Method and apparatus for manufacturing a hologram security element

Abstract

The invention relates to a method (1000) for manufacturing a hologram security element (2000) comprising the steps: Capturing (1010) image information; Calculating (1020) a phase image that corresponds to the image information in the far field; Folding (1030) the phase image with the imaging function of at least one optical element to assign the far field image information to a different display position; Arranging a holographic recording material in front of a reflective spatial phase modulator such that one side of the holographic recording material faces the spatial phase modulator, Exposure of the recording material with coherent light (52) from the side facing away from the spatial phase modulator, such that the coherent light incident on the side facing away from the spatial phase modulator interferes in the holographic recording material with the phase-modulated light reflected from the reflecting spatial phase modulator in order to store a hologram in the recording material (1100).

Description

[0001] The invention relates to a security element designed as a hologram, which stores graphic 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.

[0002] 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.

[0003] 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.

[0004] 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.

[0005] 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.

[0006] 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.

[0007] A specific type of volume reflection hologram, such as that used in identity cards, and its production are described in publication EP 0 896 260 A2.

[0008] The volume holograms described in EP 0 896 260 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, 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 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 appears green. This image is suitable for verification by a human observer.

[0009] DE 10 2018 220 099 A1 describes a device for generating a hologram, comprising an optical arrangement, wherein the optical arrangement has along an optical axis at least one laser radiation source, a diffractive optical element, and a master image in or on which a holographic recording material to be exposed and a hologram master can be arranged, and wherein the diffractive optical element is configured to focus laser radiation emitted by the laser radiation source and transmitted through the diffractive optical element onto a focal plane in a beam path of the optical arrangement, thereby irradiating an exposure area that corresponds to an area to be exposed for generating the hologram. Furthermore, an associated manufacturing process is described.

[0010] Additionally, 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 from a specific direction.

[0011] The invention is based on the objective of creating a method and a device for producing an improved hologram security element, which is particularly suitable for machine testing, is difficult to counterfeit and enables improved security of the security document and the personal or individual information stored therein, which is assigned to the person to whom a corresponding object secured with the security element, e.g. a security document, is also assigned.

[0012] The invention comprises a method for producing such a hologram security element with the features of claim 1 and a device for producing a hologram security element with the features of claim 8. Advantageous embodiments are set forth in the dependent claims.

[0013] The invention is based on the idea of ​​producing an individualized hologram which, by means of coherent light illumination, projects a diffraction pattern similar to the currently available machine-testable feature. To achieve this in a volume hologram and yet be able to create it in a simple manner, so that an individualized diffraction pattern is generated for each of the manufactured hologram security elements, it is provided that a computer-generated phase hologram is stored in a hologram layer as the diffraction pattern. This is preferably also done in an exposure geometry that resembles or is identical to a Denisyuk reflection hologram.In this process, it is sufficient for coherent light to pass through the recording material and onto a reflective master object, which reflects or diffractively reflects the light, so that the reflected light interferes with the non-diffracted light passing through the recording material and stores a holographic interference structure.While in the volume reflection holograms described above, according to the state of the art, a hologram master is arranged under the holographic recording material in contact with it, which reconstructs a homogeneous diffusion disk that is locally reconstructed with different diffraction efficiencies due to a spatial amplitude modulation of the incident light and thus copied into the finished, individualized volume hologram of the recording material with different diffraction efficiencies, the novel security element provides that the coherent light passing through the recording material and not yet modulated is spatially modulated and reflected with respect to the phase positions by a reflecting phase-modulating spatial light modulator.Unlike the production of portrait images using state-of-the-art methods, this process does not involve the local modulation of light intensity in a spatial light modulator. Instead, it modulates the phase of the object light generated for hologram exposure. A phase-modulating spatial light modulator is positioned below and adjacent to the holographic recording material. A correspondingly calculated phase hologram is used to control the reflecting phase-modulating spatial light modulator. The light reflected from this modulator is then used as the object light to generate a volume reflection hologram.

[0014] It is known that when reconstructing a calculated phase hologram stored in this way, the phase positions of the hologram are locally superimposed onto a light field representing a plane wave. In the far field, this light then projects information that is a Fourier transform of the phase information of the phase hologram. If the desired image information to be reconstructed is specified, a corresponding phase image can be calculated and stored holographically to obtain the desired information in the far field during reconstruction. This allows a high information density to be stored in a small space for machine processing.

[0015] However, in order to specify the reconstruction level of the image information, it is planned that the phase image corresponding to the image information in the far field is convolved with an imaging function of at least one optical element to obtain a modified phase image, which is exposed into the recording material as a computer-generated phase hologram.

[0016] The hologram obtained in this way can only be reconstructed using coherent light, so it is not suitable for verification by a human, but rather for machine verification. Definitions

[0017] A hologram security element is a security element that includes a hologram.

[0018] 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.

[0019] 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.

[0020] The term phase image refers to the spatially distributed, different phase positions of a light field that projects graphical image information as it propagates in the far field. This image information is understood as the image information of the phase image.

[0021] 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.

[0022] 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.

[0023] A phase hologram is the information of spatially distributed, different phase positions of coherent light that defines the object light for a holographic recording of a hologram. If a coherent light field modulated according to the phase hologram, i.e., 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.

[0024] The phase image and the phase hologram can be identical if a phase image determined from a bitmap is used directly as the 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 far-field projection of the phase hologram 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.

[0025] Graphical information, or image information, refers to information that can be captured by an imaging device. 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.

[0026] The visible wavelength range refers to the wavelengths that can be perceived by the average person with normal vision. This is typically the wavelength range between 380 nm and 780 nm. The spectrum following the long-wavelength range is called the infrared wavelength range. Light in the short-wavelength spectral range is called ultraviolet (UV) light.

[0027] Holographic recording material refers to photosensitive material that can be altered once by electromagnetic radiation during exposure to store an interference pattern of a hologram. This pattern is then stored in the holographic recording material after development and, if necessary, fixing. Photopolymers, especially those formed in a thin film layer, are particularly suitable as holographic recording materials.

[0028] A phase modulator is a device that can modulate one phase of light.

[0029] A phase-modulating spatial light modulator, or simply a spatial phase modulator, is a device that can locally modulate light differently with respect to its phase at different locations. For example, a liquid crystal layer with 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.

[0030] The exposure area is defined as an area of ​​a device in which exposure of a holographic recording material takes place.

[0031] 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. Preferred embodiments

[0032] In particular, a method for manufacturing a hologram security element is created, which includes the following steps: Capturing image information; Calculating a phase image that corresponds to the image information in the far field; folding the phase image with an imaging function of at least one optical element to assign a different display position to the image information of the far field; Arranging a holographic recording material in front of a reflective spatial phase modulator such that one side of the holographic recording material faces the spatial phase modulator; Exposure of the recording material with coherent light from the side facing away from the spatial phase modulator, such that the coherent light incident on the side facing away from the spatial phase modulator interferes with the phase-modulated light reflected from the reflecting spatial phase modulator in the holographic recording material in order to store a hologram in the recording material.

[0033] While white ambient light is sufficient to reconstruct a volume reflection hologram, as used in the prior art for storing a portrait image, the reconstruction of a phase hologram requires coherent light of the corresponding wavelength, which is correlated with the wavelength at which the phase hologram was generated. This wavelength can deviate slightly from the generation wavelength if material shrinkage effects occur during the development and / or fixing of the holographic information in the holographic recording material.While the presence of the security feature is visible to the naked eye, its stored content is not perceptible to the viewer. However, it can be reconstructed by shining coherent light of a suitable wavelength onto a graphic image at a position defined by the imaging function used in the calculation. This position can be easily captured, for example, by a spatially resolved detection device. A CCD chip or even a conventional camera can be used for this purpose. Using established image recognition and evaluation algorithms, the image information can be compared to a predefined target. Depending on the comparison, a verification decision (e.g., genuine / fake) is made and displayed.

[0034] If a large number of hologram security elements are manufactured, either simultaneously in multiple uses or sequentially, the image information stored in the hologram of each security hologram element is preferably different from the image information of the other hologram security elements. Even in multiple uses, these elements are exposed to different recording areas. This means that the individual image information is pairwise distinct. During manufacturing, a large number of different image pieces are captured, each of which is separately and individually converted into a corresponding phase image or modified phase image.

[0035] As described above, in order to generate a defined reconstruction plane at a desired distance from the hologram, the phase image that reconstructs the specified image information in the far field is convolved with an imaging function of at least one optical imaging element when calculating the phase hologram. This convolution links the imaging property associated with the optical imaging element to the far-field information. For example, if a Bessel lens imaging function is used for the convolution, an image in a specified plane can be achieved during reconstruction, the distance of which from the hologram security element corresponds to the focal length f of the Bessel lens imaging function. Thus, even at short distances from the generated hologram security element, a sharp reconstruction of the image information in a plane can be achieved.This enables the creation of compact verification devices that feature a projection plane at a fixed distance from an arrangement plane in which the hologram security element to be verified is positioned and illuminated with coherent light during verification. The distance corresponds to the focal length of the Bessel lens imaging function used in the fabrication and calculation of the modified phase image. Since the imaging optics are integrated into the phase hologram, only a spatially resolved detector, such as a CCD chip, is required, on which the information can be captured without additional imaging optics. In other embodiments, other optical imaging elements, or even the imaging functions of multiple optical imaging elements, can be convolved with the phase image, which is calculated as a far-field projection of the originally provided image information.For example, the imaging function of a blaze grid structure can be used to achieve a deflection of the reconstructed image information relative to the exposure direction, which is preferably chosen perpendicular to the recording material.

[0036] In a preferred embodiment, the exposure with the coherent light is thus carried out perpendicular to the surface of the recording material.

[0037] To enable the rapid and efficient production of a large number of hologram security elements, it is preferred that the recording material be held in physical contact with a support surface during exposure. This reliably prevents vibrations and mechanical movements of the recording material during exposure. Furthermore, the material movements that inevitably occur during transport can be dampened very quickly by bringing the material into contact with a support surface.

[0038] To achieve, in particular, spatial separation between an exposure device and a detection device or projection surface, one embodiment provides that the spatial phase modulator reflects the light at a slight angle relative to a surface normal of the holographic recording material. Preferably, the spatial phase modulator is thus slightly tilted relative to the mounting surface of the holographic recording material, which is preferably exposed perpendicularly. This slight tilt also offers the advantage of avoiding potential interference due to multiple reflections at mutually plane-parallel surfaces, which can lead to undesirable interference and light cancellation. Furthermore, this prevents direct zero-order back-reflections of the light beam.

[0039] The provided image information is preferably provided as a bitmap or converted into such a bitmap.

[0040] The phase image is preferably determined from the provided image information using an iterative Fouier transformation process. Various such methods are known to those skilled in the art for iteratively calculating the corresponding spatially resolved phase information, the phase image, from a given image information.

[0041] In a preferred embodiment, the phase information or phase image is calculated using a Gerchberg-Saxton algorithm.

[0042] Spatial phase modulation is preferably achieved using a reflective LCOS. The acronym LCOS stands for Liquid Crystal on Silicon. This technology is well-established and provides a spatial phase modulator that additionally reflects the light during phase modulation.

[0043] This creates a holographic security element that is easily verifiable by machine. It is particularly preferred to combine this holographic security element, comprising a phase hologram, with an ordinary volume reflection hologram, especially an individualized volume reflection hologram containing a holographic frosted or diffusing disk stored locally with varying intensities. Such a copied diffusing or frosted disk, for example, has the form of a portrait image of a person as a "black and white image".

[0044] The image information stored in the phase hologram complements the image information stored in the ordinary volume reflection hologram particularly well. For example, the same alphanumeric characters or even the same portrait image can be stored once as an ordinary volume reflection hologram and once as a reflection phase hologram.

[0045] Because the exposure process is the same as for a conventional Denisyuk reflection hologram, the light field of a phase image generated by the spatial phase modulator is stored as a reflection hologram within the volume hologram. This allows for its reconstruction as a reflection hologram. Furthermore, unlike other phase holograms, which are often stored on the surface as a relief or similar feature, the hologram information is stored within the volume of the recording material, providing better protection against tampering. Additionally, the volume hologram achieves high diffraction efficiency, facilitating the detection of reconstruction. The information is stored within the hologram itself, in the volume of the holographic recording material.During verification, both the image information of the phase hologram and the ordinary volume reflection hologram can be reconstructed, and the information contained therein can be compared for agreement.

[0046] Other “intertwinings” of the image information in the calculated phase hologram and the information in the ordinary volume reflection hologram are also possible.

[0047] The invention is explained in more detail below with reference to a drawing. The drawing shows: Fig. 1 a schematic view of a device for producing an individualized volume reflection hologram according to the prior art; Fig. 2 a schematic representation of a device for producing an individualized hologram security element suitable for machine verification; Fig. 3 a schematic flowchart of the procedure for producing a machine-readable individualized hologram security element; Fig. 4 a schematic representation of a device for manufacturing a hologram security element, which additionally comprises an ordinary volume reflection hologram with a second image information; and Fig. 5 A schematic diagram to illustrate the verification of a hologram security element.

[0048] In Fig. Figure 1 schematically depicts a device 1 for producing a volume reflection hologram according to the prior art. The device 1 comprises a control unit 10 configured to acquire individual image information 20. This information can be acquired, for example, from a storage device 30 or via an interface 40.

[0049] The control unit 10 is coupled to a transport unit 80. This unit comprises a material spool 81 and a take-up spool 82. A holographic film 90, comprising a holographic recording material 95, is provided on the material spool 81. The holographic recording material 95 preferably comprises a photopolymer. The holographic recording material 95, provided by the material spool 81, is guided to the take-up spool 82 via guide rollers 83. The transport unit moves the holographic film 90 section by section into an exposure area 77.

[0050] In the exposure area 77, a hologram master 70 is arranged below the holographic film 90. A top surface 71 of the hologram master 70 forms a support surface 75. The transport device 80 is designed to move the holographic film 90 section by section into the exposure area 77 such that the holographic film 90 rests against the support surface 75 of the hologram master 70 with its underside 92. For this purpose, in the illustrated embodiment, a pressure roller device 85 is provided, which is moved by rolling over a top surface 91 of the hologram film and presses the hologram film against the support surface 75 of the hologram master 70.

[0051] The control unit 10 is coupled to a light source 50, preferably designed as a laser 51. The coherent light 52 generated by the laser 51 is guided via optical elements 55 first to an amplitude-modulating spatial light modulator 60. This modulator is controlled by the control unit 10 such that the light exiting the spatial light modulator 60 is locally modulated with respect to its amplitude or light intensity according to the captured individual image information 20. The amplitude-modulated light is guided via the further optical elements 55, for example, perpendicularly through the holographic film 90 with the holographic recording material 95 to the hologram master 70 located below. The amplitude-modulated coherent light 57 is diffracted by reflection at the hologram master 70. The hologram master 70 is designed, for example, as a volume reflection hologram of a homogeneous diffusing ground glass screen.Due to the amplitude modulation of the coherent light 57, this homogeneously reflecting ground glass screen is locally copied into the holographic recording material as a volume reflection hologram with different intensities or diffraction efficiencies. The method used corresponds to the Denisjuk holography process. After an individualized hologram has been exposed, the described process is continued with new individualizing image information 20.

[0052] A fixing station 88 can be arranged between the exposure area 77 and the winding spool 82, which ensures that unexposed photopolymer areas in the holographic recording material 95 lose their reactivity to light and that the polymerization processes initiated by the exposure are terminated.

[0053] It is understood by those skilled in the art that individual process steps are described here in a highly simplified manner. For example, the holographic film can be drawn onto the support plate by creating a vacuum and separated from the support surface by blowing in a fluid before further transport in order to prevent damage to the hologram film 90 during transport.

[0054] In Fig. Figure 2 is a schematic representation of a device 1' for producing hologram security elements as proposed herein. Identical technical features as known from device 1 according to the prior art are designated with the same reference numerals and, insofar as they serve the same functions, are not explicitly described again here. At the same time, the manufacturing process is illustrated by a flowchart according to Fig. 3 described.

[0055] The control unit 10 comprises a processing unit 100. The processing unit 100 captures the individual image information 20, for example as a bitmap. Alternatively, the processing unit 100 can be configured to convert the provided image information 20 into a bitmap. It is also possible for the image information 20 to be provided abstractly, for example as alphanumeric characters, which are then converted into a corresponding bitmap using a font, thus graphically representing the alphanumeric characters.

[0056] The computational unit 100 calculates a phase image 1020 from the provided image information. Such a phase image contains the local phase information that must 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. The algorithm was first described by Gerchberg and Saxton in the 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. A number of further developments are known in the art. One example is described by P. Memmolo et al. described in the 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.

[0057] To obtain a defined projection plane for the reconstruction of the hologram security element to be manufactured, the resulting phase image is convolved with an imaging function of an optical element 1030. A modified phase image is obtained. Preferably, the imaging function of a Bessel lens is used.

[0058] From the transport device 80, a section of the hologram film 90 with the recording material 95 is transported into an exposure area 77 1040 and pressed against a support surface 175 1050.

[0059] The placement of the holographic recording material 95 against a mechanically formed support surface 175 serves to prevent movement of the holographic recording material 95 during exposure. 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 the surface 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, and a surface 161 of the spatial phase modulator 160 is slightly tilted relative to the support surface 175, for example by an angle α.

[0060] 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 in the holographic film 90 by optical elements 55 1070.

[0061] The control unit 10 controls the spatial phase modulator 160 according to the calculated modified phase image as a phase hologram. The spatial phase modulator 160 is preferably an LCOS, a so-called Liquid Crystal on Silicon device, in which liquid crystal cells are formed on a CMOS chip, which controls the different orientations of the liquid crystal in the individual cells. 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 varying phase modulation, passes through the support surface 175 and enters the holographic recording material 95 of the holographic film 90, where it interferes with the incident unmodulated light 1100. This interference information is stored as a hologram in the holographic recording material. This is also referred to as exposing the phase hologram to the holographic recording material 1100. Either immediately or after the exposure of the entire hologram film, it is developed (depending on the recording material) 1110 and / or, if necessary, fixed 1120. After one of the process steps 1100, 1110, or 1120, the process branches and begins again with process step 1000, capturing image information, until the entire hologram film is formed with various hologram security elements.This allows a large number of individualized phase holograms to be easily generated as hologram security elements, as indicated by iteration 1111.

[0062] 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.

[0063] In a further development process, the exposure of an "ordinary" volume reflection hologram into 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 into 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.

[0064] One such embodiment, in which both holograms are generated with the same wavelength, is shown schematically in Fig. 4 shown. Same technical features as in the Fig. 1 and Fig. 2 are again provided with the same reference numerals. In this embodiment, the 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 and the phase hologram, which are individualized by means of amplitude modulation.

[0065] The light 52 generated by the same light source 50, which is configured as a laser 51, is expanded, and a portion 52-1 of it, used to expose the hologram master 70, is driven by the amplitude-modulating spatial light modulator 60 with a second individualizing image information. The corresponding second image information is then exposed as a volume reflection hologram into the hologram film and its recording material in a further recording area 99. Another portion 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 it, which imprints the phase information of the phase hologram onto the reflected light 58-2. This phase hologram, or modified phase image, is also stored as a volume reflection hologram in the holographic recording medium in a recording area 97.The image information correlated with the phase hologram is a first individualizing image information, preferably linked to the second individualizing image information of the ordinary volume reflection hologram. For example, it can be supplementary information. In other embodiments, the information is identical, allowing for a simple comparison of the reconstructed holograms during verification.

[0066] In Fig. Figure 5 schematically depicts the verification device 3000 of a hologram security element 2000, part of an assembly of hologram security elements with individualized phase holograms. The hologram security element 2000 is integrated into a security document 2010, for example, as a layer. The security document 2010 itself is also a hologram security element according to the definition used here. The security document is arranged on an arrangement plane 2050. The hologram security element 2000 is illuminated with coherent laser light 52 from a laser 51. The phase information of the phase hologram 2100 is imprinted on the plane wave of the laser light 52 in the recording area 97 of the phase hologram 2100 of the hologram security element 2000 during diffraction.In a predefined reconstruction plane 2200, which is defined, for example, by a focal length f of the imaging function of a Bessel lens, the image information 2150 of the phase hologram 2100 is projected. This image information is correlated with the phase image that was convolved with the imaging function of the Bessel lens to generate the modified phase image of the stored phase hologram 2100. Thus, during the verification and reconstruction of the phase hologram 2100, the image information 2150 encoded within it is projected onto a reconstruction plane 2200 at a distance of this focal length f. This can, for example, be directly captured as a reconstruction image 2160 using a CCD chip 2350 in the reconstruction plane 2200. Alternatively, the image information 2150 projected onto the reconstruction plane 2200 can be captured using a camera.In order to make a verification decision, this image information 2150 is compared with a reference. This reference can, for example, consist of an image of information printed in a security document, such as a printed portrait image 2600.

[0067] In the illustrated embodiment, the input information is extracted from a volume reflection hologram 2500 by its reconstruction, which is stored in the same recording material, but preferably in a further recording area 99 that is spatially offset. This is in Fig. 5 also indicated. In one embodiment, the phase hologram contains image information 2150 that is identical to the image information 2550 of the ordinary volume reflection hologram 2500. The image information captured by the volume reflection hologram during reconstruction Fig. The reconstruction image 2160, captured during the reconstruction of the phase hologram, can thus be superimposed, for example, by subtraction, allowing deviations in the reconstructed image information to be easily detected in a resulting difference image 2700. If a match is found, the difference image 2700 is "empty" and the hologram security element 2000 is verified as genuine; otherwise, it is verified as fake or damaged. This decision is transferred to security document 2010. Illumination with the coherent light 52 of the laser 51 and the capture of the reconstruction image 2160 with the CCD chip 2350 and the Fig. The acquisition of the reconstructed volume reflection hologram 2500 by means of a camera 2400, as well as the formation of the difference image 2700 and its evaluation, are controlled and / or performed by an evaluation unit 2800. This unit outputs the verification result optically, acoustically, or as a signal.

[0068] Furthermore, it has surprisingly been shown that when reconstructing with white light, and only with white light in the plane of the hologram security element, the information content of the phase hologram can also be reconstructed and detected, albeit small, as an "ordinary" volume reflection hologram. The presence of this feature can be used for additional verification.

[0069] 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 phase hologram is exposed. The hologram security element with the 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 formed from several layers, preferably of plastic material, which 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 additional security elements and features. Reference symbol list 1, 1' Device for manufacturing a holographic security element 10 Control unit 20 individual image information 30 Storage device 40 interface 50 light sources 51 lasers 52 coherent light 52-1 a part of the coherent light 52-2 other part of the coherent light 55 optical elements 57 amplitude-modulated light 58-2 reflected phase-modulated light 60 amplitude-modulating spatial light modulator 70 Hologram Masters 71 Top 75 mm contact area 77 Exposure range / recording range 80 Transport equipment 81 material spool 82 Winding spool 83 pulleys 85 Pressure roller device 90 Hologram film 91 Top 92 Underside 95 holographic recording material 97 Recording area 99 additional recording area 100 calculation units 160 spatial phase modulator 175 mm contact area 176 Glass / Plastic Disc α Angle Top Hologram Film - Top Phase Modulator 1000 methods for manufacturing a hologram security element 1010 Capturing image information 1015 Creating a Bitmap 1020 Calculating a phase image 1021 iterations 1030 folds of the phase image with an imaging function of an optical element 1040 Transporting a section of the hologram film 1050 Placing the hologram film on a support surface 1060 Generating coherent light 1070 Scanning the holographic recording material 1080 Controlling the spatial phase modulator according to the calculated phase hologram 1090 Phase modulation of coherent light and reflection of light 1090 Transillumination of the holographic recording material with phase-modulated light 1100 Interference of phase-modulated and non-modulated light Exposure of the phase hologram 1111 Iteration 1110 Developing the holographic recording material 1120 Fixing the holographic recording material 1200 singling 1300 Laminating into / mounting onto a security document 2000 hologram security elements 2010 Security Document 2050 Arrangement level 2100 Phase hologram 2150 Image information 2160 Reconstruction image 2200 Reconstruction level 2350 CCD chip 2400 camera 2500 volume reflection hologram 2550 Image information of the volume reflection hologram Figure 2560 2600 printed portrait images 2700 Difference mapping 2800 Evaluation unit 3000 verification device

Claims

[1] Method (1000) for producing a hologram security element (2000) comprising the steps: Capturing (1010) image information (20); Calculating (1020) a phase image that corresponds to the image information (20) in the far field; Folding (1030) of the phase image with an imaging function of at least one optical element to generate a modified phase image in order to assign the image information (20) of the far field to a different display position; Arranging a holographic recording material (95) in front of a reflective phase-modulating spatial light modulator (160) such that one side of the holographic recording material (95) faces the phase-modulating spatial light modulator (160), Controlling (1080) the phase-modulating spatial light modulator (160) according to the modified phase image, so that the phase-modulating spatial light modulator (160) spatially modulates incident coherent light (52) according to the phase information of the modified phase image, Exposure of the recording material (95) with coherent light (52) from the side facing away from the phase-modulating spatial light modulator (160), so that the coherent light (52) incident on the holographic recording material (95) from the side facing away from the phase-modulating spatial light modulator (160) interferes with the phase-modulated light (58-2) reflected from the reflecting spatial phase modulator (160), to store a hologram in the recording material (95) (1100). [2] Method (1000) according to claim 1, characterized by, that a large number of hologram security elements (2000) are produced and for each of the hologram security elements (2000) individual image information (20) is recorded. [3] Method (1000) according to claim 1 or 2, characterized by , that the folding (1030) of the phase image with an imaging function of at least one optical element includes the folding (1030) of the calculated phase image with a Bessel lens imaging function that produces an image at a given focal length f. [4] Method (1000) according to any of the preceding claims, characterized by , that the folding (1030) of the phase image with an imaging function of at least one optical element includes the folding (1030) with a blaze grid structure that causes a deflection of the reconstructed image information relative to a normal of a film (90) in one direction. [5] Method (1000) according to any of the preceding claims, characterized by, that the exposure with the coherent light (52) is carried out perpendicular to the support surface (175) of the recording material (95). [6] Method (1000) according to any one of the preceding claims, characterized by , that the phase-modulating spatial light modulator (160) reflects the phase-modulated light slightly tilted relative to a surface normal of the holographic recording material (95). [7] Method (1000) according to any of the preceding claims, characterized by , that the phase image is determined from the image information (20) by means of an iterative Fourier transformation process. [8] Device (1) for generating hologram security elements (2000), comprising: a computing device (100) for acquiring (1010) image information (20) and calculating a phase image from the image information (20) and folding (1030) the phase image with an imaging function of at least one optical element to generate a modified phase image; a transprotein direction (80) which is designed to transport a recording material (95) designed as a film (90) section by section into an exposure area (77) and to position it in contact with a support surface (175) in the exposure area (77); a light source (50) for generating coherent light (52) and optical elements (55) for exposing the holographic recording material (95); and a phase-modulating spatial light modulator (160) arranged adjacent to the exposure area (77), wherein the phase-modulating spatial light modulator (160) and the light source (50) and the optical elements (55) are designed such that the coherent light of the light source (50) passes through the holographic recording material (95) arranged on the support surface (175) and onto the phase-modulating spatial light modulator (160), which modulates the spatial phase positions of the light according to the modified phase image and reflects back into the holographic recording material (95) in order to interfere with the unmodulated coherent light in the recording material (95) and to store a hologram. [9] Device (1') according to claim 8, characterized by , that the phase-modulating spatial light modulator (160) is an LCOS.

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