Measurement method for defining replication parameters and replication method using defined replication parameters

Abstract

The invention relates to a measurement method for defining at least one replication parameter for a replication method using at least one master element. A measurement method includes providing a master element including a reflected hologram, a light source, a detector, and a diffuser. A diffuser is positioned between the master element and the detector. The measuring method further comprises: irradiating the master element with light by means of a light source; capturing an intensity distribution of the light exiting from the diffuser by means of a detector; and defining at least one replication parameter based on the captured intensity distribution.

Description

[0001] The present invention relates to a measurement method for defining at least one replication parameter for a replication method using at least one master element. The measurement method includes providing a master element including 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 includes illuminating the master element with light using the light source; capturing an intensity distribution of the light emerging from the diffuser using the detector; and defining at least one replication parameter based on the captured intensity distribution.

[0002] Furthermore, the invention relates to a replication method for replicating a hologram from a master element into a photosensitive material by applying at least one replication parameter defined with the aid of the measurement method according to the invention.

[0003] Background and prior art

[0004] The present invention relates to the field of hologram replication.

[0005] A holographic optical element (HOE) typically refers to an optical element that uses holographic properties to achieve specific beam paths (e.g., transmission, reflection, diffraction, scattering, and / or deflection) of light. As a result, desired optical functions can be implemented compactly on any substrate. Holographic properties preferably exploit the wave nature of light, particularly coherence and interference effects. Both the intensity and phase of light are taken into account.

[0006] Such holographic elements have applications in many areas, for example in transparent displays (e.g. in display windows, refrigeration equipment, vehicle window panes), for lighting applications (such as information or warning signals in glass surfaces), and in photosensitive detection systems (e.g. for interior monitoring (eye tracking in vehicles or tracking the presence of people inside)).

[0007] Holograms are generated by the interference of a reference beam with light reflected or diffracted by the surface of an object (the object beam). Three-dimensional objects have traditionally been used to produce unique, customized holograms. In contrast, commercially available HOEs are usually mass-produced by means of a replication method. Such a replication method usually uses a master hologram with the image to be copied. Although the reproduced image is usually intended to correspond exactly to the image recorded in the master hologram, it may be desirable to introduce a target deviation from the master hologram in the replication method. Such a target deviation in the replicated image can be introduced in particular by adapting the exposure step of the replication method. The master hologram used is usually stored in a substrate body that carries the master hologram. The substrate body is preferably transparent and can have various shapes, such as a parallelepiped shape, a plate or a roller. The combination of the master hologram and the substrate body forms a master element.

[0008] The master element is exposed using a coherent light source to replicate the image from the master hologram onto a photosensitive composite. For mass production, the photosensitive composite can be provided in the form of a flowing web comprising the photosensitive material and one or more carriers or protective layers. To this end, the photosensitive web is preferably conveyed through various workstations to produce the HOE.

[0009] During exposure, the composite web is placed on the surface of the master element. To generate a reflection hologram, coherent light can pass through the composite web to the master hologram and then be reflected back by the master hologram into the composite web. The object beam and the reference beam interfere with each other in the photosensitive material to form a replicated hologram. The replication process is sensitive to changes in exposure angle, intensity, wavelength, etc., which must be adapted according to the optical functions of the master hologram. Typically, each master hologram is exposed according to a series of pre-programmed parameters. These parameters are usually configured so that a replicated hologram with exactly the same properties as the master hologram is generated. If a target deviation from the properties of the master hologram is desired in the replicated hologram, this deviation is usually calculated based on the theoretical properties of the master hologram.

[0010] To ensure error-free replication, the actual optical properties of the master hologram must correspond to the theoretical properties used to calculate the replication parameters. In practice, however, the master hologram can deviate from its target properties. This can lead to a mismatch between the exposure parameters and the master hologram, resulting in reproduction errors in the photosensitive material.

[0011] The process from the production of a master hologram to its replication involves a series of process steps that can alter the optical properties of the initially produced master hologram. For example, during the creation of the master hologram in localized areas, polymerization of the photopolymer can be accompanied by shrinkage. Shrinkage of the photosensitive material (e.g., due to partial drying and increased density due to polymerization) can reduce the wavelength required to generate the interference pattern recorded therein. Further deviations in the properties of the master hologram can occur due to temperature fluctuations during the production process or during gluing or embedding of the master hologram in a master element. Degradation of the master element over time can also occur, similarly altering the optical properties.

[0012] Such variations in the properties of the master hologram cannot be reliably predicted by simulation. Furthermore, there is a lack of feasible methods to metrologically capture the deviation of the optical function of the master hologram from the theoretical optical function.

[0013] For example, one could consider using an optical goniometer to analyze the actual optical function of a master element. However, since the optical function (and its deviation from the target value) can vary spatially across the entire master element, a large number of measurements would have to be performed to capture the variations across the entire master hologram. This complex process would require the use of equipment that analyzes the master hologram in sections over a long period of time and takes up a lot of space. Consequently, this approach is only feasible to a very limited extent. The necessary time expenditure becomes an even greater obstacle when considering that the function of the master element may also vary over time. Consequently, it may be necessary to repeat the method at regular intervals in order to monitor and / or compensate for deviations in the optical function of the master element. This is a particular obstacle in continuous production processes, as it can lead to production interruptions and reduced yields.

[0014] Therefore, there is a need for a method for analyzing the optical function of a master element, in particular for identifying deviations from a target function, which can be performed in a short time and is suitable for use in a series production facility. Furthermore, there is a need for a replication method that reliably takes into account or compensates for any errors in the master element.

[0015] Purpose of the Invention

[0016] The object of the present invention is to provide a measuring method which, using simple means, rapidly and reliably allows the optical properties of a master element to be determined, in particular any deviations of the optical function of the master element from a target function to be established. Furthermore, the object of the present invention is to enable the definition of replication parameters that increase the efficiency of a replication method using a master element, in which case it is particularly preferred to also provide the possibility of compensating for any deviations of the optical function of the master element from the target function during the replication method. Summary of the Invention

[0017] This object is achieved by the features of the independent claim. Advantageous configurations of the invention are described in the dependent claims.

[0018] In a first aspect, the invention relates to a measurement method for defining at least one replication parameter for a replication method, the replication method being implemented using a master element. The measurement method comprises the following steps:

[0019] - providing a master element comprising a reflection hologram, a light source, a detector and a diffuser, the diffuser being positioned between the master element and the detector,

[0020] - irradiating the master element with light by means of a light source,

[0021] - capturing the intensity distribution of the light emerging from the diffuser by means of a detector, and

[0022] - defining at least one replication parameter based on the captured intensity distribution.

[0023] Preferably, the master hologram is positioned in or on a substrate body to form a master element. Integrating the master hologram into the master element ensures high robustness. Because master holograms are very thin and sensitive, integration into larger components facilitates handling without having to touch the master hologram itself, which could damage it. However, the process steps used to produce the master hologram and integrate it into the master element can affect the desired optical functionality.

[0024] Firstly, the methods used to produce master holograms can lead to physical changes in the photosensitive material into which the master hologram is written. For example, polymerization during the mastering process can lead to undesirable shrinkage of the photosensitive material, causing its optical properties to change in an unfavorable manner. In addition, uncontrolled light scattering can lead to the exposure of additional structures within the photosensitive material and can reduce the effectiveness of the desired interference pattern. Perfect adjustment of the production conditions for the master hologram is generally not possible, or can only be achieved with great effort. Therefore, master holograms are usually produced within specific manufacturing tolerances. In order to counteract the effects of undesirable shrinkage or undesirable interference patterns, it is advantageous to localize and / or quantify their effects.

[0025] Furthermore, the process of integrating the master hologram into the substrate to form the master element is prone to errors. Uneven distribution of adhesive between the master hologram and the substrate, or uneven surface structure between the master hologram and the substrate, can lead to uneven distribution of optical losses across the master element. Due to the unpredictable nature of these losses and their varying spatial distribution, they cannot be directly quantified, simulated, or estimated. For reasons of economic feasibility, the integration of the master hologram into the master element must also be performed within defined manufacturing tolerances.

[0026] The invention makes it possible to define replication parameters adapted to the actual characteristics of the master element, preferably within the above-mentioned manufacturing tolerances.Thus, the replication method can be made more robust with respect to the above-mentioned tolerances.

[0027] Furthermore, replicating a master hologram into a photosensitive material can be optimally performed by directing the exposure beam (or exposure spot) along a predetermined path that is coordinated with the optical functionality of the master hologram. In this regard, the efficiency of the master element used for the replication process can depend on various parameters, such as the angle of incidence or wavelength.

[0028] In an ideal master element with a reflection master hologram illuminated from an optimal exposure point or exposure path, the exposure beam is preferably diffracted almost completely into the first order. The exposure beam (reference beam) can interfere with the reflected beam (object beam) in the intermediate photosensitive material to copy the hologram. Therefore, the portion of the exposure beam diffracted into the first order corresponds to the desired wave that can be used to replicate the 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 equal to zero, and the entire portion of the exposure beam would be reflected. Therefore, in the case of an ideal master element, no light should be transmitted through the master element to the opposite side.

[0029] However, if the master hologram has been deformed during integration into the master element, for example due to the weight of the substrate, an uneven adhesive layer or delamination effects, then the theoretical exposure point optimized for an ideal master element may not allow high efficiency over all areas of the master hologram. For example, shrinkage, an uneven adhesive layer or delamination effects may result in certain areas of the master hologram having to be illuminated from deviated exposure points or angles in order to generate sufficient waves for use.

[0030] The inventors' contribution is to have recognized that the efficiency of a master hologram for replication can be quantified and / or mapped by capturing light emerging from the side of the master element facing a detector. For this purpose, a diffuser is present between the master element and the detector.

[0031] The master element preferably comprises a side facing the detector. This may be referred to herein as the "first side of the master element" or the "side of the master element facing the detector". This is preferably the side of the master element that is not exposed, but a portion of the exposure beam (in particular the 0th order diffraction) may exit from this side.

[0032] The side of the master element on which the reference beam is incident for exposing the master hologram is preferably referred to in the present case 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 to and opposite to the first side of the master element. For example, the upper side of the master element is the first side and the lower side of the master element is the second side (or vice versa).

[0033] Within the meaning of the present invention, a "diffuser" (or "diffuser plate") is preferably a transparent plate or film configured to scatter and / or expand a light beam when it passes through the plate or film. The scattering is preferably achieved by means of a roughened surface of the diffuser, a pigment substance in the diffuser, a crystalline structure of the diffuser, and / or by taking into account the opalescent properties of the diffuser. Preferably, the function of the diffuser is roughly similar to that of a Lambertian diffuser. In a preferred embodiment, the diffuser can also be a holographically produced surface structure diffuser. Preferably, the chosen diffuser is not a volume holographic diffuser in order to avoid angular selectivity.

[0034] In a preferred embodiment, the diffuser can be applied directly to the first side of the master element, such that it is in direct contact with the master element. However, direct contact is not required. The contact can be mediated by another layer, such as an optical liquid or an optical incoupling element. Similarly, there can be no contact between the diffuser and the master element, such that the diffuser is positioned spaced apart from the first side of the master element. In some preferred embodiments of the present invention, a holding device can be provided for positioning the diffuser between the master element and the detector, the holding device for example defining the distance between the first (upper) side of the master element and the lower side of the diffuser. However, in various embodiments, the diffuser is preferably always located between the master element and the detector, and the diffuser (particularly in the embodiment of a diffuser plate) is preferably aligned parallel to the master element.

[0035] Positioning a diffuser between the detector and the master element increases the capture of the outgoing light, thereby making the measurement method more reliable. In particular, the diffuser preferably ensures that the outgoing light reaches the detector regardless of the angle of incidence. Because the surface roughness of the diffuser has the effect of scattering light transmitted by the surface in different directions, it is preferably possible to capture the outgoing light from virtually any angle within the hemisphere. This is particularly useful if the detector remains stationary while the measurement method is applied to different master elements or different exposure paths with varying illumination angles. Consequently, overly precise positioning of the detector becomes unnecessary.

[0036] By using a detector to capture the light transmitted by the diffuser, the intensity (and optionally the wavelength) of the transmitted light can be quantified. Consequently, the measurement method does not have to rely on subjective evaluation of the master element, and the expense of trial and error to compensate for deviations from the desired optical function or variations in the efficiency of the master element can be reduced and / or eliminated. Furthermore, there is no need to subjectively determine whether a master element is sufficiently damaged to warrant replacement. Instead, this can be determined objectively based on repeatable, quantitative measurements.

[0037] Capturing the intensity distribution of the light transmitted by the diffuser allows for the objective identification of areas affected by deviations or reduced efficiency in the optical function of the master element. Consequently, the measured deviations or reduced efficiency of the replicated master hologram can be used to mathematically adapt replication parameters. For example, the exposure intensity can be increased in areas with high-intensity transmitted light.

[0038] The intensity increase during replication can preferably be adapted in a manner that precisely compensates for optical losses. This can be done quickly and automatically by a processor, eliminating the need for repeated adaptations or subjective evaluation of the results. In particular, by capturing the light intensity emerging from the first side of the master element as a two-dimensional spatial distribution, the exposure light intensity can also be adapted in a spatially dependent manner. For example, the intensity values ​​at different spatially distributed points on the exposure curve can be adapted independently of each other.

[0039] By measuring the intensity of the emitted light to quantify inefficiencies in the master element, it is also possible to objectively assess whether the exposure point is suboptimal and requires adaptation. Adapting the exposure point preferably means changing the position of the exposure point from which the reference beam is directed to the master element. A large area of ​​the entire master element can be exposed from a single exposure point. In this case, the measurement method can preferably guide the selection of the optimal position of the exposure point. Similarly, 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 to a corresponding area of ​​a plurality of spatially distributed regions of the master element. In this case, capturing the light intensity as a spatially resolved distribution can visualize the efficiency of the corresponding area of ​​the master element and ensure that the exposure points are adapted according to the assignment of the exposure points to the areas of the master element.

[0040] By evaluating inefficiencies in the master element based on the intensity of the exiting light, it is also possible to determine whether the exposure angle is suboptimal and needs to be adapted. This can mean that the angle at which the reference beam impinges on the master element is changed through mathematical adaptation for the entire master element. However, since the intensity distribution is captured, rather than just a single intensity value, the exposure angle can also be adapted for individual regions of the master element.

[0041] Advantageously, the measurement method can also be performed for different exposure paths in order to identify the optimal exposure path (also referred to as "exposure curve" within the meaning of the present invention) for which the efficiency of the master hologram is maximized. Subsequent replication processes can be performed with the correspondingly optimized exposure path, and a corresponding adjustment of the intensity can optionally precisely compensate for any efficiency losses.

[0042] The measurement method thus enables a replication process that is precisely coordinated with the actual (not just theoretical) properties of the master element. The resulting holograms are of higher quality and can be produced with high reproducibility.

[0043] The placement of a diffuser between the master element and the detector, which captures the light emitted by the diffuser, enables a very compact design of the apparatus used for this measurement method. For example, a diffuser comprising a plate or film takes up very little space in the exposure chamber. The diffuser can be easily introduced and removed using a roller, a suction robot, manually, or in some other manner. Because the hologram replicated based on the measurement method is a reflection hologram, the diffuser has no effect on the positioning of the photosensitive material on the master element. This is because the photosensitive material is positioned on the opposite (second) side of the master element. The position of the rollers used to laminate or apply the photosensitive material to the master element can remain unchanged, as can the position of the devices for applying optical fluids, incoupling elements, etc. Furthermore, the detector, which is directed toward the diffuser, does not need to conflict with the exposure equipment (such as the light source, lens elements, mirrors, etc.), as these devices can also be directed toward the opposite side of the master element to replicate a reflection hologram.

[0044] The apparatus required for the measurement method can thus be easily integrated into an apparatus for continuous and / or automated replication of reflection holograms. The measurement method can be performed in a simple manner between intervals or cycles of the replication process, without requiring disassembly or rearrangement of the replication apparatus. In this regard, wear or degradation of the master element can be monitored, and / or replication parameters can be continuously adapted to compensate for variations in the master element.

[0045] Within the meaning of the present invention, a "replication parameter" is preferably a physical parameter that can be variably adjusted between rounds or individual repetitions of a hologram replication method. Preferably, the replication parameter is a physical parameter related to the exposure step of the replication method. In particular, the replication parameter is a physical property or physical parameter related to the exposure beam (used as a reference beam). Advantageously, the replication parameter can relate to the exposure of the entire master element. This is particularly applicable to replication methods in which a large area of ​​the master element is exposed from a single exposure point. Similarly, it is also advantageous that the replication parameter can be specific to a spatial region of the master element. This is particularly relevant for replication methods in which the master element is exposed gradually, preferably by gradually moving a light spot on the master element during a scanning process. In this case, for example, the replication parameter can be adapted with respect to the exposure intensity of different light spots on the master element.

[0046] The term "light spot" preferably denotes a point on the master element at which the light beam impinges on the surface of the master element, whereas the exposure point is preferably located outside the master element and denotes the point from which the light beam for exposing the master element impinges on the surface of the master element without significant deflection.

[0047] Replication parameters can also be specific to the time period of the exposure step.

[0048] For example, the replication parameters may be light intensity, wavelength, a range or selection of wavelengths, coherence, speed of movement of the exposure point, dwell time of the light point, angle of the incident exposure beam, absolute, relative, and / or angular position of the light source, absolute, relative, and / or angular position of light deflecting components (such as mirrors, prisms, lens elements, or optical fibers). In a preferred embodiment, the replication parameters may also relate to a sequence of exposure points, which is used in the form of an exposure curve for exposing the master element. It goes without saying that combinations of the aforementioned replication parameters are also conceivable and preferred, where, for example, replication parameters are defined for a plurality of anchor points of the exposure curve, with different intensity values ​​defined for each anchor point for exposing different regions of the master element.

[0049] Within the meaning of the present invention, "defining replication parameters" preferably includes estimating, calculating, selecting or determining replication parameters that produce or are intended to produce a more efficient master hologram. Preferably, defining the replication parameters involves determining an optimal radiation dose (in particular, radiation intensity and / or dwell time) to achieve the best possible exposure of the master hologram or a region thereof into the photosensitive material. The estimation, calculation, selection or determination can preferably be performed by a data processing unit. The result of the estimation, calculation, selection or determination can preferably be stored in a storage unit. The stored defined replication parameters can preferably be used in further process steps. The storage unit can preferably be accessed by a control unit for controlling the replication method in order to read out the defined replication parameters and / or transmit a signal to an actuator in order to expose the master element with the defined replication parameters.

[0050] Within the meaning of the present invention, a "detector" is preferably one or more devices for measuring and / or acquiring data. Preferably, the detector is designed to convert an analog and / or non-electrical input signal into an electrical and / or digital output signal. In this case, in addition to the light intensity, the detector can also represent another physical variable (such as wavelength) as voltage, pulse and / or current intensity. The output signal preferably includes information about the absolute or relative spatial distribution of the physical variable. The detector may comprise, for example, a camera, a scanner or a photodiode array. Preferably, the detector forwards the output signal to a processor, a memory and / or a communication unit.

[0051] Within the meaning of the present invention, a "light source" is preferably a device configured to emit electromagnetic radiation with a wavelength between 200 nm and 25 μm, in particular between 400 nm and 780 nm. The electromagnetic radiation may preferably comprise infrared radiation, visible radiation and / or ultraviolet radiation, with visible radiation being particularly preferred. In the context according to the present invention, UV radiation preferably means electromagnetic radiation in the range of 200 μm to 400 μm, particularly preferably 300 μm to 400 μm. In particular, visible radiation means electromagnetic radiation in the range of 400 nm to 780 nm, and infrared radiation means radiation in the range of 780 nm to 25 μm, preferably in the near infrared range, i.e. preferably in the range of 780 nm to 3000 nm, in particular 780 nm to 1400 nm.

[0052] The light source may include or be associated with a light deflection device (such as a lens element). The light source may preferably emit a collimated light beam, in particular a light beam with a specific width and direction. Similarly, it may be preferred that the light beam emitted by the light source has a desired divergence at the exposure point in a targeted manner. Preferably, the light source is also configured so that it emits coherent light. For example, the light source may be a laser.

[0053] Within the meaning of the present invention, an "exposure point" is preferably a point at which the light beam used to expose the master hologram is incident on the surface of the master element without significant deflection. The exposure point can be the light source itself or can be located on an element that directs the light from the light source (e.g., a mirror). For example, the exposure point can correspond to a focal point along the beam path, that is, 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 can coincide with the arrangement of a lens element or a mirror that achieves the final beam deflection before the light is incident on the master element. Variation of the exposure point preferably includes a variation in the position of the exposure point.

[0054] A "master element" is preferably a three-dimensional unit comprising at least one master hologram, whose form ensures that movement of the master element directly results in a corresponding movement of the master hologram. The master element may also comprise a plurality of master holograms, for example, two, three, five, or more. Preferably, the length and width of the master element correspond at least to the length and width of the master hologram. Preferably, the height of the master element is at least twice, preferably five times, and particularly preferably at least twenty times the height of the master hologram.

[0055] The master element preferably includes a substrate body that encloses or carries at least one master hologram. In an embodiment, the master element may include, for example, a transparent upper cover for protecting the master hologram between the cover and the substrate body. Preferably, the upper cover is also transparent. For example, the upper cover may be a transparent film or a glass layer.

[0056] The master element can preferably have the shape of a parallelepiped block, plate, pyramid or prism. The shape of the substrate body can be set accordingly.

[0057] Preferably, the base body of the master element can be formed of a material that is an optical plastic, preferably selected from the group consisting of: polymethyl methacrylate (PMMA), polycarbonate (PC), cycloolefin polymer (COP) and cycloolefin copolymer (COC), and / or formed of a material that is an optical glass, preferably selected from the group consisting of: borosilicate glass, quartz glass, B270, N-BK7, N-SF2, P-SF68, P-SK57Q1, P-SK58A and P-BK7.

[0058] Preferably, the base body and any covering of the master element have a refractive index between 1.4 and 1.6.

[0059] The material of the substrate can be selected based on the desired exposure angle or refractive index. It may also be preferred that the substrate be colored, for example, to selectively filter light wavelengths, thereby generating a hologram with a specific wavelength. In this way, a broadband light source can be used to expose different master holograms.

[0060] Preferably, the surface or cover of the master element comprises glass, PC, TAC, or PMMA. The surface material may be in the form of a film or plate for protecting the master hologram. However, the surface or cover material may also be the material of the substrate itself, and may have, for example, a parallelepiped or cylindrical shape.

[0061] Within the meaning of the present invention, a "substrate body" is preferably a three-dimensional block of material that carries or encloses the master hologram. Preferably, the substrate body is transparent. In some embodiments, the substrate body has multiple surfaces, including a planar surface that can be horizontally oriented. In some embodiments, the substrate body is prismatic, that is, it has a constant cross-section of any shape (e.g., square, polygonal).

[0062] Within the meaning of the present invention, the term "transparent" or "transparency" preferably relates to the property of a material such that it is substantially transmissive to light. Preferably, within the meaning of the present invention, a transparent material is transmissive to at least a portion of the electromagnetic spectrum preferably having a wavelength between 200 nm and 25 μm, particularly preferably between 400 nm and 780 nm. Particularly preferably, the transparent material (e.g., a transparent substrate) is transmissive to light within the wavelength range used when exposing the master hologram. The transparent material can also be colored in such a way that it selects for light radiation of one or more specific wavelengths.

[0063] Within the meaning of the present invention, a "master hologram" is preferably a holographic optical element, which comprises at least one hologram to be replicated. The master hologram is designed for optical functions (e.g. diffraction, reflection, transmission and / or refraction) for one or more wavelengths. For example, the master hologram can be a diffractive optical element (DOE). A diffractive optical element (DOE) uses a surface relief profile with a microstructure to realize its optical function. Alternatively, the basic structure can also be present in the volume of the element, for example in the form of local differences in the refractive index. Such a master hologram is considered to be a so-called "volume hologram". The light transmitted by the DOE can be converted into almost any desired distribution by diffraction and subsequent propagation. This can involve images, logos, texts, interference patterns, etc.

[0064] The process for producing a master hologram may preferably be referred to as "hologram origination" or "hologram mastering". The master hologram may be created by analog or digital methods. In an exemplary analog method, a first coherent light beam (object beam) is reflected from an object onto a recording material, which is simultaneously subjected to a second coherent light beam (reference beam). On or in the recording material, the object beam and the reference beam interfere, generating an interference pattern. This interference pattern is recorded by a photosensitive material, so that after processing this produces the shape of a surface relief pattern on the surface of the material, or a spatially varying refractive index in a material which is typically only a few micrometers thick. In order to view the 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 light beam contains the image of the original object. Subsequently, when further copies with the same image are created, the master hologram can be used as a new object.

[0065] The master hologram can also preferably be computer-generated. Microscopic gratings that generate diffraction effects can be produced, for example, by laser interference lithography. In this technique, two or more coherent light beams are configured so that they interfere at the surface of the recording material. The position of the light beams relative to the recording material can be controlled by a computer. Depending on the intensity of the laser, the recording material can be composed of almost any material. Other techniques such as electron beam lithography can also be used for the digital production of master holograms. The master hologram can preferably include glass, silicon, quartz, UV paint, photopolymer composites and / or metals such as nickel.

[0066] In a preferred embodiment of the present invention, higher values ​​of the intensity distribution indicate a lower efficiency of the master element in the replication process. Preferably, the light scattered by the diffuser corresponds to the zeroth (0th) order of diffraction of the exposure beam, which is transmitted through the master hologram and cannot be used for replication. The higher the proportion of (undesired) 0th order diffraction, the lower the proportion of 1st order diffraction, which is used as the object beam for replication. Therefore, higher values ​​of the intensity distribution at the detector indicate a higher proportion of 0th order diffraction and, therefore, a lower efficiency of the master element.

[0067] In other words, the light detected at the detector preferably corresponds to light transmitted by, and not diffracted by, the interference pattern of the master hologram. Since the angle and position of the exposure beam are selected so that it is guided by the theoretical interference pattern in the master hologram into a first-order diffraction, in the case of an ideal master hologram, the entire incident light should be reflected, thus forming an object beam. This applies particularly to an ideal master hologram designed to completely reflect the incident light. In the ideal case of such a master hologram, the proportion of the 0th-order diffraction would be zero, and the detector would not capture any light emerging from the diffuser. However, if light emerging from the diffuser is detected, this indicates that the efficiency of the master element has decreased at the point where the light exits the master element. However, reflection master holograms can also be configured, based on practical limitations or for specific applications, to reflect only a certain proportion of the incident light, even in the best possible scenario. In this case, even in the best possible scenario, the proportion of the 0th-order diffraction is not zero, but corresponds to a known theoretical target intensity that is not equal to zero. If the detected intensity exceeds this target intensity, this also preferably indicates that the efficiency of the master hologram has decreased at the point where the target intensity of the transmitted 0th order diffraction has been exceeded.

[0068] The greater the captured light intensity, the lower the local efficiency of the master element. For example, the master element may shrink at this location, resulting in a reduction in the thickness of the master hologram. This can reduce the reflection efficiency. Preferably, the intensity distribution indirectly captures the extent and distribution of this reduction in reflection efficiency.

[0069] Within the meaning of the present invention, the "efficiency" (local efficiency) of a point or region of a master hologram is preferably the ability of the master hologram to achieve the desired light-guiding function at that point or region without loss. For example, the local efficiency of a master hologram can be a measure of the intensity of the actual object beam (or used wave) compared to the intensity of an ideal object beam (or used wave). In the case of an ideal master hologram designed to completely reflect a 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. Similarly, as explained above, even in the best possible case, a reflection hologram may be designed to reflect only a certain proportion of the incident light. In this case, the intensity of the ideal object beam corresponds only to a certain proportion of the intensity of the reference beam. Thus, the target intensity of the theoretical first-order diffracted beam can correspond to the intensity of the reference beam (taking into account the Beer-Lambert law) or only to a certain proportion (a factor less than 1). The local efficiency of the master hologram can preferably be calculated by dividing the intensity of the first-order diffracted beam by the target intensity of the theoretical first-order diffracted beam. The intensity of the actual 1st order diffracted beam can be calculated by subtracting the intensity of the detected 0th order beam emerging from the diffuser from the intensity of the reference beam.

[0070] In these calculations, the Beer-Lambert law can be used to account for the distance traversed by the beam. For example, the local efficiency can be specified 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 the replication parameter.

[0071] Within the meaning of the present invention, the "efficiency" of the entire master hologram is preferably an assessment of the master hologram's ability to produce replicated holograms of 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 spatial distribution of the local efficiencies. In this regard, factors such as the location and surface area of ​​low-efficiency regions can play a role in determining the efficiency of the master hologram. This determination can be performed by a program on a data processing unit, such as an image processing algorithm known from the field of quality control.

[0072] The relationship between the captured light intensity and the efficiency of the master element can be used to select optimal replication parameters, such as the light intensity of the exposure. A computer program can be used to calculate the optimized exposure parameters based on the efficiency value of the master element. Preferably, this calculation is performed by a data processing unit. Such a data processing unit can be part of a control unit used to control the replication method.

[0073] The replication parameters are preferably defined with respect to maximizing the efficiency of the master element during the replication process or minimizing deviations from a target value. This allows the results of the measurement method to be used to optimize replication and ensure high quality of the replicated holograms. Furthermore, due to the adaptation of the replication parameters to optimize efficiency, the master element, despite potential damage, can advantageously continue to be used for a much longer period of time without significant loss of quality. This increases the economic viability of the method.

[0074] In another preferred embodiment of the present invention, the master element is illuminated with light using at least two different exposure parameters. Preferably, the intensity distribution of the light emerging from the diffuser is captured 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 parameters on the efficiency of the master element can be examined. In this regard, it can be determined in what direction (e.g., increase, decrease) the replication parameters can be corrected to improve replication efficiency.

[0075] Preferably, defining at least one replication parameter is accomplished based on at least two intensity distributions captured for at least two different exposure parameters. Multiple captures of intensity distributions for different exposure parameters can support conclusions such as whether shifting the exposure beam in a particular direction, adjusting the angle of the exposure beam in a particular direction, or increasing / decreasing the wavelength of the exposure beam increases the efficiency of the master element during a subsequent replication process. This information can be used to correspondingly adapt the replication parameters (e.g., in the direction identified as more favorable) to achieve optimal replication.

[0076] By recording a plurality of intensity distributions, it is further possible to compare these multiple intensity distributions in order to determine the intensity distribution (or the exposure parameters on which the intensity distributions are based) that indicates the highest efficiency of the master element during the replication process. This could be, for example, the intensity distribution with the largest total dark area, the intensity distribution with the lowest total brightness, or the intensity distribution of bright areas (i.e., areas with lower efficiency) corresponding to areas of the master hologram that are classified as least important (e.g., decorative areas of the hologram including text and decorative elements). On this basis, replication parameters or combinations of replication parameters that achieve the most efficient intensity distribution that is more favorable for replication can be identified. These replication parameters can be selected for use in the replication method or used to interpolate or extrapolate to more favorable replication parameters. The quality of the replicated holograms can be further improved, and the service life of the master element can be extended without loss of quality.

[0077] Compared to methods known in the prior art, the proposed measurement method advantageously provides a significantly faster and more reliable technique for improving replication efficiency and compensating for defects in master elements. In particular, measuring the effects of multiple possible exposure parameters on replication efficiency in this manner is more reliable than relying on simulations of the optical functions of the master element. The measurement method also eliminates the time-consuming analysis of multiple points on the master element using a goniometer.

[0078] In another preferred embodiment of the invention, the at least one replication parameter corresponds to the exposure intensity, the wavelength, the exposure point, the angle of the beam path of the light at the exposure point and / or the exposure curve of the exposure point.

[0079] Based on the proposed measurement method, one, several or all of the above-mentioned parameters for replicating a master element can preferably be optimized.

[0080] For example, defining exposure intensity as a replication parameter allows for simple and precise compensation of possible optical losses or reduced efficiency of the master hologram during the replication process. In this regard, for example, the exposure intensity can be locally increased or decreased depending on the local efficiency of the master element. If measurement methods have established reduced efficiency in specific areas of the master element, this reduced efficiency can be compensated for by preferably proportionally increasing the exposure intensity during replication of these areas. Advantageously, deviations from the ideal master hologram are compensated, and error-reduced, uniform replication of the master hologram is achieved.

[0081] Furthermore, the measurement method can advantageously define the wavelength as a replication parameter for the subsequent replication method. It is known that shrinking the master hologram can lead to a decrease in the wavelength of the interference pattern written therein, and that the master hologram effectively reflects at this reduced wavelength. In this case, the reference beam of the theoretical target wavelength can only be diffracted with reduced efficiency, increasing the proportion of transmitted radiation that is unavailable for the replication process. This is established in the measurement method by means of an increase in intensity at the detector that captures the light scattered by the diffuser.

[0082] If, for example, the measurement method is performed using different wavelengths as exposure parameters, the optimal wavelength can be defined (selected or interpolated) as the replication parameter for subsequent replication. As explained above, defining the optimal replication parameter can be based, for example, on the minimum intensity captured at the detector relative to that wavelength. In a preferred embodiment, the optimized wavelength can be defined for the entire area of ​​the master hologram, or different wavelengths can be defined for different areas.

[0083] If the replication parameter identified by the measurement method is the wavelength of the exposure light, the wavelength of the reference beam can therefore be brought closer to the optimally designed wavelength of the interference pattern in the master hologram. Additionally or alternatively, the master hologram can be repeatedly exposed with the target wavelength or one or more improved wavelengths to improve replication efficiency. The result is a much higher quality replicated hologram.

[0084] The measurement method can identify a multidimensional parameter space within which an ideal parameter combination is intended to be selected as a compromise solution. For example, such a parameter space can relate to the correlation between wavelength, angle, and efficiency.

[0085] Furthermore, it is known that the efficiency of reflecting a master hologram can depend, in particular, on the angle of incidence of the replication beam. Advantageously, the proposed measurement method can also be used to define the angle of the beam path of the light at the exposure point used for replication. The angle of the beam path of the light at the exposure point preferably determines the angle at which the master hologram is illuminated during replication. Depending on the configuration of the master hologram, different angles can also exist for different areas to improve the efficiency. By knowing the optical function of the master hologram, it is in principle possible to simulate an angular distribution of the master hologram at which the replication efficiency is optimized. However, this is firstly complex and, secondly, difficult to capture possible manufacturing tolerances.

[0086] Advantageously, the measurement method according to the invention allows for the rapid creation of an efficiency-angle diagram using simple means, which plots the efficiency of a master element as a function of different angles of incidence. This makes it particularly advantageous to adjust the angle of the beam path of the light used for exposure during replication so that the reference beam is incident on all areas of the master hologram at the desired angle during replication.

[0087] The measurement method even allows for reliable detection of possible deformations of the master hologram and their subsequent replication. For example, shrinkage or expansion of the master hologram can lead to different local requirements regarding the exposure angle. In the measurement method, the decrease in efficiency as a function of the illumination angle is captured as an increase in intensity at the detector. Optimizing the replication angle can thus be achieved, for example, by minimizing the intensity of the scattered light captured at the detector.

[0088] Furthermore, the efficiency of the replication method can be increased by determining more efficient exposure points based on measurement methods.

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

[0090] By capturing at least two intensity profiles at at least two exposure points, the measurement method can experimentally determine which of the at least two exposure points produces the best results. In particular, it can be determined which of the tested exposure points results in a lower brightness of the diffuser. Based on this, a preferred exposure point can be selected for the replication method. The exposure point can be the location of a point used for large-area or zone exposure of the master element. Another exposure point can also be selected based on the measured intensity profile, for example by interpolating between the two tested exposure points.

[0091] In another preferred embodiment of the present invention, the intensity distribution of the light emerging from the diffuser is repeatedly captured for at least three exposure points. Preferably, the third and further exposure points are selected based on the already captured light intensity distributions by a convergence function, in particular by an iterative process, in order to preferably converge to an exposure point at which the efficiency of the master element in the intended replication method is maximized. Alternatively or additionally, the third and / or further exposure points can be selected by a recursive process.

[0092] By capturing the intensity distribution for at least three exposure points, the replication parameters can be selected based on a large number of test results, thus approximating the exposure point with the highest possible efficiency for a specific master element.

[0093] It may be preferred to capture at least four, at least five, at least ten, at least twenty or more intensity distributions in combination with a corresponding number of exposure points. Thereby, the accuracy of determining the replication parameters may be further improved.

[0094] By selecting exposure points using a convergence function, the measurement method can be optimized so that the measurements performed are limited to those exposure points that are likely to produce the best results. This allows for faster and more reliable selection of the optimal exposure point compared to measurement methods that define all exposure points tested in advance or that do not use a convergence function to select them.

[0095] Within the meaning of the present invention, a "convergence function" for selecting parameter values ​​is preferably based on a mathematical or algorithmic process that refines the estimated variable until it is sufficiently accurate according to defined limits or converges towards an optimal value. For example, the convergence function can be based on an iterative or recursive algorithm.

[0096] In a similar manner, the convergence function can be used to optimize replication parameters other than the exposure point, such as wavelength or radiation intensity. Preferably, the convergence function is used to similarly determine the value of the replication parameter for which the efficiency of the master element in the replication method can be expected to be maximized.

[0097] For example, the first and / or second replication parameter values ​​can be selected based on the target replication parameter. The first and second replication parameters can also be selected based on a random principle, based on a maximum / minimum value of manufacturing tolerances, or based on some other formula. Based on the intensity distributions captured for the first and second replication parameters, an efficiency trend can be derived and used to select a third replication parameter. The selection of additional replication parameters and the capture of corresponding intensity distributions can be repeated until a certain number of parameter values ​​have been tested, until the difference between the efficiencies of successively tested parameter values ​​becomes less than a predefined value, or if no further increase in efficiency is captured. Preferably, the replication parameter is an exposure point. Also preferably, the replication parameter is a wavelength, angle, distance, or intensity.

[0098] The master hologram can be configured so that different locations are exposed with different replication parameters. For example, it may be necessary to expose some areas of the master hologram 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 the exposure beam. During scanning, the light spot preferably moves along a straight line. In order to achieve regional changes in the replication parameters, the exposure point can preferably also move on a nonlinear path (such as a curve). In this case, the change in intensity can be achieved by adjusting the intensity of the light source. The change in angle can be achieved by tilting the light source or the optical intermediate component so as to generate a reference beam with the desired angle. The wavelength can be adapted, for example, by turning on one or more lasers or applying a filter. The path of the exposure point and the variable parameters can be set as instructions in a memory.

[0099] In a preferred embodiment of the present invention, the master element is designed to be exposed using an exposure curve. Preferably, the exposure curve defines a path of exposure points used to replicate the master element. Besides position, further replication parameters may also be varied at different points or sections of the exposure curve. Preferably, the exposure angle is varied along the exposure curve.

[0100] When exposing a master element using an exposure curve, it is preferred to perform a zone exposure of the master element. For example, the master element can be subdivided into columns, each column being assigned a section of an exposure curve, in particular an anchor point. Similarly, the master element can be subdivided into a raster, each cell of the raster being assigned a section of an exposure curve, in particular an anchor point. Other configurations, such as free-form curves, can also be advantageous.

[0101] The use of an exposure curve advantageously allows the angle at which the reference beam impinges on the master element to be varied during exposure. In particular, the angle of incidence of the light can be varied depending on the position of the corresponding light spot on the master element. This can be achieved by means of a suitable curvature of the exposure curve. This allows compensation for curvature of the master element during a measurement or replication method, which curvature is predefined based on the process used to produce the element and deviates from the desired surface shape of the replicated hologram. In other words, a curved exposure curve can compensate for the curvature of the substrate or cover of the master hologram during exposure (this curvature being defined, for example, with respect to a reference coordinate system defined by the shape of the substrate).

[0102] This exposure profile is particularly advantageous if the replicated hologram is itself curved or is intended to be integrated into a curved surface. One example is a hologram with an optical function configured to converge the light beam to a specific point. Another example is a hologram intended to be integrated into a curved transparent screen, windshield, or some other non-planar surface.

[0103] Advantageously, the exposure curve can include multiple anchor points. A measurement method can be used to define replication parameters for one or more anchor points. The exposure curve and / or the program for calculating the exposure curve can be calculated so as to take into account a two-dimensional or three-dimensional space around the anchor points, within which the positions of the anchor points can be defined. The two-dimensional or three-dimensional space can preferably be a square or a parallelepiped and can be referred to herein as an exposure volume. The measurement method can preferably be used to determine the optimal position of the anchor points (or "exposure points") within the exposure volume. In this way, the exposure curve can be adapted without having to recalculate a completely new curve.

[0104] Within the meaning of the present invention, an "exposure curve" is preferably the path along which the exposure point moves in order to expose the master element. While this path can be linear, it is preferably curved in at least one plane. Preferably, the exposure curve connects a limited number of spatially distributed anchor points whose absolute or relative positions relative to the master element are predefined. Preferably, each anchor point is assigned a local area of ​​the master element. The exposure curve is preferably based on a mathematical function, in particular a nonlinear function, that passes 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 connecting these anchor points are stored in a memory accessible to the control unit.

[0105] In a further preferred embodiment of the measurement method, the intensity distribution is captured for a plurality of spatially distributed anchor points of the exposure curve, thereby defining at least one replication parameter which is related to a shift of the exposure curve and / or a change of the anchor points.

[0106] By capturing the intensity distribution of light emerging from the diffuser for different anchor points of the exposure curve, local inefficiencies of the master element can be compensated independently of each other. If the replication parameters of an anchor point of the exposure curve are adapted, the exposure curve can provide a smooth transition to other anchor points, where the replication parameters may not have been adapted, or may have been adapted differently. This can improve the efficiency of the master element or subsequent replications. At the same time, the replicated hologram can be of high quality overall, with seamless transitions between areas exposed with different parameters.

[0107] Advantageously, in this embodiment, defining at least one replication parameter is related to a shift of the exposure curve and / or a change of the anchor point.

[0108] The intensity distribution may indicate that the master element has uniformly distributed inefficiencies, which requires a uniform increase in the exposure intensity. This may be the case if the total brightness of all recorded intensity distributions is approximately equal. For example, the differences in the recorded intensity distributions may be smaller than a predefined absolute value. The replication parameters can be uniformly adapted to the exposure curve, for example by uniformly increasing the exposure intensity. The exposure curve can also be uniformly adapted to the actual optical function of the master element, for example by bringing it closer to the master element. As a result, the exposure intensity is increased and, depending on the embodiment, the exposure angle is adapted. The entire exposure curve can also be shifted (horizontally) in a plane parallel to the master hologram in order to bring the replication parameters closer to the actual optical function of the master element.

[0109] The intensity distribution can also indicate a total shift in the wavelength written into the master hologram (e.g., due to shrinkage or expansion of the entire master hologram), a tilt of the master hologram, or a deviation in another parameter that extends uniformly across the entire master hologram. Preferably, the corresponding replication parameter can be varied uniformly across the entire exposure curve, for example, by increasing or decreasing the wavelength by a corresponding value or by tilting the entire exposure curve by a specific angle.

[0110] By shifting the replication parameters for the entire exposure curve, fine-tuning made during the creation of the exposure curve, in particular the relative positions of the anchor points and the relative values ​​of their replication parameters, can be continued. This can easily improve the overall efficiency of subsequent replications without having to recalculate the entire exposure curve.

[0111] Alternatively, the intensity distributions measured for different anchor points can indicate different efficiencies. This allows for defining replication parameters for one anchor point independently of the other anchor points, in order to improve the efficiency of the master hologram during exposure from that anchor point. For example, the position of an anchor point can be changed, and the exposure curve adapted accordingly to achieve a smooth transition to the adjacent anchor point. Preferably, the new position of the anchor point is selected from the exposure volume. Additionally or alternatively, different replication parameters can also be defined for each anchor point. Instead of position, these could be, for example, intensity, exposure angle, or wavelength.

[0112] In a preferred embodiment of the present invention, the illumination of the master element is controlled by means of a control unit. The control unit can determine and / or monitor parameters for performing the measurement method or the replication method. For example, the control unit can be configured to determine the intensity, wavelength or angle of the light beam and / or the exposure point for performing the measurement method or the 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 associate the determined intensity distribution with one or more exposure parameters for performing the measurement method. For example, the recorded intensity distribution can be associated with a specific position of the exposure point (e.g., an xyz coordinate position). Preferably, the stored data can be retrieved via an output unit and / or used to fix the replication parameters.

[0113] In this sense, the measurement method can generate an intensity distribution that is specific to a certain exposure parameter or a certain combination of exposure parameters. This allows the influence of the exposure parameters on the efficiency of the master element to be investigated. Furthermore, the optimized replication parameters can be defined based on the exposure parameters for which the optimal intensity distribution was recorded.

[0114] Also preferably, the control unit can calculate an indication of an exposure curve for exposing the master hologram, or retrieve such indication from a memory. For example, the control unit can calculate or retrieve the positions of multiple anchor points on the exposure curve and / or a mathematical function connecting these anchor points. The control unit can also be configured to send a signal to one or more actuators to cause the exposure point to move along the exposure curve. The actuators can preferably include one or more motors, in particular one or more adjustment stages and / or one or more rotary drives. The actuators can preferably be part of a positioning module.

[0115] The speed at which the exposure point moves can be preprogrammed, and the control unit is preferably configured to move the exposure point along the exposure curve at the preprogrammed speed. Preferably, the control unit can also calculate or retrieve replication parameters to be used at each anchor point. The control unit can also calculate or retrieve replication parameters to be used between these anchor points, in which case these parameters can be determined based on a mathematical function, such as by interpolation.

[0116] Within the meaning of the present invention, the term "control unit" preferably refers to any computing unit comprising a processor, processor chip, microprocessor, or microcontroller, which is capable of automatically controlling components of the method, such as the light source intensity, exposure point position, exposure angle, and / or any actuators for adjusting exposure parameters. The components of the control unit can be configured generically or individually for the respective embodiment. Preferably, the control unit comprises a processor, a memory, and computer code (software / firmware) for controlling the components of the device.

[0117] The control unit may also comprise a programmable printed circuit board, a microcontroller, a programmable logic controller (PLC) or some other means for receiving and processing data signals from components of the device, such as data signals from sensors relating to the exposure parameters currently in use.

[0118] The control unit preferably includes 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 can be written in any desired programming language or model-based development environment, such as C / C++, C#, Objective-C, Java, Basic / VisualBasic, MATLAB, Python, Simulink, StateFlow, Lab View, or assembler, but is not limited thereto.

[0119] The software and all functional descriptions of the software by describing the control of specific components or aspects of the methods described herein are considered to be technical features directly output by the device used. Therefore, the functional descriptions of the software can be regarded as preferred and limited embodiments of the present invention.

[0120] The term "control unit configured to" perform specific working steps, such as determining the position of the exposure point, may include custom or standard software installed on the control unit and initiating and regulating these operating steps.

[0121] The control unit is preferably configured to adjust one or more exposure parameters during the measurement method. For example, the control unit can be configured to turn the light source on or off. The control unit can also be configured to adjust the brightness value, wavelength, position, tilt, direction, and / or movement speed of the light source. The control unit can also be configured to adjust the exposure parameters by moving the positioning module.

[0122] The positioning module may preferably include or carry one or more light-guiding components, such as lens elements, prisms, optical fibers, or mirrors. The control unit may control the position, inclination, and / or movement speed of one or more light-guiding components. The control unit may control, for example, the coordinate position and / or three-dimensional inclination of a scanning mirror. In this way, the orientation of the light from the light source may 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 movement speed of one of the aforementioned components. This change in speed may compensate for inefficiencies in the master element. The control unit may also be configured to control the operation of the detector, such as focusing or shutter time. The control unit may be configured to process the data from the detector with the aid of a data processing unit, for example, to compensate for the inclination of the detector relative to the first side of the master element. The control unit may also be configured to evaluate the data from the detector, for example, to assess the efficiency of the master element as acceptable or unacceptable, thereby selecting parameters for further measurement methods or defining optimized replication parameters.

[0123] In another preferred embodiment of the present invention, a control pattern for the intensity distribution is provided. This preferably involves capturing the intensity distribution of an isolated diffuser without a master element. This preferably means capturing the effect of the diffuser itself on the intensity distribution. This control pattern is preferably taken into account when determining at least one replication parameter based on the captured intensity distribution.

[0124] Within the meaning of the present invention, a stand-alone diffuser is preferably a diffuser which is not used in combination with a master element. Preferably, if a control pattern is captured, the diffuser is the only component between the diffuser and the detector.

[0125] Capturing the intensity distribution of the diffuser itself when exposed to a light source yields intensity control values ​​for each point and / or area of ​​the master element. The intensity distribution captured by the master element can be compared with the intensity distribution of the diffuser itself. This allows for the measurement method to determine optimal replication parameters based on the actual properties of the master element, taking into account any intensity losses caused by the diffuser. For example, the diffuser's material may absorb specific wavelengths of light, thereby affecting the wavelength range captured by the detector. Quantifying the effect of the diffuser avoids erroneous conclusions that the master element successfully reflects light absorbed by the diffuser. Consequently, replication parameters can be determined more accurately, improving the efficiency of the replication method. Similarly, locally varying scattering angles or transmission characteristics may occur in the diffuser and affect the intensity distribution measured at the detector. Acquiring a control pattern advantageously allows for the consideration of such diffuser effects on the measured intensity distribution.

[0126] In another preferred embodiment of the invention, the diffuser is a transmissive diffuser, which preferably behaves substantially like a Lambertian emitter.

[0127] A "Lambertian emitter" (or "Lambert emitter") is preferably a light emitter whose radiant intensity of light scattered in the direction of an observer (or detector) is independent of the direction of observation. A Lambertian diffuser preferably appears equally bright from all directions in the hemisphere from which the illuminating light emerges.

[0128] The diffuser preferably functions approximately like a Lambertian emitter. The maximum difference between the radiation intensities that can be determined from a specific point on the diffuser for two arbitrary angles in a hemisphere preferably does not exceed 50%, even more preferably does not exceed 30%, and even more preferably does not exceed 10%. The diffuser's functioning substantially or approximately like a Lambertian emitter reduces the sensitivity of the measurement method to the position of the detector. It is particularly advantageous if the detector captures the light intensity emerging from the diffuser with approximately the same sensitivity, regardless of its angle relative to the diffuser. This allows the use of a single detector for large diffusers and / or master elements, thereby increasing the reliability of the measurement method.

[0129] Preferably, the deviation of the diffuser from the Lambertian target function is determined by capturing one or more control patterns. In this way, in particular, the effect of the capture angle on the intensity distribution can be quantified. For example, if only a single, centrally positioned camera is used to capture the intensity distribution of a master element, peripheral areas of the master element may appear darker due to their non-orthogonal angle relative to the camera lens. This effect is preferably quantified and taken into account when evaluating the recorded light intensity.

[0130] In a preferred embodiment of the present invention, the diffuser has a roughened surface facing the detector. Preferably, the surface roughness Ra of the diffuser's surface facing the detector is 0.1 μm to 100 μm, particularly preferably 1 μm to 10 μm. It has been established that, for these roughnesses, the diffuser behaves essentially like a Lambertian emitter and, at the same time, produces a sufficiently precise intensity distribution.

[0131] Within the meaning of the present invention, the surface roughness Ra is preferably the average value of the profile height deviations from a surface height mean line.

[0132] The diffuser is preferably transparent to all wavelengths between 400 nm and 780 nm, in particular between 200 nm and 25 μm. Preferably, all wavelengths in the visible spectrum, in particular between 400 nm and 780 nm, are equally transmitted by the diffuser. If specific wavelengths are absorbed by the diffuser material, this is preferably taken into account when interpreting, further processing, or using the captured intensity distribution. This can be achieved with the aid of a control pattern that represents the intensity distribution of the diffuser without the master element.

[0133] The width and length of the diffuser are preferably at least equal in size to the width and length of the master element. The thickness of the diffuser is preferably much smaller 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 having one of the preferred thicknesses, the diffuser can be kept thin enough to clearly identify the intensity distribution and allow accurate conclusions to be drawn about the corresponding areas of the master element that transmit captured light. The homogenizing effect of the diffuser can be kept minimal, allowing meaningful intensity distribution patterns to be captured.

[0134] In another preferred embodiment of the present invention, the detector is a camera, preferably capturing the intensity distribution as a two-dimensional image representation of the diffuser's surface. Advantageously, the camera can quickly convert the intensity distribution into a digital image that can be stored and / or input into a processor for calculating optimized replication parameters. Furthermore, cameras with high resolution, small size, and low weight are available. A lightweight, compact camera can be moved synchronously with the scanning exposure point to generate an image of the intensity distribution of diffuser / master elements of any size. In this case, small actuators can be used, and the energy consumption of the method can be kept low.

[0135] Alternatively, partial areas of the diffuser can be illuminated sequentially, so that the camera captures the intensity distribution of each partial area. The processor can then combine these intensity distributions to reconstruct the intensity distribution over the entire diffuser. This embodiment can be used, for example, to capture intensity distributions for different anchor points of the exposure curve.

[0136] Advantageously, the camera can include 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 combine multiple images. The measurement method can be performed particularly quickly and reliably, with low energy consumption.

[0137] Preferably, the camera lens can be positioned centrally and parallel to the diffuser plane. In this way, the captured intensity distribution image can directly correspond to the image of the intensity distribution of the master element. However, for example, due to space constraints in the exposure chamber, it is also preferred that the camera be positioned off-center and / or tilted relative to the diffuser. In this case, the directly captured intensity distribution can advantageously be input into a processor configured for image correction in order to reconstruct the intensity distribution as if viewed from a central, plane-parallel position.

[0138] In some embodiments of the present invention, it is preferred that the camera be a black and white camera. In this regard, an image of the intensity distribution emerging from the diffuser can be created quickly and with low data consumption. This allows for increased resolution of the captured intensity distribution. The captured intensity distribution can be quickly processed to determine optimized replication parameters. If the goal is to investigate the efficiency of a master element when exposed at different wavelengths, a black and white camera can be used by exposing the master element to different wavelengths sequentially rather than simultaneously. Therefore, a black and white camera is a particularly flexible and usable type of detector.

[0139] In some embodiments of the present invention, the camera is preferably a full-color camera, preferably an RGB camera. Such a camera can be used to capture the intensity of different wavelengths transmitted by a master element or diffuser. In particular, if the master element is simultaneously exposed with light beams of different wavelengths, an RGB camera can be used to extract the intensity distribution of the different wavelengths from a single image. In particular, the different color channels of the captured full-color image can be isolated from each other by a processor. If the measurement method is used with an RGB camera to investigate the efficiency of the master element at different wavelengths, it is preferred that the different wavelengths be sufficiently separated from each other. For example, there may be at least 50 nm, and particularly at least 100 nm, between the two investigated wavelengths. The color channels of an RGB camera are typically represented by overlapping sensitivity curves of the camera sensor for each wavelength range corresponding to the red, green, and blue portions of the spectrum, respectively. In overlapping regions, the efficiency of such a camera in identifying light wavelengths may be low. By selecting the wavelengths used to test the master element so that they are sufficiently separated from each other, the wavelengths fall within the high sensitivity range of the RGB camera's color curve, thereby improving the accuracy of the generated results.

[0140] The replication parameters determined by the measurement method can be specific to a certain wavelength, for example by increasing the intensity of the corresponding beam or shifting its wavelength. They can also be applied globally to all investigated wavelengths, for example by increasing the intensity of all exposure beams.

[0141] In a second aspect, the invention relates to a replication method for replicating a hologram from a master element into a photosensitive material. The replication method is implemented by applying at least one replication parameter defined with the aid of the above-described measurement method.

[0142] By using the measurement method according to the present invention to determine the replication parameters for a specific master element and applying these replication parameters when executing the replication method, the replication of the actual optical function of the master element can be optimized. Based on the data experimentally captured during the measurement method, it is possible to compensate for production tolerances of the master element within certain manufacturing tolerances and for deviations of the resulting optical function from the target function. This has proven to be significantly more accurate and reliable than using simulation methods combined with specific replication parameters to estimate the efficiency of the master hologram. The replication method can be executed significantly more efficiently and with a higher degree of reproducibility. The resulting replicated holograms are of higher quality. Since the replication parameters can be determined quickly and efficiently using the measurement method, the replication method can be regularly updated to ensure that it is always adapted to the current state of the master element.

[0143] Because the switch from the measurement method to the replication method preferably involves only applying the photosensitive material to the second side of the master element and removing the diffuser from the first side of the master element, the switch can be completed quickly. Consequently, the measurement method can be performed without long production downtime or periodically. The replication method can be performed over an extended period without having to replace aged master holograms. Consequently, high replication efficiency is achieved over an extended period.

[0144] Within the meaning of the present invention, a "photosensitive material" is preferably a material that reacts to exposure to a sufficiently coherent light source by producing an interference pattern in the material volume. Examples of such materials are silver halides, dichromated gelatin, photopolymers, photochromic materials, and photothermoplastics. The photosensitive material may be provided with a carrier film on at least one side to facilitate its handling. The photosensitive material may also be enclosed in a carrier film. The carrier film is preferably transparent to the reference and object beams used to expose the photosensitive material.

[0145] Preferably, the photosensitive material is in the form of a photosensitive composite web comprising a photopolymer layer. Preferably, the photopolymer layer is enclosed between two transparent carrier films. The photosensitive composite web can be supplied in roll form, allowing it to be laminated onto the master element, exposed, and removed in sections. This allows the replication method to be performed continuously.

[0146] Within the meaning of the present invention, a "composite" is preferably a multilayer material composed of two or more different components with different physical properties, which are bonded to one another at interfaces. Preferably, the bonds between the individual components are constructed so that they cannot be separated by the slightest force and are therefore considered permanent. The composite can be composed of a photosensitive liquid, solid, or resin, for example, enclosed between two transparent carrier films. Alternatively or additionally, the composite web can include a stack of layers, each layer being photosensitive to a different spectral range.

[0147] Within the meaning of the present invention, a "photosensitive composite web" is preferably a composite material whose length is at least twice, preferably at least five times, and even more preferably at least twenty times, its width. For example, the thickness of the composite web is preferably set so that it has a certain flexibility, allowing it to be partially wound onto a roll. Preferably, the composite web has a thickness of at most 300 μm. The composite web comprises a photosensitive material. Preferably, the composite web encloses the photosensitive material between two transparent carrier films, the refractive index of which is similar to that of the photosensitive material. Preferably, the refractive index of the carrier films and the photosensitive material is between 1.4 and 1.6. The photosensitive material can be, for example, a photosensitive photopolymer or dichromated gelatin. The photosensitive material can be photosensitivity across the entire visible spectrum or wavelength-selective.

[0148] The exposure can preferably be achieved using a coherent light source. Coherence preferably refers to a property of light waves according to which a fixed phase relationship exists between two wave trains. Due to the fixed phase relationship between the two wave trains, a spatially stable interference pattern can be generated. With regard to coherence, a distinction can be made between temporal coherence and spatial coherence. Spatial coherence preferably refers to a measure of the fixed phase relationship between the wave trains perpendicular to the propagation direction and is given, for example, for parallel light beams. Temporal coherence preferably refers to a fixed phase relationship between the wave trains along the propagation direction and is given, in particular, for narrow-band, preferably monochromatic light beams.

[0149] The coherence length preferably denotes the maximum path length difference or flight time difference between two light beams starting from a starting point so as to still produce a (spatially and temporally) stable interference pattern during their superposition. The coherence time preferably refers to the time required for light to travel the coherence length.

[0150] In a preferred embodiment, the light source is a laser. Particularly preferably, the light source is a narrowband laser, preferably a monochromatic laser, preferably with a wavelength in the infrared, visible and / or UV range (preferably 200 nm to 25 μm, even more preferably 400 nm to 780 nm). A laser preferably denotes a light source that emits laser radiation. Non-exhaustive examples include solid-state lasers (preferably semiconductor lasers or laser diodes), gas lasers, or dye lasers. The laser can be selected so that it emits light with a specific wavelength or within a specific wavelength range. This can be achieved by selecting a laser composed of a suitable material. For example, a ruby ​​laser, a He-Ne laser, an Argonne laser, or a quartz crystal laser can be used. + Laser, Kr + Laser, He-Cd laser and / or Nd 3+ :YAG lasers. These or other types of lasers can be combined with an optical parametric oscillator to generate coherent beams of light with different wavelengths. Lasers with different wavelengths can also be combined, for example to produce RGB lasers.

[0151] Different types of lasers, in particular solid-state lasers, can be combined with an optical parametric oscillator (OPO) to generate coherent light beams with different wavelengths as a tunable system. The OPO preferably comprises an optical resonator and at least one nonlinear optical crystal. Preferably, a system with multiple converter crystals can be used, in which three-wave mixing (f_pump = f_signal + f_idler) is used. By varying the frequencies f_signal and / or f_idler, laser wavelengths can be generated over a very wide wavelength range. This covers, in particular, the entire visible and infrared ranges of the electromagnetic spectrum.

[0152] Other light sources, preferably coherent light sources, may also be used.Preferred are narrowband light sources, preferably monochromatic light sources, eg comprising light emitting diodes (LEDs), optionally in combination with a monochromator.

[0153] The coherence of the light beam is relatively less relevant for the generation of relief holograms. In contrast, especially for the replication of volume holograms, it is preferred that the light source used for replication has sufficient coherence.

[0154] The volume hologram is preferably written into the composite web by replicating a master hologram. Due to the interference of the object and reference beams within the hologram volume, a series of Bragg planes are preferably generated. Therefore, the volume hologram preferably has a non-negligible extent in the propagation direction of the beams, where the Bragg conditions apply at the reconstruction of the volume hologram. For this reason, the volume hologram is advantageously wavelength- and / or angle-selective.

[0155] In a preferred embodiment of the present invention, the coherence length of the light source is preferably at least 150 μm, more preferably at least 500 μm, and even more preferably at least 2 mm. Preferably, the coherence length is at least twice the distance between the photosensitive material and the master hologram. However, the coherence length is preferably not too long to avoid the presence of parasitic microstructures in the hologram, such as interference gratings. The maximum preferred coherence depends on the type of hologram and the geometry of the exposure module. In a preferred embodiment, the coherence length of the light source is less than 1 m.

[0156] The light source may comprise a plurality of light sources. The plurality of light sources may preferably be arranged such that they scan a line or area of ​​the photopolymer composite in light contact with the master element.

[0157] The steps in hologram production following exposure are generally known. For example, the exposed web of photosensitive composite material can be cured using a UV light emitter. This can be performed in a separate chamber from the exposure process. The exposed and cured composite web can then be cut into individual holograms, rolled up, or further processed in some other manner.

[0158] In another preferred embodiment of the present invention, at least one replication parameter is related to the exposure intensity with which the master element is exposed during replication. Replication using the exposure intensity defined in the measurement method can compensate for local or global efficiency losses due to the manufacturing process and / or aging of the master element. In this way, the master element can still be used for replication, maintaining nearly the replication quality achievable with an ideal master element.

[0159] Preferably, the intensity at different locations on the master element is defined based on the captured intensity distribution. This allows not only the overall deviation of the master element from the target function but also local deviations to be compensated. This allows the replication method to be performed with high quality even for unevenly deformed master elements.

[0160] In another preferred embodiment of the present invention, at least one replication parameter is related to the exposure point at which the master element is exposed, preferably in order to maximize the efficiency of the master element during replication. As explained above, the process used to manufacture the master element may alter the function of its interference pattern relative to the theoretical function. According to standard practice, the master element is exposed with parameters that are precisely coordinated with the theoretical function. Since the actual master element has an optical function that differs from the theoretical function, it is also advantageous to adapt the exposure parameters. These exposure parameters may, in particular, include the position of the exposure point.

[0161] By performing replication using exposure points determined by a measurement method, replication efficiency can be increased. For example, the exposure points selected by the measurement method can cause a greater proportion of the reference beam to be diffracted in the first order to form the object beam. As explained above, this can involve optimized exposure points for exposing the entire master element. Similarly, the exposure points can be points on an exposure curve that can be adjusted based on the results of the measurement method to adapt the exposure curve to the actual characteristics of the master element.

[0162] In another preferred embodiment of the invention at least one replication parameter is wavelength dependent, in the measurement method intensity distributions for two or more wavelengths are captured, and preferably the wavelengths used during replication are chosen to maximize the efficiency of the master element during replication.

[0163] Capturing the intensity distribution for at least two different wavelengths allows experimental determination of the effect of wavelength on the efficiency of the master element. This can be particularly useful if contraction or expansion alters the wavelength of the interference pattern stored in the master hologram volume. If the exposure wavelength is selected based on multiple investigated wavelengths, the replication method can be performed, for example, with a wavelength that was previously tested in the measurement method or calculated by interpolation or extrapolation from the tested wavelengths. Consequently, the replication method can be performed with greater efficiency and ensures holograms of extremely high quality.

[0164] For exposure of the entire master element a single optimized wavelength may be selected. Preferably, however, multiple wavelengths defined by the measurement method may be used for multiple corresponding points or regions of the exposure curve, for example by means of a tunable laser.

[0165] In another preferred embodiment of the invention, the replication method comprises exposing the photosensitive material and the master element by moving the exposure point along an exposure curve, which exposure curve preferably comprises a plurality of anchor points, and applying replication parameters defined by the measurement method during exposure for each individual anchor point and / or for the entire exposure curve, in order preferably to maximize the efficiency of the master element during replication.

[0166] Advantageously, the replication parameters determined by the measurement method can be used for only one anchor point. The other anchor points can still be replicated using the target parameters, and the remainder of the exposure curve can be recalculated. Also advantageously, the replication parameters determined by the measurement method can be used for only some anchor points, while the other anchor points are replicated using the target parameters. Accordingly, the exposure curve can also be recalculated.

[0167] By replicating a master hologram using an exposure curve, different regions of the replicated hologram can have different optical properties. These properties can closely match those of the master hologram. For example, different regions of the replicated hologram can have different reconstruction angles. This can be useful, for example, for holograms incorporated into curved surfaces, such as automotive interiors.

[0168] By adapting 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 adjacent anchor points can be seamlessly achieved, making the regional adaptation unnoticeable in the replicated hologram. The resulting holograms can be produced with high quality, and the same master element can be reused for extended periods without replacement.

[0169] If the intensity distribution captured in the measurement method indicates inefficiencies that are equally relevant for all areas of the master element, it can be advantageous to apply a single replication parameter or a single mathematical adaptation function to all points of the exposure curve. For example, the wavelength of all anchor points can be changed to a new wavelength determined by the measurement method. In this case, the replication parameter is the wavelength. It is also advantageous to shift or tilt the entire exposure curve so that the same relative distances between the anchor points are maintained. This can be preferred if the replication parameter is the intensity or exposure angle. It is also possible to combine these methods, for example by changing the wavelength of all anchor points and shifting the exposure curve. Further examples of such adaptations are listed with respect to the measurement method and can also be used for the replication method.

[0170] In another preferred embodiment of the invention, moving the exposure point comprises a change of its position and / or the angle of its beam path, the exposure point preferably being moved by means of a controlled positioning module.

[0171] Preferably, the positioning module includes one or more actuators to move the exposure point at least in a plane parallel to the master hologram. Preferably, the positioning module also includes one or more actuators to move the exposure point in a plane passing through the master hologram, that is, to bring the exposure point closer to the master hologram or move it away from the master hologram. In this case, the light source (e.g., a laser) can also be moved by the positioning module or arranged separately from the positioning module. Preferably, the positioning module includes a robotic arm having one or more adjustable axes and one or more actuators. Alternatively, the positioning module can include a multi-axis optical linear adjustment stage. Preferably, the adjustment stage also has at least one rotational degree of freedom.

[0172] The positioning module preferably also includes an optical component capable of causing the beam to deflect. Preferably, the optical component is arranged in a tiltable manner such that the tilt of the optical component can change the angle of the beam path. The optical component can be configured so that it can be tilted in a single plane, two planes, or all three planes. The optical component preferably includes a lens element, a reflector, and / or a prism.

[0173] For example, the optical component can be a mirror. The mirror can be tilted gradually using a motorized joint. This allows the reference beam reaching the master element to be tilted accordingly. In this case, the exposure point can be a point on the mirror.

[0174] The movement of the positioning module and / or the optical component may be controlled by a control unit.

[0175] In another preferred embodiment of the present invention, the photosensitive material and the second side of the master element are exposed to light in multiple steps, while a first side of the master element, opposite the second side, faces a detector, and the detector captures the intensity distribution of light emitted from the first side of the master element during the exposure. Preferably, in a later step of the exposure, the replication parameters defined in the measurement method are adapted based on the intensity distribution captured in an earlier step of the exposure.

[0176] Within the meaning of the present invention, the preceding step and the subsequent step of exposure can each be a step for replicating a single copy, a plurality of successive copies or a plurality of non-successive copies of the master hologram.

[0177] This embodiment of the present invention produces particularly good results during the replication process, as possible changes in the master hologram during replication can be reliably captured and accounted for. Furthermore, this method advantageously does not require interruption of the continuous replication process. Because the exposure of the master element and the capture of the intensity distribution are performed on different sides of the master element, they can be performed simultaneously and without conflict. Since the master hologram is a reflection hologram, the object beam is reflected by the interference pattern of the master hologram and does not exit from the first side of the master element. Therefore, during the replication process, the detector can remain in the same position on the first side of the master element as during the measurement process.

[0178] During the replication process, the reference beam can be partially scattered by the photosensitive material (e.g., in a photosensitive composite) rather than by the diffuser, which is preferably removed from the first side of the master element. In this embodiment, the photosensitive material itself can serve as the aforementioned diffuser for the measurement method. This embodiment enables further fine-tuning of replication parameters, particularly in a continuous replication method, during replication of the master hologram using the results of the measurement method (which were determined using the diffuser as described above).

[0179] This can exploit the fact that unexposed material produces greater scattering than exposed material. A detector can capture the scattered light resulting from the superposition of the first-order and reference beams. In this case, the intensity of the light scattered in the photosensitive material is related to the ratio of the first-order, which can be shown to have different magnitudes depending on the efficiency of the master element. Light emitted from the first side of the master element is preferably captured by the detector in order to provide conclusions about the state of the master element, in particular its efficiency. In this way, the replication parameters determined by the measurement method can also be subsequently controlled during the replication method. As a result, a very fine-tuned adaptation of the replication parameters to the actual properties of the master element can be achieved.

[0180] Without a separate diffuser, it is not possible to reliably ensure that the detector can capture the zero-order undiffracted exit light from multiple angles. Depending on the exit angle, the zero-order undiffracted exit light may propagate outside the detector. However, the detector used to establish the efficiency of the master hologram can advantageously capture the scattered light generated by the first-order diffraction reflected into the material to be exposed, rather than the zero-order diffraction. Here, a kind of phosphorescence may be present. In this regard, the (1st-order) light reflected by the master element can be at least partially scattered into areas of the photosensitive material that have not yet been exposed. This scattered light advantageously emerges from the photosensitive material at a wide range of angles and can therefore be reliably captured by a detector (e.g. a camera) in order to record the light intensity distribution.

[0181] In this embodiment, bright areas (high light intensities) of the light intensity distribution preferably indicate high efficiency of the master hologram, since the scattered light is positively correlated with the light reflected to the first order by the master element.

[0182] Darker areas preferably indicate that the proportion of reflection into the first order is smaller, and therefore the efficiency of the master hologram is lower. Therefore, when capturing the first-order scattering in the replication method, the ratio between brightness and efficiency is the opposite of the ratio in the embodiment of the measurement method using a diffuser to scatter the 0th order diffracted light and capturing it with the aid of a detector.

[0183] Advantageously, in this embodiment, the master element can be exposed over a large area or in steps using an exposure profile. If a large area of ​​the master element is exposed, the intensity distribution for the entire master element can be obtained during an earlier exposure step. The replication parameters for the entire master element can then be controlled based on this. For example, the replication parameters can be applied when producing subsequent copies of the master hologram in a continuous process.

[0184] In contrast, if the master element is exposed stepwise with an exposure curve, the intensity distribution for at least one anchor point can be captured. This can be used to draw conclusions about the state of the entire master element and adapt the entire exposure curve accordingly.

[0185] However, it is preferred that the corresponding intensity distribution for one or more (preferably all) anchor points of the exposure curve be captured. During subsequent exposure of the master hologram, the replication parameters for the corresponding anchor points can then be controlled on this basis. Thus, the exposure process can be continuously calibrated and adapted to the optical properties of the master element. In this respect, the replication method is efficient over a long period of time.

[0186] Terms like “substantially”, “approximately”, “about”, “around” etc. preferably describe a tolerance range of less than ±20%, preferably less than ±10%, particularly preferably less than ±5%, in particular less than ±1%, and include the exact value.

[0187] A person skilled in the art realizes that the technical features, definitions and advantages of the preferred embodiments of the measuring method according to the present invention are also applicable to the replication method according to the present invention, and vice versa.

[0188] Specific description

[0189] In the following, the invention will be explained in more detail with the aid of examples and drawings, without being restricted thereto. BRIEF DESCRIPTION OF THE DRAWINGS

[0190] Figure 1 is a schematic illustration of an ideal planar reflection master hologram being exposed from the exposure point.

[0191] Figure 2 is a schematic illustration of an actual (non-ideal) reflection master hologram in a master element. Exposure from a target exposure point and from an exposure point determined by a measurement method are schematically shown.

[0192] Figure 3 is a schematic illustration of a measurement method according to a preferred embodiment of the present invention, the diffuser and the detector are arranged on a first side of the master element.

[0193] Figure 4 is a schematic illustration of a measurement method according to a preferred embodiment of the present invention, capturing intensity distributions at a first exposure point and a second exposure point, respectively.

[0194] Figure 5 is a schematic illustration of the intensity distribution when exposing a master element from a first exposure point.

[0195] Figure 6 is a schematic illustration of the intensity distribution when exposing the master element from the second exposure point.

[0196] Figure 7 is a schematic illustration of a measurement method according to another preferred embodiment of the present invention, which captures the intensity distribution of multiple anchor points for an exposure point and realizes the shift of the exposure curve.

[0197] Figure 8 is a schematic illustration of a positioning module for moving an exposure point on an exposure curve.

[0198] Figure 9 is a schematic illustration of a positioning module for moving an exposure point on an exposure curve according to an alternative embodiment, the positioning module comprising a robotic arm.

[0199] Figure 10 Schematic illustration of a replication method according to another preferred embodiment of the present invention, wherein a photosensitive material scatters a reference beam, and the scattered light is captured as an intensity distribution. Based on the intensity distribution, replication parameters are then controlled online. DETAILED DESCRIPTION

[0200] Figure 1 The ideal reflection master hologram is shown as a horizontal dashed line. Figure 4 . Master hologram Figure 4 The optical function of the master hologram completely corresponds to its theoretical (or target) optical function. Figure 4 It preferably has a uniform thickness and the interference pattern in its volume corresponds exactly to the interference pattern recorded in the computer program used for hologram mastering. Figure 1 Shows the master hologram Figure 4 The master hologram is exposed to a reference beam 16 emitted from a target exposure point 14. The reference beam 16 may have a predetermined wavelength. A point light source may be provided at the target exposure point 14 so that a large area of ​​the master element is illuminated. Starting from the target exposure point 14, the reference beam 16 approaches the master hologram at a predefined angle. Figure 4 Since the master hologram Figure 4 The reference beam 16 is not deformed or degraded by its production or by the processing steps integrated into the master element and has maximum efficiency, so that the reference beam 16 is holographically Figure 4 Totally reflective, so as to generate a hologram relative to the master Figure 4 An object beam 18 has a predefined angle.

[0201] The target exposure point 14 is relative to the master hologram Figure 4 The position, predefined wavelength and / or target reference beam 16 is close to the master hologram Figure 4 The angles can be stored in advance as a reference for the master hologram Figure 4 The standard replication parameters stored in advance can be used as the standard replication parameters for the master hologram during the replication method. Figure 4 However, as explained below, this is only possible when the master hologram Figure 4The standard replication parameters achieve the highest possible replication efficiency only when the optical properties of the master hologram actually correspond to its theoretical optical properties. Figure 4 If the optical properties of the master hologram start to deviate from the target properties, it may be advantageous to expose the master hologram with correspondingly adapted replication parameters.

[0202] Figure 2 The master hologram embedded in the transparent substrate body 6 is shown Figure 4 . Master hologram Figure 4 Together with the substrate 6, it forms the master element 2. This master element 2 is thicker than the master hologram. Figure 4 Several times thicker and therefore significantly more robust and easier to handle in practice. However, creating a master hologram Figure 4 The process of manufacturing the optical fiber, its integration into the master element 2 and its storage or use over a period of time may all lead to changes in its optical properties.

[0203] The impact of these changes may be used to master holograms Figure 4 The target exposure parameters for exposure are no longer the most effective exposure parameters. Figure 2 The target exposure point 14, the target reference beam 16 and the target object beam 18 are shown in dashed lines. Since the assumptions based on which these target exposure parameters are determined do not take into account the current characteristics of the master element 2, the target reference beam 16 may not be reflected by the master hologram. Figure 4 Total reflection. As a result, the intensity of the generated object beam may be too low to generate the desired interference in the photosensitive material. It is not possible to create a high-quality copy of the master hologram with these replication parameters.

[0204] For this purpose, it is necessary to use 12 pairs of master holograms with different optimized exposure points Figure 4 Exposure is performed, the position of the optimized exposure point being shifted relative to the target exposure point 14. The light source used may also have a wavelength different from the target wavelength. The optimized reference beam 8 may be incident on the master element 2 at a different angle and / or at a different wavelength so as to better conform to the master hologram integrated into the master element. Figure 4 The reference beam 8 can be reflected with high efficiency to form the object beam 10. This is schematically illustrated by the solid line. The object beam 10, with sufficient intensity, can then interfere with the reference beam 8 in the photosensitive material to form the desired interference pattern. This improves the quality of the copied master hologram, allowing for continued use of the master hologram.

[0205] Figure 3A measurement method according to a preferred embodiment of the present invention is schematically illustrated. A master element 2 is positioned 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 positioned between the master element 2 and the detector 26. Although direct contact is not required for the present invention to be implemented, in this embodiment, the diffuser is in direct contact with the first side of the master element 2.

[0206] If the master element 2 is exposed from the first exposure point 14, the first reference beam 16 is incident on the second surface of the master element 2 at a predefined angle. Figure 4 The first reference beam 16 is only modified by the master hologram due to changes in its production, integration into the master element, use or storage. Figure 4 Part of the light of the first reference beam 16 is guided through the master hologram Figure 4 , passes through the substrate body 6 and then enters the diffuser 24. The diffuser 24 scatters the light of the reference beam to form scattered radiation 22, which is preferably radiated on the top side of the diffuser 24 in all directions of the hemisphere.

[0207] Due to the scattering of light radiated from the top side of diffuser 24, detector 26 having a sufficient lens angle can measure the intensity of light radiated from all areas of the diffuser. That is, even if these areas are located at different angles relative to detector 26, scattered light 22 (which can be seen on the left and right sides in the schematic diagram) can be equally captured by detector 26.

[0208] By capturing the intensity distribution during exposure of the master element 2 with the first exposure parameters, it can be established whether the first exposure parameters correspond to the master hologram. Figure 4 If the actual optical function of the hologram matches the ideal master, and if it does not match, in which areas and to what extent the exposure parameters need to be improved. Figure 4 In the case where the diffuser is designed to completely reflect the reference beam, no light will emerge from the diffuser and the detector will record a black image. Based on the captured intensity distribution, an exposure can be performed with the first exposure parameters or with new exposure parameters that are optimized globally or locally. To better illustrate, Figure 3 Also shown is a theoretical exposure volume 36 within which exposure points can be selected, in particular for the entire master hologram or regions thereof.

[0209] Figure 4 Schematically shows the master hologram when different second exposure points 12 are selected within the theoretical exposure volume 36 for large-area exposure of the master element 2. Figure 4The change in regional efficiency. The first reference beam 16 and the resulting first object beam 18 are illustrated using solid lines for comparison. The new second reference beam 8 and the resulting scattered light 22 transmitted by the diffuser 24 are illustrated by dotted lines. As indicated by the thicker dotted line in the area of ​​the scattered light radiated from the left part of the diffuser 24, the second exposure point 12 makes the light intensity in this area of ​​the diffuser higher. This shows that the exposure efficiency in the corresponding area of ​​the master hologram is poor. On the other hand, the intensity of the scattered light 22 radiated from the area to the right of the diffuser 24 is lower, as indicated by the thinner dotted line. For this area, the second exposure point 12 can make the incident angle of the second reference beam 8 consistent with the angle of incidence of the master hologram. Figure 4 This information can be used to better coordinate the actual characteristics of the master hologram. This information can be used when selecting exposure points or radiation angles for the entire master hologram or for specific areas or points. Before deriving one or more replication parameters from the results, this information is provided in the form of an intensity distribution for each test exposure point 14, 12.

[0210] Figure 5 and Figure 6 Schematically shows the process of exposing the same master hologram from two different exposure points (for example, from the first exposure point 14 and the second exposure point 12). Figure 4 The intensity distribution 28 captured for the master hologram during exposure. As can be seen, the intensity distributions are different. Figure 6 The intensity distribution in has a larger dark area overall. Since dark areas indicate high efficiency, Figure 6 The exposure point in the image may be considered more suitable. For the replication method, the same exposure point can be selected. Alternatively, a third exposure point can be selected based on a trend evident from the results of the two test exposure points. Additional exposure points can also be selected and tested based on the captured intensity distribution, preferably with the aid of an iterative process that converges to maximum exposure efficiency.

[0211] Figure 7 An embodiment of a measurement method is shown, wherein the master hologram Figure 4 The aim is to replicate with the aid of the exposure curve 32. In this embodiment, the entire master hologram is not exposed to light by a single exposure point. Figure 4 For large-area exposure, instead of holographic master Figure 4 Perform segmented exposure. Master hologram Figure 4 Each segment of the master hologram is assigned an exposure curve for exposure. Figure 4 , multiple exposure point positions were used.

[0212] 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 so that it progresses through a discrete number of anchor points 34, each having predetermined target replication parameters. The exposure curve 32 preferably spatially transitions smoothly between the anchor points 34. Preferably, the exposure curve 32 also ensures a smooth transition between exposure parameters (e.g., wavelength or intensity) at the anchor points 34.

[0213] Figure 7 The target reference beam and the resulting object beam from the fifth anchor point 42 and the seventh anchor point 44 (from left to right) are also shown with the aid of solid lines. As shown by the dashed arrow 22, part of the light upstream of the seventh anchor point 44 is not reflected by the master hologram. Figure 4 is not completely reflected, but is transmitted and scattered by the diffuser 24. Therefore, the replication parameters of at least this anchor point 44 are not optimally adapted to the master hologram Figure 4 Here, the intensity distribution and, therefore, the efficiency of the master hologram can be investigated with an alternative seventh anchor point 46. The position of the alternative seventh anchor point 46 can differ from the target position. The reference beam originating from the alternative seventh anchor point 46 is illustrated by a dashed line. The dashed line schematically illustrates that the angle of incidence of the new reference beam on the master element 2 differs from the target angle.

[0214] If it turns out that the alternative seventh anchor point 46 is more effective for exposing the master hologram, the entire exposure curve can be shifted accordingly. Figure 7 , this is schematically illustrated by the dashed curve 48. Alternatively, the exposure curve can also be recalculated so that it passes through a new seventh anchor point 46 instead of the original seventh anchor point 44. Preferably, each anchor point 34 is tested by a measurement method and new replication parameters (in particular the relative position with respect to the master element 2) are determined for each point. A new exposure curve 48 can then be calculated.

[0215] Will refer to Figure 8 The realization and adjustment of the exposure curve 32 is explained in more detail. Figure 8 The master element 2 is schematically shown arranged above a positioning module 58. The positioning module 58 is configured so that it moves an exposure point 84 along an exposure curve 32 to perform a measurement method and / or a replication method. In this example, the exposure point 84 is a point on the tiltable scanning mirror 56, from which the reference beam 8 is directed to the master element 2. A light source 50 (in this case, a laser) emits a light beam that is directed through a series of optical elements (in this case, a periscope arrangement) to reach the exposure point 84. The light source 50 is preferably fixed in position. Alternatively, the light source 50 can be configured so that it scans along a single linear path in a single horizontal plane.

[0216] To move exposure point 84 along exposure curve 32, scanning mirror 56 is positioned on positioning module 58. Positioning module 58 includes a horizontal adjustment stage 52 and a vertical adjustment stage 54. Horizontal adjustment stage 52 generates the horizontal component of the movement of exposure point 84, while vertical adjustment stage 54 generates its vertical component. Furthermore, the angle of reference beam 8 is preferably adjusted by tilting scanning mirror 56, preferably with the aid of a motor. The sequence of vertical, horizontal, and tilting movements required to move exposure point 84 along exposure curve 32 is preferably stored in advance and / or calculated by a processor. However, exposure curve 32 can be continuously re-evaluated and recalculated.

[0217] Figure 9 An alternative embodiment of the positioning module 58 is shown, which allows the exposure point 84 to be moved along the exposure curve 32 with the aid of a robotic arm 60. In this embodiment, optical fibers transmit coherent light from the light source 50 to the scanning mirror 56. An actuator in the robotic arm 60 moves the scanning mirror 56 along the exposure curve 32 while also tilting it to direct the light beam at different angles onto the master element 2. This robotic arm can accurately expose the master element 2 using a variety of different exposure curves, including linear, curved, and free-form exposure curves.

[0218] Figure 10 A preferred embodiment of the replication method is schematically shown, in which the exposure parameters are subsequently controlled online. In this case, the diffuser is removed in order to avoid adverse interference with the replication method. Instead, the scattering properties of the light-sensitive material 30 of the replicated hologram are utilized. The master hologram is then exposed to light from a predetermined exposure point 12. Figure 4 The reference beam 8 emitted from the exposure point 12 is incident on the photosensitive material 30 and the master element 2 at a predefined angle. Figure 4 The interference pattern in the light source 30 is partially reflected to generate the object beam 10. In the photosensitive material 30, the object beam 10 interferes with the reference beam 8 to form a corresponding interference pattern.

[0219] At the same time, the detector 26 can capture the scattered light resulting from the superposition of the reference beam 8 and the first-order diffracted light 38. The fact that unexposed photosensitive materials scatter more than exposed materials facilitates the capture of the intensity distribution. In this case, the intensity of the light scattered in the photosensitive material is related to the proportion of the first order of diffraction, which can be shown to have different magnitudes depending on the efficiency of the master element. In this embodiment, the bright areas of the light intensity distribution preferably indicate the master hologram. Figure 4 The efficiency is high because the scattered light is closely connected to the holographic Figure 4 The light intensity captured can be used to evaluate the master hologram. Figure 4This information can influence subsequent steps and / or subsequent rounds of the replication method in order to improve efficiency by adapting replication parameters.

[0220] List of Reference Numerals

[0221] 2 Master Components

[0222] 4 Master holograms

[0223] 6 Basal body

[0224] 8 Reference beam

[0225] 10 Object Beam

[0226] 12 Exposure Points

[0227] 14 Target exposure point / first exposure point

[0228] 16 Target reference beam / first reference beam

[0229] 18 Target object beam / first object beam

[0230] 20 0th order diffraction reference beam

[0231] 22 0th order scattered reference beam

[0232] 24 Diffuser

[0233] 26 detectors

[0234] 28 Intensity distribution

[0235] 30 Photosensitive materials

[0236] 32 Exposure Curve

[0237] 34 Anchor Point

[0238] 36 exposure points or exposure volumes around anchor points of the exposure curve

[0239] 38 First-order reference beam scattered by photosensitive material

[0240] 42 Figure 7 The fifth anchor point in

[0241] 44 Figure 7 The seventh anchor point in

[0242] 46 Figure 7 Alternative Seventh Anchor in

[0243] 48 Alternative Exposure Curves

[0244] 50 Light sources, especially lasers

[0245] 52 level adjustment table

[0246] 54 vertical adjustment table

[0247] 56 Scanning Mirror

[0248] 58 Positioning Module

[0249] 60 Robotic Arm

[0250] 62 optical fiber

[0251] 84 Exposure points on the scanning mirror

Claims

1. A measurement method for defining at least one replication parameter for a replication method using a master element (2), The method comprises the following steps: - providing a master element (2) comprising a reflection hologram (4), a light source (50), a detector (26) and a diffuser (24), the diffuser (24) being positioned between the master element (2) and the detector (26), - irradiating the master element (2) with light by means of the light source (50), - capturing the intensity distribution (28) of the light (22) emerging from the diffuser (24) by means of the detector, and - defining at least one replication parameter based on the captured intensity distribution (28).

2. The measuring method according to the preceding claim, It is characterized by: Higher values ​​of the intensity distribution (28) indicate lower efficiency of the master element (2) in the replication process, and defining the replication parameters is achieved with respect to maximizing the efficiency of the master element (2) in the replication process and / or reducing deviations of the efficiency from a target value.

3. The measuring method according to claim 1 , It is characterized by: The master element (2) is illuminated with light using at least two different exposure parameters, and defining the at least one replication parameter is performed based on at least two intensity distributions (28) captured for the at least two different exposure parameters.

4. The measuring method according to claim 1 , It is characterized by: The at least one replication parameter corresponds to exposure intensity, wavelength, exposure point (12), and / or angle of the beam path of the light (8) at the exposure point (12).

5. The measuring method according to claim 1 , It is characterized by: The at least one exposure parameter is an exposure point, an intensity distribution (28) of the light (22) emerging from the diffuser (24) being captured for at least two different exposure points (12).

6. The measuring method according to the preceding claim, It is characterized by: The intensity distribution (28) of the light (22) emerging from the diffuser (24) is repeatedly captured for at least three exposure points (12), and the third and further exposure points (12) are selected by an iterative process based on the already captured light intensity distributions (28) so as to preferably converge to the exposure point (12) at which the efficiency of the master element (2) in the intended replication method is maximized.

7. The measuring method according to claim 1 , It is characterized by: An intensity distribution (28) is captured for a plurality of spatially distributed anchor points (34) of an exposure curve (32), thereby defining at least one replication parameter related to a shift of the exposure curve (32) and / or a variation of the anchor points (34).

8. The measuring method according to claim 1, It is characterized by: By capturing the intensity distribution (28) of the isolated diffuser (24), a control pattern of the intensity distribution (28) is provided, the control pattern being taken into account when determining the at least one replication parameter based on the captured intensity distribution (28).

9. The measuring method according to claim 1 , It is characterized by: The diffuser (24) is a transmissive diffuser and preferably behaves substantially like a Lambertian emitter.

10. The measuring method according to claim 1, It is characterized by: The detector (26) is a camera, preferably capturing the intensity distribution (28) as a two-dimensional image representation of the surface of the diffuser (24).

11. A method for replicating a hologram from a master element (2) into a photosensitive material (30), It is characterized by: The replication method is implemented by applying at least one replication parameter defined with the aid of the measurement method according to any of the preceding claims.

12. The replication method according to the preceding claim, It is characterized by: The at least one replication parameter is related to the exposure intensity to which the master element (2) is exposed during replication, the intensity for different locations on the master element (2) being defined based on the captured intensity distribution (28).

13. The replication method according to claim 11 , It is characterized by: The at least one replication parameter is related to the exposure point (12) at which the master element (2) is exposed, preferably in order to maximize the efficiency of the master element (2) during replication.

14. The replication method according to any one of claims 11 to 13, It is characterized by: The at least one replication parameter is wavelength dependent, in the measurement method intensity distributions (28) are captured for two or more wavelengths, and preferably the wavelengths used during replication are selected to maximize the efficiency of the master element (2) during the replication.

15. The replication method according to any one of claims 11 to 14, It is characterized by: The replication method comprises exposing the photosensitive material (30) and the master element (2) by moving the exposure point (12) along an exposure curve (32), the exposure curve (32) preferably comprising a plurality of anchor points (34), and applying, for each individual anchor point (34) or for the entire exposure curve (32), replication parameters defined by the measurement method during exposure, preferably in order to maximize the efficiency of the master element (2) during replication.

16. Replication method according to the preceding claim, It is characterized by: Moving the exposure point (12) involves a change in its position and / or the angle of its beam path (8), the exposure point (12) preferably being moved by means of a controlled positioning module.

17. The replication method according to any one of claims 11 to 16, It is characterized by: The light-sensitive material (30) and the second side of the master element (2) are exposed to light in a plurality of steps, while a first side of the master element opposite to the second side faces a detector and the detector captures the intensity distribution (28) of the light emerging from the first side of the master element (2) during exposure, in which case preferably, In a later step of exposure, the replication parameters defined in the measurement method are adapted based on the intensity distribution (28) captured in an earlier step of exposure.

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