Measurement method for determining a replication parameter, and replication method using the determined replication parameter

Abstract

The invention relates to a measurement method for determining at least one replication parameter for a replication method using at least one master element. The measurement method involves providing: a master element comprising a reflection hologram; a light source; a detector; and a diffuser. The diffuser is positioned between the master element and the detector. The measurement method also involves irradiating the master element with light by means of the light source, sensing an intensity distribution of the light exiting the diffuser by means of the detector, and determining at least one replication parameter on the basis of the sensed intensity distribution.

Description

[0001] Measurement method for determining a replication parameter and replication method using the determined replication parameter

[0002] DESCRIPTION

[0003] The invention relates to a measurement method for determining at least one replication parameter for a replication process using at least one master element. The measurement method comprises providing a master element comprising a reflection hologram, a light source, a detector, and a diffuser. The diffuser is positioned between the master element and the detector. The measurement method further comprises irradiating the master element with light using the light source, detecting an intensity distribution of the light emerging from the diffuser using the detector, and determining at least one replication parameter based on the detected intensity distribution.

[0004] Furthermore, the invention relates to a replication method for replicating a hologram from a master element into a light-sensitive material. The replication method is carried out using at least one replication parameter determined by the measurement method according to the invention.

[0005] Background and state of the art

[0006] The invention relates to the field of hologram replication.

[0007] HOEs (Holographic Optical Elements) typically refer to optical components in which holographic properties are used to achieve a specific light beam path, such as transmission, reflection, diffraction, scattering, and / or deflection, etc. This allows desired optical functionalities to be implemented compactly in any substrate. The holographic properties preferably exploit the wave nature of light, particularly coherence and interference effects. Both the intensity and phase of the light are taken into account.

[0008] Such holographic elements are used in many areas, such as in transparent displays (e.g. in shop windows, refrigerated cabinets, vehicle windows), for lighting applications such as information or warning signals in glass surfaces, light-sensitive detection systems, for example for interior monitoring (eye tracking in vehicles or presence status tracking of people indoors).

[0009] Holograms are created by the interference of a reference beam with light reflected or diffracted from the surface of an object (object rays). Traditionally, three-dimensional objects have been used to create unique, customized holograms. Commercially available HOEs, on the other hand, are often mass-produced through duplication processes. Such duplication processes typically use a master hologram containing the image to be copied. Although the reproduced image should usually correspond exactly to the image recorded in the master hologram, it may be desirable to introduce deliberate deviations from the master hologram into the replication process. Such deliberate deviations in the replicated image can be achieved, in particular, by adjusting the exposure steps of the replication process.The master holograms used are often stored in a substrate body that carries the master hologram. The substrate body is preferably transparent and can have various shapes, such as a cuboid, a plate, or a cylinder. The combination of the master hologram and the substrate body forms a master element.

[0010] The master element is exposed to a coherent light source to replicate the image from the master hologram into a photosensitive composite. For mass production, the photosensitive composite can be provided in the form of a flowing web comprising a photosensitive material and one or more carrier or protective layers. For this purpose, the photosensitive web is preferably transported through various workstations to produce the HOEs.

[0011] During exposure, the composite sheet is placed on a surface of the master element. To create a reflection hologram, the coherent light can traverse the composite sheet before reaching the master hologram and being reflected back into the composite sheet. The object and reference beams interfere with each other in the light-sensitive material, forming the replicated hologram. The replication process is sensitive to changes in exposure angle, intensity, wavelength, etc., which must be adjusted according to the optical function of the master hologram. Typically, exposure for each master hologram is performed according to a set of preprogrammed parameters. These parameters are typically configured to produce a replicated hologram with exactly the same properties as the master hologram.If a deliberate deviation from the properties of the master hologram is desired in the replicated hologram, this is usually calculated based on the theoretical properties of the master hologram.

[0012] To ensure error-free replication, it is necessary that the actual optical properties of the master hologram match the theoretical properties used to calculate the replication parameters. In practice, however, master holograms may deviate from their target properties. This can lead to a mismatch between the exposure parameters and the master hologram, resulting in reproduction errors in the photosensitive material.

[0013] During the production of the master hologram and its replication, a number of process steps occur which can alter the optical function of the originally produced master. For example, the polymerization of a photopolymer during the creation of the master hologram can be accompanied by shrinkage in local areas. Shrinkage of the light-sensitive material, e.g. due to partial drying and an increase in its density as a result of polymerization, can reduce the wavelength required to generate an interference pattern recorded therein. Further deviations in the properties of the master hologram can occur due to temperature fluctuations in the manufacturing process or during the gluing or embedding of the master hologram in a master element. Likewise, degradation of the master element can occur over time, which also alters its optical function.

[0014] Such changes in the properties of the master hologram cannot be reliably predicted by simulation. Furthermore, there is a lack of practical methods for measuring the deviation of the optical function of the master hologram from a theoretical optical function.

[0015] For example, the use of an optical goniometer to analyze the actual optical function of the master element could be considered. However, since the optical function—and its deviation from a target value—can vary spatially across the master element, a large number of measurements would have to be performed to capture the change in the entire master hologram. This laborious process would require the use of equipment that analyzes the master hologram piecemeal over a long period of time and would require a significant amount of space. Such an approach is therefore of very limited practicality. The necessary time investment becomes an even greater obstacle when one considers that the function of a master element can also change over time.The process may therefore need to be repeated at regular intervals to monitor and / or compensate for deviations in the optical function of the master element. This is particularly problematic in a continuous production process, resulting in production interruptions and a reduction in throughput.

[0016] There is therefore a need for a method for analyzing the optical function of a master element, particularly for detecting deviations from a target function, which can be performed quickly and is suitable for use in a continuous production system. Furthermore, there is a need for a replication method in which any errors in a master element can be reliably accounted for or compensated for. Object of the invention

[0017] The object of the invention is to provide a measurement method that enables the optical properties of a master element to be recorded quickly and reliably using simple means and, in particular, can detect any deviations in the optical function of the master element from a target function. Furthermore, it was an object of the invention to be able to use such a measurement method to define replication parameters that increase the efficiency of a replication process using the master element. Particularly preferably, the possibility should also be created to compensate for any deviations in the optical function of a master element from a target function during the replication process.

[0018] The object is achieved by the features of the independent claims. Advantageous embodiments of the invention are described in the dependent claims.

[0019] In a first aspect, the invention relates to a measurement method for determining at least one replication parameter for a replication process, wherein the replication process is carried out using a master element. The measurement method comprises the following steps:

[0020] Providing a master element comprising a reflection hologram, a light source, a detector and a diffuser, wherein the diffuser is positioned between the master element and the detector,

[0021] Irradiation of the master element with light using the light source,

[0022] Detection of an intensity distribution of the light emerging from the diffuser by means of the detector and

[0023] Determination of at least one replication parameter based on the recorded intensity distribution.

[0024] Preferably, the master hologram is placed in or on a substrate body to form a master element. Integrating a master hologram into a master element ensures high robustness. Since the master hologram is very thin and delicate, integrating it into a larger component can facilitate handling and eliminate the need to touch the master hologram itself, which can lead to damage. However, the process steps for producing the master hologram and integrating it into a master element can influence the desired optical function.

[0025] Firstly, the process of producing the master hologram can lead to physical changes in the light-sensitive material in which it is written. For example, polymerization during the mastering process can cause undesirable shrinkage of the light-sensitive material, thereby unintentionally altering its optical properties. Furthermore, uncontrolled light scattering can lead to additional exposed structures in the light-sensitive material and reduce the efficiency of the desired interference pattern. Perfect control of the production conditions for a master hologram is usually impossible or only possible with great effort. Therefore, the production of the master hologram is usually carried out within certain manufacturing tolerances.To counteract the effects of unwanted shrinkage or unwanted interference patterns, it is advantageous to localize them and / or quantify their effect.

[0026] Furthermore, the process of integrating the master hologram into the substrate body to form the master element is prone to errors. An uneven distribution of an adhesive between the master hologram and the substrate body, or an uneven surface structure between the master hologram and the substrate body, can lead to unevenly distributed optical losses across the master element. Due to the unpredictable nature of such losses and their variable spatial distribution, they are not readily quantifiable, simulated, or estimated. For reasons of economic feasibility, the process of integrating the master hologram into a master element is also carried out within specified manufacturing tolerances.

[0027] The present invention enables the definition of replication parameters that are suitable for the actual properties of the master element, which preferably lie within the aforementioned manufacturing tolerances. A replication process can thus be designed more robustly with respect to the aforementioned tolerances.

[0028] Furthermore, the replication of the master hologram into a light-sensitive material is best achieved by directing the exposure light beam (or exposure spot) along a predetermined path that is tailored to the optical function of the master hologram. Thus, the efficiency of the master element for a replication process can depend on various parameters, such as the angle of incidence or the wavelength.

[0029] In an ideal master element with a reflective master hologram irradiated from an optimal exposure point or exposure path, an exposure beam is preferably almost completely diffracted to the first order. The exposure light beam (reference beam) can interfere with the reflected light beam (object beam) in an intermediate light-sensitive material to copy the hologram. The portion of the exposure beam diffracted to the first order thus corresponds to a desired useful wave, which can be used to replicate a hologram. The portion of the exposure beam that is not reflected or diffracted passes through the master hologram and the carrier substrate. In the case of an ideal master element, the portion of the transmitted 0th order diffraction would be zero, and the entire portion of the exposure beam would be reflected.In an ideal master element, no light at all should be transmitted through the master element to an opposite side.

[0030] However, if the master hologram has deformed during integration into a master element, e.g.

[0031] For example, due to the weight of the substrate body, an uneven adhesive layer, or delamination effects, the theoretical exposure point optimized for the ideal master element may not allow for high efficiency across all areas of the master hologram. For example, shrinkage, uneven adhesive layers, or delamination effects may require certain areas of the master hologram to be irradiated at different exposure points or angles to generate a sufficient effective wave.

[0032] The inventors are credited with recognizing that the replication efficiency of the master hologram can be quantified and / or mapped by detecting light emerging through a side of the master element facing the detector. For this purpose, a diffuser is provided between the master element and the detector.

[0033] The master element preferably comprises a side facing the detector. This can be referred to here as "the first side of the master element" or "the side of the master element facing the detector." This is preferably a side of the master element that is not exposed, but through which portions of the exposure light beam (in particular of a zero-order diffraction) can exit.

[0034] A side of the master element onto which a reference beam impinges to expose the master hologram is preferably referred to herein as "the second side of the master element" or "the side of the master element facing away from the detector." This side is preferably substantially parallel and opposite the first side of the master element. For example, an upper side of the master element is the first side and a lower side of the master element is the second side (or vice versa).

[0035] A "diffuser" (or "diffusing plate") within the meaning of the invention is preferably a transparent plate or film configured to scatter and / or expand a light beam as it passes through the plate or film. The scattering is preferably achieved by means of a roughened surface of the diffuser, pigments in the diffuser, a crystal structure of the diffuser, and / or due to opalescent properties of the diffuser. Preferably, the diffuser functions approximately like a Lambertian diffuser. In preferred forms, the diffuser can also be a surface-structured diffuser that has been produced holographically. Preferably, the selected diffuser is not a volume holographic diffuser to avoid angular selectivity.

[0036] In preferred embodiments, the diffuser can be applied directly to a first side of the master element, so that it is in direct contact with the latter. However, direct contact is not required. The contact can be mediated by a further layer such as an optical fluid or an optical coupling element. Likewise, there can also be no contact between the diffuser and the master element, so that the diffuser is located at a distance on the first side of the master element. In some preferred embodiments of the invention, a holding device for positioning the diffuser can be provided between the master element and the detector, wherein the holding device defines, for example, a distance between a first (upper) side of the master element and a lower side of the diffuser.In the various embodiments, however, the diffuser is preferably always located between the master element and the detector, wherein the diffuser, in particular in the embodiment of a scattering plate, is preferably aligned parallel to the master element.

[0037] By positioning a diffuser between the detector and the master element, the detectability of the emerging light can be increased, making the measurement method more reliable. In particular, the diffuser preferably ensures that the emerging light reaches the detector regardless of the exit angle. Since the surface roughness of the diffuser causes scattered light from surfaces facing in different directions to pass through, the emerging light can preferably be detected from virtually any angle within a hemisphere. This is particularly useful when the detector is held stationary but the measurement method is applied to different master elements or different exposure paths with different illumination angles. This eliminates the need for overly precise positioning of the detector.

[0038] By detecting the light transmitted through the diffuser with a detector, the intensity (and optionally the wavelength) of the transmitted light can be quantified. The measurement method therefore does not have to rely on subjective assessment of the master element, and the effort required for trial and error to compensate for deviations from a desired optical function or changes in the efficiency of the master element can be reduced and / or eliminated. Furthermore, there is no need to subjectively decide whether a master element is so damaged that it needs to be replaced. These decisions can instead be made objectively based on repeatable quantitative measurements.

[0039] By recording the intensity distribution of the light transmitted through the diffuser, the regions affected by a deviation in the optical function of the master element or a reduction in efficiency can be objectively identified. The measured deviation or reduced efficiency of the master hologram with respect to replication can thus be used to mathematically adjust a replication parameter. For example, the exposure intensity can be increased in those regions exhibiting a high intensity of transmitted light.

[0040] The increase in intensity during replication can preferably be adjusted in such a way that the optical loss is precisely compensated. This can be done quickly and automatically by a processor, eliminating the need for repeated adjustments or subjective evaluation of the result. In particular, by recording the light intensity emerging from the first side of the master element as a two-dimensional spatial distribution, the adjustment of the exposure light intensity can also be performed in a spatially dependent manner. For example, the intensity values ​​of different spatially distributed points on an exposure curve can be adjusted independently of one another.

[0041] By quantifying the inefficiency of the master element by measuring the intensity of the emerging light, it is also possible to objectively assess whether an exposure point is suboptimal and needs to be adjusted. Adjusting the exposure point preferably means changing the position of the exposure point from which the reference beam is directed onto the master element. The entire master element can be exposed over a large area from a single exposure point. In this case, the measurement method can preferably facilitate the selection of the optimal position of the exposure point. Likewise, the master element can also be exposed from multiple exposure points, in particular from a series of spatially distributed exposure points on an exposure curve. Each of these spatially distributed exposure points can be assigned one area from several spatially distributed areas of the master element.In such a case, the recording of the light intensity as a spatially resolved distribution can enable statements to be made about the efficiency of the respective areas of the master element and can ensure an adjustment of the exposure points depending on their assignment to the areas of the master element.

[0042] By evaluating the inefficiency of the master element based on the intensity of the emerging light, it is also possible to determine whether the exposure angle is suboptimal and needs to be adjusted. This may mean changing the angle at which the reference beam hits the master element through a mathematical adjustment for the entire master element. However, since not just a single intensity value but an intensity distribution is recorded, the exposure angle can also be adjusted for individual areas of the master element.

[0043] It is also advantageously possible to perform the measurement process for different exposure paths in order to identify an optimal exposure path (also referred to as an "exposure curve" in the sense of the invention) for which the efficiency of the master hologram is maximized. A subsequent replication process can be carried out with a correspondingly optimized exposure path, with any efficiency losses optionally being precisely compensated for by appropriate intensity regulation.

[0044] The measurement method can therefore enable a replication process that is precisely tailored to the actual (and not just theoretical) properties of a master element. The resulting holograms are of higher quality and can be produced with high reproducibility.

[0045] By placing a diffuser between the master element and a detector that captures the light emerging from the diffuser, the device for the measurement process can be designed very compactly. A diffuser, which may comprise a plate or foil, for example, takes up very little space in an exposure chamber. The diffuser can be easily inserted and removed using rollers, vacuum robots, manually, or by other means. Since the holograms replicated based on the results from the measurement process are reflection holograms, the diffuser has no influence on the placement of the photosensitive material on the master element. This is because the photosensitive material is placed on the opposite (second) side of the master element.Rollers for laminating or applying light-sensitive material to the master element can remain in their positions, as can devices for applying optical fluids, coupling elements, and the like. Furthermore, a detector directed toward the diffuser does not need to interfere with the exposure devices such as light sources, lenses, mirrors, etc., since these can also be directed toward the opposite side of the master element to replicate a reflection hologram.

[0046] The device required for the measurement process can thus be easily integrated into a device for continuous and / or automated replication of a reflection hologram. The measurement process can be easily performed at intervals or between runs of the replication process without having to dismantle or rearrange the replication devices. This allows wear or degradation of a master element to be monitored and / or replication parameters to be continuously adjusted to compensate for changes in the master element.

[0047] A "replication parameter" within the meaning of the invention is preferably a physical parameter that can be variably adjusted between runs or between individual repetitions of a hologram replication process. The replication parameter is preferably a physical parameter that relates to the exposure step of the replication process. In particular, the replication parameter is a physical property or a physical parameter that relates to the exposure light beam (which acts as a reference beam). It can be advantageous for a replication parameter to relate to the exposure of the entire master element. This is particularly the case for replication processes in which the master element is exposed over a large area from a single exposure point. It can also be advantageous for the replication parameter to be specific to a spatial region of the master element.This is particularly relevant for replication processes in which the master element is preferably exposed gradually by moving a light spot on the master element during a scanning process. In such a case, for example, a replication parameter can be adjusted with respect to the intensity of the exposure for different light spots on the master element.

[0048] The term “light point” preferably refers to a point on the master element at which the light beam strikes the surface of the master element, while the exposure point is preferably located outside the master element and refers to a point from which a light beam for exposing the master element strikes a surface of the master element without significant deflection.

[0049] The replication parameter can also be specific to a temporal portion of the exposure step.

[0050] The replication parameter can be, for example, a light intensity, a wavelength, a range or selection of wavelengths, a coherence, a movement speed of the exposure point, a dwell time of the light point, an angle of the incident exposure light beam, an absolute, relative, and / or angular position of the light source, an absolute, relative, and / or angular position of a light-directing component such as a mirror, prism, lens, or optical fiber. In preferred forms, the replication parameter can also relate to a sequence of exposure points, which is to be used in the form of an exposure curve for exposing the master element.Likewise, a combination of the aforementioned replication parameters is of course conceivable and preferred, in which, for example, replication parameters are defined for several anchor points of an exposure curve, with different intensity values ​​being defined for each anchor point for the exposure of different areas of the master element.

[0051] A "determination of a replication parameter" within the meaning of the invention preferably comprises an estimation, calculation, selection, or determination of a replication parameter at which a higher efficiency of the master hologram results or is expected. The determination of the replication parameter preferably involves the determination of an optimal radiation dose (in particular radiation intensity and / or residence time) which achieves the best possible exposure of a master hologram or a region thereof into a light-sensitive material. The estimation, calculation, selection, or determination can preferably be carried out by a data processing unit. The results of the estimation, calculation, selection, or determination can preferably be stored in a memory unit. The stored, determined replication parameters can preferably be used for a further process step.The storage unit can preferably be accessed by a control unit for controlling a replication process in order to read out the specified replication parameter and / or to send a signal to an actuator in order to expose the master element with the specified replication parameter.

[0052] A "detector" in the sense of the invention is preferably one or more devices for measuring and / or recording data. The detector is preferably configured to convert an analog and / or non-electrical input signal into an electrical and / or digital output signal. In addition to the light intensity, the detector can represent other physical quantities (e.g. wavelength) as an electrical voltage, pulse and / or current. The output signals preferably comprise information about an absolute or relative spatial distribution of the physical quantities. The detector can comprise, for example, a camera, a scanner or an array of photodiodes. The detector preferably forwards the output signals to a processor, memory and / or a communications unit.

[0053] A “light source” within the meaning of the invention is preferably a device that is configured to emit electromagnetic radiation with a wavelength between 200 nm and 25 pm, in particular between 400 and 780 nm. The electromagnetic radiation can preferably comprise infrared, visible and / or ultraviolet radiation, with visible radiation being particularly preferred. In the context of the invention, UV radiation preferably means electromagnetic radiation in the range from 200 pm to 400 pm, particularly preferably 300 pm to 400 pm. Visible radiation means in particular electromagnetic radiation in the range from 400 to 780 nm and infrared radiation from 780 nm to 25 pm, preferably in the near infrared range, ie preferably from 780 nm to 3000 nm, in particular from 780 nm to 1400 nm.

[0054] The light source may include or be associated with light-directing devices such as lenses. The light source may preferably emit a collimated beam, in particular with a specific width and direction. It may also be preferred that a beam emitted by the light source specifically exhibits a desired divergence at an exposure point. The light source is also preferably configured to emit coherent light. The light source may, for example, be a laser.

[0055] For the purposes of the invention, an "exposure point" is preferably a point from which a light beam for exposing the master hologram strikes a surface of the master element without significant deflection. The exposure point can be the light source itself or be located on an element that directs the light from the light source, such as a mirror. For example, the exposure point could correspond to a focal point along the beam path, i.e., the light can have a smaller beam cross-section at the focal point than downstream or upstream along the beam path. Alternatively or additionally, the exposure point could be coincident with the arrangement of a lens or a mirror that implements a final beam deflection before the light strikes the master element. Changing the exposure point preferably comprises changing the position of this exposure point.

[0056] A "master element" is preferably a three-dimensional unit comprising at least one master hologram in a shape that ensures that a movement of the master element directly leads to a corresponding movement of the master hologram. A master element can also comprise a plurality of master holograms, for example, 2, 3, 5, or more. The master element preferably has a length and a width that at least correspond to the length and width of the master hologram. The master element is preferably at least twice, preferably five times, and particularly preferably at least twenty times as high as the master hologram.

[0057] The master element preferably comprises a substrate body that either encloses or supports the at least one master hologram. In embodiments, the master element may, for example, comprise a transparent top cover for protecting a master hologram located between the cover and the substrate body. Preferably, the top cover is also transparent. The top cover may, for example, be a transparent film or a glass layer.

[0058] The master element can preferably have the shape of a cuboid block, a plate, a pyramid, or a prism. The substrate body can be shaped accordingly.

[0059] Preferably, the substrate body of the master elements can be formed from a material which is an optical plastic, preferably selected from the group: polymethyl methacrylate (PMMA), polycarbonate (PC), cycloolefin polymers (COP) and cycloolefin copolymers (COC) and / or an optical glass, preferably selected from the group: borosilicate glass, quartz glass, B270, N-BK7, N-SF2, P-SF68, P-SK57Q1, P-SK58A and P-BK7.

[0060] Preferably, both the substrate body and any cover of the master element have a refractive index between 1.4 and 1.6.

[0061] The choice of material for the substrate body may depend on the desired exposure angle or refractive index. It may also be preferable for a substrate body to be colored, for example, to filter light wavelength-selectively to create a hologram with a specific wavelength. In this way, a broadband light source can be used to expose various master holograms.

[0062] It is preferred that the surface or cover of the master element comprises glass, PC, TAC, or PMMA. The surface material can be in the form of a film or plate to protect the master hologram. However, the surface or cover material can also be the material of the substrate body itself and, for example, have a cuboid or cylindrical shape.

[0063] A "substrate body" within the meaning of the invention is preferably a three-dimensional block of material that carries or encloses the master hologram. The substrate body is preferably transparent. In some embodiments, the substrate body has multiple surfaces, including a flat surface that may be horizontally oriented. In some embodiments, the substrate body is prismatic, ie, it has a constant cross-section of any shape, e.g., square or polygonal.

[0064] For the purposes of the invention, the term "transparent" or "transparency" preferably refers to a property of a material whereby it is substantially permeable to light. A transparent material within the meaning of the invention is preferably transmissive for at least part of the electromagnetic spectrum, preferably with a wavelength between 200 nm and 25 pm, particularly preferably between 400 nm and 780 nm. A transparent material, for example a transparent substrate body, is particularly preferably permeable to light of a wavelength range with which exposure of the master hologram takes place. A transparent material can also be colored in such a way that it selects the light radiation of one or more specific wavelengths.

[0065] A "master hologram" within the meaning of the invention is preferably a holographic-optical element comprising at least one hologram to be replicated. The master hologram is designed for an optical function (e.g., diffraction, reflection, transmission, and / or refraction) for one or a plurality of wavelengths. The master hologram can, for example, be a diffractive optical element (DOE). Diffractive optical elements (DOEs) utilize a surface relief profile with a microstructure for their optical function. Alternatively, the microstructure can also be present in the volume of the element, e.g., in the form of a local difference in the refractive index. Such a master hologram is considered a so-called "volume hologram." The light transmitted by a DOE can be converted into almost any desired distribution through diffraction and subsequent propagation. This can be an image, a logo, text, an interference pattern, or the like.

[0066] The process for producing the master hologram can preferably be referred to as "hologram origination" or "hologram mastering." The master hologram can be created using an analog or digital process. In an exemplary analog process, a first coherent beam, the object beam, is reflected from an object and onto a recording material, which is simultaneously exposed to a second coherent beam, the reference beam. The object beam and the reference beam interfere, creating an interference pattern on or in the recording material. This interference pattern is recorded by light-sensitive material, so that after processing, the shape of a surface relief pattern on a surface of the material or a spatially varying refractive index is created in the material, which is usually only a few micrometers thick.To view an image of the original object, the master hologram can be illuminated with light diffracted by the recorded surface relief pattern or refractive index pattern. This diffracted beam contains the image of the original object. The master hologram can then be used as a new object when creating further copies with the same image.

[0067] The master hologram can preferably also be computer-generated. The microscopic gratings that produce the diffraction effects can be produced, for example, by laser interference lithography. In this technique, two or more coherent light beams are configured to interfere at the surface of a recording material. The positions of the light beams relative to the recording material can be controlled by a computer. Depending on the strength of the laser, the recording material can be made of almost any material. Other techniques such as electron beam lithography can also be used to digitally produce the master hologram. The master hologram can preferably comprise glass, silicon, quartz, UV varnish, a photopolymer composite, and / or a metal such as nickel.

[0068] In a preferred embodiment of the invention, higher values ​​of the intensity distribution indicate a lower efficiency of the master element in a replication process. Preferably, the light scattered by the diffuser corresponds to a zeroth (0th) diffraction order of an exposure beam, which is transmitted through the master hologram and cannot be used for replication. The higher the proportion of the (unwanted) 0th diffraction order, the lower the proportion of the 1st diffraction order used as the object beam for replication. Higher values ​​of the intensity distribution at the detector thus indicate a higher proportion of 0th diffraction order and thus a lower efficiency of the master element.

[0069] In other words, the light detected at the detector preferably corresponds to the light transmitted by the interference pattern of the master hologram without being diffracted by the interference pattern of the master hologram. Since the angle and position of the exposure beam are chosen such that it is directed into a first-order diffraction by the theoretical interference pattern in the master hologram, in an ideal master hologram all incident light should be reflected, thus forming an object beam. This is especially true for an ideal master hologram, which is designed to completely reflect all incident light. In an ideal case for such a master hologram, the proportion of a zero-order diffraction would be zero, and the detector would not detect any light emerging from the diffuser.However, if light leakage from the diffuser is detected, this indicates that the efficiency of the master element is reduced at the point where the light leaves the master element. However, reflection master holograms can also be configured, due to practical limitations or with regard to specific applications, to reflect only a portion of the incident light even in the best possible case. In this case, the portion of a 0th diffraction order is not zero, even in the best possible case, but corresponds to a known theoretical target intensity other than 0. If the detected intensity exceeds such a target intensity, this also preferably indicates a reduced efficiency of the master hologram at the point where the target intensity of the transmitted 0th diffraction order is exceeded.

[0070] The greater the detected light intensity, the lower the local efficiency of the master element. For example, the master element may have shrunk at this point, reducing the thickness of the master hologram. This can reduce the reflection efficiency. It is preferably the extent and distribution of this reduction in reflection efficiency that is indirectly detected by the intensity distribution. For the purposes of the invention, an "efficiency" of a point or region of a master hologram (the local efficiency) is preferably the ability of the master hologram at this point or region to perform a desired light-directing function without losses. The local efficiency of the master hologram can, for example, be a measure of the intensity of the real object beam (or the wanted wave) compared to the intensity of an ideal object beam (or the wanted wave).In the case of an ideal master hologram, which is designed for the complete reflection of the reference beam, the intensity of the ideal object beam preferably corresponds to the intensity of the reference beam, taking into account the Beer-Lambert law. Likewise, as explained above, even in the best possible case, the reflection hologram can be designed to reflect only a portion of the incident light. In this case, the intensity of an ideal object beam corresponds only to a portion of the intensity of the reference beam. A target intensity of a theoretical first-order diffracted beam can thus correspond to an intensity of the reference beam taking into account the Beer-Lambert law, or only to a portion (factor less than 1). The local efficiency of the master hologram can preferably be calculated by multiplying the intensity of the first-order diffracted beam byThe intensity of the first-order diffracted beam is divided by the desired intensity of a theoretical first-order diffracted beam. The intensity of the actual first-order diffracted beam can be calculated by subtracting the intensity of the detected zero-order beam exiting the diffuser from the intensity of the reference beam.

[0071] These calculations can take into account the distances traveled by the beams using the Beer-Lambert law. The local efficiency can be expressed, for example, as a percentage. This efficiency can vary spatially across the master hologram and can also depend on the physical properties of the reference beam. In particular, the efficiency of the master hologram can depend on the value of a replication parameter.

[0072] For the purposes of the invention, the "efficiency" of the entire master hologram is preferably an assessment of its ability to produce a replicated hologram with the desired quality. The efficiency of the master hologram as a whole can be a function of the local efficiencies across the entire master hologram. However, it can also depend on the intensity distribution and / or the spatial distribution of the local efficiencies. For example, the position and surface area of ​​inefficient regions can play a role in determining the efficiency of the master hologram. Such a determination can be performed by a program on a data processing unit, for example, an image processing algorithm, as known from the field of quality control.

[0073] The relationship between the detected light intensity and the efficiency of the master element can be used to select the optimal replication parameter, for example, a light intensity of the exposure. A computer program can be used to calculate optimized exposure parameters from the efficiency values ​​of the master element. Preferably, the calculation is performed by a data processing unit. Such a data processing unit can be part of a control unit for controlling a replication process.

[0074] The replication parameter is preferably determined with a view to maximizing the efficiency of the master element in a replication process or with a view to reducing the deviation of the efficiency from a target value. In this way, the result of the measurement process can be used to optimize replication and ensure high quality of the replicated holograms. Furthermore, by adjusting the replication parameters to optimize efficiency, master elements can be used for significantly longer periods without significant quality losses, despite any deterioration. This increases the cost-effectiveness of the process.

[0075] In a further preferred embodiment of the invention, the master element is irradiated with light using at least two different exposure parameters. Preferably, the intensity distribution of the light emerging from the diffuser is recorded for each of the at least two exposure parameters. By performing the measurement method for at least two different replication parameters, the effect of varying the replication parameter on the efficiency of the master element can be investigated. This allows the direction (e.g., increase, decrease) of a replication parameter to be determined to improve replication efficiency.

[0076] Preferably, the at least one replication parameter is determined based on at least two intensity distributions recorded for the at least two different exposure parameters. The multiple recording of intensity distributions for different exposure parameters can, for example, support the conclusion that shifting the exposure light beam in a specific direction, adjusting the angle of the exposure light beam in a specific direction, or increasing / decreasing the wavelength of the exposure light beam increases the efficiency of the master element in a subsequent replication process. This information can be used to adjust a replication parameter accordingly (for example, in the direction identified as more favorable) to achieve optimal replication.

[0077] By recording multiple intensity distributions, it may also be possible to compare them to determine an intensity distribution (or its underlying exposure parameters) that indicates the highest efficiency of the master element in the replication process. This could, for example, be an intensity distribution that has the largest total dark area, an intensity distribution with the lowest total illuminance, or the intensity distribution where bright areas (i.e., areas with lower efficiency) correspond to regions of the master hologram that are considered to be the least critical (e.g., decorative regions in a hologram that includes text and decorative elements).Based on this, the replication parameter or combination of replication parameters that achieves the most efficient intensity distribution can be identified as being more favorable for replication. These replication parameters can be selected for use in a replication process or used for interpolation or extrapolation to a more favorable replication parameter. The quality of the replicated holograms can be further improved, and the service life of the master element can be extended without any loss of quality.

[0078] The proposed measurement method advantageously provides a significantly faster and more reliable technique for improving replication efficiency and compensating for defects in the master element than state-of-the-art methods. In particular, it is more reliable to measure the influence of several possible exposure parameters on replication efficiency in this way than to rely on simulating the optical function of the master element. The measurement method also eliminates the time-consuming analysis of numerous points on the master elements with a goniometer.

[0079] In a further preferred embodiment of the invention, the at least one replication parameter corresponds to an exposure intensity, a wavelength, an exposure point, an angle of the beam path of the light in the exposure point and / or an exposure curve of the exposure point.

[0080] Based on the proposed measurement method, one, several or all of the aforementioned parameters can preferably be optimized for replication of the master element.

[0081] For example, by specifying an exposure intensity as a replication parameter, any optical losses or efficiency reductions of the master hologram can be easily and precisely compensated for during the replication process. For example, the exposure intensity can be locally increased or decreased depending on the local efficiency of the master element. If the measurement method has identified reduced efficiency for certain areas on the master element, this can be compensated for by a preferably proportional increase in the exposure intensity during replication for those areas. This advantageously compensates for deviations from an ideal master hologram, and an error-reduced, homogeneous replication of the master hologram is achieved.

[0082] Furthermore, the measurement method can advantageously specify a wavelength as a replication parameter for a subsequent replication process. It is known, for example, that shrinkage of master holograms can lead to a reduction in the wavelength of the interference pattern written within them, which is efficiently reflected by the master hologram. In such a case, a reference beam with a theoretical target wavelength can only be diffracted with reduced efficiency. The proportion of transmitted radiation that cannot be used for the replication process is increased. In the measurement process, this is detected by an increased intensity at the detector, which detects the light scattered by the diffuser.

[0083] If the measurement method is performed, for example, using different wavelengths as exposure parameters, an optimal wavelength can be defined (selected or interpolated) as the replication parameter for subsequent replication. As explained above, the definition of an optimal replication parameter can be achieved, for example, by minimizing the intensity detected at the detector with respect to the wavelength. In preferred embodiments, an optimized wavelength can be defined for the entire area of ​​the master hologram, or different wavelengths can be defined for different areas.

[0084] If the replication parameter identified by the measurement method is a wavelength of the exposure light, the wavelength of the reference beam can be brought closer to the wavelength for which the interference pattern in the master hologram is optimally designed. Additionally or alternatively, the master hologram can be exposed several times at the target wavelength or at one or more improved wavelengths to increase the efficiency of replication. The result is replicated holograms of significantly higher quality.

[0085] The measurement method can identify a multidimensional parameter space within which an ideal parameter combination can be selected as a compromise. Such a parameter space could, for example, concern correlations between wavelength, angle, and efficiency.

[0086] Furthermore, it is known that the efficiency of reflective master holograms in particular can depend on the angle of incidence of a replication beam. Advantageously, the proposed measurement method can also be used to determine an angle of the light beam path at the exposure point for replication. The angle of the light beam path at the exposure point preferably determines the angle at which the master hologram is illuminated during replication. Depending on the design of a master hologram, there may also be different angles for different areas that exhibit increased efficiency. With knowledge of the optical function of the master hologram, it would be fundamentally possible to simulate an angular distribution for the replication of a master hologram with optimized efficiency. However, this is complex and, on the other hand, any manufacturing tolerances are difficult to capture.

[0087] Advantageously, the measuring method according to the invention allows for the rapid creation of an efficiency-angle map using simple means, which map records the efficiency of the master element as a function of different angles of incidence. This particularly advantageously allows for the angle of the light beam path for exposure during replication to be adjusted such that the reference beam hits the master hologram at the required angle in all areas during replication. Even any deformations of the master hologram can be reliably recorded using the measuring method and taken into account for subsequent replication. For example, shrinkage or swelling of the master hologram can lead to locally different requirements for an exposure angle. In the measuring method, the reduced efficiency as a function of the irradiation angle is recorded as an increase in intensity at the detector.The angle for replication can therefore be optimized, for example, with a view to minimizing the intensity of the scattered light detected at the detector.

[0088] The efficiency of the replication process can also be improved by determining a more efficient exposure point based on the measurement method.

[0089] In a further preferred embodiment of the invention, the at least one exposure parameter is an exposure point. Preferably, an intensity distribution of the light emerging from the diffuser is recorded for at least two different exposure points.

[0090] By recording at least two intensity distributions at at least two exposure points, the measurement method can experimentally determine which of the at least two exposure points delivers the better results. In particular, it can be determined which of the tested exposure points results in a lower illuminance of the diffuser. On this basis, a preferred exposure point can be selected for a replication process. The exposure point can be the position of a point for a large-area or a region-specific exposure of a master element. Another exposure point can also be selected based on the measured intensity distributions, for example, by interpolation between two tested exposure points.

[0091] In a further preferred embodiment of the invention, the detection of an intensity distribution of the light emerging from the diffuser is repeated for at least three exposure points. Preferably, the third and further exposure points are selected using a converging function, in particular using an iterative process based on the previously detected intensity distributions, in order to preferentially converge on an exposure point at which maximum efficiency of the master element for a replication process is expected. Alternatively or additionally, the third and / or further exposure points can be selected using a recursive process.

[0092] By capturing the intensity distribution for at least three exposure points, the replication parameter can be selected based on a larger number of experimental results, thus approximating an exposure point with the highest possible efficiency for a specific master element. It may be preferable to capture at least four, at least five, at least ten, at least twenty, or more intensity distributions for a corresponding number of exposure points. The accuracy with which the replication parameters are determined can thereby be further increased.

[0093] By selecting exposure points using a converging function, the metering method can be optimized so that the measurements taken are limited to the exposure point positions likely to produce the best results. An optimal exposure point can be selected more quickly and reliably than with a metering method in which all tested exposure points are determined in advance or are not selected using a converging function.

[0094] For the purposes of the invention, a "converging function" for selecting a parameter value is preferably a mathematical or algorithmic process based on refining an estimated value until it is sufficiently accurate within defined limits or converges to an optimum. The converging function can be based, for example, on an iterative or recursive algorithm.

[0095] Similarly, a converging function can be used to optimize a replication parameter other than an exposure point, such as a wavelength or radiation intensity. Preferably, the converging function is used analogously to determine the value of the replication parameter at which maximum efficiency of the master element is expected for a replication process.

[0096] A first and / or a second replication parameter value can be selected, for example, in light of the target replication parameters. The first and second replication parameters can also be selected randomly, based on maximum / minimum values ​​from the manufacturing tolerances, or according to another formula. An efficiency trend can be derived from the intensity distributions acquired for the first and second replication parameters and used to select a third replication parameter. The selection of further replication parameters and the acquisition of corresponding intensity distributions can be repeated until a certain number of parameter values ​​have been tested, until the difference between the efficiencies of consecutive tested parameter values ​​is smaller than a predetermined value, or until no further increase in efficiency is detected. Preferably, the replication parameter is an exposure point.It may also be preferred that the replication parameter is a wavelength, an angle, a distance or an intensity.

[0097] A master hologram can be configured so that different locations are to be exposed with different replication parameters. For example, it may be necessary for some areas of the master hologram to be exposed with a higher or lower intensity, a predetermined angle of the reference beam, or a predetermined wavelength. This can be achieved by scanning the master element with an exposure beam. During scanning, a light spot is preferably moved along straight lines. To achieve regional variations in the replication parameters, the exposure point can also be moved, preferably along a non-linear path, e.g., a curve. Variations in intensity can be achieved by adjusting the intensity of the light source.Angle variations can be achieved by tilting a light source or an intermediate optical component to create a reference beam with the desired angle. A wavelength can be adjusted, for example, by switching on one or more lasers or by applying filters. The path of the exposure point and the variable parameters can be provided as instructions in a memory.

[0098] In a preferred embodiment of the invention, the master element is designed for exposure via an exposure curve. The exposure curve preferably defines the path of the exposure point for replication of the master element. Other replication parameters besides the position can vary at different points or sections of the exposure curve. Preferably, the exposure angle varies across the exposure curve.

[0099] When exposing a master element with an exposure curve, the master element is preferably exposed in sections. The master element can, for example, be divided into columns, with each column assigned a section of the exposure curve—in particular, an anchor point. Likewise, the master element can be divided into a grid, with each cell of the grid assigned a section of the exposure curve—in particular, an anchor point. Other configurations, such as freeform curves, can also be advantageous.

[0100] By using an exposure curve, a variable angle of incidence of the reference beam onto the master element can preferably be enabled during exposure. In particular, the angle of incidence of the light can be varied as a function of the location of a corresponding light spot on the master element. This can be achieved by a suitable curvature of the exposure curve. This can compensate for a curvature of the master element during the measurement or replication process, which is predetermined due to its manufacturing process and deviates from the desired surface shape of a replicated hologram. In other words, a curvature of the substrate or the cover of the master hologram during the exposure process can be compensated for by a curved exposure curve (where this curvature can, for example,with respect to a reference coordinate system defined by the shape of the substrate).

[0101] Such an exposure curve is particularly advantageous when the replicated hologram itself is curved or is to be integrated into a curved surface. One example is a hologram with an optical function configured to converge light rays to a specific point. Another example is a hologram that is to be integrated into a curved transparent screen, a windshield, or other non-planar surface.

[0102] It may be advantageous for the exposure curve to comprise multiple anchor points. The measurement method may be used to set a replication parameter at one or more anchor points. The exposure curve and / or the program for calculating it may be configured to consider a two- or three-dimensional space around the anchor point, within which its position may be set. The two- or three-dimensional space may preferably be a square or a cuboid and may be referred to herein as the exposure volume. The measurement method may preferably be used to determine the optimal position (or "exposure point") of an anchor point within the exposure volume. In this way, the exposure curve can be adjusted without having to recalculate a completely new curve.

[0103] An "exposure curve" in the sense of the invention is preferably a path along which an exposure point is moved in order to expose a master element. Although the path can be linear, it is preferably curved in at least one plane. The exposure curve preferably connects a limited number of spatially distributed anchor points, whose absolute positions or relative positions to the master element are predetermined. Preferably, each anchor point is assigned a sub-region of the master element. The exposure curve is preferably based on a mathematical function, in particular a non-linear function, which runs through these anchor points. One or more exposure curves can be provided for a master element. Preferably, the positions of the anchor points and / or the mathematical function of the curve that connects them are provided in a memory that can be accessed by a control unit.

[0104] In a further preferred embodiment of the measuring method, an intensity distribution is recorded for a plurality of spatially distributed anchor points of an exposure curve, wherein a determination of the at least one replication parameter relates to a shift of the exposure curve and / or a variation of the anchor points.

[0105] By detecting the intensity distribution of the light emerging from the diffuser at different anchor points of the exposure curve, local inefficiencies of the master element can be compensated independently of one another. If the replication parameters of an anchor point of the exposure curve are adjusted, the exposure curve can offer a smooth transition to the other anchor points whose replication parameters may not have been adjusted or may have been adjusted in a different way. The efficiency of the master element or of a subsequent replication can be increased. At the same time, the replicated holograms can have an overall high quality, with a seamless transition between regions exposed with different parameters. In this embodiment, setting the at least one replication parameter preferably relates to a shift in the exposure curve and / or a variation of the anchor points.

[0106] The intensity distributions may indicate that the master element has a uniformly distributed inefficiency, requiring a uniform increase in exposure intensity. This may be the case if the total illuminances of all recorded intensity distributions are approximately equal. For example, the recorded intensity distributions may differ by less than a specified amount. A replication parameter can be uniformly adjusted for the exposure curve, such as a uniform increase in exposure intensity. The exposure curve can also be uniformly adjusted to the actual optical function of the master element, for example, by bringing it closer to the master element. This increases the intensity of the exposure and—depending on the design—adjusts an exposure angle.The entire exposure curve can also be shifted in the plane parallel to the master hologram (horizontally) to bring the replication parameters closer to the actual optical function of the master element.

[0107] The intensity distributions can also indicate an overall shift of the wavelength written in the master hologram (e.g., due to shrinkage or swelling of the entire master hologram), a tilt of the master hologram, or a deviation of another parameter, whereby the deviation extends uniformly across the entire master hologram. It may be preferable to change the corresponding replication parameter uniformly across the entire exposure curve, e.g., increasing / decreasing the wavelength by a corresponding value or tilting the entire exposure curve by a certain angle.

[0108] By shifting a replication parameter for the entire exposure curve, the fine-tuning during the creation of the exposure curve, particularly the relative positions of the anchor points and the relative values ​​of their replication parameters, can be reused. The overall efficiency of subsequent replication can be easily improved without having to recalculate the entire exposure curve.

[0109] Alternatively, the intensity distributions at the various anchor points for which they were measured may indicate different efficiencies. This may lead to the setting of a replication parameter for one anchor point independently of the others in order to improve the efficiency of the master hologram when exposed from that anchor point. For example, the position of the anchor point can be changed and the exposure curve adjusted accordingly to create a smooth transition to the neighboring anchor points. Preferably, a new anchor point position is selected from an exposure volume. Additionally or alternatively, a different replication parameter can also be set for the anchor point. Instead of the position, this could be, for example, an intensity, an exposure angle, or a wavelength.

[0110] In a preferred embodiment of the invention, the irradiation of the master element is controlled by means of a control unit. The control unit can determine and / or monitor the parameters with which the measurement method or replication method is carried out. For example, the control unit can be configured to determine the intensity, wavelength, or angle of a light beam and / or the exposure point used to carry out the measurement method or replication method. Preferably, the control unit has access to a storage unit on which these and other relevant parameters are recorded. Preferably, the control unit is configured to link the determined intensity distribution to one or more exposure parameters with which the measurement method was carried out.For example, a recorded intensity distribution can be linked to a specific exposure point position, e.g., an xyz coordinate position. Preferably, the stored data can be retrieved via an output unit and / or used to set the replication parameters.

[0111] In this sense, the measurement method can provide intensity distributions specific to a particular exposure parameter or combination of exposure parameters. This allows the influence of the exposure parameter on the efficiency of the master element to be investigated. Furthermore, an optimized replication parameter can be determined based on the exposure parameters for which the best intensity distribution was recorded.

[0112] It may also be preferred for the control unit to calculate information about the exposure curve for exposing the master hologram or to retrieve it from a memory. For example, the control unit may calculate or retrieve the positions of a plurality of anchor points on the exposure curve and / or a mathematical function connecting the anchor points. The control unit may also be configured to send a signal to one or more actuators so that the exposure point is moved along the exposure curve. The actuators may preferably comprise one or more motors, in particular one or more adjustment stages and / or one or more rotary drives. The actuators may preferably be part of a positioning module.

[0113] The speed of movement of the exposure point can be preprogrammed, with the control unit preferably being configured to move the exposure point along the exposure curve at the preprogrammed speed. Preferably, the control unit can also calculate or retrieve the replication parameters to be used at each anchor point. The control unit can also calculate or retrieve the replication parameters to be used between the anchor points, which can be determined according to a mathematical function, for example, by interpolation.

[0114] For the purposes of the invention, the term "control unit" preferably refers to any computing unit with a processor, a processor chip, a microprocessor, or a microcontroller that enables automatic control of the components of the method, such as the intensity of the light source, the position of the exposure point, the exposure angle, and / or possible actuators for adjusting the exposure parameters. The components of the control unit can be conventional or individually configured for the respective implementation. The control unit preferably comprises a processor, a memory, and computer code (software / firmware) for controlling the components of the device.

[0115] The control unit may also comprise a programmable circuit board, a microcontroller, a programmable logic controller (PLC) or other device for receiving and processing data signals from the components of the device, e.g. from sensors relating to the exposure parameters currently used.

[0116] The control unit preferably comprises a computer-usable or computer-readable medium, such as a hard disk, random access memory (RAM), read-only memory (ROM), flash memory, etc., on which computer software or code is installed. The computer code or software for controlling the components of the device may be written in any programming language or model-based development environment, such as, but not limited to, C / C++, C#, Objective-C, Java, Basic / VisualBasic, MATLAB, Python, Simulink, StateFlow, Lab View, or Assembler.

[0117] The software and all functional descriptions of the software through the description of the control of specific components or aspects of the methods described herein are considered technical features due to a direct physical output on the devices used. Functional descriptions of software can therefore be considered preferred and defining embodiments of the invention.

[0118] The term "control unit is configured to" perform a specific operation, such as determining the position of the exposure point, may include custom or standard software installed on the control unit that initiates and regulates these operational steps.

[0119] The control unit is preferably configured to adjust one or more exposure parameters during the measurement process. For example, the control unit may be configured to turn a light source on or off. The control unit may also be configured to adjust a brightness value, wavelength, position, inclination, direction, and / or speed of movement of the light source. The control unit may also be configured to adjust an exposure parameter by moving the positioning module.

[0120] The positioning module may preferably comprise or carry one or more light-directing components such as a lens, a prism, a fiber, or a mirror. The control unit may control the position, inclination, and / or speed of movement of one or more light-directing components. For example, the control unit may control the coordinate position and / or three-dimensional inclination of a scanning mirror. In this way, the orientation of the light from the light source can also be controlled, thereby determining the angle of incidence of the exposure beam on the master element. The control unit may also be configured to control the speed of movement of one of the aforementioned components. Changing the speed can compensate for inefficiencies of the master element. In addition, the control unit may be configured to control the operation of the detector, e.g., the focus or shutter speed.The control unit can be configured to process the detector data using a data processing unit, for example, to compensate for an inclination of the detector relative to the first side of the master element. The control unit can further be configured to evaluate the detector data, for example, to assess the efficiency of a master element as acceptable or unacceptable, to select a parameter for a further measurement method, or to determine an optimized replication parameter.

[0121] In a further preferred embodiment of the invention, a control pattern for the intensity distribution is provided. In this case, an intensity distribution for an isolated diffuser—without a master element—is preferably recorded. This preferably means that the effect of the diffuser itself on the intensity distribution is recorded. The control pattern is preferably taken into account when determining the at least one replication parameter based on the recorded intensity distribution.

[0122] For the purposes of the invention, an isolated diffuser is preferably a diffuser that is not used in combination with a master element. Preferably, the diffuser is the only component between the diffuser and the detector when a control pattern is acquired.

[0123] By recording the intensity distribution of the diffuser itself when illuminated by a light source, a control value of the intensity is obtained at each point and / or area of ​​the master element. The intensity distribution recorded with the master element can be compared with the intensity distribution of the diffuser itself. Any intensity losses caused by the diffuser can be taken into account, allowing the measurement method to determine an optimal replication parameter based on the actual properties of the master element. For example, the diffuser material may absorb light of a certain wavelength and thus influence the wavelength range detected by the detector. By quantifying the influence of the diffuser, the erroneous conclusion that the master element successfully reflected the light absorbed by the diffuser can be avoided.The replication parameters can thus be determined more precisely, improving the efficiency of the replication process. Likewise, local variations in scattering angles or transmission properties can occur in the diffuser, which influence the measured intensity distribution at the detector. By recording a control sample, such diffuser influences on the measured intensity distribution can be advantageously taken into account.

[0124] In a further preferred embodiment of the invention, the diffuser is a transmissive diffuser, which preferably behaves substantially like a Lambertian radiator.

[0125] A "Lambertian radiator" (or "Lambert radiator") is preferably a light-emitting body in which the radiant intensity of the light scattered toward an observer (or a detector) is independent of the direction of observation. A Lambertian diffuser preferably appears equally bright from all directions in the hemisphere from which the irradiated light emerges.

[0126] It may be preferred for the diffuser to function approximately like a Lambertian radiator. The maximum difference between the radiation intensity detectable from a given point on the diffuser from any two angles of a hemisphere is preferably no more than 50%, more preferably no more than 30%, even more preferably no more than 10%. By providing a diffuser that functions substantially or approximately like a Lambertian radiator, the sensitivity of the measurement method to a detector position can be reduced. It is particularly advantageous for the detector to detect the light intensity emerging from the diffuser with virtually the same sensitivity, regardless of its angle to different points on the diffuser. This allows a single detector to be used with large diffusers and / or master elements. The reliability of the measurement method is increased.

[0127] Preferably, a deviation of the diffuser from a Lambertian nominal function is determined by capturing one or more control patterns. This allows, in particular, the influence of the recording angle on the intensity distribution to be quantified. For example, if only a single, centrally positioned camera is used to capture the intensity distribution of a master element, peripheral regions of the master element may appear darker due to their non-orthogonal angle to the camera lens. This effect is preferably quantified and taken into account when evaluating the recorded light intensities.

[0128] In a preferred embodiment of the invention, the diffuser has a rough surface facing the detector. Preferably, the surface of the diffuser facing the detector has a surface roughness Ra of 0.1-100 pm, particularly preferably 1-10 pm. It has been found that at these roughnesses, the diffuser essentially acts like a Lambertian radiator while simultaneously providing a sufficiently precise intensity distribution.

[0129] The surface roughness Ra in the sense of the invention is preferably the average of the profile height deviations from a center line of the height of a surface.

[0130] The diffuser is preferably transparent to all wavelengths between 400 and 780 nm, particularly between 200 nm and 25 pm. Preferably, all wavelengths in the visible spectrum, particularly between 400 and 780 nm, are equally transmitted by the diffuser. Should certain wavelengths be absorbed by the diffuser material, these wavelengths are preferably taken into account when interpreting, further processing, or using the recorded intensity distributions. This can be done using a control sample representing an intensity distribution of the diffuser without the master element.

[0131] The width and length of the diffuser are preferably at least as large as the width and length of the master element. The diffuser preferably has a thickness that is significantly less than its width and length. The thickness of the diffuser is preferably no more than 50 mm, more preferably no more than 20 mm, no more than 10 mm, no more than 5 mm, or no more than 2 mm. The diffuser is preferably in the form of a film. By providing a diffuser with one of the preferred thicknesses, the diffuser can be kept so thin that an intensity distribution is clearly visible and precise conclusions can be drawn about the corresponding areas of the master element that transmit the detected light. A homogenizing effect of the diffuser can be kept low, so that meaningful intensity distribution patterns can be detected.

[0132] In a further preferred embodiment of the invention, the detector is a camera, which preferably captures the intensity distribution as a two-dimensional image of the diffuser surface. Advantageously, a camera can quickly translate the intensity distribution into a digital image, which can be stored and / or input into a processor to calculate an optimized replication parameter. Furthermore, cameras with high resolution, small dimensions, and low weight are available. A compact, lightweight camera can be moved synchronously with a scanning exposure point to generate images of the intensity distributions of diffusers / master elements of any size. Small actuators can be used, and the energy consumption of the process can be kept low.

[0133] Alternatively, partial areas of the diffuser can be illuminated sequentially, allowing the camera to capture the intensity distribution of the individual partial areas. A processor can then combine the intensity distributions to reconstruct the intensity distribution across the entire diffuser. This embodiment can be used, for example, to capture intensity distributions for different anchor points of an exposure curve. It may be advantageous for the camera to comprise a wide-angle lens. Advantageously, such a camera can capture the intensity distribution emerging from a large-area diffuser without having to move the camera or merge multiple images. The measurement method can be carried out particularly quickly and reliably with low energy consumption.

[0134] Preferably, the camera lens can be positioned centrally and plane-parallel to the diffuser. In this way, the captured image of the intensity distribution can directly match that of the master element. However, it may also be preferable—for example, due to space constraints in an exposure chamber—for the camera to be off-center and / or tilted relative to the diffuser. In such cases, it may be advantageous to input the directly captured intensity distribution into a processor configured for image correction to reconstruct an intensity distribution as if viewed from a central and plane-parallel position.

[0135] In some embodiments of the invention, it may be preferred for the camera to be a black-and-white camera. This allows an image of the intensity distribution emerging from a diffuser to be created quickly and with low data consumption. This could make it possible to increase the resolution of the acquired intensity distribution. The acquired intensity distribution can be quickly processed to determine an optimized replication parameter. If the efficiency of the master element upon exposure to different wavelengths is to be investigated, the black-and-white camera can be used by exposing the master element to the different wavelengths sequentially rather than simultaneously. The black-and-white camera is therefore a particularly flexible detector type.

[0136] In some embodiments of the invention, it may be preferred that the camera is a full-color camera, preferably an RGB camera. Such a camera can be used to capture the intensities of the different wavelengths transmitted by the master element or the diffuser. In particular, an RGB camera can be used to extract the intensity distribution of the different wavelengths from a single image when the master element is simultaneously illuminated with light beams of different wavelengths. In particular, the different color channels of a recorded full-color image can be isolated from each other by a processor. If the measurement method with an RGB camera is used to investigate the efficiency of the master element at different wavelengths, it is preferred that the different wavelengths are sufficiently far apart.For example, there may be at least 50 nm, and especially at least 100 nm, between two wavelengths under investigation. The color channels of an RGB camera are typically represented by overlapping sensitivity curves of the camera sensors for each wavelength range, corresponding to the red, green, and blue parts of the spectrum, respectively. In the area of ​​overlap, such cameras may be less effective at detecting the wavelength of light. By selecting the wavelengths used to test the master element so that they are far enough apart, they can fall into the high-sensitivity regions of the RGB camera's color curves, improving the accuracy of the resulting analysis.

[0137] The replication parameters determined by the measurement method can be specific to a particular wavelength, e.g., by increasing the intensity of the respective light beam or shifting its wavelength. The determined replication parameter can also apply generally to all wavelengths under investigation, e.g., by increasing the intensity of all exposure beams.

[0138] In a second aspect, the invention relates to a replication method for replicating a hologram from a master element into a light-sensitive material. The replication method is carried out using at least one replication parameter, which was determined by means of a measurement method as described above.

[0139] By determining a replication parameter for a specific master element using the measurement method according to the invention and using this replication parameter when performing a replication process, the replication can be optimized to the actual optical function of the master element. The production of the master element within certain manufacturing tolerances and the resulting deviations of the optical function from a target function can be compensated for based on the data experimentally acquired in the measurement process. This has proven to be significantly more precise and reliable than the use of simulation methods to estimate the efficiency of a master hologram for specific replication parameters. The replication process can be performed significantly more efficiently and with a higher degree of repeatability. The replicated holograms produced exhibit higher quality.Since the replication parameters can be determined quickly and efficiently by the measurement method, the replication method can be updated regularly so that it is always adapted to the current state of the master element.

[0140] Since switching from the measurement process to the replication process preferably involves applying only a light-sensitive material to the second side of the master element and removing the diffuser from the first side of the master element, the changeover can be completed quickly. The measurement process can therefore be performed regularly or without a long production stoppage. The replication process can be performed over a long period of time without the need to replace the aging master hologram. This ensures high replication efficiency over a long period of time.

[0141] For the purposes of the invention, a "light-sensitive material" is preferably a material that reacts upon exposure to a sufficiently coherent light source to produce an interference pattern within the volume of the material. Examples of such materials are silver halides, dichroic gelatin, photopolymers, photochromic materials, and photothermoplastics. The light-sensitive material may be provided with a carrier film on at least one side to facilitate its handling. The light-sensitive material may also be enclosed in carrier films. The carrier films are preferably transparent to the reference and object beams used to expose the light-sensitive material.

[0142] It may be preferred that the photosensitive material be in the form of a photosensitive composite sheet comprising a photopolymer layer. Preferably, the photopolymer layer is enclosed between two transparent carrier films. The photosensitive composite sheet can be supplied as a roll, allowing the photosensitive composite sheet to be laminated to the master element in portions, exposed, and removed. This allows the replication process to be carried out continuously.

[0143] A "composite" within the meaning of the invention is preferably a multilayer material consisting of two or more different components with different physical properties that are bonded together at an interface. Preferably, the bond between the individual components is such that it cannot be severed by the application of slight force and is therefore considered permanent. The composite can consist, for example, of a light-sensitive liquid, a solid, or a resin enclosed between two transparent carrier films. Alternatively or additionally, the composite web can comprise a stack of layers, each light-sensitive to different spectral ranges.

[0144] A “photosensitive composite web” within the meaning of the invention is preferably a composite material with a length that is at least twice, preferably at least five times, and even more preferably at least twenty times its width. The thickness of the composite web is preferably adjusted to have a certain flexibility so that it can, for example, be partially wound around a roller. Preferably, the composite web has a thickness of up to 300 μm. The composite web comprises a photosensitive material. Preferably, the composite web encloses the photosensitive material between two transparent support films that have a similar refractive index to the photosensitive material. Preferably, the refractive index of the support films and the photosensitive material is between 1.4 and 1.6. The photosensitive material can be, for example, a photosensitive photopolymer or a dichroic gelatin.The light-sensitive material can be light-sensitive to the entire visible spectrum or wavelength-selective.

[0145] The exposure can preferably be carried out using a coherent light source. Coherence preferably refers to the property of optical waves according to which there is a fixed phase relationship between two wave trains. As a result of the fixed phase relationship between the two wave trains, spatially stable interference patterns can arise. With regard to coherence, a distinction can be made between temporal and spatial coherence. Spatial coherence preferably represents a measure of a fixed phase relationship between wave trains perpendicular to the propagation and is given, for example, for parallel light beams. Temporal coherence preferably represents a fixed phase relationship between wave trains along the propagation direction and is given in particular for narrowband, preferably monochromatic light beams.

[0146] The coherence length preferably refers to the maximum path length or travel time difference between two light beams from a starting point, so that a (spatially and temporally) stable interference pattern is still created when they superpose. The coherence time preferably refers to the time it takes for the light to travel a coherence length.

[0147] In preferred embodiments, the light source is a laser. Particularly preferably, the light source is a narrowband, preferably monochromatic laser with a preferred wavelength in the infrared, visible, and / or UV range (preferably 200 nm - 25 pm, more preferably 400 nm to 780 nm). Lasers preferably refer to light sources that emit laser radiation. Non-exhaustive examples include solid-state lasers, preferably semiconductor lasers or laser diodes, gas lasers, or dye lasers. Lasers can be selected to emit light of a specific wavelength or wavelength range. This can be achieved by selecting a laser made of a suitable material. Examples include ruby ​​lasers, He-Ne lasers, Ar + -Laser, Kr + -Laser, He-Cd laser and / or Nd 3+YAG lasers can be used. These or other laser types can be combined with an optical parametric oscillator to generate coherent beams of different wavelengths. Lasers with different wavelengths can also be combined, for example, to create an RGB laser.

[0148] Various laser types, particularly solid-state lasers, can be combined with an optical parametric oscillator to generate coherent beams of different wavelengths as a tunable system. The optical parametric oscillator preferably comprises an optical resonator and at least one nonlinear optical crystal. Systems with a plurality of converter crystals can be used, in particular, using three-wave mixing (f_pumpe = f_signal + f_dler). By varying the frequency of f_signal and / or f_dler, laser wavelengths can be generated in a very broad wavelength range. This includes, in particular, the entire visible and infrared ranges of the electromagnetic spectrum.

[0149] Other light sources, preferably coherent light sources, can also be used. Narrowband light sources, preferably monochromatic light sources, such as light-emitting diodes (LEDs), optionally in combination with monochromators, are preferred.

[0150] For the generation of relief holograms, the coherence of the light beams is of lesser relevance. However, particularly for the replication of volume holograms, it is preferable that the light source used for replication be sufficiently coherent. Preferably, a volume hologram is inscribed into the composite path by replicating the master hologram. Interference of object and reference beams within the hologram volume preferably creates a sequence of Bragg planes. A volume hologram therefore preferably exhibits a non-negligible extension in the propagation direction of the light beams, with the Bragg condition applying to reconstruction on a volume hologram. For this reason, volume holograms advantageously exhibit wavelength and / or angle selectivity.

[0151] In preferred embodiments of the invention, the coherence length of the light source is preferably at least 150 pm, more preferably at least 500 pm, and even more preferably at least 2 mm. The coherence length is preferably at least twice the distance between the light-sensitive material and the master hologram. However, the coherence length is preferably not so long that parasitic microstructures, such as interference grids, appear in the hologram. The maximum preferred coherence depends on the hologram type and the geometric dimensions of the exposure module. In preferred embodiments, the coherence length of the light source is less than 1 m.

[0152] The light source may comprise multiple light sources. These may preferably be configured to scan a line or region of the photopolymer composite in optical contact with the master element.

[0153] The steps of hologram production following exposure can be familiar. For example, the exposed photosensitive composite sheet can be cured with a UV light source. This can be done in a separate chamber from the exposure. The exposed and cured composite sheet can then be cut into individual holograms, rolled up, or otherwise processed.

[0154] In a further preferred embodiment of the invention, the at least one replication parameter relates to an exposure intensity with which the master element is exposed during replication. Since local or general efficiency losses occur due to the manufacturing process and / or aging of the master element, using the exposure intensity determined during the measurement process for replication can compensate for this loss of efficiency. In this way, the master element can continue to be used for replication while maintaining a replication quality that would be almost identical to that achieved with an ideal master element.

[0155] Preferably, the intensity for different positions on the master element is determined based on the recorded intensity distribution. In this way, not only a general but also a localized deviation of the master element from a target function can be compensated. The replication method can thus be carried out with high quality even with unevenly deformed master elements. In a further preferred embodiment of the invention, the at least one replication parameter relates to an exposure point from which the master element is exposed, preferably in order to maximize the efficiency of the master element during replication. As explained above, the manufacturing process of the master element can change the function of its interference pattern compared to a theoretical function. By default, the master element is exposed with parameters that are precisely matched to the theoretical function.Since the real master element has a different optical function than the theoretical one, it makes sense to also adjust the exposure parameters. This can include, in particular, the position of an exposure point.

[0156] By performing replication with an exposure point determined by the measurement method, the efficiency of replication can be improved. For example, the exposure point selected by the measurement method can result in a larger proportion of the reference beam being diffracted in the first order to form the object beam. This can be an optimized exposure point for exposing the entire master element, as explained above. Likewise, the exposure point can be a point on an exposure curve that can be adjusted based on the results of the measurement method to adapt the exposure curve to the actual properties of the master element.

[0157] In a further preferred embodiment of the invention, the at least one replication parameter relates to a wavelength, wherein intensity distributions for two or more wavelengths are detected in the measuring method and the wavelength used in the replication is preferably selected in order to maximize an efficiency of the master element during the replication.

[0158] By recording intensity distributions at at least two different wavelengths, the influence of wavelength on the efficiency of the master element can be determined experimentally. This can be particularly useful when shrinkage or swelling changes the wavelength of the interference pattern stored in the volume of the master hologram. If the exposure wavelength is selected based on a variety of wavelengths tested, the replication process can be performed, for example, using a preferred wavelength previously tested in the measurement process or using a wavelength calculated by interpolation or extrapolation from tested wavelengths. The replication process can thus be performed with greater efficiency, ensuring the highest quality holograms.

[0159] A single optimized wavelength can be selected for the exposure of the entire master element. However, it may be preferred that several wavelengths determined by the measurement method are used for several corresponding points or regions of an exposure curve, e.g. with the aid of a tunable laser. In a further preferred embodiment of the invention, the replication method comprises the exposure of the light-sensitive material and the master element by moving an exposure point along an exposure curve, wherein the exposure curve preferably comprises several anchor points, and for each individual anchor point and / or for the entire exposure curve, a replication parameter determined by the measurement method is applied during the exposure in order to preferably maximize the efficiency of the master element during replication.

[0160] It may also be advantageous to use a replication parameter determined by the measurement method for only one anchor point. The remaining anchor points can continue to be replicated using target parameters, and the remainder of the exposure curve can be recalculated. It may also be preferable to use a replication parameter determined by the measurement method only for some of the anchor points, while other anchor points are replicated using target parameters. The exposure curve can be recalculated accordingly.

[0161] By replicating a master hologram with an exposure curve, different regions of the replicated hologram can exhibit different optical properties. These can be closely matched to the properties of the master hologram. For example, different regions of the replicated hologram can exhibit different reconstruction angles. This can be useful, for example, for holograms that are incorporated into curved surfaces, such as car interiors.

[0162] By adjusting the replication parameters for one or more individual anchor points of the exposure curve, regional inefficiencies in the master element can be compensated. The transition to the parameters of neighboring anchor points can be seamless, so that the regional adjustment is unnoticeable in the replication hologram. The resulting holograms can be produced in high quality, and the same master element can be reused for longer periods without replacement.

[0163] Applying a single replication parameter or a single mathematical fitting function to all points of the exposure curve can be advantageous when the intensity distributions detected in the measurement procedure indicate an inefficiency that affects all regions of the master element equally. For example, the wavelength of all anchor points can be changed to a new wavelength determined by the measurement procedure. In this case, the replication parameter is a wavelength. It can also be advantageous to shift or flip the entire exposure curve to maintain the same relative distances between the anchor points. This may be preferred when the replication parameter is an intensity or an exposure angle. It is also possible to combine these approaches, e.g., by changing the wavelength of all anchor points and shifting the exposure curve.Further examples of such adjustments are presented with reference to the measurement method and can also be used in the replication method. In a further preferred embodiment of the invention, moving the exposure point comprises changing its position and / or an angle of its beam path, wherein the exposure point is preferably moved by means of a controlled positioning module.

[0164] The positioning module preferably comprises one or more actuators for moving an exposure point at least in a plane parallel to the master hologram. The positioning module preferably also comprises one or more actuators for moving the exposure point in a plane that passes through the master hologram, i.e. for bringing the exposure point closer to or further away from the master hologram. The light source (e.g. the laser) can also be moved by the positioning module or arranged separately from it. The positioning module preferably comprises a robot arm with one or more adjustable axes and one or more actuators. Alternatively, the positioning module could comprise a multi-axis optical linear adjustment stage. The adjustment stage preferably also has at least one rotational degree of freedom.

[0165] The positioning module preferably also includes an optical component capable of deflecting the beam. The optical component is preferably arranged to be tiltable, so that tilting the optical component can change the angle of the beam path. The optical component can be configured to be tiltable in a single plane, in two planes, or in all three planes. The optical component preferably includes a lens, a mirror, and / or a prism.

[0166] The optical component can be a mirror, for example. The mirror can be tilted stepwise using a motorized joint. This can lead to a corresponding tilt of the reference beam reaching the master element. In this case, the exposure point can be a point on the mirror.

[0167] The movement of the positioning module and / or the optical components can be controlled by a control unit.

[0168] In a further preferred embodiment of the invention, the light-sensitive material and a second side of the master element are exposed to light in several steps, while a first side of the master element opposite the second side faces a detector, and the detector detects the intensity distribution of the light emerging from the first side of the master element during the exposure. Preferably, in a later exposure step, the replication parameter defined in the measurement method is adjusted based on the intensity distribution detected in an earlier exposure step. Within the meaning of the invention, an earlier step and a later exposure step can each be steps for replicating a single copy, several consecutive, or several non-consecutive copies of a master hologram.

[0169] Such an embodiment of the invention leads to particularly good results in the replication process, since any changes to the master hologram can be reliably detected and taken into account during replication. Furthermore, the method advantageously does not require interruption of a continuous replication process. Since the exposure of the master element and the detection of an intensity distribution take place on different sides of the master element, they can be performed simultaneously and do not have to conflict with each other. Since the master hologram is a reflection hologram, the object beam is reflected by the interference pattern of the master hologram without exiting the first side of the master element. The detector can therefore remain in the same position on the first side of the master element during the replication process as during the measurement process.

[0170] Instead of being scattered by a diffuser, which is preferably removed from the first side of the master element during the replication process, a reference beam can instead be partially scattered by the photosensitive material (e.g., in the photosensitive composite). In this embodiment, the photosensitive material itself can act as the above-described diffuser for the measurement process. When replicating a master holgram using a result of the measurement process determined with the diffuser as described above, this embodiment allows for further fine-tuning of the replication parameters, particularly in the continuous replication process.

[0171] This takes advantage of the fact that unexposed material scatters more strongly than exposed material. This allows a detector to detect scattered light from the superposition of first-order light and a reference beam. The intensity of the light scattered in the light-sensitive material correlates with the first-order component, which can vary depending on the efficiency of the master. The light emerging from the first side of the master element is preferably detected by the detector in order to provide information about the condition, particularly the efficiency, of the master element. In this way, the replication parameter determined by the measurement method can be additionally adjusted during the replication process. This allows a very finely tuned adaptation of the replication parameters to the actual properties of the master element.

[0172] Without a separate diffuser, it cannot be reliably guaranteed that the emerging zeroth, undiffracted order light can be detected by the detector from a variety of angles. Depending on the exit angle, the emerging zeroth, undiffracted order light can instead bypass the detector. However, instead of the zeroth order, the detector can advantageously detect scattered light to determine the efficiency of the master hologram. This results from the first order of diffraction being reflected into the material to be exposed. This can result in a type of phosphorescence. This allows the light reflected by the master element (1st order) to be at least partially scattered into areas of the light-sensitive material that have not yet been exposed. This scattered light advantageously exits the light-sensitive material over a wide range of angles and can therefore be detected by a detector, such as aa camera, to reliably record a light intensity distribution.

[0173] In this embodiment, bright areas of the light intensity distribution (high light intensity) preferably indicate a high efficiency of the master hologram, since the scattered light correlates positively with the light reflected by the master element to the first order.

[0174] Darker areas preferably indicate a lower proportion of first-order reflection and thus a lower efficiency of the master hologram. The relationship between brightness and efficiency is thus inverse when detecting first-order scattering in the replication method compared to embodiments of the measurement method in which a diffuser is used to scatter zero-order diffracted light and detect it with a detector.

[0175] In this embodiment, it may be advantageous for the master element to be exposed over a large area or in steps using an exposure curve. If the master element is exposed over a large area, an intensity distribution for the entire master element can be taken during an earlier exposure step. Based on this, a replication parameter for the entire master element can be adjusted. This replication parameter can be applied, for example, in the production of a subsequent copy of the master hologram in a continuous process.

[0176] If, however, the master element is exposed step by step using an exposure curve, an intensity distribution can be captured for at least one anchor point. This could provide insights into the condition of the entire master element, and the entire exposure curve can be adjusted accordingly.

[0177] However, it may be preferable to record an intensity distribution for one or more, preferably all, anchor points of the exposure curve. Based on this, a replication parameter for the respective anchor points can be adjusted during the subsequent exposure run of the master hologram. The exposure process can thus be continuously calibrated and adapted to the optical properties of the master element. This ensures that the replication process is efficient over a long period of time.

[0178] Terms such as substantially, approximately, about, approximately, nearly, etc. preferably describe a tolerance range of less than ± 20%, preferably less than ± 10%, more preferably less than ± 5% and especially less than ± 1% and include the exact value.

[0179] The average person skilled in the art recognizes that technical features, definitions and advantages of preferred embodiments of the measurement methods according to the invention also apply to the replication method according to the invention, and vice versa.

[0180] Detailed description

[0181] In the following, the invention will be explained in more detail using examples and illustrations, without being limited to these.

[0182] Short description of the figures

[0183] Fig. 1 is a schematic representation of an ideal planar reflection master hologram exposed from one exposure point.

[0184] Fig. 2 is a schematic representation of an actual (non-ideal) reflection master hologram in a master element. The exposure from a target exposure point and from an exposure point determined by the measurement method are shown schematically.

[0185] Fig. 3 is a schematic representation of a measuring method according to a preferred embodiment of the invention, wherein a diffuser and a detector are arranged on a first side of the master element.

[0186] Fig. 4 is a schematic representation of a measuring method according to a preferred embodiment of the invention, wherein an intensity distribution is recorded at a first exposure point and a second exposure point.

[0187] Fig. 5 is a schematic representation of an intensity distribution upon exposure of the

[0188] Master elements from a first exposure point.

[0189] Fig. 6 is a schematic representation of an intensity distribution upon exposure of the

[0190] Master element from the second exposure point.

[0191] Fig. 7 is a schematic representation of a measuring method according to a further preferred embodiment of the invention, wherein an intensity distribution for several anchor points of an exposure point is recorded and a shift of the exposure curve takes place.

[0192] Fig. 8 is a schematic representation of a positioning module for moving an exposure point across an exposure curve.

[0193] Fig. 9 is a schematic representation of a positioning module according to an alternative embodiment for moving an exposure point along an exposure curve, wherein the positioning module comprises a robotic arm. Fig. 10 is a schematic representation of a replication method according to another preferred embodiment of the invention, wherein a light-sensitive material scatters the reference beam and the scattered light is detected as an intensity distribution. Based on the intensity distribution, a replication parameter is adjusted in-line.

[0194] Detailed description of the illustrations

[0195] Fig. 1 shows an ideal reflection master hologram 4 as a horizontal dashed line. The master hologram 4 has an optical function that exactly corresponds to its theoretical (or nominal) optical function. This means that the master hologram 4 preferably has a uniform thickness and has an interference pattern within its volume that exactly corresponds to the interference pattern recorded in a computer-implemented program for hologram mastering. Fig. 1 shows the master hologram 4 being illuminated by a reference beam 16 emanating from a nominal exposure point 14. The reference beam 16 can have a predetermined wavelength. A point light source can be provided at the nominal exposure point 14 so that the master element is illuminated over a large area. From the nominal exposure point 14, the reference beam 16 approaches the master hologram 4 at a predetermined angle.Since the master hologram 4 has not undergone any deformation or degradation due to its manufacture or due to process steps of integration into a master element and has a maximum efficiency, the reference beam 16 is completely reflected by the master hologram 4 to generate the object beam 18, which has a predetermined angle to the master hologram 4.

[0196] The position of the target exposure point 14 relative to the master hologram 4, the specified wavelength, and / or the angle of approach of the target reference beam 16 to the master hologram 4 can be pre-stored as standard replication parameters for copying the master hologram 4. The pre-stored standard replication parameters can serve as instructions for exposing the master hologram 4 during a replication process. However, as explained below, the standard replication parameters only lead to the highest possible replication efficiency if the optical properties of the master hologram 4 actually correspond to its theoretical optical properties. If the optical properties of the master hologram 4 begin to deviate from the target properties, it may be advantageous to expose the master hologram with appropriately adjusted replication parameters.

[0197] Fig. 2 shows a master hologram 4 embedded in a transparent substrate body 6. Together, the master hologram 4 and the substrate body 6 form a master element 2. Such a master element 2 is several times thicker than the master hologram 4 and is therefore significantly more robust and much easier to handle in practice. However, the process of creating the master hologram 4, its integration into the master element 2, and its storage or use over time can lead to changes in its optical properties.

[0198] These changes can result in the target exposure parameters for exposing the master hologram 4 no longer being the most effective exposure parameters. The target exposure point 14, the target reference beam 16, and the target object beam 18 are shown as dashed lines in Fig. 2. Since the assumptions underlying the determination of these target exposure parameters do not take into account the current properties of the master element 2, the target reference beam 16 may not be completely reflected by the master hologram 4. The intensity of the generated object beam may therefore be too low to produce the desired interference in the light-sensitive material. A high-quality copy of the master hologram cannot be created with these replication parameters.

[0199] Instead, for this purpose, the master hologram 4 must be exposed with a different, optimized exposure point 12 that is shifted in position with respect to the target exposure point 14. The light source used can also have a different wavelength than the target wavelength. An optimized reference beam 8 can be incident on the master element 2 at a different angle and / or with a different wavelength, which leads to a better match with the requirements of the interference pattern of the master hologram 4 integrated into the master element. The reference beam 8 can be reflected with greater efficiency to form the object beam 10. This is shown schematically with solid lines. The sufficiently intense object beam 10 can then interfere with the reference beam 8 in the light-sensitive material to form the desired interference pattern.The quality of the copied master hologram can thus be improved and the master hologram can be reused.

[0200] Fig. 3 schematically shows a measurement method according to a preferred embodiment of the invention. A master element 2 is provided between a first exposure point 14 and a detector 26, in this case a camera. The top side of the master element 2 is referred to as the first side, and the bottom side of the master element 2 is referred to as the second side. A diffuser 24 is located between the master element 2 and the detector 26. Although direct contact is not required to practice the invention, in this embodiment the diffuser is in direct contact with the first side of the master element 2.

[0201] When the master element 2 is exposed from the first exposure point 14, a first reference beam 16 strikes the second surface of the master element 2 at a predetermined angle. Since the master hologram 4 has undergone changes due to its manufacture, integration into a master element, use, or storage, the first reference beam 16 is only partially reflected by the master hologram 4 and forms the first object beam 18. A portion of the light of the first reference beam 16 is guided through the master hologram 4, through the substrate body 6, and then into the diffuser 24. The diffuser 24 scatters the light of the reference beam to form the scattered radiation 22, which preferably radiates in all directions of a hemisphere on top of the diffuser 24.

[0202] Due to the scattering of the light emitted from the top of the diffuser 24, the detector 26, with a sufficient lens angle, can measure the intensity of the light emitted from all areas of the diffuser. This means that the scattered light 22, visible on the left and right in the schematic drawing, can be equally detected by the detector 26, even though these areas are at different angles to the detector 26.

[0203] By recording the intensity distribution during the exposure of the master element 2 with the first exposure parameters, it can be determined whether the first exposure parameters match the actual optical function of the master hologram 4 and, if not, in which areas and to what extent the exposure parameters need to be improved. With an ideal master hologram 4, which is designed for the complete reflection of the reference beam, no light would emerge from the diffuser and the detector would register a black image. Based on the recorded intensity distribution, an exposure can be carried out with the first exposure parameters or with generally or locally optimized new exposure parameters. For better illustration, Fig.3 also a theoretical exposure volume 36, within which an exposure point, in particular for the whole or a region of the master hologram, can be selected.

[0204] Fig. 4 schematically shows a change in the regional efficiency of the master hologram 4 when a different second exposure point 12 is selected within the theoretical exposure volume 36 to expose the master element 2 over a large area. The first reference beam 16 and the resulting first object beam 18 are shown in solid lines for comparison. The new second reference beam 8 and the resulting scattered light 22 transmitted by the diffuser 24 are shown by dashed lines. As indicated by the thicker dashed lines in the area of ​​the scattered light emitted by the left part of the diffuser 24, the second exposure point 12 results in a higher light intensity for this area of ​​the diffuser. This indicates a poorer exposure efficiency in the corresponding region of the master hologram.On the other hand, the scattered light 22 emitted from the right-hand area of ​​the diffuser 24 has a lower intensity, indicated by the thinner dashed lines. For this area, the second exposure point 12 can result in an angle of incidence of the second reference beam 8 that is better matched to the actual properties of the master hologram 4. This information can be used in selecting the exposure point or radiation angle for the entire master hologram or for specific regions or points thereof. This information is provided in particular in the form of an intensity distribution for each tested exposure point 14, 12 before one or more replication parameters are derived from the results. Fig.5 and 6 schematically show the intensity distributions 28 recorded for the same master hologram 4 when exposed from two different exposure points (e.g., from the first exposure point 14 and the second exposure point 12). As can be seen, the intensity distributions vary, with the intensity distribution in Fig. 6 showing a larger dark area overall. Since the dark areas indicate high efficiency, the exposure point of Fig. 6 may be considered more suitable. The same exposure point may be selected for a replication process. Alternatively, a third exposure point may be selected based on a trend evident from the results for the two tested exposure points.Based on the acquired intensity distributions, further exposure points can also be selected and tested, preferably through an iterative process that converges to maximum exposure efficiency.

[0205] Fig. 7 shows an embodiment of a measurement method in which the master hologram 4 is to be replicated using an exposure curve 32. In this embodiment, the entire master hologram 4 is not exposed over a large area using a single exposure point; instead, the master hologram 4 is exposed in sections. Each section of the master hologram 4 is assigned a section of an exposure curve for exposure. Thus, multiple exposure point positions are used for a master hologram 4.

[0206] This can be achieved, for example, by moving at least one exposure point (e.g., a point on a mirror) along an exposure curve 32. The exposure curve 32 is preferably configured to pass through a discrete number of anchor points 34, each having predetermined target replication parameters. The exposure curve 32 preferably provides a smooth spatial transition between the anchor points 34. Preferably, the exposure curve 32 also provides a smooth transition between the exposure parameters of the anchor points 34, such as wavelength or intensity.

[0207] Fig. 7 further shows the desired reference beams and the resulting object beams from the fifth 42 and seventh anchor point 44 (from left to right) using solid lines. As illustrated by the dashed arrows 22, a portion of the light in front of the seventh anchor point 44 is not completely reflected by the master hologram 4 and is instead transmitted and scattered by the diffuser 24. The replication parameters of at least this anchor point 44 are therefore not optimally adapted to the actual properties of the master hologram 4. Here, the intensity distribution and therefore the efficiency of the master hologram can be examined at an alternative seventh anchor point 46. The position of the alternative seventh anchor point 46 may differ from the desired position. The reference beams originating from the alternative seventh anchor point 46 are illustrated by dashed lines.The dashed lines schematically show that the angles of incidence of the new reference rays on the master element 2 are different from the target angles. Should it turn out that the alternative seventh anchor point 46 enables more efficient exposure of the master hologram, the entire exposure curve can be shifted accordingly. This is schematically illustrated by the dashed curve 48 in Fig. 7. Alternatively, the exposure curve can also be recalculated so that it passes through the new seventh anchor point 46 instead of the original seventh anchor point 44. Preferably, each anchor point 34 is checked by the measurement method, and a new replication parameter (in particular, a relative position to the master element 2) is determined for each point. A new exposure curve 48 can then be calculated.

[0208] The execution and adjustment of the exposure curve 32 is explained in more detail with reference to Fig. 8. Fig. 8 schematically shows a master element 2 arranged above a positioning module 58. The positioning module 58 is configured to move an exposure point 84 along the exposure curve 32 for the measurement process and / or for the replication process. In this example, the exposure point 84 is a point on a tiltable scanning mirror 56, from which a reference beam 8 is directed onto the master element 2. A light source 50, in this case a laser, emits a light beam that is guided through a series of optical elements (in this case a periscope arrangement) to the exposure point 84. The light source 50 is preferably stationary. Optionally, the light source 50 can be configured to scan along a single linear path in a single horizontal plane.

[0209] To move the exposure point 84 along the exposure curve 32, the scanning mirror 56 is positioned on the positioning module 58. The positioning module 58 comprises a horizontal adjustment stage 52 and a vertical adjustment stage 54. The horizontal adjustment stage 52 effects a horizontal component of a movement of the exposure point 84, while the vertical adjustment stage 54 effects a vertical component thereof. In addition, the angle of the reference beam 8 is preferably adjusted by tilting the scanning mirror 56, preferably with the aid of a motor. The sequence of vertical, horizontal, and tilting movements required to move the exposure point 84 across the exposure curve 32 are preferably stored in advance and / or calculated by a processor. However, the exposure curve 32 can be continuously evaluated and recalculated.

[0210] Fig. 9 shows an alternative embodiment of the positioning module 58, wherein an exposure point 84 is moved along an exposure curve 32 using a robot arm 60. In this embodiment, a fiber optic cable delivers coherent light from the light source 50 to a scanning mirror 56. Actuators in the robot arm 60 move the scanning mirror 56 along the exposure curve 32 and simultaneously tilt it to direct light beams from different angles onto the master element 2. Such a robot arm can precisely expose the master element 2 with a variety of different exposure curves, including linear, curved, and free-form exposure curves. Fig. 10 schematically shows a preferred embodiment of the replication process in which the exposure parameters are adjusted inline. In this case, the diffuser is removed to avoid unwanted interference with the replication process.Instead, the scattering properties of the light-sensitive material 30 into which the hologram is replicated are exploited. The master hologram 4 is exposed from a predetermined exposure point 12. The reference beams 8 emanating from the exposure point 12 are incident on the light-sensitive material 30 and the master element 2 at predetermined angles. The reference beam 8 is partially reflected by the interference patterns in the master hologram 4 to generate the object beam 10. The object beam 10 interferes with the reference beam 8 and forms a corresponding interference pattern in the light-sensitive material 30.

[0211] At the same time, a detector 26 can detect scattered light from a superposition of the reference beam 8 and the first-order diffracted light 38. The detection of the intensity distribution is facilitated by the fact that unexposed light-sensitive material scatters more strongly than exposed material. The intensity of the light scattered in the light-sensitive material correlates with the proportion of first-order diffracted light, which can vary depending on the efficiency of the master. In this embodiment, bright regions of the light intensity distribution preferably indicate a high efficiency of the master hologram 4, since the scattered light correlates positively with the light reflected into the first order by the master hologram 4. Darker regions, on the other hand, indicate a lower proportion of first-order reflection and thus a lower efficiency of the master hologram.The detected light intensities can therefore be used to evaluate the local efficiencies of the master hologram 4. This information can be incorporated into later steps and / or later runs of the replication process to improve efficiency by adjusting the replication parameters.

[0212] List of reference symbols

[0213] 2 Master element

[0214] 4 Master hologram

[0215] 6 substrate bodies

[0216] 8 Reference beam

[0217] 10 Object beam

[0218] 12 exposure points

[0219] 14 Target exposure point / first exposure point

[0220] 16 Target reference beam / first reference beam

[0221] 18 Target object beam / first object beam

[0222] 20 diffracted 0th order reference beam

[0223] 22 scattered reference beam of the 0th order

[0224] 24 Diffuser

[0225] 26 Detector

[0226] 28 Intensity distribution

[0227] 30 light-sensitive material

[0228] 32 Exposure curve

[0229] 34 Anchor point

[0230] 36 Exposure volume around exposure point or anchor point of the exposure curve

[0231] 38 first-order reference beam scattered by the light-sensitive material

[0232] 42 fifth anchor point in Fig. 7

[0233] 44 seventh anchor point in Fig. 7

[0234] 46 alternative seventh anchor point in Fig. 7

[0235] 48 alternative exposure curve

[0236] 50 Light source, especially laser

[0237] 52 horizontal adjustment tables

[0238] 54 vertical adjustment stage 56 scanning mirror

[0239] 58 Positioning module

[0240] 60 robot arm

[0241] 62 Fiber optic 84 Exposure point on scanning mirror

Claims

PATENT CLAIMS 1 . A measurement method for determining at least one replication parameter for a replication process using a master element (2) comprising the following steps: Providing a master element (2) comprising a reflection hologram (4), a light source (50), a detector (26) and a diffuser (24), wherein the diffuser (24) is positioned between the master element (2) and the detector (26), Irradiating the master element (2) with light by means of the light source (50), detecting an intensity distribution (28) of the light (22) emerging from the diffuser (24) by means of the detector and Determination of at least one replication parameter based on the recorded intensity distribution (28).

2. Measuring method according to the preceding claim, characterized in that higher values ​​of the intensity distribution (28) indicate a lower efficiency of the master element (2) in a replication process and the replication parameter is determined with a view to maximizing the efficiency of the master element (2) in a replication process and / or reducing the deviation of the efficiency from a target value.

3. Measuring method according to one of the preceding claims, characterized in that an irradiation of the master element (2) with light is carried out using at least two different exposure parameters and a determination of the at least one replication parameter is carried out on the basis of at least two intensity distributions (28) which were recorded for the at least two different exposure parameters.

4. Measuring method according to one of the preceding claims, characterized in that the at least one replication parameter corresponds to an exposure intensity, a wavelength, an exposure point (12) and / or an angle of the beam path of the light (8) in the exposure point (12).

5. Measuring method according to one of the preceding claims, characterized in that the at least one exposure parameter is an exposure point, wherein an intensity distribution (28) of the light (22) emerging from the diffuser (24) is detected for at least two different exposure points (12).

6. Measuring method according to the preceding claim, characterized in that a detection of an intensity distribution (28) of the light (22) emerging from the diffuser (24) is repeated for at least three exposure points (12), wherein the third and further exposure points (12) are selected by an iterative process on the basis of the already detected intensity distributions (28) in order to preferably converge to an exposure point (12) at which a maximum efficiency of the master element (2) for a replication process is to be expected.

7. Measuring method according to one of the preceding claims, characterized in that an intensity distribution (28) is detected for a plurality of spatially distributed anchor points (34) of an exposure curve (32), wherein a determination of the at least one replication parameter relates to a shift of the exposure curve (32) and / or a variation of the anchor points (34).

8. Measuring method according to one of the preceding claims, characterized in that a control pattern for the intensity distribution (28) is provided by detecting an intensity distribution (28) for an isolated diffuser (24), wherein the control pattern is taken into account when determining the at least one replication parameter on the basis of the detected intensity distribution (28).

9. Measuring method according to one of the preceding claims, characterized in that the diffuser (24) is a transmissive diffuser and preferably behaves essentially like a Lambert radiator.

10. Measuring method according to one of the preceding claims, characterized in that the detector (26) is a camera which preferably records the intensity distribution (28) as a two-dimensional image of the surface of the diffuser (24).

11. Replication method for replicating a hologram from a master element (2) into a light-sensitive material (30), characterized in that the replication method is carried out using at least one replication parameter which was determined by means of a measuring method according to one of the preceding claims.

12. Replication method according to the preceding claim, characterized in that the at least one replication parameter relates to an exposure intensity with which the master element (2) is exposed during the replication, wherein the intensity for different positions on the master element (2) is determined on the basis of the detected intensity distribution (28).

13. Replication method according to one of claims 11 or 12, characterized in that the at least one replication parameter relates to an exposure point (12) from which the master element (2) is exposed, preferably in order to maximize an efficiency of the master element (2) during replication.

14. Replication method according to one of claims 11 - 13, characterized in that the at least one replication parameter relates to a wavelength, wherein in the measuring method intensity distributions (28) for two or more wavelengths are detected and the wavelength used in the replication is preferably selected in order to maximize an efficiency of the master element (2) during the replication.

15. Replication method according to one of claims 11 - 14, characterized in that the replication method comprises the exposure of the light-sensitive material (30) and the master element (2) by moving an exposure point (12) along an exposure curve (32), wherein the exposure curve (32) preferably comprises a plurality of anchor points (34), and for each individual anchor point (34) or for the entire exposure curve (32) a replication parameter determined by the measuring method is applied during the exposure in order to preferably maximize an efficiency of the master element (2) during replication.

16. Replication method according to the previous claim, characterized in that the movement of the exposure point (12) comprises a change in its position and / or an angle of its beam path (8), wherein the exposure point (12) is preferably moved by means of a controlled positioning module.

17. Replication method according to one of claims 11 - 16, characterized in that the light-sensitive material (30) and a second side of the master element (2) are exposed to light in several steps, while a first side of the master element opposite the second side faces a detector, and the detector measures the intensity distribution (28) of the light emitted from the first side of the master element. (2) emerging light is detected during the exposure, wherein preferably in a later step of the exposure the replication parameter defined in the measuring method is adapted on the basis of the intensity distribution (28) detected in an earlier step of the exposure.

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