Method for producing a functional element having a surface structure and functional element

Abstract

The present invention relates to a method for producing a functional element comprising a substrate consisting essentially of a polymer, the substrate having, on at least one surface, at least one zone having a surface texture that differs from the surface texture in an area surrounding the zone. To generate the zone, a surface region of the substrate is irradiated with laser radiation in a laser processing operation such that a change in the volume of the polymer is generated in a region of the volume of the substrate near the surface, induced by the interaction of the laser radiation with the polymer, resulting in a permanent change in the surface texture in the zone. As a result, a substrate consisting of a water-containing polymer is provided with an absorbance at the operating wavelength of the laser processing operation, selected or set based on a functional relationship between the wavelength of the laser radiation, the water content of the polymer, and the absorbance.

Description

[Technical Field]

[0001] The present invention relates to a method for producing / manufacturing a functional element comprising a substrate made of a polymer, at least one surface of said substrate having at least one zone with a surface shape that deviates from the surface shape of the surroundings of said zone.

[0002] A preferred field of application is in the production of optical functional elements (optical elements), for example optical elements for ophthalmic applications, in order that the interaction with the functional elements influences the propagation of light in the case. [Background technology]

[0003] In this method, creating a zone in a laser processing operation involves irradiating a surface region of a substrate with laser radiation such that interaction of the laser radiation with the polymer causes a change in volume of the polymer in a near-surface volume region of the body within the irradiated region, and this change in volume results in a (persistent) change in surface shape within the zone.

[0004] A method of this type is disclosed in EP 2184127. In a variant embodiment of the method for producing permanent markings for optical elements made of polymers transparent in the visible spectral range, the beam parameters of laser radiation having a wavelength in the near-infrared range are set so that a laser-induced volume increase is produced in the region near the irradiated surface without destroying the polymer. The resulting structural elements of the marking are raised relative to adjacent non-irradiated regions. The idea is that the polymer partially swells and / or optionally melts under the influence of the incident laser radiation and then solidifies again after irradiation is complete, thus creating a zone in the irradiated region near the surface that is either less dense or has an increased volume compared to before irradiation. If the power density of the laser radiation is not too high, the irradiated region can maintain a substantially intact surface that extends with a smooth and continuous curvature over the region of increased volume, like skin. In this way, lens elements with a convex lens surface can be produced in the irradiated region. If multiple adjacent irradiated regions are irradiated, a microlens array can be formed.

[0005] WO 2020 / 180817 discloses a method for providing an ophthalmic lens having a prescribed optical power, the ophthalmic lens having a surface with a base curvature corresponding to the prescribed optical power. The surface of a material is exposed to laser radiation sufficient to locally reshape the material to form a number of lenses on the surface, each having a corresponding optical power different from the prescribed optical power of the ophthalmic lens. The method is intended to work with substrates made of inorganic glass and substrates made of organic polymers. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] European Patent No. 2184127 [Patent Document 2] International Publication No. 2020 / 180817 [Non-patent literature]

[0007] [Non-Patent Document 1] M. Cumme and A. Deparnay, "From regular periodic micro-lens arrays to randomized continuous phase profiles," Optical Technology, 2015, 4(1), pp. 47-61. Summary of the Invention [Problem to be solved by the invention]

[0008] Against this background, the present invention addresses, inter alia, the problem of providing a method of the kind described in the introduction, which is suitable for serial production and allows the systematic production of structured functional elements with highly reproducible properties. Further problems are to provide an apparatus suitable for carrying out this method and to provide corresponding functional elements. [Means for solving the problem]

[0009] To achieve this goal, the present invention provides a method having the features of claim 1. Furthermore, it provides an apparatus for implementing the method having the features of claim 22 and a functional element having the features of claim 28. Advantageous developments are specified in the dependent claims. All claim phrases are incorporated into the content of this description by reference.

[0010] The method is suitable and designed for producing, i.e., manufacturing, a functional element comprising a substrate made of a polymer, at least one surface of which has at least one zone with a surface shape that deviates from the surface shape of the surroundings of the zone. In this context, the term "zone" denotes a spatially limited area surrounded by a more or less sharply defined "zone boundary" and transitioning within the zone boundary region into a surface region located outside the zone. The untreated surface can, for example, be flat (as in the case of a flat plate, for example) or can have a continuum of the functional base curvature of the functional element (as in the case of an ophthalmic lens, for example). In that case, in the zone region, there is a surface shape morphology that deviates from the base curvature.

[0011] Thus, a zone refers to a near-surface structure with a particular shape and dimensions. For example, a zone can be characterized by its lateral extent in at least one direction, its height, and the specification of the shape of the surface or its curvature within the zone boundary. The lateral extent can also be defined by a diameter or aperture in the case of a fully rounded zone. The height is the maximum distance of the surface in the zone's area from an imaginary extension of the surrounding surface outside the zone. A convex surface that is elevated above the surrounding surface and has a smaller mean radius of curvature than the surrounding surface has a positive height, while the height can be negative in the case of a concave zone surface.

[0012] In this method, creating a zone in a laser processing operation involves irradiating a surface region of a substrate with laser radiation such that interaction of the laser radiation with the polymer causes a volume change in the polymer in a near-surface volumetric region of the substrate, which volume change results in a change in surface topography within the zone. Upon completion of the laser processing, the zone remains with a surface topography that has changed relative to its surroundings. This volume change is a specific volume change and is performed non-destructively below the ablation threshold, i.e., without removing material and without associated thermal or photochemical decomposition of the irradiated polymer.

[0013] An essential step of the method is providing a substrate made of a water-containing polymer having an absorptivity at the operating wavelength of the laser processing operation, selected or set by taking into account the functional relationship between the wavelength of the laser radiation, the water content of the polymer, and the absorptivity. The absorptivity (similar to an absorption coefficient) defines the fraction of incident radiation that is absorbed. The absorptivity can take values ​​between 0 and 1.

[0014] By strict definition, a polymer is a chemical substance composed of macromolecules. Within the scope of this application, the term "polymer" describes a material that consists essentially of polymers or has polymeric materials as an essential component. The term polymer therefore refers to a polymeric material that consists predominantly or primarily of polymers or macromolecules and that additionally contains or may contain small amounts of further substances that are not macromolecules. Polymers may contain additive(s) that modify their properties. Polymers, especially polymers with additives, are often also called plastics.

[0015] This method is based on the irradiation of a polymer with a laser beam, the optical transparency of which for the respective laser wavelength allows interaction in the volume region immediately below the surface in the direction of the incident radiation. In particular, this method is suitable for polymers that exhibit partial transparency at the operating wavelength, i.e., the laser wavelength used for laser processing purposes. In other words, the treated polymer should exhibit partial absorption for the utilized laser wavelength, i.e., be completely transparent or completely devoid of absorption in the vicinity of the laser wavelength. Strictly speaking, this partial transparency is a specific property of initially dry polymers, e.g., polymers that have been freed from all physisorbed water by vacuum heating.

[0016] A measure of this partial transmission is the absorptance, which should be greater than zero and less than 1 in the vicinity of the laser wavelength. The absorptance selected or set or used for laser processing purposes can be, for example, in the range of 2% to 50%, particularly in the range of 5% to 40%.

[0017] Many polymers have the ability to absorb small amounts of water (generally a few weight percent (wt.%) or less). The degree of water absorption in this regard depends primarily on the chemical structure of the polymer (e.g., polar or non-polar), but also on the ambient conditions (water absorption through air or by direct contact with water) and the exposure time in a water-containing environment. For example, cyclic olefin copolymers (COC) should exhibit particularly low water absorption, on the order of only 0.01 wt.%, while polyamide resins should be able to absorb relatively large amounts of water (up to 10% of their specific weight); for example, the water absorption of PMMA can be about 2 wt.%.

[0018] The inventors have recognized that water physisorbed onto a polymer substrate can significantly contribute to absorption behavior and absorbance, particularly in specific wavelength ranges. For example, structural modifications to a polymer optical substrate that can be made to swell locally given a typical water content will no longer swell following extensive drying. Controlling the water content therefore makes it possible to precisely tailor the absorbance for a given wavelength within a wavelength range. Conversely, in some cases, it is possible to select an appropriate laser wavelength that results in a definable absorption behavior for a particular polymer with a predetermined water content, although the selection of available laser wavelengths is naturally limited. Therefore, for a particular application, it is possible to provide a substrate made of a polymer material with a selected water content, dimensioned in a targeted manner so that the substrate has a desired absorbance upon processing at the operating wavelength provided for irradiation, taking into account the determinable functional relationship between laser wavelength, water content, and absorbance. Thus, water content is a “set screw” that can be actively influenced to set the desired absorbance.

[0019] The inventors currently believe that water exists in a physisorption mode between entangled polymer chains and is converted into a gas phase by irradiation with a laser, provided that the energy input is sufficient. The resulting increase in the volume of the polymer material causes a pressure increase in the interaction volume, whereby the gaseous water acts as a driving force for the polymer, which has been softened but not structurally damaged by the increase in temperature. The process parameters should be set to have a certain base temperature so that, on the one hand, the water (asymmetric molecules that can be excited to vibrate) is gently activated, and, on the other hand, the polymer can also disentangle, and the free volume can increase. Preferably, the polymer is a thermoplastic polymer. It is possible that the water aggregates absorbed in the polymer have a very small volume (a few nm), as is the case for typical polymers in optical applications. 3 If the polymer has only a small molecular weight (of the order of magnitude below 1000), it cannot be resolved by light or scanning electron microscopy and only very small cavities that are irrelevant to the optical properties are produced when the polymer swells.

[0020] We considered that the water bound in the polymer (if the content is not too high) could be excited by laser radiation to obtain an increase in free volume. The power of coupling laser radiation into a suitable amount of water contributes to an absorption that depends on the water content and wavelength, and therefore affects the absorbance of the water-containing polymer. Within certain limits, the heat introduced (by exciting the bound water in the polymer) can be adapted for process optimization purposes, for example, by controlling the laser output power and / or by controlling the effective irradiation time at one location.

[0021] Against the background of this insight, the present invention enables a reproducible processing regime so that functional components with desired properties can be produced systematically and within close tolerances.

[0022] This method is particularly relevant for applications in which optically effective near-surface structures are intended to be produced. This is possible because local, damage-free expansion or contraction of the polymer allows the production of structures with defined optical properties, thus enabling targeted processing of components according to specific requirements, for example, for applications in the fields of microoptics or medical engineering. For example, spherical, aspherical, astigmatic, or cylindrical microlenses can be produced in this way. Prismatic structures can also be produced. In the case of lenticular surface structures, it is possible to produce both optically focusing or diverging optical structures and optical structures that guide or scatter light. However, it is also possible to produce functional elements in other non-optical technical fields, such as the technical fields of microfluidics or test structures for determining the layer adhesion of inorganic functional coatings on polymer substrates.

[0023] The shape of the zone, i.e., the shape of the area enclosed by the zone boundary, can be adapted in a targeted manner to the intended purpose. Circular zones are often envisaged. This allows, for example, the creation of microlenses that resemble round optical elements and can be characterized by an aperture or diameter. Zones with different aspect ratios between their longest and shortest sides are also possible, such as elliptical zones or rod-like elongated zones with an aspect ratio of 2 or more. Zones can also have a polygonal shape, for example a rectangular shape, in particular a square shape, or a polygonal shape with only three or more corner regions. As a rule, the corner regions are slightly rounded for technical reasons.

[0024] The number of zones may also vary depending on the intended use. In some applications, a single zone on the surface is sufficient. For example, in the case of multifocal lenses, a zone of greater curvature (near zone) may be incorporated into a zone of medium base curvature (for distance vision). In the field of micrometrology, for example, it is possible to precisely set a small receptacle volume by irradiating the base zone, resulting in arching and thus the desired reduction in receptacle volume. Similarly, irradiating the base zone with a laser may allow a small but accurately determinable increase in receptacle volume.

[0025] Many applications envisage embodiments with a large number of similar or dissimilar, i.e. different, zones that can be distributed over a surface according to a particular pattern, as is the case for example with microlens arrays.

[0026] The polymer in its original as-supplied state is generally not considered optimal for the planned production process. For example, the nominal water content in the as-supplied state may be significantly less than or significantly more than the water content that results in the required absorption rate within the process. Some method variations solve this problem by controlled modification of the water content of the polymer of the initial substrate, including at least one drying operation to reduce the water content and / or at least one loading operation to increase the water content, to set the desired absorption rate for the laser processing operation.

[0027] In principle, variant embodiments of the method in which the controlled modification of the water content comprises a combination of at least one drying operation and at least one dosing operation carried out before or after the drying operation are particularly advantageous in terms of a reproducible treatment regime.

[0028] For example, to set the water content in a targeted manner, the polymer substrate to be treated can first be dried in an oven below its softening temperature. Thermal aging in a vacuum or under negative pressure is particularly advantageous here, since the expelled water is induced and therefore cannot be reabsorbed. The dried component can then be exposed to water or a humid ambient atmosphere for a defined time and in a defined manner, so that a specific water content in the workpiece is set. The relative loss or gain of weight during this process can be measured, for example, gravimetrically or by spectroscopy (e.g., FTIR, Raman spectroscopy). Thus, drying here is carried out starting from a defined low initial value of water content and reintroducing water in a targeted manner.

[0029] In an alternative procedure, the polymer can first be aged to become saturated with water by aging in water and / or humidity, and then dried in a defined manner, whereby the dosing operation precedes the drying operation. In either case, the combination of the drying and dosing operations creates a defined initial condition for each subsequent operation, thereby systematically achieving a precise final result.

[0030] Alternatively or additionally, varying the process parameters allows for reaction to small deviations in water content from the target water content, and thus allows for optional control without costly measures for setting the water content precisely.

[0031] A series of experiments can be performed to ascertain as precise knowledge as possible about the functional relationship between laser wavelength, water content, and resulting absorption for a particular polymer material. For example, a time / weight curve up to a weight constant can be recorded for a particular sample geometry to accurately determine the moisture or water absorption of a polymer. For example, water absorption can be tested according to the EN ISO 62 standard.

[0032] However, precise knowledge of the absolute value of the water absorption or water content is not essential. In some method variants, the functional relationship between the wavelength of the laser radiation and the water content of the polymer and / or measurable quantities dependent on the water content is experimentally determined through numerous trials in order to ascertain data on the property map or a corresponding property map. The property map thus represents the behavior of the relevant polymer. The process parameters for laser processing can then be set based on data from the property map. In particular, the optical and rheological properties of the polymer, the selected laser parameters (including the laser wavelength), and the (local) water content of the polymer in the area designated for irradiation are crucial process parameters in this regard.

[0033] By a series of experiments, it is also possible to create a database containing database entries for a large number of different polymer materials and parameter sets that depend, for example, on the polymer, the thickness traversed by the radiation of the substrate, and the absorption and / or water content, from which an appropriate recipe for laser processing can be derived at a later stage, optionally in the form of a look-up table.

[0034] In some method variations, absorption measurements are performed prior to and / or during the laser processing operation to determine the absorptivity of the polymer for at least one wavelength of laser radiation. For example, the absorption measurements can include measuring the attenuation of a laser beam passing through a substrate of the functional element.

[0035] As already mentioned, the invention is used in a preferred field of application to produce optical functional elements, which are also referred to within the scope of this application as optical elements for short. In this application, the zones can be designed as optically effective lenses. The surface shape within the zones present during the intended use therefore determines the optical effect of the respective lens, which can have a converging or diverging effect.

[0036] For applications in the field of ophthalmic products, polymers should be as transparent as possible in the visible spectral range. In these cases, laser processing systems and processes with laser wavelengths in the 1.1 μm to 9.2 μm wavelength range are particularly preferred. Consequently, the interaction mechanism between laser radiation and water-containing polymers can be used to particular advantage. The use of thulium fiber lasers with an operating wavelength of approximately 1.9 μm appears to be particularly advantageous. One of the reasons for this is, inter alia, the high absorption by water, which can be found alongside the low absorption by polymers.

[0037] The inventors have also gained important insights relating to the details of advantageous process regimes: for example, to generate circular zones, the region where the zone is to be created can be irradiated with laser radiation over its entire area.

[0038] In contrast, preferred embodiments provide for the generation of zones using a focused laser beam, including a focal region within the zone having a diameter substantially smaller than the average diameter of the zone to be generated, guided across the zone along at least one trajectory according to a processing pattern, such that different locations within the zone are exposed to the focused laser radiation one or more times in succession. In this case, the term "trajectory" refers to the processing path followed by the focused laser beam one or more times. This allows the surface topography, i.e., the surface shape within the zone, to be set in a controlled and well-defined manner. This is particularly important for optical applications, where the zone should have a specific optical effect (e.g., focusing, divergence). This trajectory-based scanning regime, for example, allows for very precise setting of the focal length of a lens. For example, the focal region can have an average diameter on the order of 10 μm to 20 μm, while the zone can be several times larger, e.g., up to 400 μm.

[0039] According to one development, some or all locations within the zone exposed to laser radiation are traversed not just once, but multiple times, i.e., two, three, four or even more frequently, where each traverse involves the introduction of only a portion of the globally introduced laser energy. In particular, individual, several or all trajectories can be traversed multiple times. As a result, heat generated in a locally delimited manner within the substrate can be distributed to some extent between the traverses, and local overheating can be avoided. Furthermore, the global energy to be introduced can be controlled more precisely than in the case of only a single traverse.

[0040] To generate a zone in a variant embodiment of the method, a focused laser beam is successively directed in the scanning direction along linearly adjacent, spaced tracks within a surface scanning operation. For example, the ratio between the spacing and the diameter of the main focus can be in the range of 2:1 to 5:1. In this case, the tracks are used to limit the energy input by the laser to the shape of the zone to be obtained, e.g., circular or rectangular. Preferably, the zone is not irradiated only once in one scanning operation, but multiple times in different scanning directions, such that a surface scanning operation is followed by at least one further surface scanning operation with a further scanning direction oriented at an angle to the scanning direction. This procedure takes into account the fact that polymers generally have very poor thermal conductivity, and scanning in different directions allows for sufficiently uniform irradiation of the entire surface. The overall heat input level can be influenced by setting an appropriate distance between adjacent linear tracks. This can also be achieved by controlling the traversal speed of the focal spot along the track.

[0041] In another embodiment, to generate a zone, a focused laser beam is directed over the zone along two or more closed tracks of different dimensions. Often, three or more tracks, for example, three or four tracks of different dimensions, are provided. These tracks may be similar to each other, i.e., have a similar course but differ in the dimensions of the covered or enclosed area. The radial distance between the tracks and the number of tracks can be adapted to the desired final shape.

[0042] To generate a circular zone in one configuration, a focused laser beam is directed across the zone along two or more concentric circular tracks of different diameters. Often, three or more circular tracks are provided, for example, three or four circular tracks of different diameters. The radial distance between the circular tracks and the number of circular tracks can be matched to the desired final shape.

[0043] In order to achieve as uniform a heat distribution as possible, in the case of irradiation along a closed trajectory, for example a circular trajectory, the starting points of trajectories of different dimensions or diameters can be provided so as to be offset from one another in the circumferential direction.

[0044] It is sometimes the case that a trajectory, such as a closed, enclosing trajectory, such as a circular trajectory, is irradiated only once, i.e., in a single traverse, which may be sufficient whenever the required heat input is very small. Preferably, the laser beam is guided along the trajectory in a predetermined number of traverses for at least one trajectory, and preferably for all trajectories. As a result, the heat generated during one traverse can be distributed within the polymer during the period before the next traverse, and thus a relatively large amount of energy can be deposited in a step-by-step manner in the form of a scattering of material.

[0045] For processing regimes involving the creation of closed trajectories, particularly concentric circular trajectories, different strategies are possible. In one variant, a first trajectory, for example a circular trajectory, is first irradiated with a predetermined total number of trajectories, followed by at least one second trajectory of a different size or diameter, with the total number of trajectories provided for this trajectory. This allows each closed trajectory to be irradiated over its entire intended range before processing begins in the area of ​​the second trajectory. The trajectories can be ordered from outside to inside (e.g., from larger diameter to smaller diameter) and vice versa, although other orders are also possible.

[0046] In another processing strategy, a first iteration, or run, involves irradiating each of the differently sized trajectories exactly once, for example, with fewer trajectories than the total number of trajectories anticipated for each trajectory. Two or more further iterations / runs are then performed, in which some or all of the trajectories of varying, i.e., different, sizes or diameters are again irradiated with fewer than a predetermined total number of trajectories for each trajectory. This procedure continues until each trajectory has been irradiated the total number of trajectories anticipated.

[0047] A particularly uniform heat distribution and dispersion process occurs if each of the irradiated trajectories, e.g., circular trajectories, is traversed only once in each repetition, although this is not essential.

[0048] It is possible within the scope of the present invention to design the surface shapes within the zones to be very different in a defined manner, depending on the targeted use of the functional relationship between water content, polymer material, laser wavelength, etc. Some method variants produce zones with a convex, arc-shaped surface shape over part of the zone or over the entire zone. These can subsequently have an effect in optical functional elements such as focusing lenses. In this process, the surface is preferably produced with a rotationally symmetric, spherically or aspherically curved shape. In this process, it is also possible to set the focal length of the surface shape in a targeted manner. In this case, the surface shape can be set largely independently of the shape of the zone (e.g., round or polygonal).

[0049] However, it is also possible to create zones with a concave arc-shaped surface profile within the entire zone or, for example, within a circular partial zone. In this regard, it is sometimes discovered that in the case of water-containing polymers, laser radiation can also be used in a targeted manner for local drying by expelling the water, thereby resulting in a more specific material shrinkage in a targeted manner. Therefore, the creation of a concave arc-shaped surface profile involves irradiation with laser radiation, preferably below the softening temperature of the polymer, inducing locally limited drying, thereby resulting in a reduction in the specific volume of the polymer while forming the concave arc-shaped surface profile.

[0050] However, this is not the only option for forming a concave arc-shaped surface profile. In some variants, the creation of a concave arc-shaped surface profile, for example in a circular partial zone of a zone, involves irradiating the area to be irradiated with laser radiation so that the increase in specific volume in the radially outer region, for example in the annular region, is greater than the specific volume in the inner partial zone surrounded by the outer region (for example in the circular region). The idea here is to generate, for example, a heat ring, inside which heat may accumulate. However, this may contribute to the formation of a defined topographical structure. Thus, in this way, a recess having a diverging effect in optical applications is formed, the surface of which is surrounded by a raised edge relative to the periphery of the zone.

[0051] In very general terms, for example, it is possible to irradiate a zone in this way, which results in a different distribution of the energy input caused by the laser radiation, rotationally symmetric with respect to the center of the zone, which results in different noticeable changes in volume.

[0052] In many cases, the processing task consists of generating a number of similar or different zones within the area of ​​the surface to be structured, said zones being distributed on the surface at different locations within the area to be structured according to a predeterminable pattern.

[0053] Examples of this purpose are the production of microlens arrays or multifocal eyeglass elements for correcting visual defects, where spatially limited areas should be additionally structured with microlenses. The inventors recognized that, given the low thermal conductivity of polymers (e.g., approximately 0.19 W / m*K for PMMA), particular shaping problems may arise as a result of the fact that the energy input during the production of microlenses can affect the shape and dimensions of additional microlenses located nearby and processed in rapid succession. Therefore, the inventors propose special measures for global thermal management or global temperature control, especially in such cases. Such thermal management on macroscopic length scales is particularly important when the process window, taking into account the required energy introduced for volume change, is particularly tight, as in the case of relatively small and flat lenses, for example. According to a development, such a processing task provides zones to be generated successively according to a heat input-optimized processing strategy, preferably with the generation of a first zone at a first location followed by the generation of a second zone further away before the generation of a third zone closest to the first zone. This provides a particularly advantageous way to distribute the heat load in the preheated area on the polymer substrate without creating a lens. Also, the heat input is relevant in view of the amount of water in the polymer, since a laser-induced volume increase (laser expansion) is only observed if a sufficient amount of water is present, and subsequent drying, which may lead to undesired shrinkage, can only be determined with insufficient energy input.

[0054] To verify the processing strategy according to the development, the processing sequence of the zones is defined using temperature criteria, distance criteria and zone size criteria, and preferably a finite element simulation is performed to verify the processing strategy. As a result, it is possible to define the order in which the zones are successively processed in order to ensure that the local temperature of the substrate does not exceed a predeterminable temperature threshold at any time, or to ensure that similar optimization criteria are followed despite the poor thermal conductivity of the polymer. As a result of the corresponding simulation, an appropriate definition of the processing target function can be provided in order to verify the optimized processing sequence and to perform the structuring process accordingly.

[0055] According to the development, multiple different zones are generated within the region of the surface to be structured, and the zones are distributed on the surface at different locations within the region to be structured according to a laterally random distribution. For example, the zones can differ in their shape and / or their dimensions and / or their optical effect. In such a random distribution, some or all of the zones can have asymmetric polygonal shapes. For example, the zones can have three, four, five, six, seven, or more corners and a corresponding number of outer edges. The irregularly shaped zones can form a surface-packing arrangement such that every zone is immediately adjacent to its immediate neighbor across a corner or outer edge in all lateral directions, except for zones located at the edges of the structured region. The structured region can be densely packed with optically effective, irregularly designed microlenses having a refractive power (typically positive, but optionally negative). Preferably, the surfaces of the zones have randomly distributed curvatures and heights so that the zones also have a randomly distributed optical effect. For example, the distribution of the zones can be predetermined using a Voronoi tessellation.

[0056] Advantageously, an optical functional element of this kind (especially in a surface-filling manner and with a laterally random distribution of zones) can be designed, for example, as a beam shaping element, in particular as a diffuser, such that when partially coherent or coherent radiation (e.g. from a laser) passes through it, it can generate an intensity distribution in its far field that is more uniform than in the case of a microlens array with uniformly distributed microlenses of similar dimensions.

[0057] For a further explanation of the function and possible applications of random microlens arrays, please refer to the academic paper by M. Cumme and A. Deparnay, "From regular periodic micro-lens arrays to randomized continuous phase profiles," Optical Technology, 2015, 4(1), pp. 47-61. The inventive method and apparatus described herein can be advantageously used for the production of such random microlens arrays.

[0058] According to a development, a plurality of preferably similar zones are generated in the region of the surface to be structured, said zones being distributed on the surface according to a regular distribution at different locations within the region to be structured without surface filling or gaps. The zones can fill the region to be structured in the manner of a tessellation. Some or all of the zones can have a symmetrical polygonal shape. For example, the zones can have a triangular, rectangular or hexagonal shape. The zones can form a surface-filling arrangement such that, except for zones located at the edges of the structured region, every zone is immediately adjacent to its immediate neighbors in all lateral directions, across corners or outer edges. The structured region can be filled without gaps with optically efficient microlenses with curved surfaces.

[0059] In particular, when operating optical functional elements, for example for the production of zones of special optical power in multifocal eyeglass elements, it can be advantageous if the structure produced by laser processing is followed by a controlled heat treatment and / or drying treatment for the functional element to stabilize it at ambient temperature before its intended use. For example, the post-treatment can include a heat treatment below the softening temperature of the polymer to stabilize the lens geometry.

[0060] Functional coatings (e.g., hard lacquer layers, anti-reflection coatings, etc.) are widespread for polymer-based optical functional elements. The inventors have recognized that even for the methods of the type considered here, it is possible to coat the surface to be structured with a desired functional layer or sub-layer of the coating before the laser processing operation, during selected steps of the laser processing operation and / or after the laser processing operation is completed. According to a development, the type of coating (layer material, layer structure, etc.) and / or the parameters of the coating process (e.g., temperature during coating) can be matched to the water content and / or water absorption capacity and / or structural relaxation capacity of the polymer so that the coating contributes to shaping and / or stabilizing the surface shape in the zone area. For example, an important selection criterion can be the water permeability or transparency of the coating. By using a substantially water-impermeable coating, water loss or absorption is inhibited or completely suppressed, thereby stabilizing the surface shape generated by the laser processing operation against gradual changes in shape during the intended use. Alternatively or additionally, a primarily mechanically acting stabilization of the surface shape is also possible as a result of the stable functional coating.

[0061] If the coating and / or coating operation quantitatively affects the surface shape of a zone, i.e., modifies the shape to have changing properties, this can be taken into account in the overall process. According to the development, the laser processing operation is performed so that the surface shape generated thereby does not correspond to the desired target surface shape, but has a defined shape deviation from the target surface shape. Applying the coating can then cause small changes in shape, thereby allowing the desired target surface shape to be set very precisely. Thus, the coating can be used to adjust the surface shape. The change in shape can generally be described as a change in the surface curvature. For example, the change in shape can be reduced, optionally with the possibility of correcting the sense of curvature (inversion).

[0062] A significant advantage of laser-based methods is the option to generate zones of various shapes and dimensions in a positional distribution on the substrate that can be freely predetermined in an application-specific manner by programming the laser processing system. Correspondingly, a well-equipped and tuned system can operate with a positioning accuracy on the order of 1 μm or more, for example, down to 0.5 μm. The positioning accuracy defines the process-related tolerance within which zones can be generated precisely at predetermined surface locations. Regular, periodic arrays of zones, as desired for some microlens arrays, can be produced, among other things. To generate an array with multiple similar or different zones, it is possible to predetermine the positional distribution of the zones, with individually predefined positions for each zone, and to generate the zones sequentially in a laser processing operation at the predetermined locations with the positioning accuracy specific to the laser processing operation.

[0063] The distribution of the zones has considerable design freedom and can also be intentionally irregularly arranged. In some embodiments, the position of the distribution of positions in one or more regions of the surface is offset from the closest position of the two-dimensionally periodic distribution of positions by a lateral offset greater than the positioning accuracy and less than the periodic distance from the closest position of the periodic distribution of positions. Thus, it is possible to accurately generate irregular distributions of positions. In this process, one or more or all of the zones can have, for example, a circular, elliptical, polygonal, particularly rectangular, or rod-like shape with an aspect ratio between length and width of 2 or more. Other shapes are also possible.

[0064] The arrangement of the multiple zones can therefore also be easily adapted to external requirements. For example, if a microlens array is to be generated for system integration, and its arrangement is adapted to other system components such as microLEDs or the pixels of a camera chip, slight deviations in the arrangement from this perfect grid can be accounted for by measuring and generating the appropriate arrangement of the individual microlenses. The arrangement of the multiple zones can therefore also be easily and individually adapted to the unevenness of the substrate or the geometric peculiarities of the preprocessed semi-finished product. This can therefore be used to generate microlens arrays adapted to different optical elements. In that case, this arrangement still has to be properly positioned once with respect to the other elements.

[0065] In principle, this method can be used in many applications where polymer-based optics are used. For example, the method can be used to correct the shape of molded or other lenses for the optically effective structuring of free-form optics. Use for oblate optics, for example in microscopes or illumination optics, is also possible. Corresponding components can then find use in the fields of automotive, display technology or microscope / camera inspection.

[0066] However, particularly great potential for the application of the manufacturing method is found in the technical field of medical engineering, in particular in the production of personalized multifocal optical devices in the form of ophthalmic lenses or intraocular lenses (IOLs). While previously only molded manufacturing techniques were used, the described method offers the option of creating flexible structures without molds, making it possible for the first time to process patient-optimized ophthalmic lenses, such as for myopia management in children, progressive lenses, or multifocal IOLs. In this context, a further advantage of the method is that it allows the production of optically effective but visually invisible microlenses. If necessary, the zoned regions can be identified with optical aids, for example, ellipsometrically, by possible stress-induced birefringence in the zoned regions.

[0067] Furthermore, the invention can be used in the field of microfluidics, for example for volume calibration or structuring of channel structures. Uses in the field of product marking and batch labelling are also possible.

[0068] This method can be used, for example, in determining the adhesion of thin layers on polymer substrates or the functional structuring of piezo- or pyroelectric polymers (e.g., polyvinylidene fluoride (PVDF)).

[0069] The present invention also relates to a functional element which can be obtained when the method is applied and which comprises a substrate which consists essentially of a polymer, at least one surface of which has at least one zone with a surface shape which deviates from the surface shape of the surroundings of said zone.

[0070] The invention also relates to an apparatus for producing functional elements comprising a substrate made of a polymer, at least one surface of which has at least one zone with a surface shape that deviates from the surface shape of the surroundings of the zone. The apparatus comprises a substrate holder for receiving the substrate, a laser system having a laser radiation source emitting laser radiation at an operating wavelength, and a beam guidance system for directing the laser beam to the surface of the substrate. Furthermore, a movement system is provided for generating a relative movement between the substrate and the laser beam, which allows the substrate to be irradiated by the laser beam at different points in the area to be structured. The apparatus is configured to perform a method.

[0071] Further advantages and aspects of the invention arise from the claims and the description of exemplary embodiments of the invention, which are explained below on the basis of the drawings. [Brief explanation of the drawings]

[0072] [Figure 1] FIG. 1 shows the transmission (in percent) as a function of wavelength (in nm) for selected polymers. [Figure 2] FIG. 2 shows a diagram of the wavelength dependence of the absorption of water. [Figure 3] Figure 3 shows the effect of drying treatment on the water content and weight of the polymer substrate. [Figure 4A] FIG. 4A shows a cross-sectional profile through a microlens element, illustrating the lens geometry without drying the substrate. [Figure 4B] FIG. 4B shows a cross-sectional profile through the microlens element, illustrating the lens geometry after vacuum drying. [Figure 5] FIG. 5 shows a graph of the time dependence of the attenuation of a laser beam through a polymer substrate in its applied state, without a preceding drying operation. [Figure 6] FIG. 6 shows a graphical representation of the time dependence of the attenuation of a laser beam through a polymer substrate after a preceding drying operation. [Figure 7]Figure 7 shows three surface scanning operations with different fill directions for localized thermal management during the production of circular microlenses formed in a convex arc shape. [Figure 8A] FIG. 8A shows a different irradiation strategy, where a circular zone is successively irradiated along four equidistant ring-shaped trajectories of varying diameter. [Figure 8B] FIG. 8B shows a different irradiation strategy, where a circular zone is successively irradiated along four equidistant ring-shaped trajectories of varying diameter. [Figure 9A] FIG. 9A shows the azimuthal offset relative to the start of the trajectory for a range ring trajectory. [Figure 9B] FIG. 9B shows the azimuthal offset relative to the start of the trajectory for an equidistant ring trajectory. [Figure 10A] FIG. 10A shows the height profile of the microlenses of the microlens array. [Figure 10B] FIG. 10B shows an optical microscopy recording of the relevant treated area with numerous similar microlenses. [Figure 11] FIG. 11 shows a schematic diagram of the laser trajectory for generating an elliptical surface structure by external irradiation with four concentric elliptical trajectories. [Figure 12] FIG. 12 shows a schematic diagram of a linear laser trajectory for generating a rectangular surface structure by filling a rectangular contour with parallel lines. [Figure 13] FIG. 13 shows a schematic of the laser trajectory for creating the open Z-shaped zone. [Figure 14] FIG. 14 shows a schematic diagram of a processing strategy with elliptical laser trajectories positioned next to each other with a spatial offset. [Figure 15] FIG. 15 shows a selection of different possible zone geometries in sub-views 15A-15E. [Figure 15A] FIG. 15A shows a selection of different possible zone geometries. [Figure 15B] FIG. 15B shows a selection of different possible zone geometries. [Figure 15C]FIG. 15C shows a selection of different possible zone geometries. [Figure 15D] FIG. 15D shows a selection of different possible zone geometries. [Figure 15E] FIG. 15E shows a selection of different possible zone geometries. [Figure 16A] FIG. 16A shows a schematic cross section through the geometric zones of different surface shapes. [Figure 16B] FIG. 16B shows a schematic cross section through zones of different surface topography. [Figure 16C] FIG. 16C shows a schematic cross section through zones of different surface topography. [Figure 17] FIG. 17 shows, on the left, an optical microscope image and, on the right, a detail of the microlens array in the case of a poor match of the processing sequence to the poor thermal conductivity of the polymer substrate. [Figure 18] FIG. 18 shows a schematic flow chart of a method for defining the processing order of zones in a processing pattern that takes into account the poor thermal conductivity of polymer substrates. [Figure 19] FIG. 19 shows in four sub-views the temperature distribution determined by simulation in an ophthalmic lens when producing a microlens array in the peripheral viewing area at four successive times in time. [Figure 20] Figure 20 shows an optical microscope image of a microlens array produced with optimized thermal management, with increasing magnification (see Figure 17). [Figure 21] FIG. 21 shows the relative change in microlens height as a function of different aging temperatures. [Figure 22] FIG. 22 shows a scanning electron microscope image of a cross section of a microlens array on a multifocal ophthalmic lens produced through a hard lacquer layer. [Figure 23] FIG. 23 shows a scanning electron microscope image of a cross section of a microlens array on a multifocal ophthalmic lens, which has been provided with an inorganic multilayer stack through a hard lacquer layer after laser expansion. [Figure 24]FIG. 24 shows a comparative illustration of the lens geometry of the microlenses before (V) and after (N) deposition of the inorganic layer stack. [Figure 25A] FIG. 25A shows the cross-sectional profile of an areally concave microlens (FIG. 25A) in a polymer substrate. [Figure 25B] FIG. 25B shows a scanning electron microscope image of the cross section, where the surface topography was modified in the targeted manner by the post-coating method. [Figure 26A] FIG. 26A shows a schematic cross-sectional diagram to illustrate the option of inverting the surface shape in the region of the zone by coating. [Figure 26B] FIG. 26B shows a schematic cross-sectional diagram to illustrate the option of inverting the surface shape in the region of the zone by coating. [Figure 26C] FIG. 26C shows a schematic cross-sectional diagram to illustrate the option of inverting the surface shape in the area of ​​the zone by coating. [Figure 27A] FIG. 27A shows a schematic plan view of a randomly distributed microlens structure. [Figure 27B] FIG. 27B shows a schematic portion of a randomly distributed microlens structure. [Figure 27C] FIG. 27C shows a regular distribution of surface filling of substantially hexagonal microlenses. [Figure 28] FIG. 28 illustrates an exemplary embodiment of a laser processing apparatus for producing functional elements according to the methods described herein. DETAILED DESCRIPTION OF THE INVENTION

[0073] Below, several exemplary embodiments are described for producing functional elements for optical applications. These functional elements are therefore also referred to as optical functional elements or optical elements. What the exemplary embodiments have in common is that they are used with a substrate that is essentially made of a polymer material, and that at least one zone is generated or present on at least one surface of the substrate, the surface of which has a surface shape that deviates from the surface shape of the substrate in the vicinity of the zone. The surface in the area of ​​the zone is elevated or depressed relative to the surrounding surface.

[0074] An exemplary embodiment of a polymer optical system using microlenses is that of a multifocal ophthalmic lens for slowing the progression of myopia in children, in which the superimposed focus in the periphery should slow or even completely stop the over-proportional vertical growth of the eye that causes myopia.

[0075] The inventors have discovered a method for systematically producing functional elements with surface structures having optical properties that are highly reproducible and can be set with high precision on an individual basis. For this purpose, polymer substrates are used that have a specific or determinable water content and are treated with laser radiation at an operating wavelength adapted thereto. Using the functional relationship between the wavelength of the laser radiation, the water content of the polymer, and the absorption coefficient of the polymer material, which can be significantly influenced thereby, it is possible to achieve the desired goal.

[0076] Effect of water content on material properties and laser processing parameters For optical applications in the visible wavelength range, polymeric materials with sufficiently good transmittance across the visual spectrum are problematic. Figure 1 plots the transmittance (in percent) as a function of wavelength (in nm) for some polymers that can be used in polymer optical applications. Specifically, these include polymethyl methacrylate (PMMA), polycarbonate (PC), cyclic olefin copolymer (COC), polyvinyl acetate (e.g., PVB), and ultraviolet acrylic (UV). Equivalent curves also exist for specialty polymers optimized for medical applications, such as those known as MR-7, MR-8, MR-10, MR-174, or CR-39 from Mitsui Chemicals, Inc. The measured curves in Figure 1 show high transmittance across the visible wavelength range (approximately 400 nm to approximately 750 nm) and partial transmittance at shorter and especially longer wavelengths. In regions of partial transmittance or a specific corresponding absorptance, the material can absorb a portion of the laser energy at a specific wavelength. In the example given, this is especially the case at wavelengths in the near infrared (NIR) range above 1.1 μm, especially above 1.6 μm.

[0077] The inventors have realised that a substantial contribution to the absorption behaviour of a polymer can be made by its water content and, accordingly, controlling the water content makes it possible to very precisely set the absorptivity of the polymer for a particular application or for a particular wavelength range of laser radiation, leading to the existence of very precise design options with precisely controllable heat input.

[0078] All of the aforementioned polymers can absorb water to a greater or lesser extent, for example, in the range of 0.01 wt. % to about 10 wt. %. Figure 2 reveals that water can significantly contribute to absorption capacity. Figure 2 shows the wavelength dependence of water absorption (1 / m). For example, it is clear that water sometimes exhibits significant absorption in the wavelength range above 1 μm or 1.1 μm, with a particular maximum around 2 μm. From this, the inventors surmised that controlling the water content for a given wavelength should enable precise setting of the absorption rate, thereby enabling the creation of controllable and reproducible processing conditions.

[0079] According to this finding, in this method, water stored between polymer chains is converted to a gas phase under laser irradiation at an appropriate wavelength and intensity. The resulting volume increase causes a pressure increase in the interaction volume, whereby the gaseous water acts as a driving force for the polymer, which has been softened but not structurally damaged by the temperature increase. The extent of the volume change can be fine-tuned by process parameters, such as laser wavelength, laser energy, polymer type, and water content (to set the effective absorption during laser processing).

[0080] For example, this interaction mechanism can be particularly well induced by laser radiation in the NIR range, e.g., by using a thulium fiber laser with an operating wavelength of about 1.9 μm. One reason for this is, among other things, the high absorption by water (see Figure 2) but the low absorption by polymers (see Figure 1). As a result of the partial transparency of water-loaded polymers, the laser radiation can penetrate deep enough into the near-surface region of the polymer to cause a volume change.

[0081] A series of experiments demonstrated that trapped water plays an essential role in this process, and that an interaction mechanism appears to exist as expected. For example, a polymer substrate made of MR-7, a specialty polymer used in high-quality ophthalmic lenses, was locally irradiated with laser light to create a lens geometry with a convex arc-shaped surface in the irradiated area. The irradiated workpieces were then stored in a vacuum oven at 75 °C for over two weeks (the x-axis is in days [d]). Figure 3 shows a schematic diagram showing the weight change, ΔG, of several MR-7 polymer ophthalmic lens blanks after drying in a vacuum oven at 75 °C. The gradual weight loss due to the loss of water in the polymer material is evident. This also verifies that the water content can be reduced in a targeted manner by drying in an appropriate atmosphere.

[0082] Figures 4A and 4B show cross-sectional profiles through microlens elements created by irradiating MR-7 material at 410 mW. Figure 4A shows the lens geometry without drying the substrate in a vacuum oven. Figure 4B shows the lens geometry after 14 days of vacuum drying at 75 °C. While the undried (water-containing) condition results in a lens height H of over 20 μm (Figure 4A), the same laser parameters only result in a variable buildup of approximately 80 nm in height after 14 days of drying. This is taken as a strong indication that the ability of polymeric materials to expand, i.e., their ability to increase in volume induced by a laser beam, is significantly dependent on the water content of the polymer and can therefore be influenced in a targeted manner by controlling the water content.

[0083] The water content of a polymer processing material significantly influences its absorption behavior, but it also influences other parameters that may influence the specific selection of laser parameters. These include, among others, the thickness of the material or the presence of a coating. As a result, it is advantageous to measure the respective partial absorption present in the preparation stage leading up to and / or during the laser processing process. For this purpose, for example, it is possible to perform power measurements through the processing material to be processed. Laser parameters can then be adapted to the partial absorption present in that case.

[0084] This relationship is clearly evident based on the schematic diagrams in Figures 5 and 6. Figure 5 is a graph of the attenuation ABS (percent) of a laser beam at a wavelength of 1940 nm and a power of 150 mW or 300 mW while passing through an approximately 1 mm thick MR-7 substrate in its application state, i.e., without a preceding drying operation. Under the selected conditions, interaction with the laser beam results in only drying, not swelling. It is clear that, especially during the initial period of irradiation, the attenuation decreases significantly until it asymptotically reaches a state with only a slight, constant absorption decrease. Comparison with Figure 6 (attenuation due to a dry lens) reveals that the slight decrease in attenuation can only be determined during a relatively short initial phase, after which the attenuation decreases only slightly over time. These results are considered to be a strong indication that the absorption rate of water-containing polymeric materials effective during laser processing operations significantly depends on their water content and can accordingly be set in a targeted manner by controlling the water content. It has also been found that laser drying can be achieved with surface irradiation significantly below the threshold swelling-up fluence (greater fluences than can cause volume increase or laser swelling).

[0085] In preparation for serial production, the water content-dependent absorption behavior presented here as an example was measured in a series of experiments, and database entries were generated and used for appropriate parameter settings depending on the material, workpiece thickness, and absorbed water content. For this purpose, appropriate power measurements or beam diagnostics were performed under the sample. Alternatively or additionally, camera inspection in transmitted or reflected light can be used to measure areas that have swelled / dried out due to the test process, e.g., outside the target area, and to highlight any necessary adaptations to the process parameters.

[0086] Details of the selected treatment process The energy input via the laser beam is directed to a defined heat input into the water-containing polymer below the ablation threshold. The shape of the interaction zone between the laser and the polymer can be set laterally in a defined manner by the type of treatment regime, in particular by the choice of the laser trajectory and / or by setting the beam profile. The height of the zone of modified volume can be decisively influenced by the degree of local energy input. As a result of the appropriate selection of the treatment pattern, the surface topography can be set in a clearly defined manner, in the process of obtaining the desired optical properties.

[0087] In this case, the topography of the surface corresponds to the surface shape of the area, which corresponds to the area boundary that represents the transition from a zone or adjacent area of ​​the surface to the superstructure within the zone, as long as a monotonic or strictly monotonic transition can be represented as a discontinuous transition. In this regard, the method can be used both to structure the surface on the front side facing the laser beam and to create a structure on the back side through the workpiece.

[0088] The inventors' key insight lies in the fact that due to the typically low thermal conductivity of polymers for optical applications, the design of the processing strategy should ensure the operation of both local thermal management to generate individual structures (i.e., individual zones, e.g., one microlens) and global temperature control to generate a defined, optically effective overall structure, e.g., a microlens array.

[0089] FIG. 7 illustrates an example of localized thermal management when creating a circular zone Z for producing a convex arc-shaped microlens. To create a spherical or aspherical microlens, the laser energy input is limited to the circular shape of the zone Z, achieved by a laser processing trajectory TR, represented by dashes. Within this boundary, a spherical arching process can be created, for example, by filling equidistant lines. In this regard, the left-hand sub-view shows the path of a linear trajectory TR when the fill direction FR extends from left to right. However, this results in uneven heat distribution due to the poor thermal conductivity of polymers. To counter this, this exemplary embodiment involves completely filling the zone multiple times in different fill directions (center and right sub-views), with the fill being rotated, following each completed iteration, through a specific angle, for example, between 30° and 60°, relative to the previous fill and output. Thus, localized heat accumulation can occur at the center of the trajectory, causing the zone to undergo arching that is substantially rotationally symmetrical with respect to the center of the zone.

[0090] From the standpoint of thermal management and the resulting surface shape, it has often been found to be more advantageous to guide the irradiated area across the zone along two or more closed trajectories TR of different dimensions. These trajectories can be similar to one another. This is intended to be explained based on FIGS. 8 to 10 for the case of circular zones. In this case, the zones are generated along concentric circular trajectories with a spacing that matches the final shape. This allows for two different approaches to be taken in terms of the allocation of laser parameters. In the figures, the rings highlighted in bold in each case represent the rings currently being processed, while the light dashes represent rings that have already been processed. In the variant embodiment of FIGS. 8A and 8B, the zone is irradiated by four equidistant trajectories TR of different diameters in each case. In this process, each individual ring (each circular trajectory) is completely irradiated with a focused laser according to the pre-calculated total number of required traverses (for example, from one to four, five, or six, rarely more than seven), and only then does it jump to the next ring, and the operation continues in the same way. The ordering of the rings can be done from outside to inside (FIG. 8A) or from inside to outside (FIG. 8B). Doing so allows each ring to be assigned an individual speed along the trajectory. Preferably, each ring can be kept the same for all traverses along the trajectory. The traverse speeds, which should typically be chosen differently for the rings, take into account the fact that the local energy input along the trajectory is greater at slower traverses, which can result in different inflation heights at the beginning (lower) versus the end (higher) of the trajectory, even for individual traverses.

[0091] It has been observed that the initial rings tend to resemble Landolt rings, as a result of too little heat accumulation and before bulging has even begun. To prevent this, it is preferable to provide for the initial or starting points (SP) of the laser trajectory to be offset in a defined manner, either between the rings and / or between the respective trajectories on the rings. Figures 9A and 9B each show the starting points (SP) of the trajectories on the rings. It is clear that these starting points are azimuthally offset from one another. As a result, a more uniform surface shape can be generated. In any case, to generate a bulged area (e.g., a spherical microlens) in a defined manner, the local energy input, the number of rings, their relative spacing, and the filling direction should be aligned with one another to set the target geometry (e.g., its aperture and height) in a defined manner. In this case, the term "aperture" refers to the dimensions of the zone within its perimeter or zone boundary. Often, this is not a sharply defined boundary, but rather a smooth transition between regions of different general curvature. In this case, the rings do not necessarily have to be processed consecutively: a staggered order in processing the rings is also possible, and optionally the laser parameters should be adapted in that case.

[0092] According to an alternative processing strategy, all orbits provided for the generation of a zone (e.g., between three and five rings) are swept continuously once by a focused laser beam before starting with one of these rings, and the next series of processing steps is performed, during which all or some circular orbits are traversed again at another time. Thus, within a complete iteration, there is only one traversal per circular orbit, and the total number of traversals for the rings corresponds to the number of rings. In this case, the introduced energy can be introduced in a very homogeneous and location-specific manner by selecting a high speed or traversal speed (e.g., hundreds of millimeters to several meters per second), with multiple traversal laser powers and only very short pauses for jumps between circular orbits. If necessary, variations in the starting point (see Figures 9A and 9B) can be additionally implemented.

[0093] According to the inventors' experience, the first-mentioned irradiation strategy is often particularly advantageous for the production of tall structures, but may have limitations if the intention is to produce zones with low heights (e.g., less than 1 μm) and at the same time relatively small apertures (e.g., less than 500 μm). The height of the laser expansion can be controlled very precisely in the case of the second processing strategy (regime 2). This makes it possible to produce lenses over a wide range of heights for a given dimension or a given aperture. For example, the height of the zones can range from a few tens of nanometers to a few tens of micrometers. In this context, the term "height" generally denotes the maximum height of the arc-shaped surface, measured perpendicular to the extended imaginary surface on which the zones lie.

[0094] As illustrative evidence of the suitability of this variant of the method for producing small, flattened microlenses ML, Figure 10A shows the microlens height profile of a microlens array measured by white light interferometry, and Figure 10B shows a stereomicroscope recording of a processed area with numerous microlenses ML on a polymer substrate SUB made of the special polymer MR-7. The absolute water content was less than 1 wt. % and the absorption was on the order of about 45%.

[0095] In principle, microlenses can also be generated using different patterns, such as spirals, etc. However, our experience suggests that trajectories characterized by many jumps or discontinuous vector sequences should rather be avoided.

[0096] Regarding the basic choice of laser power and number of traverses, the interaction that determines the energy introduced appears to be such that the combination of higher laser power with a reduced number of traverses is usually more advantageous than processing with a higher number of traverses with a lower laser power.

[0097] The above examples illustrate some basic principles of the preferred embodiment based on the generation of circular zones. However, the principles may be applied accordingly to generate zones whose basic shape or form deviates significantly from circular. In this regard, Fig. 11 shows a schematic diagram of a laser trajectory for generating an elliptical surface structure by external irradiation with four concentric elliptical trajectories. Fig. 12 shows a schematic diagram of a linear laser trajectory for generating a rectangular surface structure by filling a rectangular contour with parallel lines.

[0098] In an alternative embodiment to the generally convex closed surface shape described above, it is also possible to generate shapes that deviate from this surface shape. In this regard, Figure 13 shows, by way of example, a schematic diagram of a laser trajectory for generating an open Z-shaped surface structure or zone described by a polygon.

[0099] 14 shows a schematic diagram of a processing strategy with elliptical laser trajectories arranged next to each other with a spatial offset. In this way, it is possible to generate, for example, elongated surface structures with a relatively high aspect ratio between length and width, such as rod lenses.

[0100] To illustrate the options within the scope of embodiments of the present invention, FIG. 15 shows a non-exhaustive list of different possible geometric shapes of the zones in sub-views 15A-15E. In this regard, the upper sub-view in each case shows an oblique perspective view on plane Z of the polymer substrate SUB, while the lower sub-view shows a plan view of the zones intended to illustrate their basic shape or aperture, and the lower sub-view shows partial cross-sections of their basic shape or aperture along directions A and B. FIG. 15A shows the condition for a circular zone Z with a convex arc-shaped surface. FIG. 15B shows an example of a circular zone with a rotationally symmetric aspherical shape. FIG. 15C shows an example of an astigmatic lens with an elliptical aperture. FIG. 15D shows an example of a rod lens, the extent of which in its longitudinal direction (along direction B) is several times greater than its extent in its width direction (direction A). FIG. 15E shows a zone with an approximately rectangular basic shape and an approximately wedge-shaped surface shape, due to which optical microelements with a prismatic effect are created.

[0101] Although the effect of laser expansion is characterized by a volume increase near the surface, concave lenses can also be produced by this method. For this purpose, at least two different approaches can be used, as illustrated in FIGS. 16A-16C. FIG. 16 shows a schematic diagram of different lens types that can be produced by a variant embodiment of the appropriate method. FIG. 16A shows a convex structure resulting from a greater expansion of the polymer material of the substrate SUB in the center of zone Z relative to the zone edge ZR. FIG. 16B shows a concave structure in the region of zone Z, produced by localized drying with laser radiation. Localized drying using a laser beam can be performed below the softening temperature of the polymer, and by using a suitable energy input, laser expansion can be performed as described above. This is typically designed for heat accumulation in the center of the overall trajectory when producing convex lens geometries; therefore, higher expansion occurs in the center than at the edge (FIG. 16A), and the region at the edge can be made to bulge higher in the case of a concave lens geometry than at the center, as illustrated in FIG. 16C. In this case, it may be useful to accommodate the transition to the adjacent surface by laser expansion.

[0102] Previous production processes have produced lenticular or prismatic zones with diameters or apertures ranging from about 5 μm to about 500 μm, with heights that can be reliably produced typically ranging from about 20 nm to greater than 20 μm.

[0103] In some embodiments, relatively small zones in the form of flat micro-lenses are systematically generated, which have a height H and a diameter D, and the condition 1000 > V > 500 is applied to the relationship V = D / H. Further, the conditions 10 nm < H < 100 nm, particularly the condition 15 nm < H < 50 nm, and / or the condition 15 μm < D < 30 μm are preferably applied. For example, the height may be in the range of 30 nm to 40 nm, and the diameter may be in the range of 20 μm to 25 μm. The advantage of such small and flat lenses is that the lenses are no longer visually distinguishable (non-scattering), but nevertheless are optically effective by generating additional foci in addition to the basic refractive power of the optical system substrate. A useful application is in the manufacture of plastic ophthalmic lenses for myopia management comprising a microlens array including such small flat lenses.

[0104] Overall temperature control Often, the intention is to generate a surface structuring in which a number of similar or different zones with special surface shapes are closely distributed together over the surface according to a pattern. The inventors have recognized that this can give rise to certain problems and may be traced back to the very low thermal conductivity of the polymer. For example, this is on the order of 0.19 W / m×K for PMMA. Due to the low thermal conductivity, the energy input during the generation of the microlenses or any other structural zones can critically affect the shape and dimensions of further microlenses located in the immediate vicinity and processed rapidly and continuously. The process window for the introduced and necessary energy for expansion is relatively narrow, especially for small and / or flat lenses. According to the inventors' insights, thermal management on a macroscopic length scale is also very important. For illustration, the left of FIG. 17 shows an optical microscope image of a microlens array on an MR-7 ophthalmic lens blank with insufficient adaptation of the heat distribution. In the enlarged detail on the right of FIG. 17, instead of the desired microlenses ML of the same dimensions, an uneven distribution of microlenses with different apertures and / or heights has occurred, and it is even clear that some surface areas lack microstructure.

[0105] According to the inventor's insight, in many cases, the extended microlens array and / or the small distance between the lenses requires special and layout-adaptive measures to distribute the heat load, with the goal of not creating lenses in areas on the substrate that are too preheated. Also, the heat input is relevant in terms of the amount of water in the polymer, since expansion, i.e., laser-induced volume increase, can only be observed if a sufficient amount of water is present, and indeed drying can be determined in case of insufficient energy input or temperature.

[0106] To overcome this challenge, it is often important to adapt the processing pattern to the required geometric shape of the lens array, taking into account, among other things, the physical and thermal properties of the substrate material, the number of lenses, their arrangement, and the energy and heat input required to produce the lenses. A convenient variant of defining the processing pattern is described based on the flowchart in FIG. 18. In a first step S1, the processing pattern (pattern, denoted PAT) is defined, taking into account, among other things, the number of lenses, their spacing, their arrangement (e.g., hexagonal or according to a rectangular pattern), and the lens dimensions (and therefore the local energy input by the laser). This is followed in step S2 by the calculation of the coordinates (denoted x, y) of each lens. Based on this, the applied temperature (denoted T) is estimated in step S3 for each coordinate of the individual lenses, e.g., based on the thermal conductivity (denoted λ) and convection in the material. Based on this, a processing order (denoted SEQ) is defined or optimized in step S4 using temperature and distance criteria, complemented for example by introducing waiting times or varying laser parameters.

[0107] A characteristic of this advantageous treatment strategy is the creation of a first zone at a first location, followed by the creation of a second zone at a relatively large distance before the creation of a third zone located closer to the first zone. In this regard, numerical simulations using the finite element method (FEM) have proven particularly advantageous for defining the treatment strategy. In this regard, Figure 19 shows, in four sub-views, the temperature distribution determined by the FEM method in an ophthalmic lens during the creation of a microlens array in the peripheral visual field at arbitrarily selected times t1-t4. It is clear how zones of local temperature increase gradually develop in different areas located at relatively large distances. The heating of the target area with increasing numbers of introduced microlenses is also clearly discernible. In this case, the fact that a local temperature threshold of 30°C must not be exceeded was a stipulation of the simulation. Other target functions, such as a minimum temperature at the longest distance or a minimum temperature at the shortest distance, can also be selected.

[0108] Therefore, after appropriate optimization of the processing strategy in view of the order of the microlenses produced, it is also possible to produce extended microlens arrays with high packing densities. In this regard, Figure 20 shows optical microscope images of a ring microlens array MLA on an MR-7 ophthalmic lens blank with optimized thermal management as the magnification increases. It is clear that the problems with irregular lens distribution and dimensions discussed based on Figure 17 have been corrected.

[0109] For targeted processing, the substrate to be processed is mounted on a suitable substrate holder, which should preferably be configured so that heated back-reflections of the laser radiation transmitted through the workpiece cannot introduce unwanted, additional, and position-dependent energy input into the substrate. In a preferred method, the substrate is mounted only around its periphery and maintained at a sufficient distance from a base located below the workpiece.

[0110] Alternatively or additionally, a beam trap can be integrated below the workpiece. In addition to temperature control by targeted optimization of the energy input by the laser, heat dissipation can be increased by complementary technical means. For example, a gas (e.g., compressed air or an inert gas) can be applied to the workpiece during processing. For example, the gas flow can be directed substantially coaxially with the laser beam, or at an acute angle and / or symmetrically relative to the laser beam. In the inventor's experience, the temperature and volumetric flow rate of the gas have a decisive influence on the heat transfer to the surroundings by convection. Unwanted and unsteady water input can be addressed by further drying the gas.

[0111] Post-processing after laser processing In some cases, heat treatment and / or drying can be useful after the laser processing operation. For example, by storing the component or polymer substrate processed by laser expansion in a drying cabinet or oven, the geometry can be further adapted or modified in a targeted manner by removing the water after the laser expansion is complete. How pronounced this effect is can be controlled by the storage period and storage temperature. However, in this regard, the storage temperature should be significantly lower than the softening temperature of the polymer or, optionally, layers located on the polymer, since the expanded or dried structure may relax and / or layer effects may occur at the interface.

[0112] The fact that target storage can affect the geometry of surface features in a controlled manner is evidenced by the diagram in Figure 20. Figure 21 shows the relative change in height ΔH / H of microlenses on an MR-7 plastic substrate as a function of their lateral dimension or aperture, which is represented on the x-axis by the perimeter of width B. The y-axis shows the relative change in height ΔH / H. It was found that moderate storage temperatures compared to the softening temperature (85°C) can induce small relative changes in height, while higher temperatures can lead to significant relaxation or shrinkage of height, especially for larger microlenses. A further insight from the trial is that relaxation of lens geometry results in a significant reduction in lens height, but not in a significant reduction in lens size or aperture.

[0113] These measurable and controllable effects can be used to fine-tune the surface geometry through heat and / or drying processes after laser processing is complete. Substrates with uncoated surfaces can be processed using this method. It can also be performed on already coated substrates, i.e., through one or more layers located on the substrate, provided that the optical properties of the coating, on the order of the wavelength used, are comparable to those of the substrate and the layer adhesion or deformability allows for form-fitting during expansion of the substrate without structural failure. For illustrative purposes, Figure 22 shows a scanning electron microscope image of the cross section of a microlens array on a multifocal ophthalmic lens created through a hard lacquer layer. The inaccuracy of laser expansion after layer construction is clearly visible.

[0114] It was also possible to show that the structures produced by this method can be post-coated using appropriate coating methods. To prevent the subsequent coating process from causing uncontrollable shape changes, the resulting temperature in the coating process should be below the temperature at which the structure relaxes. Such coating methods, especially by physical vapor deposition (PVD), are routinely used in the optical field.

[0115] It was possible to show that, with the right processing regime, non-thermal post-coating of a polymer substrate structured by laser expansion does not significantly alter the initially established lens geometry. In this regard, Figure 23 shows a scanning electron microscope image of a cross section of a microlens array on a multifocal ophthalmic lens, which was provided with an inorganic multilayer stack via a hard lacquer layer by PVD after laser expansion.

[0116] 24 shows a comparison of the lens geometry of microlenses in an MR-7 substrate before (V) and after (N) deposition of an inorganic layer stack, as measured by white light interferometry. It is clear that the coating can be produced in such a way that the surface geometry is largely maintained in the zones.

[0117] However, it is also possible to introduce targeted modifications to the surface shape by special post-coating methods, for example, converting initially convex bulged structures into concave lens structures. In this regard, Figure 25B shows the cross-sectional profile of a microlens in an MR-7 substrate as detected by white light interferometry, and Figure 25A shows a scanning electron microscope image of its cross section.

[0118] Furthermore, the design of the layer stack, especially its permeability to water, may allow the swelling behavior to be further controlled by water: thus, a water-permeable coating may facilitate post-processing of the microlenses by thermal post-processing, while an impermeable coating that is largely impermeable to water may better preserve the impregnation state.

[0119] A suitable arrangement of the coating operation in the process chain for producing an optically functional element makes it possible, inter alia, to invert, adjust or stabilize the produced optically functional element, if necessary. In this respect, the selection of a suitable coating method and coating process parameters is also important. Several embodiments will be described below with reference to Figures 26A to 26C.

[0120] As a result of the inversion, the originally convex surface can be transformed into an optically effective concave structure in the region of the zone. In an exemplary case, optical functional elements in the form of raised microlenses or zones with a convex, arched surface are initially generated on an uncoated substrate SUB. The substrate is then coated with a hard lacquer layer HS. Due to the surface tension and flow properties of the coating material, the surface of this hard layer is initially smooth before curing, and its thickness locally decreases above the optical functional elements due to their arching. The viscosity of the hard layer increases during the curing process, while the optical functional elements, in the exemplary case, relax slightly. With the increase in viscosity, the surface tension is no longer sufficient to level or pull the surface straight. Thus, following complete curing of the hard layer and partial or complete relaxation of the optical functional elements generated in the substrate, inverse optical functional elements in the form of "dents" DL of a defined depth and curvature appear in the finished product in the region of the originally generated convex microlenses.

[0121] To adjust the surface shape to a certain extent, i.e. within a zone, it is possible to proceed in such a way that, for example, optical functional elements are first produced by laser machining operations on an uncoated substrate or on a substrate coated with part of a complete coating system, in order to modify the surface shape consistently in a targeted manner. The height of the optical functional elements can be reduced and / or their shape modified by appropriate selection of process parameters (e.g. temperature, pressure, moisture) during subsequent coating steps.

[0122] Because the mechanical properties of most functional coatings deviate significantly from those of polymer-based substrates, subsequent coating processes can stabilize the surface structure if the layer properties are appropriately selected. Furthermore, by selecting an appropriate deposition method and other parameters related to the coating process (e.g., ion-assisted, atomic layer deposition), it is possible to create coating systems that are essentially impermeable to water. As a result, moisture-induced aging of the substrate material and relaxation of the generated optical functional elements can be suppressed. This can also allow for the capture of moisture within the substrate for structure generation within the method or protect dry areas from the absorption of ambient moisture. Furthermore, structure generation by functional coatings offers the option of using the volume changes generated by the described method to induce mechanical stresses in the coating at the interface between the coating and the substrate and within the substrate. Defects can be generated in the layer system as a result, for example, by delamination. The type and frequency of defects can be correlated with the selected process parameters of the method and can therefore be used to quantify the layer adhesion of functional coatings. Therefore, layer adhesion tests are also feasible within the scope of the method according to the present invention.

[0123] 27A and 27B are used to describe further advantageous possible uses of the methods and devices of the type described herein. Fig. 27A shows a schematic plan view of an optical functional element FE with microlenses MLZ, which, as a diffuser, are designed to generate an intensity distribution in the far field that is as homogeneous as possible for coherent or partially coherent light radiating therethrough. Fig. 27B shows a schematic cross section through a functional element with randomly distributed microlenses MLZ. These figures are taken from the academic paper by M. Cumme and A. Deparnay, "From regular periodic microlens arrays to randomized continuous phase profiles," Optical Technology 2015, 4(1), pp. 47-61, and are intended to illustrate the possibilities of the invention presented here.

[0124] A functional element FE designed as a microlens array can be produced starting from a parallel, flat plate made of a polymer material containing water. In an exemplary case, the entire surface, e.g., a square, should be filled without gaps using randomly distributed microlenses with different shapes and refractive powers. The lateral distribution of the zones Z in which the microlenses MLZ will be formed is determined using Voronoi tessellation. For this purpose, a number of initial positions AP are randomly distributed over the area to be structured. The initial positions AP form the future central lens positions. Individual Voronoi cells are defined for each of these initial positions, covering areas closer to this particular initial position AP than to any of the others. This creates polygonal zones Z of asymmetric shape around each initial position. The zones can have three, four, five, six, seven, or more corners connected by the zone's linear outer edges. Immediately adjacent zones adjoin each other at their common outer edges so that the area is filled without gaps. Each of these zones Z is then irradiated along a trajectory TR using laser radiation in a manner similar to the exemplary embodiment described above until the desired surface morphology in the respective zone is produced by controlled laser expansion. Figure 27B shows a possible cross section through the functional element after irradiation is complete. In the example shown, the randomly distributed microlens elements MLZ have approximately the same radius of curvature but different heights.

[0125] When using a coherent plane wave as the input source, such a diffuser produces a random speckle intensity distribution in the far field. In comparison, a conventional periodic microlens array produces a regular arrangement of diffraction spots in the far field when the same light source is used. When a partially coherent light source is used, the far-field distribution of a regular microlens array can have troublesome periodic non-uniformities. When the same partially coherent light source is used, a random microlens array with typical lens dimensions similar to that of a corresponding regular array exhibits a far-field with non-periodic non-uniformities that do not adversely affect illumination applications.

[0126] For comparison purposes, Figure 27C shows an image of the surface of a transmission feature element with a similar regular, area-filling distribution of microlenses ML having substantially hexagonal shapes, again with adjacent zones abutting each other without any gaps.

[0127] FIG. 28 illustrates an exemplary embodiment of an apparatus (LAS) for generating functional elements from a polymer substrate according to a preferred variant of the method described herein. This apparatus, also referred to as a laser processing apparatus, includes a computer-assisted control unit (STR) that controls the components communicating with it. Control software resides in the control unit's memory. A stored database contains database entries for numerous different polymer materials and experimentally determined parameter sets, depending on the polymer, the radiation transmission thickness and absorption coefficient of the substrate, and / or the water content. In a material-specific manner, characteristic map data representing the functional relationship between the wavelength of the laser radiation and the water content of the polymer and / or measurable quantities dependent on the water content, can be stored for a particular polymer material. The control unit has access to the stored data and can derive and set parameter sets for the laser processing conditions expected to be suitable in the form of a look-up table.

[0128] The substrate holder SH serves to receive a respective substrate SUB, on the front surface V of which a microlens array with a large number of small, flat lenses is to be produced. For example, the substrate can be an ophthalmic lens made of a special polymer, such as MR-7.

[0129] The apparatus further comprises a laser system controllable by a control unit STR and including a laser radiation source LQ for emitting laser radiation at an operating wavelength in the wavelength range between approximately 1.9 μm and 2 μm. In an exemplary case, a thulium fiber laser with an operating wavelength of approximately 1.9 μm is provided. A beam guidance system SFS guides the laser beam and creates a laser focus FOC in the area of ​​the front surface V of the substrate. The laser beam is focused, for example, with a focal diameter that can be within a range of less than 15 μm, optionally approximately 10 μm. In this case, the laser beam passes successively through a shutter or closure ST, an attenuator AB, a beam-shaping optics FO, and a scanner SC. A distance meter ABM is attached to the scanner head to measure the distance from the front surface of the substrate.

[0130] The substrate holder SH is constructed and arranged so that heated back reflections of the laser radiation transmitted through the workpiece cannot introduce unwanted, additional, and position-dependent energy input into the substrate. The substrate holder is positioned at a distance above the surface below it. For example, this distance can be at least as large as half the diameter or the full diameter of the substrate. Alternatively or additionally, a beam trap can be integrated below the substrate. In this case, the substrate is gripped only at three points on its outer edge, offset around the periphery.

[0131] A movement system, not depicted in further detail, is configured to generate a relative movement between the substrate SUB and the laser beam, so that the substrate can be irradiated by the laser beam at different points of the area to be structured and according to a predefinable processing recipe. In this process, the substrate can remain stationary or can be moved (see double-headed arrow), and a scanner SC is used to displace the focal spot and to guide it over the surface along a trajectory.

[0132] The camera K connected to the control unit STR is part of a reflexively operating camera-based pattern recognition system.

[0133] The laser processing system allows for in-process absorption measurements to determine the partial absorption of the substrate at the operating wavelength before and / or during the laser processing operation. In this case, the absorption measurement is the measurement of the attenuation of the laser light LS as it passes through the substrate SUB. For this purpose, a power measurement head LMK is installed below the substrate holder. Based on the measurement results from the absorption measurement system, a control loop is established by the device's control unit STR, which is configured to control at least one laser parameter, in particular the laser power. As a result, the laser power can be accurately matched to the measured absorption of the irradiated polymer material.

[0134] A cooling device COL is also provided for actively cooling the substrate during the laser processing operation in order to stabilize the processing conditions. In this case, the cooling device is embodied as a non-contact convection cooling unit for applying cooling gas to the substrate. The cooling gas is blown onto the processed front side V via a nozzle. This ensures gradual heat dissipation and accurate temperature control within the thermal management range. Deviating from the figure, in other embodiments, the gas flow is blown onto the substrate substantially coaxially and / or symmetrically to the laser beam.

[0135] The components of the system can be housed in a temperature-stable, humidity-controlled housing that ensures stable processing conditions over time.

Claims

1. 1. A method for producing a functional element comprising a substrate consisting essentially of a polymer, the method comprising: The method comprises:

1. A method of laser processing a substrate, comprising: at least one surface of the substrate having at least one zone having a surface shape that deviates from the surface shape of the surroundings of the zone; and wherein, for generating the at least one zone in a laser processing operation, laser radiation is emitted onto a surface region of the substrate such that interaction of the polymer with the laser radiation generates a volume change of the polymer in a near-surface volumetric region of the substrate, the volume change of the polymer leading to a sustained change in the surface shape of the zone; The method comprises:

1. A method comprising: providing a substrate comprising a water-containing polymer having an absorptivity at an operating wavelength of a laser processing operation selected or set taking into account a functional relationship between the wavelength of the laser radiation, the water content of the polymer, and the absorptivity.

2. controlled modification of the water content of the polymer of the initial substrate to set the absorption before the start of the laser processing operation comprises at least one drying operation to reduce the water content and / or at least one loading operation to increase the water content; Preferably, the controlled modification of the moisture content comprises a combination of at least one drying operation and at least one loading operation carried out before or after the at least one drying operation, In particular, during said at least one drying operation, said substrate is dried in an oven, preferably in vacuum or under negative pressure, to below the softening temperature of said polymer, and the dried material is then exposed to water or a moist ambient atmosphere for a predetermined extended period in one loading operation, 2. The method according to claim 1, wherein the relative weight loss or the relative weight gain is preferably measured in a laser process.

3. experimentally determining a functional relationship between the wavelength of the laser radiation and the water content of the polymer and / or a measurable quantity that is dependent on the water content by multiple trials to identify a characteristic map; 3. A method according to claim 1 or 2, wherein processing parameters of the laser processing operation are preferably set based on data from the characteristic map.

4. 1. A method characterized by absorption measurements measuring the fractional absorption of the polymer for at least one wavelength of laser radiation prior to and / or during a laser processing operation, 4. A method according to any one of claims 1 to 3, wherein the absorption measurements comprise measurements of the attenuation of a laser beam while passing through a substrate, preferably whereby process parameters of a laser processing operation are controlled based on results of the absorption measurements.

5. 5. A method according to claim 3 or 4, characterized in that a database is created with database entries of parameter sets that depend on the polymer, the thickness of the substrate through which the radiation passes, and the absorption measurements and / or the water content.

6. the functional element is designed as an optical functional element, The zone or zones are formed as optically effective lenses and / or prisms; Preferably, the polymer is transparent in the visible spectral range, 6. The method according to any one of claims 1 to 5, wherein the laser radiation has an operating wavelength in the wavelength range of 1.1 μm to 9.2 μm.

7. generating the zone comprises using a focused laser beam having a focal region in the region of the zone with a diameter substantially smaller than a diameter of the zone to be generated; the focal region is guided along the zone along at least one trajectory corresponding to a treatment pattern such that different locations within the zone are exposed to laser radiation successively in time; some or all of the locations within the zone exposed to the laser radiation are traversed multiple times, in particular two, three, four or more times, each traverse involves introducing only a portion of the total introduced laser energy; A method according to any one of the preceding claims, characterized in that preferably each, several or all of the tracks are traversed several times.

8. the focused laser beam is directed in a scanning direction along linearly spaced adjacent tracks in a surface scanning motion to generate the zones; 8. The method according to any one of claims 1 to 7, characterized in that at least one further surface scanning operation is performed after said surface scanning operation in a further scanning direction oriented at an angle to said scanning direction.

9. To generate the zone, the focused laser beam is directed over the zone along two or more closed surrounding trajectories, in particular concentric circular trajectories of different diameters; Preferably, in at least one of said two or more closed surrounding trajectories, preferably in all trajectories, the laser beam is directed on a circular trajectory for a predeterminable number of multiple traverses; 9. The method according to any one of claims 1 to 8, characterized in that the starting points of the trajectories of different dimensions are preferably offset from one another in the circumferential direction when providing irradiation along a closed, encircling trajectory, in particular a circular trajectory.

10. 10. The method according to claim 1, wherein a first trajectory, in particular a first circular trajectory, is illuminated with all the possible trajectories, and subsequently at least one second trajectory having different dimensions is illuminated with all the possible trajectories.

11. In a first implementation, each of the trajectories of different size is irradiated with a number of trajectories that is less than a predetermined total number for the respective trajectory; This is followed by two or more further runs, some or all of the tracks of different sizes are irradiated with fewer traverses than the predetermined total number of traverses for each track until each of the tracks has been irradiated with the full number of traverses anticipated; A method according to any one of the preceding claims, characterized in that preferably each of the trajectories to be illuminated is traversed only once in each run.

12. 12. The method according to any one of claims 1 to 11, characterized in that a zone is generated which has a convex arc-shaped surface shape over part of the zone or over the entire zone, said surface being preferably rotationally symmetric and spherically or aspherically curved.

13. 13. The method according to any one of claims 1 to 12, characterized in that a zone with a concave arc-shaped surface shape is created in the entire zone or in a partial zone of a circle.

14. the generation of the concave arc-shaped surface features involves irradiation with laser radiation to induce locally limited drying of the polymer below its softening temperature, thereby leading to a reduction in the specific volume of the polymer while forming the concave arc-shaped surface features; and / or 14. The method of claim 13, wherein generating a concave arc-shaped surface profile in a partial zone of a zone involves irradiating the zone with laser radiation such that the increase in specific volume in a radially outer annular region is greater than the specific volume in a partial zone surrounded by the annular region.

15. 15. The method according to any one of claims 1 to 14, characterized in that a plurality of similar or dissimilar zones are generated in an area of ​​the surface to be structured, said plurality of similar or dissimilar zones being distributed on the surface at different locations in the area to be structured according to a predeterminable pattern.

16. the plurality of similar or dissimilar zones are generated sequentially according to a heat input optimization strategy; Preferably, the creation of a first zone at a first location is followed by the creation of a second zone further away before the creation of a zone closest to said first zone; Preferably, the processing order of the zones is defined using temperature criteria, distance criteria and zone size criteria to ascertain the heat input optimization processing strategy; 16. The method of claim 15, wherein a finite element simulation is preferably performed to verify the heat input optimization process strategy.

17. A plurality of dissimilar zones are generated in the area of ​​the surface to be structured, and are distributed on the surface at different locations within the region to be structured, preferably according to a laterally random distribution, in order to fill the area of ​​the surface to be structured, Preferably, some or all of the zones have an asymmetric polygonal shape, in particular with 3, 4, 5, 6, 7 or more corners and a corresponding number of outer edges, Alternatively, a plurality of preferably similar zones are generated within the area of ​​the surface to be structured, and distributed over the area of ​​the surface at different locations within the region to be structured according to a regular distribution so as to fill the area of ​​the surface, 17. A method according to claim 15 or 16, characterized in that preferably some or all of the zones have a symmetrical polygonal shape, in particular a triangular, quadrangular or pentagonal shape.

18. 18. The method according to any one of claims 1 to 17, characterized in that after the laser processing operation has been completed, the functional element is subjected to a controlled heat treatment and / or drying treatment in order to stabilize the structure created by the laser processing before its intended use at ambient temperature.

19. the surface to be structured is coated with a functional coating before the laser processing operation, during selected steps of the laser processing operation, and / or after the laser processing operation is completed; 19. A method according to any one of claims 1 to 18, characterized in that the type of functional coating and / or the treatment of said functional coating is matched to the water content and / or water absorption capacity and / or water release capacity and / or structural relaxation capacity of said polymer, so that said functional coating contributes to shaping and / or stabilizing the surface shape in the region of said zone.

20. 20. The method of any one of claims 1 to 19, wherein the laser machining operation is performed such that the surface shape generated by the laser machining operation does not correspond to a desired target surface shape but has a defined shape deviation from the desired target surface shape, and the application of the functional coating results in a change in shape such that the desired target surface shape is set.

21. relatively small zones in the form of flattened microlenses are produced, said microlenses having a height H and a diameter D, and the condition 1000>V>500 holds true for the relationship V=D / H, 21. The method according to claim 1, further characterized in that the condition 10 nm < H < 100 nm, in particular the condition 15 nm < H < 50 nm and / or the condition 15 μm < D < 30 μm preferably applies to the relationship V = D / H.

22. a distribution of the locations of the zones, each having a distinct predetermined location, is predetermined to generate an array having a plurality of similar or dissimilar zones; the zones are successively generated in a laser processing operation at the predetermined locations with a positioning accuracy specific to the laser processing operation; Preferably, the position of the position distribution in one or more regions of the surface is shifted in two dimensions from the nearest position of the periodic position distribution by a lateral offset that is greater than the positioning accuracy and less than the periodic distance from the nearest position of the periodic position distribution; 22. The method according to any one of the preceding claims, characterized in that the one or more total zones preferably have the form of a circle, an ellipse, a polygon, in particular a rectangle, or a rod having an aspect ratio between its length and its width greater than 2.

23. 1. An apparatus for producing a functional element comprising a substrate made of a polymer, at least one surface of said substrate having at least one zone with a surface shape that deviates from the surface shape of the surroundings of the zone, The device comprises: a substrate holder (SH) for receiving a substrate (SUB); a laser system (LS) having a laser radiation source (LQ) for emitting laser radiation at an operating wavelength and a beam guidance system (SF) for directing a focused laser beam to the surface of said substrate; a movement system for generating a relative movement between the substrate and the laser system (LS) so that the substrate can be irradiated by a laser beam at different points in the area to be structured, Apparatus, characterized in that the apparatus is configured to carry out the method according to any one of claims 1 to 22.

24. the substrate holder (SH) is designed such that the held substrate (SUB) has a distance from its lower surface in the direction of the incident laser beam (LS), and / or 24. Apparatus according to claim 23, characterized in that the substrate holder (SH) is designed in such a way that the held substrate (SUB) is held only at its edge area.

25. an absorption measurement system measures the absorption of the substrate (SUB) or a measurable quantity dependent on said absorption before and / or during said laser processing operation; 25. Apparatus according to claim 23 or 24, characterized in that the absorption measurement system is preferably configured for measurement of the attenuation of the laser beam as it passes through the substrate.

26. 26. The device according to any one of claims 23 to 25, characterized in that a control loop is configured to control at least one laser parameter, in particular the laser power, depending on the measurement results from the absorption measurement system.

27. the apparatus comprises a cooling device (COL) for actively cooling the substrate (SUB) during the laser processing operation; Apparatus according to any one of claims 23 to 26, characterized in that the cooling device preferably comprises a convection cooling unit for directing cooling gas onto the substrate.

28. 28. Apparatus according to any one of claims 23 to 27, characterized in that the laser radiation source (120) has an operating wavelength in the wavelength range between 1.1 μm and 9.2 μm, in particular in the wavelength range between 1.5 μm and 5.0 μm.

29. An optical element in the form of a functional element, in particular an ophthalmic, contact or intraocular lens, having a substrate (SUB) that consists essentially of a polymer that is transparent in the visible spectral range, In a functional element, at least one optical surface (OB) of the substrate has an area with at least one zone (Z) having a surface shape deviating from the surface shape around the zone (Z), A functional element, characterized in that the functional element is obtainable or is obtained by a method according to any one of claims 1 to 21.

30. a microlens array having a number of adjacent raised zones formed on the at least one optical surface (OB), the number of adjacent raised zones each forming a lens of the microlens array (ML); Preferably, the functional element is formed as a multifocal ophthalmic lens for slowing the progression of myopia, and 30. A functional element according to claim 29, comprising a microlens array (MLA) having a number of microlenses (ML) arranged on a surface (OB) in a ring shape around a central zone.

31. 31. A functional element according to claim 29 or 30, characterized in that zones in the form of flattened microlenses (ML) are formed on the at least one optical surface (OB), said zones having a height H and a diameter D, and the following condition applies to the ratio V=D / H: 1000>V>500, and further the following condition preferably applies to the ratio V=D / H: 10 nm<H<100 nm, in particular 15 nm<H<50 nm and / or 15 μm<D<30 μm.

32. Functional element according to any one of claims 29 to 31, wherein the polymer is polycarbonate (PC), polymethylmethacrylate (PMMA), acrylic or any other polymer material suitable for optical substrates, in particular eyeglass substrates.

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