Security hologram element with three-dimensional effect

Abstract

The invention relates to a method (1000) and a device for producing hologram security elements, each of which stores a spatial shape of a three-dimensional object. These preferably each store the shape of another object. Spatial image information relating to an object is captured, and the outer contours are determined in different parallel sectional planes spaced apart from one another and are stored in bitmaps (25). A phase image (30) is calculated for each bitmap (25) and convolved using a mapping function in order to generate a modified phase image (40). A plurality of modified phase images (40) is thus generated for the plurality of sectional planes. The phase images (30) are convolved using mapping functions which each have a focal length which changes incrementally. If these modified phase images (40) are exposed as computer-generated holograms in the same recording region (97) of a hologram, they are jointly reconstructed when exposed to coherent light. The outer contours of the different sectional planes of the object are projected in adjacent reconstruction planes. The three-dimensional shape of the object can thus be captured during reconstruction.

Description

[0001] Security hologram element with three-dimensional effect

[0002] The invention relates to a security element designed as a hologram, which stores graphic three-dimensional information that is preferably unique to each individual security element of a series of identical security elements. In particular, the invention relates to a hologram security element comprising a diffraction element, which is particularly suitable for machine reading, so that verification of a security document or similar object bearing the security element is possible based on the detected diffraction.

[0003] It is known from the prior art to equip objects, in particular documents and data carriers such as identity cards, driver's licenses, identification cards, but also valuable items such as tickets, packaging, or similar items, with so-called security features. These security features have at least one characteristic by which the authenticity of the respective object and / or a forgery, falsification, unauthorized duplication, or similar can be recognized. Such a feature is referred to as a security feature. A physical object with a security feature is referred to here as a security element.

[0004] A group of security elements is designed for optical verification. Optical verification involves checking properties and / or stored information, either through a human observer or by capturing an image, or by verifying and / or evaluating optical effects for their presence and / or design.

[0005] Diffraction elements are a group of security features. A diffraction element has at least one diffraction structure capable of influencing light due to the physical effect of diffraction. Commonly used diffraction elements include holograms, but also kinegrams, other embossed surface structures, and similar devices.

[0006] Embossed surface holograms are very common. In these holograms, a diffraction pattern embossed into the surface, provided it is coated with a metal layer or a transparent layer with a high refractive index, diffracts light at the structured interface. Embossed surface holograms belong to the group of so-called thin holograms. Such holograms are widely used, for example, to secure credit and debit cards. This type of hologram is not easily individualized in mass production.

[0007] Another group of holograms comprises volume holograms, in which the diffraction pattern is stored within the volume of a material. In contrast to surface holograms, which are thin holograms, these are referred to as thick holograms.

[0008] A specific type of volume reflection hologram, such as that used in identity cards, and its production are described in publication EP 0 896260 A2.

[0009] The volume holograms described in EP 0 896260 A2 are used, for example, in German identity cards to store image information from a portrait printed in color onto a substrate layer of a security document, additionally as a black and white or grayscale image in a superimposed and laterally offset hologram. For this purpose, a master hologram of a homogeneous diffuser, which diffracts perpendicularly incident monochromatic light (e.g., green light) at a 45° angle, is locally copied into the hologram with image information from the portrait at varying intensities. This creates the "black and white or grayscale portrait image," which reconstructs itself in ambient light and exhibits a green color. This image is suitable for verification by a human observer.

[0010] In addition to the portrait image, which is designed as a volume reflection hologram, the same hologram layer in a German identity document contains further diffraction structures, such as kinegraphic structures or a parallax-inducing hologram of an eagle. The latter, for example, is stored in the hologram using red coherent light. Furthermore, the hologram used under the brand name Identigramm in German identity documents also features a non-individualized, machine-readable characteristic that reconstructs a predefined, easily verifiable light field when illuminated with coherent light under a specific direction.

[0011] It is generally known to create holograms of real three-dimensional objects, such as the eagle mentioned above. When these are designed as volumetric holograms, they exhibit the property that different views of the real object can be perceived when reconstructed from different viewing angles. This is also known as parallax. Such holograms, or hologram masters for a copying process, can only be produced from a real three-dimensional object using complex exposure techniques. Therefore, producing a large number of individualized holograms of this type is not economically feasible.

[0012] The production of hologram security elements in which three-dimensional and, in particular, individual three-dimensional information is stored for each hologram security element of a set of identical hologram security elements, has not been satisfactorily solved.

[0013] The invention is based on the objective of creating a method and a device for manufacturing hologram security elements, as well as hologram security elements that reproduce spatial information of an object during reconstruction based on the diffraction of light and are preferably easy to manufacture, so that a large number of these hologram security elements can be produced, which store different spatial image information or reproduce it during reconstruction, wherein these are preferably individualizing or personalizing for persons or objects.

[0014] The invention comprises a method for manufacturing such a hologram security element with the features of claim 1, a hologram security element with the features of claim 6, an assembly of hologram security elements with the features of claim 7, and a device for producing a hologram security element with the features of claim 8. Advantageous embodiments are described in the dependent claims. Basic idea of ​​the invention

[0015] The invention is based on the idea of ​​capturing spatial information from various individual objects, for example, spatial image information such as data from three-dimensional facial scans of people. For the spatial image information of one of these objects (i.e., a person), a phase image is calculated for a plurality of parallel cross-sectional planes with the object. This image specifies the spatially distributed phase positions that must be modulated onto a light field so that the light field projects the outer contour of the object in the corresponding cross-sectional plane in the far field. These phase images are then modified so that their projections take place in different, adjacent reconstruction planes. For this purpose, the phase images are convolved with the imaging function of an optical element, whereby the focal length f of the imaging function is incrementally changed for the different phase images.This process yields a plurality of modified phase images. These are then exposed into the same recording area of ​​a holographic recording material. This is achieved by using a phase-modulating spatial light modulator to generate the object light for the hologram exposures. Each of the modified phase images is thus exposed as a computer-generated hologram into the same recording area of ​​the recording material. The modulation of the object light takes place adjacent to the recording material.

[0016] For this purpose, an exposure method is particularly suitable in which the phase-modulating spatial light modulator is designed to be reflective and is positioned below the transparent recording material. Exposure is achieved with coherent light, similar to a Denisyuk holography process, shining from above onto the recording material. The coherent light passing through the recording material is phase-modulated and reflected, interfering with the unmodulated light within the material. In this way, the modified phase images for an object are exposed to the same recording area in sequential succession. During reconstruction, the majority of the individual computer-generated holograms are reconstructed together, so that the components projecting the outer contours of the different cross-sectional planes are projected onto adjacent reconstruction planes, thus enabling the three-dimensional shape of the underlying object to be captured.These different exposures can be carried out in quick succession, for example in a holographic recording material based on a photopolymer, because the polymerization processes triggered by the individual exposures are so "sluggish" in time that the exposures are completed before the polymerization processes triggered by them are completed, which store the individual phase holograms.

[0017] The steps described here for the spatial image information of an object are also carried out for different objects. This makes it possible to produce hologram security elements in a hologram film in immediate succession, storing individualizing three-dimensional information for different objects or people.

[0018] The advantage lies in the fact that only one set of modified phase images needs to be calculated for each individual three-dimensional object. These different sets can then be exposed into different recording areas of a holographic film, either with a time delay or, in multiple applications, even simultaneously.

[0019] This makes it possible to produce easily manufactured, individualized three-dimensional holograms as security elements, which offer better protection against counterfeiting than two-dimensional holograms.

[0020] Definitions

[0021] A hologram security element is a security element that includes a hologram.

[0022] A hologram is a stored diffraction pattern that can be reconstructed using coherent light. This diffraction pattern is generated by the interference of two coherent light fields. The information contained in the diffracted light during reconstruction is also referred to as the information stored in the hologram. The resulting light field thus contains this information and can be captured during the reconstruction process. This resulting light field is also called a reconstructed hologram.

[0023] A volume hologram is a hologram in which the stored information is stored in a larger volume area. This is distinct from so-called thin holograms, in which the information is essentially stored in a single plane.

[0024] The term phase image refers to the spatially distributed, different phase positions of a light field that, as it propagates in the far field, projects graphical image information from which the phase image is calculated. This image information is understood as the image information of the phase image.

[0025] A modified phase image is defined as the information of the spatially distributed different phase positions of a coherent light field, which results from the convolution of a phase image with an imaging function of at least one optical element.

[0026] An imaging function of at least one optical element is the function that describes the optical imaging of a phase image by the corresponding optical element. Convolving this imaging function with that of the phase image yields a modified phase image. The convolution of the phase image with the imaging function results in a coherent light field, modulated with respect to phase positions by the modified phase image, reproducing the image information associated with the phase image not in the far field, but at a different position in space. This imaging plane is defined by the at least one optical element or its imaging function. Since this plane appears during reconstruction, it is also called the reconstruction plane.

[0027] A phase hologram, as used here, refers to the information about the spatially distributed, different phase positions in a plane of a coherent light field that defines the object light for a holographic recording of a hologram. If a coherent light field modulated according to the phase hologram—that is, according to the phase positions defined therein—is exposed as a hologram into a holographic recording material with reference light that has the structure of a plane wave, then the light field generated during the reconstruction by diffraction at the hologram is identical to the light field defined by the phase hologram. It is assumed here that the modulated light field, which serves as the object light, is exposed into the holographic recording material spatially close to the location of the modulation, i.e., it is brought into interference with the reference light in the holographic recording material.

[0028] The phase image and the phase hologram can be identical if, for example, a phase image determined from a bitmap is used directly as a phase hologram. However, if such a phase image is convolved with an imaging function, such as an imaging lens, the resulting phase hologram corresponds to the modified phase image. In the latter case, the resulting graphic information in the far field differs from the image information of the original phase image. The projection of the phase hologram in the far field differs because the convolution with the imaging function has "shifted" the projection of the image information of the original phase image to a different position in space.

[0029] Graphical information, or image information, refers to information that can be captured by a spatially resolved sensor. This information manifests itself in varying contrasts or colors and is perceptible to a human observer, at least when projected onto a flat surface. Information stored in a bitmap can be considered image information, where each bit is assigned a pixel. For example, a bit with a value of zero is assigned a dark pixel, and a bit with a value of one is assigned a light pixel. The resulting pattern of light pixels against a dark background is then the graphical representation of the information in the bitmap.

[0030] Spatial image information refers to information that describes the three-dimensional shape of an object and from which different views of that three-dimensional object can be derived. This information can be provided, for example, in the form of a 3D point cloud. However, it can also be provided in other ways, such as a construction model or similar.

[0031] Holographic recording material refers to photosensitive material that can be altered once by electromagnetic radiation during exposure to record an interference pattern of a hologram. This pattern is then stored in the holographic recording material, possibly after development and / or fixing. Photopolymers, especially those formed in a thin film layer, are particularly suitable as holographic recording materials.

[0032] A phase modulator is a device that can modulate one phase of light.

[0033] A phase-modulating spatial light modulator, or spatial phase modulator for short, is a device that can locally modulate light differently with respect to its phase at different positions.

[0034] For example, a liquid crystal layer that has different liquid crystal cells can modulate light differently in the individual cells if the liquid crystals in the individual cells are oriented and aligned differently.

[0035] The exposure area is defined as an area of ​​a device in which exposure of a holographic recording material takes place.

[0036] The recording area is the region of a holographic recording material into which a hologram is projected. A holographic recording material, or a planar section of a holographic recording material, can have several adjacent and disjoint or overlapping recording areas.

[0037] Preferred embodiments

[0038] A method for generating three-dimensional hologram security elements includes the following steps:

[0039] (a) Capturing spatial image information of at least one object;

[0040] (b) Determining the outer contours of the at least one object in a plurality of spaced-apart parallel cutting planes,

[0041] (c) Determining a phase image for each outer contour of the plurality of cutting planes, such that a light field spatially modulated in the far field according to the phase image with respect to the phase positions projects the respective outer contour,

[0042] (d) Folding each of the phase images with an imaging function of an optical imaging element with a predetermined focal length to produce a modified phase image, wherein the focal lengths of the imaging functions are chosen differently for different phase images, such that the focal lengths are correlated with the distances of the cutting planes whose outer contours are graphically represented in the respective bitmaps,

[0043] (e) Arranging an unexposed exposure area of ​​holographic recording material in front of a phase-modulating spatial light modulator,

[0044] (f) Exposure of the majority of the generated modified phase images into the same recording area of ​​the holographic recording material by generating coherent light to form reference light and object light and causing the object light and the reference light to interfere in the holographic recording material, wherein the object light for each of the majority of exposures is generated by means of the phase-modulating spatial light modulator controlled according to the generated modified phase images.

[0045] Furthermore, a device for manufacturing a hologram security element is proposed, comprising: a control unit with a computing unit for calculating modified phase images; a light source for generating coherent light, a phase-modulating spatial light modulator, and a transport device for transporting holographic recording material section by section into an exposure area, and optical elements that guide the coherent light at least partially onto the phase-modulating spatial light modulator, which is controlled by the control unit according to the at least one phase hologram, in order to generate the phase-modulated object light and to cause the phase-modulated light in the exposure area in the recording material to interfere with at least a part of the non-phase-modulated light as a reference light, characterized in that the computing unit is configuredThe steps (a) to (d) are to be carried out according to the specified procedure, and the control device is configured to control the light source and the phase-modulating spatial light modulator in such a way that the multitude of generated modified phase images are exposed into the same recording section of the holographic recording material. The advantage is that a readily reproducible, individual hologram security element storing three-dimensional information, suitable for machine verification, is created in a simple manner.

[0046] In a particularly preferred embodiment, steps (a) to (f) are performed iteratively. This means that differently individualized hologram security elements are produced successively.

[0047] In a preferred embodiment, in process step (b) the outer contours of the at least one object are determined in a plurality of spaced-apart parallel cutting planes, and a bit pattern is generated for each of the cutting planes in which the determined outer contour of the cutting plane of the at least one object is graphically represented, resulting in a plurality of bit patterns. In process step (c) a phase image is then calculated for each bit pattern.

[0048] The determination of the outer contours and the generation of bit patterns are particularly well adapted to the computational process. Preferably, the size of the bitmaps is adapted to the number of rows of the spatial phase modulator. Particularly preferably, the number of rows of the phase modulator in one spatial direction corresponds to at least one number of bits along one direction of the bit pattern. In the case of a planar spatial phase modulator, its number of rows is preferably equal to or greater than the number of bits of the bitmaps. Preferably, the geometry of the bitmaps is adapted to that of the phase modulator so that the phase modulator can "represent" the bitmaps, meaning that the phase modulator has a controllable modulation cell for each bit.

[0049] In one embodiment, it is provided that the spatial image information of different objects is provided sequentially, and that these objects differ from one another.

[0050] A Bessel lens imaging function is particularly suitable as an imaging function.

[0051] A Bessel lens produces an image similar to that of a converging lens and is very well suited for holographic encoding. In one embodiment, the spatial image information is provided as a 3D point cloud. An advantage of this embodiment is that the data can be acquired from 3D scanners that capture objects and represent them as a 3D point cloud. This makes it possible, for example, to use facial scanners to capture not only a person's portrait image but also the geometric shape of their head. This results in security documents that are much more difficult to forge, since the three-dimensional structure of the head, which then serves as the basis for the 3D point cloud, contains a multitude of biometric features that are very difficult to counterfeit.

[0052] The modified phase images are particularly favored when exposed as volume reflection holograms into the holographic recording material. This enables exceptionally good and simple reconstruction, as it creates a wavelength- and angle-selective security feature. Only when light of the correct wavelength and at the correct angle is applied are the individual phase holograms exposed into the volume hologram correctly reconstructed. Thus, a hologram security element is created that, during reconstruction using different, parallel cross-sectional planes of a spatial object, reconstructs corresponding outer contours in different imaging planes.This makes it possible to capture different views of the object underlying the different imaging planes during reconstruction, as these are all reproduced simultaneously in spatially closely adjacent imaging planes. Depending on the specific orientation during capture relative to the hologram security element, different views, all producing a three-dimensional effect, can be captured. This allows the three-dimensional information of the underlying object to be captured and analyzed.

[0053] Due to the manufacturing process, it is possible to create a hologram security element assembly with a multitude of hologram security elements, characterized by the fact that each hologram security element reconstructs corresponding outer contours in adjacent parallel projection planes, based on different cross-sectional planes of another spatial object. Each hologram security element in the assembly thus represents the three-dimensional information of a three-dimensional object associated with it, the three-dimensional objects being distinct from one another. Preferably, these differ in pairs, so that the assembly does not comprise two hologram security elements that represent the same three-dimensional object by means of outer contours projected onto adjacent projection planes.

[0054] The phase images underlying the individual modified phase images, which are exposed into the same recording area in a hologram security element, are preferably approximated from the bitmaps representing the respective outer contour in the section planes using an iterative Fourier transform process. The starting point is the bitmap of the outer contour of a section plane and a corresponding phase image with arbitrary phase positions. The phase image can be calculated iteratively via Fourier transforms and inverse transforms, and by calculating differences between the phase image determined in the previous iteration or the calculated far-field projection compared to the image information of the bitmap. This is preferably performed, for example, using a Gerchberg-Saxton algorithm.

[0055] In principle, other methods can be used to determine a phase image corresponding to the graphical image information of a bitmap representing the outer contour of the object to be stored three-dimensionally. To prevent the various phase images determined in this way from all being superimposed in the far field during playback, each one must be convolved with an imaging function of an imaging optic. For the outer contours corresponding to different cutting planes, the imaging functions of the imaging optic with different focal lengths are convolved.

[0056] A particularly suitable phase modulator has proven to be a so-called phase-modulating LOOS (Liquid Crystal on Silicon), which is a phase-modulated spatial light modulator. This reflects light that is phase-modulated differently at different positions. Such a phase-modulating spatial light modulator exhibits a low latency between the differently switched modulation states, making it possible to expose the various modified phase images—which together store the three-dimensional object by means of its outer contours in differently reconstructed image planes—into the same recording area of ​​a holographic recording material in rapid succession. No transport of the holographic recording material is necessary between the individual exposure steps.Only electronic control of the phase-modulating LCOS is necessary to change the modulation properties of the phase-modulating spatial light modulator. The inertia of the holographic recording material, which comprises a photopolymer, is exploited in this process.

[0057] In a further development, the described overall hologram, which stores the three-dimensional contour information of an object, is combined with another, preferably individualized, ordinary volume reflection hologram. Therefore, in one embodiment, the phase-modulating spatial light modulator is integrated into a reflecting diffracting hologram master. Simultaneously or with a time delay, but without physically moving the holographic recording material, the hologram constructed from the different phase holograms for the three-dimensional representation of an object, as well as an individualized volume reflection hologram, can thus be exposed into different recording areas of the same holographic recording material.In this case, an exposure area of ​​the holographic device is preferably designed such that it can simultaneously expose the two spatially separated recording areas of the holographic recording material. The preferably also individualized volume reflection hologram is generated by exposing a hologram master, designed as an image of a reflective diffuser, with amplitude-modulated light in a contact copying process into the further recording area of ​​the holographic recording material.

[0058] In addition, further diffraction patterns with the same or different wavelengths can of course be exposed into the same holographic recording material. This allows for the creation of a complex holographic security element that is highly resistant to counterfeiting and incorporates both individualized and, if necessary, non-individualized security features.

[0059] The invention is explained in more detail below with reference to a drawing.

[0060] Here, Fig. 1 shows a schematic representation of a device for manufacturing a plurality of hologram security elements, each storing the three-dimensional information of an individual object, wherein the individual objects of the individual hologram security elements are different;

[0061] Fig. 2 shows a schematic flowchart of the process for manufacturing the hologram security elements storing individual three-dimensional objects; and

[0062] Fig. 3 shows a schematic representation of a device for manufacturing hologram security elements with two individualized holograms.

[0063] Figure 1 schematically depicts a device 1 for producing hologram security elements as proposed here. Figure 2 shows a schematic flowchart of method 1000 for producing such hologram security elements.

[0064] Hologram security elements 2000 are shown. Device 1 and method 1000 are described together here.

[0065] The device 1 comprises a control unit 10. The control unit 10 comprises a processing unit 100. The processing unit 100 acquires the individual spatial image information 20 of a three-dimensional object. For example, the data of a 3D face scan or a 3D head scan of a person is acquired.

[0066] The processing unit 100 is configured to determine an outer contour of the three-dimensional object in each of a plurality of different, parallel, and preferably equidistant cutting planes 1012. The two-dimensional image information is stored in a bitmap 25 1015. Thus, for each cutting plane, two-dimensional image information is obtained in the form of the outer contour of the object in the cutting plane, and a bitmap 25 representing this image information is also obtained. For each of these bitmaps 25, the processing unit 100 calculates a phase image 1020. Such a phase image 30 contains the local phase information that is to be superimposed on a light field so that it projects the graphic image information correlated with the phase image in the far field.Such a phase image can be approximated in an iterative Fourier transform process, for example, using the Gerchberg-Saxton algorithm. This algorithm was first described by Gerchberg and Saxton in their article: Gerchberg, RW; Saxton, WO (1972). "A practical algorithm for the determination of the phase from image and diffraction plane pictures", Optik. 35: 237-246. Several further developments are known in the art. One example is described by P. Memmolo et al. in their article of January 1, 2014, "Investigation on specific solutions of Gerchberg-Saxton algorithm", Optics and Lasers in Engineering, 52: 206-211. The iterative process is indicated by an arrow 1021.

[0067] To obtain a defined projection plane for the reconstruction of the hologram security element to be manufactured, each resulting phase image 30 is convolved with an imaging function of an optical element 1030. Modified phase images 40 are obtained in this way. Preferably, the imaging function of a Bessel lens is used. However, a slightly different imaging function is used for each of the calculated phase images 30. These differ in the focal length f of the imaging device described by the imaging function. If the bitmaps 25 and phase images 30 are determined based on equally spaced cutting planes, the focal length is preferably also changed incrementally. Light fields modulated according to these modified phase images thus project the underlying two-dimensional image information (outer contours) onto spaced-apart reconstruction planes.The outer contours determined in the different section planes are thus reconstructed in different reconstruction planes.

[0068] The process steps 1012 to 1030 are therefore repeated for each of the cutting planes.

[0069] The calculated modified phase images 40 are stored in a memory 45, from which they can be read back in.

[0070] In order to reproduce the three-dimensional shape of the object underlying the modified phase images during reconstruction via the outer contours, it is therefore necessary that these outer contours are projected simultaneously into the corresponding reconstruction planes during the reconstruction process.

[0071] Therefore, it is planned to expose the modified phase images 40 together as computer-generated holograms into a recording area 97 of a holographic recording material 95.

[0072] A section of a hologram film 90 with a recording material 95 is transported by a transport device 80 into an exposure area 77 1040 and pressed against a support surface 175 1050.

[0073] The application of the hologram film 90 with its underside 92 to a mechanically formed support surface 175 serves to prevent movement of the holographic recording material 95 during exposure. This application can be accomplished with a pressure roller device 85. In one embodiment, the support surface 175 can be realized by means of a thin transparent glass or plastic disc 176. In other embodiments, this can also be a surface 161 of a phase-modulating spatial light modulator 160, which is also referred to as a spatial phase modulator 160. In the illustrated embodiment, the support surface 175 and the spatial phase modulator 160 are formed separately from one another.

[0074] Coherent, plane light is generated by a light source 50, which is designed as a laser 51 1060. The light is preferably directed perpendicularly onto the holographic recording material 95 into the holographic film 90 by optical elements 55 1070. However, other exposure directions are also possible.

[0075] The control unit 10 controls the spatial phase modulator 160 according to the calculated modified phase image as a phase hologram at 1080. The spatial phase modulator 160 is preferably a LOOS, a so-called Liquid Crystal on Silicon device, in which liquid crystal cells are formed on a CMOS chip, and the different orientations of the liquid crystal in the individual cells are controlled by the LOOS. Depending on the orientation of the liquid crystal molecules, their refractive index and the associated propagation speed of light change locally. The light is reflected at the silicon surface. Due to the locally varying propagation speed, the phase position of the electric field of the reflected light changes locally. The phase information of the phase hologram, i.e., the modified phase image, is thus imprinted on an incident plane wave.In this process, the incident light is phase-modulated 1090. The reflected light, with its locally different phase modulation, passes again through the support surface 175 into the holographic recording material 95 of the holographic film 90 and interferes there with the incident unmodulated light 1100. This interference information is stored as a hologram in the holographic recording material.

[0076] Since the polymerization processes triggered by exposure are slow, i.e. inert, a large number of exposures in the same recording area 97 of the holographic recording material 95 can be carried out at different times before the polymerization processes are completed, which lead to refractive index variations in the volume of the recording material and store the exposed interference structures.

[0077] A preferred number of used cutting planes and thus simultaneously stored modified phase images n in a recording area is between 2 and 50.

[0078] The exposure intensity used for each exposure process is adjusted to the number of modified phase images to be stored in the same recording area.

[0079] Multiple exposure, also known from normal photography, can usually be carried out on other holographic recording materials that are not photopolymer-based, provided that the exposure intensities and durations are appropriately chosen.

[0080] For a holographic recording material with a photopolymer, the individual exposures preferably last from 1 to 100 seconds. A spatial light modulator is typically controllable at 50 Hz, so it does not limit the exposure duration or sequence. Process steps 1060 to 1090 are thus repeated and executed for each of the calculated modified phase images, which are used to generate spatial image information. These can be read from memory 45 for this purpose.

[0081] Either immediately after the exposure of all modified phase images exposed into a recording area, or after the exposure of the entire hologram film, the recording material of the recording area is developed (depending on the recording material) and / or fixed (depending on the recording material). After one of the process steps (1100, 1110, 1120), the process branches and begins again with process step 1010, capturing spatial image information, until the entire hologram film is composed of various hologram security elements, each storing a three-dimensional shape of an object, which, however, are individual objects for the individual hologram security elements. This allows a large number of individualized three-dimensional hologram security elements to be generated easily.

[0082] When the hologram film 90 is fully exposed, the individual hologram security elements are, as already indicated above, possibly developed 1110 and / or fixed 1120 and then separated from the hologram film 1200 and further processed, for example laminated or mounted into a security document as a document layer 1300.

[0083] In a further development process, the exposure of an "ordinary" volume reflection hologram onto the same hologram film can also occur simultaneously or at a later time. For this, a homogeneously luminous diffuser disk is used as a hologram master, which is exposed with spatially amplitude-modulated light to individually copy this diffuser disk onto the hologram film. A recording area for the phase hologram and another recording area for the ordinary volume reflection hologram are preferably arranged side by side and disjointly. This allows for the maximum possible diffraction efficiency for both holograms. The two holograms can be exposed with the same wavelength. Other embodiments can provide for different wavelengths for their exposure. An embodiment of a device in which both holograms are generated with the same wavelength is shown schematically in Fig. 3.The same technical features as in Figures 1 and 2 are again provided with the same reference numerals.

[0084] In this embodiment, a hologram master 70 and the spatial phase modulator 160 together form the support surface 275 for the hologram film 90 during the exposure of the volume reflection hologram individualized by amplitude modulation and the majority of the modified phase images 40. The hologram master 70 is preferably a volume reflection hologram of a uniformly homogeneously luminous ground glass or diffuser, which reflects and diffracts perpendicularly incident light at an angle. To achieve individualization, this ground glass is locally copied using coherent light modulated spatially with varying intensity or amplitude in the Denisyuk process.

[0085] The control unit 10 thus additionally acquires two-dimensional image information 21 for individualizing the volume reflection hologram. The two-dimensional image information 21 is preferably a portrait image of a person, and the associated spatial image information 20 is a three-dimensional head scan of the same person. Advantageously, this can also be only a face scan. When creating the cross-sectional images, preferably only the outer contours of the face are determined.

[0086] The light 52 generated by the same light source 50, which is designed as a laser 51, is expanded and a part 52-1 of it, which is used to expose the hologram master 70, is controlled by means of the amplitude-modulating spatial light modulator 60 according to the two-dimensional image information 21 and exposed as a volume reflection hologram into the hologram film 90 and its recording material 95 in a further recording area 99.

[0087] Another part 52-2 of the coherent light falls as a plane wave perpendicularly through the hologram film 90 onto the phase-modulating spatial phase modulator 160 located below, which successively imprints the phase information of the modified phase images, calculated to form the spatial image information 20, onto the reflected light 58-2 in rapid succession. These modified phase images are also stored as superimposed volume reflection holograms in the holographic recording material 95 in a recording area 97.

[0088] The amplitude-modulating light modulator 60 may block the component 52-1 while some of the modified phase images 40 are exposed.

[0089] The result is a Hologram Security Element 2000, which reconstructs a three-dimensional, individualized facial image using coherent light and additionally reconstructs an individualized volume reflection hologram in the form of a portrait using white light. Both holograms of the Hologram Security Element 2000 store biometric characteristics of the same person. Furthermore, some of these biometric characteristics can be extracted from both holograms and used for verification. For example, measurements such as the distance between the eyes and the length of the nose can be derived from both holograms and compared. This creates a hologram that is extremely difficult to forge.

[0090] It will be understood by those skilled in the art that only exemplary embodiments are described here. The features described in the various embodiments can be combined to realize further embodiments of the invention. In particular, further diffraction elements with light of the same or a different wavelength can be exposed simultaneously or at different times into the holographic recording material into which the modified phase images are exposed. The hologram security element with the three-dimensional phase hologram can be integrated into security documents in various ways. Preferably, it is applied as a full-surface layer to or integrated into a document body, which is formed from several layers, preferably of plastic material, that are bonded together to form a document body in a lamination process.This is preferably done by applying heat and pressure. The individual substrate layers can include a number of further safety elements and features. Reference numeral list.

[0091] 1 Device for manufacturing a holographic security element

[0092] 10 Control unit

[0093] 20 (individual) spatial image information

[0094] 25 Bitmap

[0095] 30-phase image

[0096] 40 modified phase image

[0097] 45 storage

[0098] 50 light sources

[0099] 51 Laser

[0100] 52 coherent light

[0101] 52-1 a part of the coherent light

[0102] 52-2 other part of the coherent light

[0103] 55 optical elements

[0104] 58 reflected phase-modulated light

[0105] 58-2 reflected phase-modulated light

[0106] 60 amplitude-modulating spatial light modulator

[0107] 70 Hologram Masters

[0108] 77 Exposure range / recording range

[0109] 80 T transport equipment

[0110] 81 material spool

[0111] 82 Winding spool

[0112] 83 pulleys

[0113] 85 Pressure roller device

[0114] 90 Hologram film

[0115] 91 Top

[0116] 92 Underside

[0117] 95 holographic recording material

[0118] 97 Recording area

[0119] 99 additional recording area

[0120] 100 calculation units

[0121] 160 spatial phase modulator

[0122] 175 mm contact area

[0123] 176 G Ias- / Plastic disc 275 Contact surface

[0124] 1000 methods for manufacturing a hologram security element

[0125] 1010 Capturing image information

[0126] 1012 Determining an outer contour in a section plane

[0127] 1015 Creating a Bitmap

[0128] 1020 Calculating a phase image

[0129] 1021 Arrow (to indicate iteration)

[0130] 1030 folds of the phase image with an imaging function of an optical element

[0131] 1040 Transporting a section of the hologram film

[0132] 1050 Applying / pressing the hologram film onto a contact surface

[0133] 1060 Generating coherent light

[0134] 1070 Scanning the holographic recording material

[0135] 1080 Controlling the spatial phase modulator according to the calculated

[0136] Phase hologram

[0137] 1090 Phase modulation of coherent light and reflection of light

[0138] 1100 Interference of phase-modulated and non-modulated light

[0139] Exposure of the phase hologram

[0140] 1110 Developing the holographic recording material

[0141] 1120 Fixing the holographic recording material

[0142] 1200 singulations

[0143] 1300 Laminating into / mounting onto a security document

[0144] 2000 hologram security elements

Claims

Patent claims 1. Method (1000) for generating three-dimensional hologram security elements comprising the steps: (a) Capturing (1010) spatial image information of at least one three-dimensional object; (b) Determining (1012) outer contours of the at least one object in a plurality of spaced-apart parallel cutting planes, (c) Determining (1020) a phase image (30) for each outer contour of the plurality of cutting planes, such that a light field spatially modulated in the far field according to the phase image (30) with respect to the phase positions projects the respective outer contour, (d) Folding (1030) of each of the phase images (30) with an imaging function of an optical imaging element with a predetermined focal length to generate a modified phase image (40), wherein the focal lengths of the imaging functions are chosen differently for different phase images (30) such that the focal lengths are correlated with the distances of the cutting planes whose outer contours are determined in the respective cutting planes, (e) Arranging an unexposed section of holographic recording material (95) in front of a phase-modulating spatial light modulator (160), (f) Exposure (1100) of the majority of the generated modified phase images (40) into the same recording area (97) of the holographic recording material (95) by generating coherent light (52) to form reference light and object light and causing the object light (58-2) and the reference light (52-2) to interfere in the holographic recording material (95), wherein the object light (58-2) is generated for each of the majority of the exposures by means of the phase-modulating spatial light modulator (160) which is controlled according to the generated modified phase images (40).

2. Method (1000) according to claim 1 , characterized in that steps (a) to (f) are performed iteratively with spatial image information of a plurality of objects, each having a different three-dimensional shape.

3. Method (1000) according to claim 2, characterized in that the method step (b) determining outer contours of the at least one object in a plurality of mutually spaced parallel cutting planes comprises generating a bit pattern (25) for each of the cutting planes in which the determined outer contour of the cutting plane of the at least one object is graphically represented, such that a plurality of bit patterns (25) is obtained, and method step (c) determining a phase image (30) for each of the plurality of bit patterns (25) is carried out such that a light field, which is modulated with respect to its phase positions according to the phase image (30), projects a representation of the graphic information stored in the bit pattern (25) in the far field.

4. Method (1000) according to one of the preceding claims, characterized in that the imaging function is a Bessel lens imaging function.

5. Method (1000) according to one of the preceding claims, characterized in that the spatial image information is provided as a 3D point cloud.

6. Method (1000) according to one of the preceding claims, characterized in that the modified phase images (40) are exposed as volume reflection holograms into the holographic recording material (95).

7. Hologram security element (2000) comprising a hologram which includes a plurality of computer-generated phase holograms exposed in the same recording area and designed as volume reflection holograms, which, during reconstruction, reconstruct different outer contours of at least one three-dimensional object corresponding to different mutually parallel cutting planes of a spatial object in different mutually adjacent parallel reconstruction planes.

8. Hologram security element assembly comprising a plurality of hologram security elements (2000) according to claim 7, characterized in that, that each of the hologram security elements (2000) reconstructs the outer contours of another three-dimensional object corresponding to different cutting planes of another spatial object in different adjacent parallel imaging planes.

9. Device (1) for producing a hologram security element comprising: a control unit (10) with a calculation unit (100) for calculating at least one modified phase image; a light source (50) for generating coherent light, a phase-modulating spatial light modulator (160), and a transport device (80) for transporting a holographic recording material (95) section by section into an exposure area (77) and optical elements (55) which direct the coherent light (52) at least partially onto the phase-modulating spatial light modulator (160), which is controlled by the control unit (10) according to the at least one modified phase image (40) in order to generate the phase-modulated object light and to cause the phase-modulated light in the recording area (97) in the recording material (95) to interfere with at least a part of the non-phase-modulated light as a reference light, characterized in thatthat the computing unit (100) is configured to perform steps (b) to (d) of the method according to claim 1 and the control device (10) is configured to control the light source (509) and the phase-modulating spatial light modulator (160) such that the plurality of generated modified phase images (40) are exposed into the same recording area (97) of the holographic recording material (95).

10. Device (1) according to claim 9, characterized in that the phase-modulating spatial light modulator is a reflective liquid crystal on silicon phase modulator.

11. Device (1) according to claim 9 or 10, characterized in that the control device (10) is configured to iteratively perform steps (a) to (f) of the method according to claim 1 in order to produce an assembly of hologram security elements.

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