN) to produce a predetermined deflection geometry, wherein the process parameter is selected from a group consisting of: a spectrum, a pulse energy, a fluence, a temporal pulse width, a temporal pulse shape, a spatial pulse shape, a beam dynamics, a polarization, in particular polarization direction, a pulse repetition rate, a micropulse repetition rate, a focus size, a focus cross-sectional shape, and a focus profile, a feed of a laser spot per unit time relative to the substrate (7), a pulse number per laser spot, and an overlap of directly adjacent interaction regions (9) with one another, wherein a diffractive deflection geometry or a scattering deflection geometry is generated.

2. The method according to claim 1, characterized in that the at least one process parameter is changed within at least one path (P1, P2, PN) selected from the first path (P1), the second path (P2), and optionally a further path (PN) according to one of steps c) and d), in order to generate the predetermined deflection geometry.

3. The method according to one of the preceding claims, characterized in that at least one of the paths (P1, P2, PN), selected from the first path (P1), the second path (P2) and optionally a further path (PN) according to one of steps c) and d), runs along a straight line, and / or in that at least one of the paths (P1, P2, PN), selected from the first path (P1), the second path (P2) and optionally a further path (PN) according to one of steps c) and d), has a finite curvature at least in certain regions.

4. The method according to one of the preceding claims, characterized in that the interaction regions (9) are generated simultaneously or successively in time at least along one path (P1, P2, PN) selected from the first path (P1), the second path (P2) and optionally a further path (PN) according to one of steps c) and d), in particular by shifting a focus region of the at least one laser beam relative to the substrate (7).

5. The method according to one of the preceding claims, characterized in that a predetermined temporal shape is imposed on individual pulses of the at least one laser beam.

6. The method according to one of the preceding claims, characterized in that the substrate (7) is heated after step b), at least in certain regions, in order to change the generated type II modifications.

7. A use of a substrate (7) with a light deflection structure (3), produced in a method according to one of claims 1 to 6, as an optical fiber, as a laser disk, as a glass display, or as a solar cell, the substrate (7) consisting of a material which is transparent or partially transparent for the pulsed laser radiation used to produce the light deflection structure (3), with a first series of spatially overlapping interaction regions (9), and with a second series of spatially overlapping interaction regions, wherein type II modifications of the substrate material (5) are produced, wherein the type II modifications result from self-organizing effects due to multiple irradiation of a same location, and wherein a diffractive deflection geometry or a scattering deflection geometry is produced.

8. A light deflection unit (1) comprising a substrate (7) with a light deflection structure (3) produced in a method according to any one of claims 1 to 6, wherein the substrate (7) is made of a material which is transparent or partially transparent to the pulsed laser radiation used to produce the light deflection structure (3), with a first series of spatially overlapping interaction regions, characterized by a second series of spatially overlapping interaction regions, wherein type II modifications of the substrate material (5) are generated, wherein the type II modifications result from self-organizing effects due to multiple irradiation of a same location, and wherein a diffractive deflection geometry or a scattering deflection geometry is generated.