Method for producing a functional element with surface structures, and functional element

Abstract

The invention relates to a method for producing a functional element comprising a substrate which consists substantially of a polymer and on at least one surface has at least one zone with a surface texture that differs from a surface texture in an area surrounding the zone. In order to produce the zone a surface region of the substrate is irradiated with laser radiation in a laser-processing operation in such a way that in a region of the volume of the substrate that is near the surface a change in the volume of the polymer is produced, induced by interaction of the laser radiation with the polymer and resulting in a permanent change in the surface texture in the zone. As a result, a substrate is provided which consists of a hydrous polymer which, at a working wavelength of the laser-processing operation, has a degree of absorption which is selected or set on a basis which allows for a functional relationship between the wavelength of the laser radiation, a water content of the polymer and the degree of absorption.

Description

[0001] Method for producing a functional element with surface structures and functional element

[0002] FIELD OF APPLICATION AND STATE OF THE ART

[0003] The invention relates to a method for producing a functional element comprising a substrate consisting of a polymer which has at least one zone on at least one surface with a surface shape that differs from a surface shape in an environment of the zone.

[0004] A preferred field of application is the production of optical functional elements (optical elements) for influencing the propagation of light upon interaction with the functional element, for example for optical elements for ophthalmic purposes.

[0005] In the method, in order to create a zone in a laser processing operation, a surface region of the substrate is irradiated with laser radiation in such a way that in a volume region of the base body close to the surface in the irradiated region, a volume change of the polymer induced by interaction of the laser radiation with the polymer is generated, which leads to a (permanent) change in the surface shape in the zone.

[0006] A method of this type is disclosed in document EP 2 184 127 B1. In one method variant for producing a permanent marking on an optical element consisting of a polymer transparent in the visible spectral range, beam parameters of laser radiation with wavelengths from the near-infrared range are adjusted such that a laser-induced volume increase is generated in the irradiated near-surface region without destroying the polymer. The generated structural elements of the marking are raised relative to the adjacent, non-irradiated regions. It is assumed that the polymer swells and / or possibly partially melts under the influence of the irradiated laser radiation and solidifies again after irradiation, resulting in a zone of reduced density or larger volume in the near-surface irradiation region than before irradiation.If the laser radiation power density is not too high, the irradiated area can retain a largely undamaged surface, which extends smoothly and continuously curved over the volume-enlarged area, similar to skin. In this way, a lens element with a convex lens surface can be created in an irradiated area. If many adjacent irradiation areas are irradiated, a microlens array can be formed.

[0007] WO 2020 / 180817 A1 discloses a method for providing an ophthalmic lens with a prescribed optical power, the ophthalmic lens having a surface with a base curvature corresponding to the prescribed optical power. The surface of the material is exposed to laser radiation sufficient to locally reshape the material to form a plurality of lenses on the surface, each of the lenses having a corresponding optical power that differs from the prescribed optical power of the ophthalmic lens. The method is intended to work with substrates made of inorganic glasses and with substrates made of organic polymers.

[0008] TASK AND SOLUTION

[0009] Against this background, the invention is based, among other things, on the object of providing a method of the type described in the introduction that is suitable for series production and allows the systematic production of structured functional elements with highly reproducible properties. A further object is to provide a device suitable for carrying out the method, as well as corresponding functional elements.

[0010] To achieve this object, the invention provides a method having the features of claim 1. Furthermore, a device for carrying out the method having the features of claim 22 and a functional element having the features of claim 28 are provided. Advantageous further developments are specified in the dependent claims. The wording of all claims has been incorporated by reference into the content of the description.

[0011] The method is suitable and intended for the production of a functional element comprising a substrate made of a polymer, which has at least one zone on at least one surface with a surface shape that deviates from a surface shape in the vicinity of the zone. The term "zone" refers to a spatially limited area that is enclosed by a more or less sharply defined "zone boundary" and, in the region of the zone boundary, merges into the areas of the surface lying outside the zone. The untreated surface can, for example, be flat (e.g., as in the case of a flat plate) or have a base curvature determined by the function of the functional element (e.g., as in the case of a spectacle lens). In the region of the zone, the surface shape deviates from the base curvature. A zone therefore refers to a near-surface structure of a specific shape and size. The zone can, for example,characterized by a lateral extension in at least one direction, a height, and information about the shape of the surface or its curvature within the zone boundary. For sufficiently round zones, the lateral extension can also be specified by a diameter or an aperture. The height is the maximum distance of the surface within the zone from an imaginary extension of the surrounding surface outside the zone. A convex surface raised above the surrounding surface, whose mean radius of curvature is smaller than that of the surrounding surface, has a positive height; the height can also be negative for concave zone surfaces.

[0012] In this method, a surface area of ​​the substrate is irradiated with laser radiation to create a zone during a laser processing operation. This induced volume change in the polymer is generated in a volume region of the substrate close to the surface, resulting in a change in the surface shape of the polymer. After laser processing is complete, the surface shape in the zone remains different from that of the surrounding area. The volume change is a change in the specific volume and occurs non-destructively below the ablation threshold, i.e., without material removal and without significant thermal or photochemical decomposition of the irradiated polymer.

[0013] A key step in the process is the provision of a substrate consisting essentially of a water-containing polymer. At the operating wavelength of the laser processing operation, this polymer exhibits an absorption coefficient that is selected or adjusted taking into account a functional relationship between the wavelength of the laser radiation, the water content of the polymer, and the absorption coefficient. The absorption coefficient indicates the fraction of the incident radiation that is absorbed. The absorption coefficient can assume values ​​between 0 and 1.

[0014] According to a strict definition, a polymer is a chemical substance consisting of macromolecules. In the context of this application, the term "polymer" refers to a material that essentially consists of a polymer or that has a polymer material as an essential component. The term polymer thus stands for a polymer material that consists predominantly or mainly of a polymer or macromolecules and additionally contains or can contain small amounts of other substances that are not macromolecules. A polymer can contain one or more property-modifying additives. Polymers, especially those with additives, are often also referred to as plastics.

[0015] The process is based on irradiating a polymer with a laser beam, whereby the optical transparency of the polymer for the respective laser wavelength enables interaction in a volume region which lies below the immediate surface in the direction of incidence. The process is particularly suitable for polymers which exhibit partial transparency for the working wavelength, i.e. for the laser wavelength used for laser processing. In other words, the polymer to be processed should exhibit partial absorption for the laser wavelength used, i.e. be not completely transparent or completely absorption-free in the range of the laser wavelength. Strictly speaking, this partial transparency is initially a specific property of the dry polymer, e.g. a polymer which has been freed of all physisorbed water by vacuum heating.

[0016] A measure of this partial transparency is the absorption coefficient, which should be greater than zero and less than 1 in the laser wavelength range. The absorption coefficient selected, adjusted, or used for laser processing can, for example, be in the range of 2% to 50%, especially in the range of 5% to 40%.

[0017] Many polymers can absorb water to a small extent (usually a few percent by weight at most). The extent of water absorption depends on the chemical structure (e.g. polar or non-polar) of the polymer, but also on the environmental conditions (absorption of water via the air or through direct contact with water) and the exposure time in a water-containing environment. Cycloolefin copolymers (COC), for example, are said to have a particularly low water absorption in the range of only 0.01% by weight, whereas polyamides are said to be able to absorb larger amounts of water (up to 10% of their own weight) and the water absorption for PMMA, for example, can be around 2% by weight.

[0018] The inventors have recognized that the water physisorbed in polymer substrates can contribute significantly to the absorption behavior and the magnitude of the absorption coefficient, especially in certain wavelength ranges. For example, a structural change in a polymer optical substrate, which can swell locally at a typical water content, can no longer swell after extensive drying. Therefore, in certain wavelength ranges, the absorption coefficient can be precisely adjusted by controlling the water content for a given wavelength. Conversely, in some cases, it is also possible to select a suitable laser wavelength for a specific polymer with a given water content, leading to a definable absorption behavior. However, the selection of available laser wavelengths is, of course, limited.Thus, by taking into account the definable functional relationships between laser wavelength, water content, and absorption coefficient, it is possible to specifically provide a polymer substrate for a specific application with a selected water content that ensures the substrate exhibits the desired absorption coefficient for processing at the operating wavelength intended for irradiation. The water content thus represents an actively controllable "adjustment screw" for setting the desired absorption coefficient.

[0019] The inventors currently assume that the water is physically sorbed between the intertwined polymer chains and is converted into the gas phase by laser irradiation with sufficient energy input. The resulting increase in volume of the polymer material causes an increase in pressure in the interaction volume, whereby the gaseous water acts as a propellant for the polymer, which has been softened by the temperature increase but not structurally damaged. The processing parameters must be adjusted so that, on the one hand, the water (an asymmetric molecule that can be excited to vibrate) is gently activated and, on the other hand, the polymer also has a certain base temperature so that it can de-entangle and the increase in free volume can take place. The polymer is preferably a thermoplastic polymer. If the water agglomerates embedded in the polymer have only very small volumes (in the range of a few nm 3or below), as is the case for typical polymers for optical applications, only very small cavities are formed when the polymer swells, which as such cannot be resolved by light and scanning electron microscopy and are irrelevant for the optical properties.

[0020] It is assumed that water bound in the polymer (if its content is not too high) can be excited by the laser radiation to increase the free volume. Coupling the laser radiation into a suitable amount of water contributes to the absorption depending on the water content and wavelength, and thereby influences the absorption coefficient of the water-containing polymer. The heat introduced (by exciting the water bound in the polymer) can be adjusted within certain limits for process optimization, e.g., by controlling the laser output power and / or by controlling the effective irradiation time at a particular location. Based on these findings, the invention enables reproducible process control, so that functional elements with the desired properties can be manufactured systematically and within close tolerances.

[0021] The process is particularly interesting for applications where optically effective, near-surface structures are to be created. This is possible because the local, damage-free swelling or shrinking of the polymer creates structures with defined optical properties. Therefore, components for applications in, for example, the field of micro-optics or medical technology can be processed specifically according to the specific requirements. For example, spherical, aspherical, astigmatic, or cylindrical microlenses can be produced. Prismatic structures can also be produced. With lens-like surface structures, both optically focusing or scattering, as well as light-guiding or scattering optical structures can be created. However, functional elements for other, non-optical applications can also be produced, e.g.for microfluidics or for test structures to determine the layer adhesion of inorganic functional coatings on polymer substrates.

[0022] The shape of the zones, i.e. the shape of an area enclosed by a zone boundary, can be precisely adapted to the intended use. In many cases, circular zones are provided. This makes it possible to produce, for example, microlenses that look like round optical components and can be characterized by an aperture or a diameter. Zones with an aspect ratio between a longest and a shortest lateral extent that differs from one are also possible, e.g. elliptical zones or rod-like long zones with an aspect ratio of more than two. A zone can have a polygonal shape, e.g. a rectangular shape, in particular a square shape, or a polygonal shape with only three or more than four corners. Corner areas are usually slightly rounded for technical reasons.

[0023] The number of zones can also vary depending on the intended use. For some applications, a single zone on the surface is sufficient. For example, in a multifocal lens, a zone of greater curvature (for close-up vision) can be incorporated within an area with a moderate base curvature (for distance vision). In the field of micro-measurement, for example, the recording volume of a small cup can be precisely adjusted by irradiating the base area, resulting in a curvature that leads to a desired reduction in the recording volume. Likewise, a slight but very precisely specifiable enlargement of the recording volume would be possible by laser irradiation of the base area. For many applications, embodiments are provided that have a large number of similar or dissimilar zones that can be distributed over a surface according to a specific pattern. This is the case, for example, with microlens arrays.

[0024] It can be assumed that polymers in their original delivery state are generally not optimally suited for a planned manufacturing process. For example, the nominal water content in the delivery state may be significantly lower or significantly higher than the water content that results in the absorption level required in the process. Some process variants solve this problem by a controlled change in the water content of the polymer of a starting substrate to adjust the absorption level desired for the laser processing operation. The controlled change comprises at least one drying operation to reduce the water content and / or at least one loading operation to increase the water content.

[0025] Process variants in which the controlled change in the water content comprises a combination of at least one drying operation and at least one loading operation carried out before or after the drying operation are particularly advantageous in terms of reproducible process control.

[0026] For a targeted adjustment of the water content, for example, polymer substrates to be processed can first be dried in an oven below their softening temperature. Thermal aging under vacuum or negative pressure is particularly advantageous in this case, as the expelled water can be removed and therefore cannot be re-stored. The dried components can then be exposed to water or a humid ambient atmosphere for a defined period of time in order to set a specific water content in the workpiece. The relative weight loss or gain can be measured, for example, gravimetrically or using spectroscopic methods (e.g. FTIR, Raman spectroscopy). In this case, the material is first dried and then specifically reloaded with water starting from a defined, low initial water content value.

[0027] An alternative approach could involve first exposing the polymer to water and / or atmospheric moisture until it reaches saturation, followed by a controlled drying process. This precedes the loading process before the drying process. In both cases, the combination of the drying and loading processes creates a defined initial state for the subsequent process, allowing for systematically achieving precise end results.

[0028] Alternatively or additionally, slight deviations in the water content from a target water content can be responded to by varying the process parameters, so that cost-intensive measures for the exact adjustment of the water content can be dispensed with.

[0029] To determine the functional relationship between laser wavelength, water content, and resulting absorption coefficient for a specific polymer material as accurately as possible, a series of experiments can be conducted. For example, to precisely determine the moisture or water absorption of a polymer for a specific sample shape, the time-weight curve can be recorded until constant weight is reached. Water absorption can be tested, for example, according to the EN ISO 62 standard.

[0030] However, it is not absolutely necessary to know the absolute values ​​for water absorption or water content precisely. In some process variants, an experimental determination of the functional relationship between the wavelength of the laser radiation and the water content of the polymer and / or a measured variable dependent on the water content is carried out through a large number of tests in order to determine a characteristic map or data for a corresponding characteristic map. The characteristic map thus represents the relevant behavior of the polymer. The process parameters for laser processing can then be adjusted based on data from the characteristic map. The key process variables for this are primarily 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 intended for irradiation.

[0031] Using series of experiments, for example, a database can be created with database entries for a variety of different polymer materials and parameter sets depending on the polymer, the irradiated thickness of the substrate, and the absorption and / or water content. This can then be used later, if necessary, to derive suitable recipes for laser processing using a look-up table.

[0032] In some process variants, an absorption measurement is performed to determine the polymer's absorption level for at least one wavelength of the laser radiation before and / or during the laser processing operation. The absorption measurement can, for example, comprise a measurement of the attenuation of a laser beam as it passes through the substrate of the functional element.

[0033] As already mentioned, in a preferred field of application, the invention is used to produce optical functional elements, which in this application are also referred to as optical elements for short. For this application, a zone can be designed as an optically effective lens. Thus, the surface shape in the zones during intended use determines the optical effect of the individual lenses, which can have a converging or collecting or diverging effect.

[0034] For applications in the field of ophthalmology, the polymer should be as transparent as possible in the visible spectral range. Laser processing systems and processes with laser radiation at a wavelength in the range between 1.1 pm and 9.2 pm are particularly preferred for these applications. This allows the interaction mechanism between laser radiation and the water-containing polymer to be utilized particularly advantageously. The use of thulium fiber lasers with an operating wavelength of approximately 1.9 pm appears particularly advantageous. Reasons for this include the high absorption by water and simultaneously low absorption by the polymer.

[0035] The inventors have also gained important insights into details of an advantageous process. For example, to create a circular zone, the entire area in which the zone is to be created could be irradiated with laser radiation.

[0036] In contrast, preferred embodiments provide for the use of a focused laser beam to generate a zone, said beam having a focus region in the zone with a diameter substantially smaller than the average diameter of the zone to be generated, and for the focus region to be guided over the zone according to a processing pattern along at least one trajectory such that different locations in the zone are exposed to focused laser radiation once or multiple times in succession. A "trajectory" here is a processing path that is traversed once or multiple times with the focused laser beam. This allows the topography of the surface, i.e. the surface shape within the zone, to be controlled and precisely defined. This is particularly important for optical applications when zones are intended to have a specific optical effect (e.g. focusing, diverging).Using this scanning process along trajectories, the focal length of a lens, for example, can be adjusted with high precision. The focal area can have an average diameter in the range of 10 pm to 20 pm, while a zone can be many times larger, e.g., up to 400 pm.

[0037] According to a further development, some or all of the locations in a zone to be irradiated with laser radiation are traversed not just once, but multiple times, i.e., twice, three times, four times, or even more often, with each trajectory applying only a portion of the total laser energy to be applied. In particular, individual, several, or all trajectories can be traversed multiple times. This allows the locally generated heat to be somewhat distributed within the substrate between trajectories, and local overheating can be avoided. Furthermore, the total energy to be applied can be controlled more precisely than with a single trajectory.

[0038] In one method variant, the focused laser beam is guided successively along straight trajectories that are spaced apart from one another in a scanning direction to create a zone in an area scanning operation. The ratio between the spacing and the average focus diameter can be, for example, in the range of 2:1 to 5:1. The energy input by the laser is limited by the trajectories to the desired shape of the zone, which can be circular or rectangular, for example. Preferably, a zone is irradiated not just once in a scanning operation, but multiple times in different scanning directions, so that after an area scanning operation, at least one further area scanning operation is carried out with a further scanning direction oriented at an angle to the scanning direction.This approach takes into account the fact that polymers generally have very poor thermal conductivity, but scanning in different directions allows for sufficiently uniform irradiation across the surface. The overall level of heat input can be influenced by setting appropriate distances between adjacent straight-line trajectories. The same is also possible by controlling the focus's overrun speed along a trajectory.

[0039] In another embodiment, the focused laser beam is guided over the zone along two or more self-contained trajectories of different sizes to create a zone. Frequently, there are more than two trajectories, for example three or four trajectories of different sizes. The trajectories can be similar to one another, i.e. they can have a similar course regardless of the size of the covered or enclosed area. The radial distances between trajectories and their number can be adjusted to the desired final shape. In one embodiment, the focused laser beam is guided over the zone along two or more concentric circular trajectories of different diameters to create a circular zone. Frequently, there are more than two circular trajectories, for example three or four circular trajectories of different diameters.The radial distances between circular trajectories and their number can be adjusted to the desired final shape.

[0040] In order to achieve the most uniform heat distribution possible, it can be provided that during irradiation along closed trajectories, e.g. circular trajectories, the starting points of trajectories of different size or diameter are offset from one another in the circumferential direction.

[0041] In some cases, a trajectory, e.g., a closed-circuit trajectory such as a circular trajectory, may be irradiated only once, i.e., in a single pass. This may be sufficient, especially if the desired heat input is very small. Preferably, the laser beam is guided over the trajectory in at least one of the trajectories, and preferably in all trajectories, with a predetermined number of passes. This allows the heat generated during one pass to be distributed within the polymer between the next pass, allowing even higher amounts of energy to be deposited gradually in a material-friendly manner.

[0042] Different strategies are possible for process control involving the generation of closed trajectories, particularly concentric circular trajectories. In one variant, a first trajectory, e.g., a circular trajectory, is irradiated with a specified total number of passes, and then at least a second trajectory of a different size or diameter is irradiated with a total number of passes specified for this trajectory. Each closed trajectory thus receives the specified complete irradiation before processing begins in the area of ​​the second trajectory. The sequence of trajectories can proceed either from the outside in (e.g., from a larger diameter to a smaller diameter) or vice versa, from the inside out, if necessary, in other sequences.

[0043] In another processing strategy, in a first pass, each of the trajectories of different sizes is irradiated with a number of passes that is less than the total number of passes planned for the respective trajectory, e.g., exactly once. Two or more additional passes are then performed, in which some or all of the trajectories of different sizes or diameters are irradiated again with a number of passes that is less than the specified total number of passes for the respective trajectory. This process is continued until each of the trajectories has been irradiated with the planned total number of passes.

[0044] Particularly even heat distribution and gentle processing are achieved when each trajectory to be irradiated, e.g., circular trajectories, is traversed only once in each pass. However, this is not mandatory.

[0045] Within the scope of the invention, due to the targeted use of functional relationships between water content, polymer material, laser wavelength, etc., it is possible to design the surface shape within the zones in a very different way in a defined manner. In some process variants, zones are created which have a convex surface shape in part of the zone or over the entire zone. These can then act in optical functional elements such as converging lenses. The surface is preferably created such that it is spherically or rotationally symmetrically aspherically curved. Focal lengths can also be specifically adjusted for the surface shape. The shape of the surface can be adjusted largely independently of the shape of the zone (e.g. round or square).

[0046] However, it is also possible to create zones that have a concavely curved surface shape across the entire zone or, for example, in a circular partial zone. In some cases, use is made of the knowledge that, in the case of water-containing polymers, laser radiation can also be used specifically for local drying by expelling water, whereby a certain degree of material shrinkage can be brought about in a targeted manner. Thus, to create a concavely curved surface shape, the laser radiation is preferably irradiated in such a way that locally limited drying of the polymer below its softening temperature is induced, which leads to a decrease in the specific volume of the polymer with the formation of the concavely curved surface shape.

[0047] However, this is not the only way to create concavely curved surface shapes. In some variants, to create a concavely curved surface shape in, for example, a circular sub-zone of a zone, the area to be irradiated is irradiated with laser radiation in such a way that the increase in specific volume in a radially outer region, e.g. a circular ring, is greater than in an inner sub-zone enclosed by the outer region (e.g. circular region). The idea here is to create, for example, a heat ring, in the interior of which heat can build up. This can, however, contribute to the formation of a defined topographical structure. In this variant of the process, a concave surface is formed which has a scattering effect in optical applications and is surrounded by an edge that is raised compared to the area surrounding the zone.

[0048] In general, a zone can be irradiated in such a way that a rotationally symmetric, non-uniform distribution of an energy input caused by the laser radiation results in varying degrees of volume changes.

[0049] In many cases, the machining task consists of creating a large number of similar or dissimilar zones in an area of ​​the surface to be structured, which are distributed over the surface at different locations in the area to be structured according to a predefined pattern.

[0050] An example of this is the production of a microlens array or the production of a multifocal spectacle element for correcting vision defects, in which a spatially limited area is to be additionally structured with microlenses. The inventors have recognized that specific problems with shaping can arise because, given the low thermal conductivity of polymers (e.g., approximately 0.19 W / m*K for PMMA), the energy input during the creation of a microlens can influence the shape and size of another microlens processed in close proximity and in quick succession. Therefore, the inventors propose special measures for global heat management or global temperature control, especially for such cases.Such heat management on a macroscopic length scale is particularly important when the process window is particularly narrow with regard to the energy input required for the volume change, as is the case, for example, with lenses that are relatively small and flat. According to a further development, for such processing tasks, the zones are generated successively according to a heat input-optimized processing strategy, wherein preferably after the generation of a first zone at a first location, a distant second zone is generated before a third zone closest to the first zone is generated. This results in a particularly favorable strategy for distributing the thermal load with the goal of avoiding the generation of lenses in preheated areas on the polymer substrate.Heat input is also relevant with regard to the water content in the polymer, since the laser-induced volume increase (laser swelling) can only be observed in the presence of a sufficient amount of water, and with insufficient energy input, in some cases only drying was observed, which can then lead to undesirable shrinkage. According to a further development, a processing sequence of the zones is defined using temperature criteria, spacing criteria, and zone size criteria to determine the processing strategy. A finite element simulation is preferably performed to determine the processing strategy.This allows the sequence in which the zones are processed to be determined, ensuring that the local temperature of the substrate never exceeds a predefined temperature threshold or follows a similar optimization criterion, despite the polymer's poor thermal conductivity. With appropriate simulation and appropriate definition of the process's objective functions, an optimized processing sequence can be determined, and the structuring process can be carried out accordingly.

[0051] According to a further development, a large number of dissimilar zones are created in a region of the surface to be structured, which zones are distributed over the surface according to a laterally random distribution at different locations in the region to be structured. The zones can differ, for example, in terms of their shape and / or their size and / or their optical effect. In such a random distribution, some or all of the zones can have an asymmetrical polygonal shape. A zone can, for example, have three, four, five, six, seven or more corners and a corresponding number of side edges. The irregularly shaped zones can form a surface-filling arrangement in such a way that, with the exception of the zones located at the edge of a structured region, each zone is directly adjacent to an immediately adjacent zone on all lateral sides via a corner or a side edge.The structured area can be completely filled with optically effective, irregularly shaped microlenses with refractive power (usually positive, but possibly also negative). The surfaces of the zones preferably have randomly distributed curvatures and heights, so that the zones also have randomly distributed optical power. The distribution of the zones can be predetermined, for example, using a Voronoi mosaic.

[0052] An optical functional element of this type (with a laterally random distribution of zones, particularly area-filling) can advantageously be designed as a beam-shaping element, particularly as a diffuser. When irradiated with partially coherent or coherent radiation (e.g., a laser), it can generate an intensity distribution in its far field that is more uniform than that of a microlens array with uniformly distributed microlenses of similar dimensions.

[0053] For further explanations on the functionality and possible applications of random microlens arrays, please refer to the technical article "From regular periodic microlens arrays to randomized continuous phase profiles" by M. Cumme and A. Deparnay in: Adv. Opt. Techn. 2015; 4(1): 47-61. Methods and devices of the invention described in this application can be advantageously used for the production of such random microlens arrays.

[0054] According to a further development, a multiplicity of preferably similar zones is created in a region of the surface to be structured, which zones are distributed over the surface in a regular manner at different locations in the region to be structured, filling the area or without gaps. The zones can fill the area to be structured in the manner of a tiling. Some or all of the zones can have a symmetrical polygonal shape. A zone can, for example, have the shape of a triangle, a quadrilateral or a hexagon. The zones can form a surface-filling arrangement in such a way that, with the exception of the zones located at the edge of a structured region, each zone directly borders an immediately adjacent zone on all lateral sides via a corner or a side edge. The structured region can be filled without gaps with optically effective designed microlenses with curved surfaces.

[0055] Particularly in the manufacture of optical functional elements, for example, for the production of zones of special refractive power in multifocal spectacle elements, it can be advantageous if, after completion of the laser processing operation, a controlled heat treatment and / or drying treatment of the functional element is carried out at ambient temperature to stabilize the structures created by the laser processing before its intended use. The post-treatment can, for example, include a heat treatment below the softening temperature of the polymer to stabilize the lens geometry.

[0056] In the field of polymer-based optical functional elements, functional coatings (e.g., hard coating, anti-reflective coating, etc.) are widespread. The inventors have recognized that, even with processes of the type considered here, it is possible to coat the surface to be structured with a functional coating or sub-layers of a desired coating before the laser processing operation, between selected steps of the laser processing operation, and / or after completion of the laser processing operation. According to a further development, the type of coating (layer materials, layer structure, etc.) and / or parameters of the coating process (e.g.,Temperatures during coating) can be matched to the water content and / or water absorption capacity and / or water release capacity and / or structural relaxability of the polymer in such a way that the coating contributes to the shaping and / or stabilization of the surface shape in the region of the zone. An important selection criterion can be, for example, the permeability of the coating to water. A substantially water-impermeable coating can be used to stabilize the surface shape created by a laser processing operation against gradual changes in shape during intended use by inhibiting or completely preventing water loss or water absorption. Alternatively or additionally, a predominantly mechanical stabilization of the surface shape is also possible using a stable functional coating.

[0057] If a coating and / or a coating operation is designed in such a way that it has a quantifiable influence on the surface shape of a zone, i.e., exhibits shape-changing properties, this can be taken into account in the overall process. According to a further development, the laser processing operation is carried out in such a way that the resulting surface shape does not correspond to the desired target surface shape, but exhibits a defined shape deviation from it. By applying the coating, a slight shape change can then be brought about, whereby the desired target surface shape can be set with high precision. A coating can therefore be used to trim the surface shape. The shape change can usually be described as a change in the surface curvature. This can, for example, be reduced, or if necessary, the direction of curvature can also be changed (inversion).

[0058] A major advantage of the laser-based process is the ability to create zones of varying shape and size on a substrate, with a position distribution that can be freely specified for each application by programming the laser processing system. With appropriately well-equipped and adjusted systems, a positioning accuracy in the range of 1 pm or less, e.g., down to 0.5 pm, is possible. The positioning accuracy indicates the process-related tolerance with which zones can be created precisely at their specified location on the surface. This makes it possible to produce, among other things, regular periodic arrays of zones, as required for some microlens arrays.To generate an array with a plurality of similar or dissimilar zones, a position distribution of the zones with individually specified positions for each of the zones can be specified and the zones can be successively generated at the specified positions in a laser processing operation with a positioning accuracy specific to the laser processing operation.

[0059] There is considerable design freedom with regard to the distribution of the zones, which can also be deliberately arranged unevenly. In some embodiments, positions of the position distribution in one or more areas of the surface deviate from nearest positions of a two-dimensional periodic position distribution by a lateral offset that is greater than the positioning accuracy and smaller than one period distance to the nearest position of the periodic position distribution. This makes it possible to create precisely uneven position distributions. One or more or all zones can, for example, have a circular shape, an elliptical shape, a polygonal shape, in particular a rectangular shape, or a rod-shaped shape with an aspect ratio of more than two between length and width. Other shapes are also possible.

[0060] The arrangement of several of the zones can thus be easily adapted to external requirements. For example, if microlens arrays are to be created for system integration whose arrangement is adapted to other system components, such as microLEDs or pixels of a camera chip, the slight deviations of the arrangement from a perfect grid can be taken into account by measuring and creating a suitable arrangement of individual microlenses. The arrangement of several of the zones can thus also be easily and individually adapted to inhomogeneities in substrates or geometric peculiarities of pre-processed semi-finished products. This allows the creation of a microlens arrangement adapted to a different optical element. This arrangement then only needs to be correctly aligned once relative to the other elements.

[0061] The process can be used in many applications involving polymer-based optics. For example, the process can be used for the shape correction of embossed lenses or for the optically effective structuring of freeform optics. It can also be used to produce flat optics, for example, for use in microscope or illumination optics. Corresponding components can then be used in the automotive, display technology, or microscopy / camera inspection sectors.

[0062] However, the manufacturing process has particularly great potential for application in the field of medical technology, particularly for the production of customized, multifocal optics in the form of ophthalmic lenses or intraocular lenses (IOLs). Since only mold-based manufacturing techniques have been used for this to date, the process described offers the possibility of flexible structuring without embossing molds. This means that, for the first time, patient-optimized ophthalmic lenses, e.g. for myopia management in children, progressive lenses, or multifocal IOLs, could be processed. A further advantage of the process is that microlenses can be created that are optically effective but visually invisible. If necessary, areas with zones can be detected using optical aids, e.g. ellipsometrically using stress-induced birefringence possible in the area of ​​zones.

[0063] Furthermore, the invention can be used in the field of microfluidics, e.g., for volume calibration or the structuring of channel structures. It can also be used in product marking and batch labeling.

[0064] In addition, the method can be used, for example, to determine the adhesion of thin films to polymer substrates or the functional structuring of piezo- or pyroelectric polymers (e.g. polyvinylidene fluoride (PVDF)).

[0065] The invention further relates to a functional element obtainable using the method, which comprises a substrate consisting essentially of a polymer, which has on at least one surface at least one zone with a surface shape that deviates from a surface shape in an environment of the zone.

[0066] The invention further relates to a device for producing a functional element comprising a substrate made of a polymer, which has at least one zone on at least one surface with a surface shape that differs from a surface shape in a surrounding area of ​​the zone. The device comprises a substrate holder for receiving a substrate, a laser system with a laser radiation source for emitting laser radiation of an operating wavelength, and a beam guidance system for guiding a laser beam onto a surface of the substrate. Furthermore, a movement system for generating a relative movement between the substrate and the laser beam is provided such that the substrate can be irradiated by the laser beam at different locations in a region to be structured. The device is configured to carry out the method.

[0067] BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Further advantages and aspects of the invention emerge from the claims and from the description of embodiments of the invention, which are explained below with reference to the figures.

[0069] Fig. 1 shows the transmission (in percent) as a function of wavelength (in nm) for selected polymers; Fig. 2 shows a diagram of the dependence of water absorption on wavelength;

[0070] Fig. 3 shows diagrams of the influence of a drying treatment on the water content and the weight of a polymer substrate;

[0071] Fig. 4A and 4B show cross-sectional profiles through microlens elements, where Fig. 4A shows the lens geometry without drying of the substrate and Fig. 4B shows the lens geometry after vacuum drying;

[0072] Fig. 5 shows a graphical representation of the time dependence of the attenuation of a laser beam by a polymer substrate in its as-delivered state without prior drying operation;

[0073] Fig. 6 shows a graphical representation of the time dependence of the attenuation of a laser beam through a polymer substrate after a preliminary drying operation;

[0074] Fig. 7 shows three area scan operations with different filling directions for local heat management in the fabrication of a convex circular microlens;

[0075] Fig. 8A and 8B show different irradiation strategies in which a circular zone is successively irradiated along four equidistant annular trajectories of different diameters;

[0076] Fig. 9A and 9B each illustrate an azimuthal offset of starting points of a crossing for equidistant annular trajectories;

[0077] Fig. 10A and Fig. 10B show a height profile of microlenses of a microlens array (Fig. 10A) and an optical microscopy image of a corresponding machined area with a plurality of similar microlenses (Fig. 10A);

[0078] Fig. 11 shows a schematic representation of laser trajectories for generating an elliptical surface structure by irradiating with four concentric elliptical trajectories from the outside to the inside; Fig. 12 shows a schematic representation of rectilinear laser trajectories for generating a rectangular surface structure by filling the rectangular contour with parallel lines;

[0079] Fig. 13 shows a schematic representation of the laser trajectories for generating an open, Z-shaped zone;

[0080] Fig. 14 shows a schematic representation of a machining strategy with elliptical laser trajectories arranged offset next to each other in one spatial direction;

[0081] Fig. 15 shows in the sub-figures 15A to 15E a selection of different possible geometries of zones;

[0082] Fig. 16A to 16C show schematic cross-sections through zones of different surface shape;

[0083] Fig. 17 shows on the left a light microscopic image and on the right a detail of a microlens array with insufficient adaptation of the processing sequence to the poor thermal conductivity of the polymer substrate;

[0084] Fig. 18 shows a schematic flow diagram of a method for determining the processing sequence of zones of a processing pattern taking into account the poor thermal conductivity of the polymer substrate;

[0085] Fig. 19 shows in four sub-figures the temperature distribution in a spectacle lens determined by simulations during the creation of a microlens array in a peripheral field of vision at four successive points in time;

[0086] Fig. 20 shows light microscopic images of a microlens array manufactured with optimized thermal management with increasing magnification (cf. Fig. 17);

[0087] Fig. 21 shows the relative height change of microlenses as a function of different aging temperatures; Fig. 22 shows a scanning electron micrograph of the cross-section of a microlens array on a multifocal ophthalmic lens, which was produced through a hard coating layer;

[0088] Fig. 23 shows a scanning electron micrograph of the cross-section of a microlens array on a multifocal ophthalmic lens which was provided with an inorganic multilayer stack through a hard coating layer after laser swelling;

[0089] Fig. 24 shows a diagram comparing the lens geometry of a microlens before (V) and after (N) the deposition of an inorganic layer stack;

[0090] Fig. 25A and 25B show a cross-sectional profile of a partially concave microlens (Fig. 25A) in a polymer substrate and in Fig. 25 the scanning electron microscopic image of the cross-sectional area, wherein the surface shape was deliberately changed by a post-coating process;

[0091] Fig. 26A to 26C show schematic cross-sectional views to explain possibilities of inverting the surface shape in the area of ​​a zone by means of coating;

[0092] Fig. 27A to 27C show a schematic plan view (Fig. 27A) and a schematic section (Fig. 27B) of a randomly distributed microlens structure and, in Fig. 27C, a surface-filling regular distribution of essentially hexagonal microlenses; and

[0093] Fig. 28 shows an embodiment of a laser processing device for producing functional elements according to the method explained here.

[0094] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0095] The following explains some exemplary embodiments for the production of functional elements for optical applications, which are accordingly also referred to as optical functional elements or optical elements. What these exemplary embodiments have in common is that they use a substrate consisting essentially of a polymer, i.e., a polymeric material, and that at least one zone is created or present on at least one surface of the substrate, which zone has a surface shape that deviates from the surface shape of the substrate in the vicinity of the zone. In the region of the zone, the surface can be raised or recessed relative to the surrounding surface.

[0096] One example of such polymer optical systems using microlenses is multifocal ophthalmic lenses for slowing the progression of myopia in children. Using an overlapping focal point in the periphery, the disproportionate longitudinal growth of the eye, which causes myopia, is slowed or even completely stopped.

[0097] The inventors have found ways to systematically produce such surface-structured functional elements with highly reproducible and individually adjustable optical properties with high precision. For this purpose, polymer substrates are used that have a specific or determinable water content and are processed with laser radiation of a suitable operating wavelength. By exploiting the functional relationships between the wavelength of the laser radiation, the water content of the polymer, and the resulting highly controllable absorption coefficient of the polymer material, the desired goals can be achieved.

[0098] Influence of water content on material properties and laser processing parameters

[0099] For optical applications in the visible wavelength range, polymer materials that exhibit sufficiently good transparency in the visible spectral range are suitable. Fig. 1 shows the transmittance (in percent) as a function of wavelength (in nm) for some polymers that can be used for polymer optical applications, namely polymethyl methacrylate (PMMA), polycarbonate (PC), cycloolefin copolymers (COC), polyvinyl acetate (e.g. PVB), and ultraviolet acrylic (UV). Comparable curves also exist for specialty polymers that are optimized for medical applications, for example those from the manufacturer Mitsui Chemicals, Inc., which are known under the names MR-7, MR-8, MR-10, MR-174 or CR-39. The measurement curves in Fig. 1 generally demonstrate high transparency in the visible wavelength range (approx. 400 nm to approx. 750 nm) as well as partial transparency at shorter and, in particular, at longer wavelengths. In the ranges of partial transparency orWith a certain corresponding absorption coefficient, the materials can absorb a portion of the laser energy at certain wavelengths. In the examples, this is the case, among other things, at wavelengths in the near infrared range (NIR) above 1.1 pm, in particular above 1.6 pm. The inventors have recognized that the water content of a polymer can make a significant contribution to its absorption behavior and that, accordingly, by controlling the water content, it is possible to adjust the absorption coefficient of the polymer so precisely for a specific application or a specific wavelength range of the laser radiation that, with the help of precisely controllable heat input, very precise design options exist.

[0100] All of the polymers mentioned can absorb water to a greater or lesser extent, for example in the range from 0.01 wt.% up to approximately 10 wt.%. That water can make a significant contribution to absorption capacity is clear from Fig. 2. Fig. 2 shows a diagram showing the dependence of water absorption (in 1 / m) on wavelength. This shows, for example, that in the wavelength range above 1 pm or 1.1 pm water sometimes exhibits considerable absorption, including a local maximum in the range around 2 pm. The inventors have concluded that by controlling the water content for a given wavelength it should be possible to precisely adjust the degree of absorption and thus create controllable and reproducible processing conditions.

[0101] According to current knowledge, the process converts the water embedded between the polymer chains into the gas phase by irradiation with laser radiation of a suitable wavelength and intensity. The resulting increase in volume causes a rise in pressure in the interaction volume, whereby the gaseous water acts as a blowing agent for the polymer, which has been softened by the temperature increase but not structurally damaged. The extent of the volume change can be precisely tuned by the process parameters, such as laser wavelength, laser energy, polymer type, and water content (to adjust the absorption coefficient effective during laser processing).

[0102] This interaction mechanism can be induced particularly well by laser radiation in the NIR range, for example using thulium fiber lasers at an operating wavelength of approximately 1.9 pm. Reasons for this include the high absorption by the water (see Fig. 2) and the low absorption by the polymer (see Fig. 1). Due to the partial transparency of the water-laden polymer, the laser radiation can penetrate sufficiently deep into the region of the polymer close to the surface and cause the volume change. Series of experiments have shown that the embedded water plays a key role in this process and that the interaction mechanism presumably exists as assumed. For example, a polymer substrate made of the special polymer MR-7, used for high-quality ophthalmic lenses, was locally irradiated with laser radiation in order to create lens geometries with convexly curved surface shapes in the irradiated zones.The irradiated workpieces were then aged at 75 °C in a vacuum oven for more than two weeks (x-axis in days [d]). The diagram in Fig. 3 shows the change in weight AG of several polymer ophthalmic lens blanks made of MR-7 after drying by aging in a vacuum oven at 75 °C. The gradual weight loss due to the loss of water in the polymer material is clearly visible. This also demonstrates that the water content can be specifically reduced by drying treatment in a suitable atmosphere.

[0103] Figures 4A and 4B show cross-sectional profiles through microlens elements created by irradiating the 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 vacuum drying for 14 days at 75 °C. While the (water-containing) state without drying (Figure 4A) results in a lens height H of over 20 pm, with identical laser parameters after 14 days of drying, only an undefined projection of approximately 80 nm in height can be generated. This is considered strong evidence that the swelling capacity of the polymer material, i.e., its ability to expand in volume due to laser radiation, depends significantly on the water content of the polymer and can therefore be specifically influenced by controlling the water content.

[0104] Although the water content of a polymer workpiece has a significant influence on the absorption behavior, there are other factors that can affect the specific choice of laser parameters. These include, among others, the thickness of the material or the presence of coatings. Therefore, it is advantageous to measure the respective partial absorption prior to and / or during the laser processing. For this purpose, power measurements can be performed, for example, through the workpiece being processed. Laser parameters adapted to the existing partial absorption can then be used.

[0105] The relationships are clearly visible in the diagrams in Figs. 5 and 6. Fig. 5 shows a graphic representation of the attenuation ABS of a laser beam (in percent) with a wavelength of 1,940 nm and a power of 150 mW or 300 mW as it passes through an approximately 1 mm thick MR-7 substrate in its as-delivered state, i.e., without any prior drying operation. Under the selected conditions, the interaction with the laser beam only achieves drying, but no swelling. It can be seen that, particularly in the initial period of irradiation, the attenuation decreases significantly before asymptotically reaching a state with only a slight, constant decrease in absorption. A comparison with Fig. 6 (attenuation with a dried lens) shows that there is only a slight reduction in attenuation in a relatively short initial phase, and that the attenuation then decreases only slightly over time.Such results are considered strong evidence that the effective absorption coefficient of the water-containing polymer material during laser processing depends significantly on its water content and can therefore be specifically adjusted by controlling the water content. Furthermore, it is shown that laser drying can be achieved by surface irradiation well below the threshold fluence (the fluence above which a volume increase or laser threshold can be generated).

[0106] In preparation for series production, a series of experiments were conducted to measure the water content-dependent absorption behavior shown here as an example. Database entries for suitable parameter sets were generated and used depending on the material, workpiece thickness, and absorption / water content. For this purpose, a corresponding power measurement or beam diagnostics was performed beneath the sample. Alternatively or additionally, camera inspections in transmission or reflected light can be used to measure the swollen / dried areas through test processing, for example, outside the target area, and to identify the necessary adjustments to the process parameters.

[0107] Details of selected processing processes

[0108] The energy input via a laser beam aims at a defined heat input into the water-containing polymer below the ablation threshold. The shape of the interaction zone between laser and polymer can be defined laterally by the type of process control, in particular by the choice of laser trajectories and / or by adjusting the beam profile. The height of the zone of altered volume can be significantly influenced by the extent of the local energy input. By appropriately selecting the processing pattern, the topography of the surface can be adjusted so that the desired optical system properties can be achieved. The topography of the surface corresponds to the surface shape of the zone or the areas within the zone boundaries, which represent the transition from the adjacent area of ​​the surface to the superstructure in the zone.Monotonous or strictly monotonous transitions can be represented, as can discontinuous transitions. The process can be used both to structure a surface on the front side facing the laser beam and to create structures on the back side of the workpiece.

[0109] An important finding of the inventors is that, due to the typically low thermal conductivity of polymers for optical applications, the design of the processing strategy should include both local thermal management for the creation of a single structure (i.e., a single zone, for example, a microlens) and global temperature control for the production of defined optically effective overall structures, such as microlens arrays.

[0110] Fig. 7 illustrates an example of local heat management in the creation of a circular zone Z for the production of a convexly curved microlens. To create spherical or aspherical microlenses, the energy input by the laser is limited to the desired shape, for example, of the circular zone Z, using the laser processing trajectories TR represented by the lines. Within this limitation, spherical bulges can be generated, for example, by filling with equidistant lines. The left-hand part of the figure shows the course of straight-line trajectories TR with a filling direction FR running from left to right. However, due to the poor thermal conductivity of the polymer, this results in uneven heat distribution.To counteract this, in this embodiment, a zone is completely filled multiple times in different filling directions. After each complete pass, the filling is rotated by a specific angle, for example, between 30° and 60°, relative to the previous filling and then dispensed again (middle and right sub-figures). This creates a local heat buildup in the center of the trajectory, giving the zone a curvature that is essentially rotationally symmetrical to the center of the zone.

[0111] It has been shown that in many cases, from the point of view of heat management and the achievable surface shape, it can be more advantageous to guide the area to be irradiated along two or more self-contained trajectories TR of different sizes across the zone. The trajectories can be similar to one another. For circular zones, this will be explained using Figs. 8 to 10. Here, the zone is created along concentric circular trajectories with spacing matched to the final shape. Two approaches can be distinguished with regard to the assignment of laser parameters. In the figures, the ring highlighted in bold represents the one currently being processed, while the thin lines represent the rings already processed. In the variants shown in Figs. 8A and 8B, the zone is irradiated with four equidistant trajectories TR of different diameters.Each individual ring (each circular trajectory) is completely irradiated with the focused laser for the previously calculated total number of necessary passes (e.g., from one to four, five or six, rarely more). Only then does the system move on to the next ring and continue the process in the same way. The rings can be sequenced from outside to inside (Fig. 8A) or from inside to outside (Fig. 8B). Each ring can be assigned an individual path speed along the trajectory. This speed should preferably be kept the same for all passes along a trajectory. The different overrun speeds, which are normally selected for the rings, take into account the fact that the local energy input along the trajectory is greater when passing over more slowly, which can result in different threshold heights at the beginning (lower) relative to the end point of the trajectory (higher), even for individual passes.

[0112] It was observed that the rings initially resemble Landolt rings due to the swelling not yet having begun due to insufficient heat accumulation. To prevent this, it is preferable that the starting points SP of the laser trajectories are offset in a defined manner either between the rings and / or between the respective passes on the rings. Figs. 9A and 9B each show the starting points SP of a pass on a ring. It can be seen that the starting points are offset azimuthally from one another. This allows for the creation of more uniform surface shapes. In any case, to create defined swollen areas (e.g., spherical microlenses), the local energy input, the number of rings, their relative spacing, and the filling direction should be coordinated in order to precisely adjust the target geometry (especially its aperture and height).The term "aperture" here refers to the size of the zone within its outer border or zone boundary. In many cases, this is not a sharply defined boundary, but rather a smooth transition between areas of different general curvature. The respective rings do not necessarily have to be processed sequentially. A different processing order for the rings is also possible. If necessary, the laser parameters should be adjusted.

[0113] According to an alternative machining strategy, all trajectories intended to create a zone (e.g., between three and five rings) are successively scanned once by the focused laser beam, before the next sequence of machining operations begins at one of the rings, in which all or part of the circular trajectories are traversed again. Consequently, only one pass is required per circular trajectory within a complete pass, and the total number of passes for the rings corresponds to the number of passes. The energy input can be very homogeneous and location-specific by selecting high path speeds or overrun speeds (e.g., several hundred millimeters per second to a few meters per second) with a simultaneous high number of passes, low laser power, and only very short jump pauses between the circular ring trajectories. A variation of the starting points (see Fig.9A and 9B) can be additionally implemented if required.

[0114] According to the inventors' experience, the first irradiation strategy is often particularly advantageous for producing tall structures. Limitations may arise when zones with a relatively small aperture (e.g., less than 500 pm) and a simultaneously low height (e.g., less than 1 pm) are to be produced. In the case of the second processing strategy (Regime 2), the height of the laser threshold can be controlled very precisely. This allows lenses to be produced over a wide height range for a given size or aperture. The height of a zone can, for example, be in the range of a few tens of nanometers to a few tens of micrometers. The term "height" generally refers to the maximum height of a curved surface measured perpendicular to the imaginary extended surface in which the zone is located.

[0115] As an exemplary demonstration of the suitability of this process variant for producing small, flat microlenses (ML), Fig. 10A shows a height profile of microlenses of a microlens array measured using a white light interferometer, and Fig. 10B shows a stereomicroscopic image of a processed area with a large number of 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 coefficient was in the range of approximately 45%.

[0116] In principle, microlenses can also be created using other patterns, such as spirals. However, based on the inventors' experience, trajectories characterized by numerous jumps or discontinuous vector paths should be avoided.

[0117] When it comes to the fundamental choice of laser power and number of passes, which together define the introduced energy, a combination of higher laser power with a reduced number of passes usually appears more advantageous than processing with a higher number of passes at a lower laser power. The above examples explain some basic principles of preferred embodiments using the generation of circular zones. However, the principles can be applied accordingly to create zones whose basic shape or form deviates significantly from circular. Fig. 11 shows a schematic representation of laser trajectories for creating an elliptical surface structure by irradiation with four concentric elliptical trajectories from the outside to the inside.12 shows a schematic representation of rectilinear laser trajectories for generating a rectangular surface structure by filling the rectangular contour with parallel lines.

[0118] As an alternative to the previously described, generally convex, closed surface shapes, other shapes can also be created. Figure 13 shows an example of a schematic representation of the laser trajectory for generating an open, Z-shaped surface structure or zone described by polygons.

[0119] Fig. 14 shows an example schematic representation of a processing strategy with elliptical laser trajectories arranged offset next to one another in one spatial direction. This allows, for example, the creation of elongated surface structures with a higher aspect ratio between length and width, such as rod lenses.

[0120] To illustrate the possibilities within the scope of embodiments of the invention, Fig. 15 shows a non-exhaustive list of different possible zone geometries in sub-figures 15A to 15E. The upper sub-figure shows an oblique perspective view of an individual zone Z on an otherwise flat surface OB of a polymer substrate SUB, the sub-figure below shows a plan view of the zone to illustrate its basic shape or aperture, and the sub-figures below each show vertical sections along the directions A and B. Fig. 15A shows the conditions for a circular zone Z with a convexly curved surface, Fig. 15B shows an example of a circular zone with a rotationally symmetrical aspherical surface shape, Fig. 15C shows an example of an astigmatic lens with an elliptical aperture, Fig.Fig. 15D shows an example of a rod lens whose extension in the longitudinal direction (along B) is many times greater than the extension in the width direction (direction A), and Fig. 15E shows a zone with a generally rectangular basic shape and a substantially wedge-shaped surface shape, which creates an optical microelement with the effect of a prism.

[0121] Although the effect of laser swelling is characterized by a volume increase near the surface, concave lenses can also be produced using the process. At least two different approaches can be used for this, which are illustrated in Figs. 16A to 16C. Fig. 16 shows schematic representations of different lens types that can be produced using suitable process variants. Fig. 16A shows a convex structure due to a higher swelling 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 that was produced by local drying using laser radiation. Local drying using a laser beam can take place below the softening temperature of the polymer or by laser swelling, as described above, but using an adapted energy input.While this is typically designed for heat accumulation in the center of the overall trajectory when creating convex lens geometries, resulting in higher swellings in the center than at the edge (Fig. 16A), for concave lens shapes, the areas at the edge can be swollen higher than in the center, as illustrated in Fig. 16C. In this case, it can be useful to adjust the transition to neighboring surfaces by laser thresholding.

[0122] The manufacturing processes used to date have produced lens-like or prismatic zones with diameters or apertures ranging from approximately 5 pm to approximately 500 pm. The reliably producible heights were usually in the range of approximately 20 nm to over 20 pm.

[0123] In some embodiments, relatively small zones in the form of flat microlenses were systematically created, which had a height H and a diameter D, wherein the condition 1000 > V > 500 applies for a ratio V = D / H, wherein the condition 10 nm < H < 100 nm, in particular 15 nm < H < 50 nm and / or the condition 15 pm < D < 30 pm preferably also applies. The height can, for example, be in the range from 30 nm to 40 nm, the diameter in the range from 20 - 25 pm. One advantage of such small and flat lenses is that the lenses are no longer visually recognizable (no scattering), but are nevertheless optically effective by generating additional foci in addition to the basic refractive power of the optical substrate. A useful application is the manufacture of plastic spectacle lenses for myopia management using microlens arrays that have such small, flat lenses.

[0124] Global temperature control

[0125] Surface structures often require the creation of a large number of similar or dissimilar zones with specific surface shapes distributed closely adjacent to one another across the surface according to a pattern. The inventors have recognized that specific problems can arise in this regard, which are due to the very low thermal conductivity of polymers. For PMMA, for example, this is in the range of 0.19 W / mx K. Due to the low thermal conductivity, the energy input during the creation of a microlens or another structured zone can significantly affect the shape and size of another microlens processed in close proximity and in quick succession.Since the process window with regard to the energy required for swelling is relatively narrow, especially for small and / or flat lenses, heat management on the macroscopic length scale is also of great importance, according to the inventors' findings. To illustrate this, Fig. 17 (left) shows an optical microscopic image of a microlens array on an MR-7 ophthalmic lens blank with inadequate heat distribution adjustment. The enlarged detail in Fig. 17 (right) clearly shows that instead of the desired, equally sized microlenses ML, an uneven distribution of microlenses with different apertures and / or heights has been created, with some surface areas even lacking any microstructures.

[0126] According to the inventors' findings, for extended microlens arrays and / or small distances between the lenses, a special and layout-adapted strategy for distributing the thermal load is often required, with the goal of avoiding the creation of lenses in excessively preheated areas on the substrate. The heat input is also relevant with regard to the water content in the polymer, since swelling, i.e., the laser-induced volume increase, was only observed in the presence of a sufficient amount of water, and drying can even be observed with insufficient energy input or insufficient temperature.

[0127] To counteract this problem, it is often advisable to specifically adapt the processing pattern to the required geometry of the lens arrays, taking into account in particular the physical and thermal properties of the substrate material, the number of lenses, the arrangement of the lenses and the energy and heat input required to produce a lens. A practical variant of defining a processing pattern is explained using the flow chart in Fig. 18. In a first step S1, the processing pattern (pattern, symbol PAT) is defined, particularly with regard to the number of lenses, spacing between the lenses, arrangement of the lenses (for example, hexagonal or rectangular), and size of the lenses (and thus the local energy input by the laser). This is followed in step S2 by calculating the coordinates (symbols x, y) of the respective lenses.Based on this, in step S3, the imprinted temperature (symbol T) is estimated based on, for example, the thermal conductivity (symbol X) in the material, convection, etc. for the respective coordinates of the individual lenses. Based on this, in step S4, the processing sequence (symbol SEQ) is determined or optimized using temperature and distance criteria and supplemented by, for example, the introduction of waiting times or variations in the laser parameters.

[0128] A characteristic of an advantageous processing strategy is that after the creation of a first zone at a first location, a second zone further away is created before a third zone closer to the first zone is created. Numerical simulation using the finite element method (FEM) has proven to be particularly advantageous for determining the processing strategy. Fig. 19 shows, in the four sub-figures, the temperature distribution in a spectacle lens determined using an FEM method during the creation of a microlens array in a peripheral field of vision at arbitrarily chosen, successive times L to t4. It can be seen how zones of increased local temperature gradually develop in different areas further apart from one another. The heating of the target area with an increasing number of microlenses introduced is also clearly visible.The simulation was specified so that a local temperature threshold of 30 °C must not be exceeded. Other objective functions, such as the lowest temperature at the greatest distance or the lowest temperature at the smallest distance, can also be selected.

[0129] After appropriate optimization of the processing strategy with regard to the sequence of microlenses to be created, it is therefore possible to produce extended microlens arrays, even with high packing densities. Figure 20 shows light microscopic images of an annular microlens array (MLA) on an MR-7 ophthalmic lens blank with optimized thermal management with increasing magnification. It can be seen that the problems of uneven lens distribution and size explained in Figure 17 have been resolved.

[0130] For precise processing, the substrates to be processed are held in a suitable substrate holder. This holder should be designed in such a way that no heating reflection of the laser radiation transmitted through the workpiece can lead to an unwanted, additional, and position-dependent energy input into the substrate. In a preferred method, the substrate is held only at its periphery, maintaining sufficient distance from a support located beneath the workpiece. Additionally or alternatively, a beam trap could be integrated beneath the workpiece.

[0131] In addition to temperature control through targeted optimization of the laser's energy input, heat dissipation can be increased with the help of additional technical measures. For example, the workpiece can be exposed to a gas (such as compressed air or inert gas) during processing. The gas flow can, for example, be directed essentially coaxially to the laser beam or at an acute angle and / or symmetrically to the laser beam. According to the inventors' experience, the temperature and volume flow of the gas have a significant influence on heat transfer to the environment by convection. Unwanted and undefined water ingress can be counteracted by additional drying of the gas.

[0132] Post-treatment after laser processing

[0133] In some cases, heat treatment and / or drying after laser processing can be useful. By aging the components or polymer substrates processed by laser swelling, for example, in a drying cabinet or oven, the geometry can be further adjusted or specifically modified after laser swelling by removing water. The extent of this effect can be controlled by the aging time and temperature. However, the aging temperature should be well below the softening temperature of the polymer or any layers present on it, as otherwise the swollen or dried structures could relax and / or layer effects could occur at interfaces.

[0134] The diagram in Fig. 20 demonstrates that the geometry of the surface shape can still be influenced in a controlled manner using targeted aging. Fig. 21 shows the relative height change AH / H of microlenses in an MR-7 plastic substrate as a function of their lateral dimension or aperture, which is represented by the parameter width B on the x-axis. The y-axis represents the relative height change AH / H. It can be seen that for moderate aging temperatures relative to the softening temperature (85 °C), small relative height changes can be induced, whereas higher temperatures, particularly in the case of large microlenses, could lead to a strong relaxation or reduction in height. Another finding from the experiments is that the relaxation of the lens geometry leads significantly to a reduction in the height of the lenses, but not to a significant reduction in their size or aperture.

[0135] These measurable and controllable effects can be used to fine-tune the surface geometry after laser processing by heat treatment and / or drying. The process can be used to process substrates with uncoated surfaces. The process can also be performed on already coated substrates, i.e., through one or more layers on the substrate, provided the optical properties of the coatings in the wavelength range used are comparable to those of the substrate and the layer adhesion or deformability of the layer allows for form closure upon swelling of the substrate without structural failure. To illustrate this, Fig. 22 shows a scanning electron microscope image of the cross-section of a microlens array on a multifocal ophthalmic lens, which was produced through a hard coating layer.The integrity of the layer structure after laser swelling is clearly visible.

[0136] It was further demonstrated that the structures created with this method can also be post-coated using suitable coating techniques. To prevent the subsequent coating process from leading to uncontrollable deformation, the temperatures resulting from the coating process should be below the temperature at which the structures relax. Such coating processes (especially using physical vapor deposition (PVD)) are routinely used in the field of optics.

[0137] It has been demonstrated that athermal post-coating of polymer substrates structured using laser thresholding, with appropriate process control, does not result in any significant changes to the initially set lens geometry. Figure 23 shows a scanning electron micrograph of the cross-section of a microlens array on a multifocal ophthalmic lens, which, after laser thresholding, was coated with an inorganic multilayer stack through a hard coating layer using a PVD process.

[0138] Fig. 24 shows a diagram comparing the lens geometry of a microlens measured using a white-light interferometer in an MR-7 substrate before (V) and after (N) the deposition of an inorganic layer stack. It can be seen that the coating can be produced in such a way that the surface geometry in the zone is largely preserved.

[0139] However, it is also possible to specifically alter the surface shape using special post-coating processes, for example, converting initially convex, swollen structures into a concave lens structure. Fig. 25B shows a cross-sectional profile of a microlens in an MR-7 substrate captured using a white light interferometer. Fig. 25A shows the scanning electron microscopic image of the cross-sectional area.

[0140] In addition, the design of the layer stack, and especially its water permeability, can further control the swelling behavior due to water. Water-permeable coatings can therefore facilitate the subsequent fabrication of microlenses through thermal post-treatment, while largely impermeable, non-permeable coatings can better preserve the imprinted state.

[0141] By appropriately positioning a coating operation in a process chain for manufacturing an optical functional element, the resulting optical functional elements can be inverted, trimmed, or stabilized, among other things, as needed. The selection of suitable coating methods and coating process parameters is also important for this. Some aspects are explained below using Figures 26A to 26C.

[0142] By inverting, originally convex surfaces can be transformed into an optically effective concave structure in the area of ​​the zones. In the example case, the optical functional elements in the form of raised microlenses or zones with a convexly curved surface are first created on an uncoated substrate SUB. The substrate is then coated with a hard coating layer HS. Due to the surface tension and flow properties of the coating material, the surface of this hard coating is initially smooth before curing; the hard coating thickness above the optical functional elements is locally thinner due to their curvature. During the curing process, the viscosity of the hard coating increases, while the optical functional elements in the example case relax slightly. With the increased viscosity, the surface tension is no longer sufficient to level or smooth the surface.After complete curing of the hard layer and partial or complete relaxation of the optical functional elements produced in the substrate, an inverted optical functional element in the form of a “dent” DL of defined depth and curvature is created on the finished product in the area of ​​the originally produced convex microlenses.

[0143] To specifically change the surface shape by a specific amount, i.e., to trim the surface shape of a zone, one can, for example, first create the optical functional elements using laser processing on a substrate that is uncoated or coated with part of the complete coating system. By appropriately selecting the process parameters (e.g., temperature, pressure, humidity) during the subsequent coating steps, the height of the optical functional elements can be reduced and / or their shape can be changed.

[0144] Since the mechanical properties of most functional coatings differ significantly from those of polymer-based substrates, subsequent coating processes can stabilize the surface structures with appropriate selection of the coating properties. It is also possible to create coating systems that are essentially impermeable to water by selecting suitable deposition methods and other parameters relevant to the coating process (e.g., ion assistance, atomic layer deposition). This can suppress moisture-induced aging processes of the substrate material and relaxation of the resulting optical functional elements. Furthermore, moisture in the substrate can be captured for structure creation in accordance with the process, or dried areas can be protected from absorbing ambient moisture.Furthermore, the creation of structures through functional coatings makes it possible to use the volume change generated by the described process to induce mechanical stress in the coating at the interface between the coating and the substrate, as well as within the substrate. This allows defects to be created in the layer system, for example, through delamination. The type and frequency of the defects can be correlated with the selected process parameters and thus used to quantify the layer adhesion of the functional coating. Thus, a layer adhesion test can also be implemented within the framework of the inventive process.

[0145] Figures 27A and 27B describe a further advantageous possible use of methods and devices of the type described here. Figure 27A shows a schematic plan view of an optical functional element FE with microlenses MLZ, which is designed as a diffuser to generate the most uniform intensity distribution possible when irradiated with coherent or partially coherent light in the far field. Figure 27B shows a schematic cross-section through the functional element with randomly distributed microlenses MLZ. The figures are taken from the technical article "From regular periodic micro-lens arrays to randomized continuous phase profiles" by M. Cumme and A. Deparnay in: Adv. Opt. Techn. 2015; 4(1): 47-61 and are intended to illustrate the potential of the invention presented in this application.

[0146] The functional element FE, designed as a microlens array, can be manufactured starting from a plane-parallel plate made of water-based polymer material. In the example case, the entire square surface, for example, is to be completely filled with randomly distributed microlenses of different shapes and refractive powers. The lateral distribution of the zones Z, which are to form the microlenses MLZ, is specified using a Voroni mosaic. For this purpose, a large number of starting positions AP are randomly distributed across the surface to be structured. The starting positions AP form the future central lens positions. For each of these starting positions, an individual Voroni cell is defined that covers the area that is closer to this specific starting position AP than to any other. This creates an asymmetrically shaped, polygonal zone Z around each starting position.The zones can have three, four, five, six, seven, or more corners, which are connected by straight side edges of the zones. Immediately adjacent zones border one another along a common side edge, creating a seamless surface fill. Each of the zones Z is then irradiated with laser radiation along trajectories TR, analogous to the previously described embodiments, until the desired surface shape for the respective zone is created by controlled laser source radiation. Fig. 27B shows a possible cross-section through the functional element after irradiation. In the example shown, the randomly distributed microlens elements MLZ have approximately the same radii of curvature but different heights.

[0147] 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 using the same source produces a regular arrangement of diffraction spots in the far field. When using a partially coherent light source, the far-field distribution of a regular microlens array can exhibit disruptive periodic inhomogeneities. When using the same partially coherent light source, a random microlens array with similar typical lens sizes as a corresponding regular array exhibits a far field with non-periodic inhomogeneities, which have a less disruptive effect on lighting applications.

[0148] For comparison, Fig. 27C shows an image of the surface of a transparent functional element with a regular, area-filling distribution of similar microlenses ML, which essentially have a hexagonal shape. Here, too, the neighboring zones adjoin one another without gaps.

[0149] An exemplary embodiment of a device LAS for producing functional elements from polymeric substrates according to preferred variants of the method described here is explained with reference to Fig. 28. The device, also referred to as a laser processing device, has a computer-aided control unit STR for controlling components communicating with it. The control software resides in a memory of the control unit. A stored database contains experimentally determined database entries for a large number of different polymer materials and parameter sets depending on the polymer, a penetrating thickness of the substrate and the absorption and / or the water content. For certain polymer materials, characteristic map data can be stored which, in a material-specific manner, represent the functional relationship between the wavelength of the laser radiation and the water content of the polymer and / or a measured variable dependent on the water content.The control unit can access the stored data and, in the manner of a look-up table, derive and set parameter sets for expected suitable laser processing conditions.

[0150] A substrate holder SH serves to accommodate a substrate SUB, on whose front surface V a microlens array with a multitude of small flat lenses is to be created. The substrate can be, for example, an ophthalmic lens made of a special polymer, such as MR-7.

[0151] The device further comprises a laser system controllable via the control unit STR, having a laser radiation source LQ for emitting laser radiation at an operating wavelength from the wavelength range between approximately 1.9 pm and 2 pm. In the example, a thulium fiber laser with an operating wavelength of approximately 1.9 pm is provided. A beam guidance system SFS serves to guide the laser beam and to create a laser focus FOC in the region of the front surface V of the substrate. The laser beam is focused; the focus diameter can, for example, be in the range below 15 pm, possibly around 10 pm. The laser beam passes successively through a shutter ST, an attenuator AB, an optics FO for beam shaping, and a scanner SC. A distance meter ABM is attached to the scanner head and measures the distance to the front surface of the substrate.

[0152] The SH substrate holder is designed and arranged in such a way that no heating reflection of the laser radiation transmitted through the workpiece can lead to an unwanted, additional, and position-dependent energy input into the substrate. The substrate holder is positioned at a distance above an underlying surface. The distance can, for example, be at least half or the entire diameter of the substrate. Additionally or alternatively, a beam trap can be integrated beneath the substrate. In this case, the substrate is only detected at three circumferentially offset locations on the outer edge.

[0153] A motion system (not shown in detail) is configured to generate a relative movement between the substrate SUB and the laser beam in such a way that the substrate can be irradiated by the laser beam at different locations within an area to be structured according to a predefined processing strategy. The substrate can remain stationary or be moved (see double arrows); the focus is shifted by the scanner SC and guided along trajectories across the surface. A camera K connected to the control unit STR is part of a camera-based pattern recognition system that operates in reflection mode.

[0154] The laser processing system enables in-process absorption measurement to determine the partial absorption of the substrate at the operating wavelength before and / or during the laser processing operation. The absorption measurement here is a measurement of the attenuation of the laser beam LS as it passes through the substrate SUB. For this purpose, a power measurement head LMK is installed below the substrate holder. A control loop is set up via the device's control unit STR, which is configured to control at least one laser parameter, in particular the laser power, depending on a measurement result from the absorption measurement system. This allows the laser power to be precisely adjusted to the absorption coefficient of the irradiated polymer material determined by measurement.

[0155] To stabilize the processing conditions, a cooling device (COL) is also installed for actively cooling the substrate during the laser processing operation. The cooling device is designed as a non-contact convection cooling unit for applying cooling gas to the substrate. This gas is blown onto the processed front side (V) via a nozzle. This ensures gentle heat dissipation and precise temperature control as part of the thermal management. In contrast to the illustration, in other embodiments, the gas stream is blown onto the substrate essentially coaxially and / or symmetrically to the laser beam.

[0156] The components of the system can be housed in a housing with a climate-controlled interior in which a stable temperature and a controlled humidity level prevail, so that stable processing conditions can be ensured over time.

Claims

Patent claims 1. A method for producing a functional element comprising a substrate consisting essentially of a polymer, which has at least one zone on at least one surface with a surface shape that differs from a surface shape in a surrounding area of ​​the zone, wherein, to produce the zone, a surface area of ​​the substrate is irradiated with laser radiation in a laser processing operation in such a way that, in a volume region of the substrate close to the surface, a volume change of the polymer is produced which is induced by interaction of the laser radiation with the polymer, which leads to a permanent change in the surface shape in the zone, characterized by: Providing a substrate consisting of a water-containing polymer which has an absorption level at an operating wavelength of the laser processing operation which is selected or adjusted taking into account a functional relationship between the wavelength of the laser radiation, a water content of the polymer and the absorption level.

2. The method according to claim 1, characterized by a controlled change in the water content of the polymer of a starting substrate to adjust the absorption level before the start of the laser processing operation, wherein the controlled change comprises at least one drying operation to reduce the water content and / or at least one loading operation to increase the water content, wherein preferably the controlled change in the water content comprises a combination of at least one drying operation and at least one loading operation carried out before or after the drying operation, wherein in particular in a drying operation the substrate is dried below the softening temperature of the polymer in an oven, preferably under vacuum or reduced pressure, and then the dried substrate is exposed to water or a humid ambient atmosphere in a loading operation for a specified duration,wherein preferably a relative weight loss or weight gain is measured., 3. Method according to one of claims 1 or 2, characterized by an experimental determination of the functional relationship between the wavelength of the laser radiation and the water content of the polymer and / or a measured variable dependent on the water content by a plurality of tests to determine a characteristic field, wherein process parameters of the laser processing operation are preferably adjusted based on data from the characteristic map.

4. Method according to one of the preceding claims, characterized by an absorption measurement for measuring a partial absorption of the polymer for at least one wavelength of the laser radiation before and / or during the laser processing operation, wherein the absorption measurement preferably comprises a measurement of an attenuation of a laser beam when passing through the base body, wherein preferably a control of processing parameters of the laser processing operation takes place depending on results of the absorption measurement.

5. Method according to one of claims 3 or 4, characterized by the creation of a database with database entries for parameter sets depending on the polymer, an irradiated thickness of the substrate and the absorption and / or the water content.

6. Method according to one of the preceding claims, characterized in that the functional element is designed as an optical functional element and a single zone or a plurality of zones is / are designed as optically effective lenses and / or prisms, wherein preferably the polymer is transparent in the visible spectral range and the laser radiation has an operating wavelength from the wavelength range between 1.1 pm and 9.2 pm.

7. Method according to one of the preceding claims, characterized in that a focused laser beam is used to generate a zone, which has a focus area in the region of the zone with a diameter which is substantially smaller than a diameter of the zone to be generated, and in that the focus area is guided over the zone along at least one trajectory according to a processing pattern in such a way that different locations in the zone are irradiated with laser radiation one after the other, wherein some or all of the locations in a zone to be irradiated with laser radiation are passed over several times, in particular twice, three times, four times or more often, wherein only a fraction of a total laser energy to be introduced is introduced during each pass, wherein preferably a single, several or all trajectories are passed over several times.

8. Method according to one of the preceding claims, characterized in that the focused laser beam is guided in a scanning direction along straight trajectories lying next to one another at a mutual distance in order to generate a zone in an area scanning operation, wherein preferably after the area scanning operation at least a further area scanning operation is carried out in a further scanning direction oriented obliquely to the scanning direction.

9. Method according to one of the preceding claims, characterized in that the focused laser beam is guided over the zone along two or more self-contained trajectories, in particular concentric circular trajectories of different diameters, to generate a zone, wherein the laser beam is preferably guided over a circular trajectory in at least one of the trajectories, preferably in all trajectories, with a predeterminable number of multiple passes, wherein preferably during irradiation along self-contained trajectories, in particular circular trajectories, starting points of trajectories of different sizes are offset from one another in the circumferential direction.

10. Method according to one of the preceding claims, characterized in that a first trajectory, in particular a first circular trajectory, is irradiated with a predetermined total number of passes and then at least one second trajectory of a different size is irradiated with a predetermined total number of passes.

11. Method according to one of claims 1 to 9, characterized in that in a first pass, each of the trajectories of different sizes is irradiated with a number of passes which is less than the total number of passes specified for the respective trajectory, and that two or more further passes are then carried out, in which some or all of the trajectories of different sizes are irradiated with a number of passes which is less than the total number of passes specified for the respective trajectory, until each of the trajectories has been irradiated with the specified total number of passes, wherein preferably in each pass each of the trajectories to be irradiated is passed over only once.

12. Method according to one of the preceding claims, characterized in that zones are produced which have a convexly curved surface shape in part of the zone or over the entire zone, wherein the surface is preferably spherically or rotationally symmetrically aspherically curved.

13. Method according to one of the preceding claims, characterized in that zones are produced which have a concavely curved surface shape in the entire zone or in a circular partial zone.

14. The method according to claim 13, characterized in that to produce a concavely curved surface shape the laser radiation is irradiated in such a way that a locally limited drying of the polymer below the softening temperature of the polymer is induced, which leads to a decrease in the specific volume of the polymer with formation of the concavely curved surface shape and / or that to produce a concavely curved surface shape in a partial zone of a zone the zone is irradiated with laser radiation in such a way that an increase in the specific volume in a radially outer annular region is greater than in a partial zone enclosed by the annular region.

15. Method according to one of the preceding claims, characterized in that in a region of the surface to be structured, a plurality of similar or dissimilar zones are generated, which are distributed over the surface according to a predeterminable pattern at different locations in the region to be structured.

16. The method according to claim 15, characterized in that the zones are generated successively according to a heat input-optimized processing strategy, wherein preferably after generating a first zone at a first location, a distant second zone is generated before a zone closest to the first zone is generated, wherein preferably for determining the processing strategy, a processing sequence of the zones is defined using temperature criteria, distance criteria and zone size criteria, wherein preferably for determining the processing strategy, a finite element simulation is carried out.

17. The method according to claim 15 or 16, characterized in that in a region of the surface to be structured, a plurality of dissimilar zones are generated, which are distributed according to a laterally random distribution at different locations of the region to be structured, preferably in an area-filling manner over the surface, wherein preferably some or all of the zones have an asymmetrical polygonal shape, in particular with three, four, five, six, seven or more corners and a corresponding number of side edges, or that in a region of the surface to be structured, a plurality of preferably similar zones are generated, which are distributed according to a regular distribution at different locations of the region to be structured, preferably in an area-filling manner over the surface, wherein preferably some or all of the zones have a symmetrical polygonal shape, in particular the shape of a triangle, a quadrilateral or a hexagon.

18. Method according to one of the preceding claims, characterized by a controlled heat treatment and / or drying treatment of the functional element after completion of the laser processing operation in order to stabilize the structures produced by the laser processing before intended use at ambient temperature.

19. Method according to one of the preceding claims, characterized in that the surface to be structured is coated with a functional coating before the laser processing operation, between selected steps of the laser processing operation and / or after completion of the laser processing operation, wherein preferably a type of coating and / or the coating process are matched to the water content and / or a water absorption capacity and / or water release capacity and / or structural relaxation capacity of the polymer in such a way that the coating contributes to the shaping and / or stabilization of the surface shape in the region of the zone.

20. Method according to one of the preceding claims, characterized in that the laser processing operation is carried out in such a way that the surface shape produced thereby does not correspond to the desired target surface shape and has a defined shape deviation from this, wherein by applying the coating a shape change is brought about in such a way that the desired target surface shape is set.

21. Method according to one of the preceding claims, characterized in that relatively small zones in the form of flat microlenses are produced which have a height H and a diameter D, wherein for a ratio V = D / H the condition 1000 > V > 500 applies, wherein preferably the condition 10 nm < H < 100 nm, in particular 15 nm < H < 50 nm and / or the condition 15 pm < D < 30 pm also applies.

22. Method according to one of the preceding claims, characterized in that, in order to produce an array with a plurality of similar or dissimilar zones, a position distribution of the zones with individually predetermined positions is predetermined for each of the zones, and the zones are successively produced in a laser processing operation with a positioning accuracy specific to the laser processing operation at the predetermined positions, wherein preferably positions of the position distribution in one or more areas of the surface deviate from nearest positions of a two-dimensional periodic position distribution by a lateral offset which is greater than the positioning accuracy and smaller than a period distance to the nearest Position of the periodic position distribution, wherein preferably one or more or all zones have a shape, a circular shape, an elliptical shape, a polygonal shape, in particular a rectangular shape or a rod-shaped shape with an aspect ratio of more than 2 between length and width.

23. A device for producing a functional element comprising a substrate made of a polymer, which has at least one zone on at least one surface with a surface shape that differs from a surface shape in an area surrounding the zone, comprising: a substrate holder (SH) for receiving a substrate (SUB); a laser system (LS) with a laser radiation source (LQ) for emitting laser radiation of an operating wavelength and a beam guidance system (SF) for guiding a focused laser beam onto a surface of the substrate; a movement system for generating a relative movement between the substrate and the laser beam (LS) such that the substrate can be irradiated by the laser beam at different locations in a region to be structured; characterized in that the device is configured to carry out a method according to one of the preceding claims.

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

25. Device according to claim 23 or 24, characterized by an absorption measuring system for measuring the absorption of the substrate (SUB) or a measurement variable dependent on the absorption at the working wavelength of the laser radiation before and / or during the laser processing operation, wherein the absorption measuring system is preferably configured for measuring an attenuation of the laser beam when passing through the substrate.

26. Device according to one of claims 23 to 25, characterized by a control circuit which is configured to control at least one laser parameter, in particular the laser power, as a function of a measurement result of the absorption measuring system.

27. Device according to one of claims 23 to 26, characterized by a cooling device (COL) for actively cooling the substrate (SUB) during the laser processing operation, wherein the cooling device preferably has a convection cooling unit for supplying the substrate with cooling gas.

28. Device according to one of claims 23 to 27, characterized by the laser radiation source (120) has an operating wavelength from the wavelength range between 1.1 pm and 9.2 pm, in particular from the wavelength range between 1.5 pm and 5.0 pm.

29. Functional element with a substrate (SUB) consisting essentially of a polymer which is transparent in the visible spectral range, in particular an optical element in the form of a spectacle lens, contact lens or intraocular lens, wherein at least one optical surface (OB) of the substrate has a region with at least one zone (Z) which has a surface shape which deviates from a surface shape in an environment of the zone (Z), characterized in that the functional element is obtainable or obtained by a method according to one of claims 1 to 21.

30. Functional element according to claim 29, wherein a microlens array with a plurality of adjacent raised zones is formed on the surface (OB), each forming a lens of the microlens array (ML), wherein preferably the functional element is designed as a multifocal ophthalmic lens for slowing the progression of myopia and has on one surface (OB) a microlens array (MLA) with a plurality of microlenses (ML) arranged in a ring around a central zone.

31. Functional element according to one of claims 29 or 30, characterized in that zones in the form of flat microlenses (ML) are formed on the surface (OB), which have a height H and a diameter D, wherein for a ratio V = D / H the condition 1000 > V > 500 applies, wherein preferably the condition 10 nm < H < 100 nm, in particular 15 nm < H < 50 nm and / or the condition 15 pm < D < 30 pm also applies.

32. Functional element according to one of claims 29 to 31, wherein the polymer is polycarbonate (PC), polymethyl methacrylate (PMMA), acrylic, or another polymer material suitable for optical, in particular ophthalmic, substrates.

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