# Patent

## Title
Holographic data-storage medium

## Abstract

In an example holographic data storage medium, which has a polymer film which serves as a storage layer and can be changed locally by heating, the polymer film is set up as a top layer of the data storage medium. Arranged underneath the polymer film is an absorber layer which has an absorber dye. The absorber dye is set up to at least partly absorb a write beam serving to put information in and to discharge the heat produced in the process at least partly locally to the polymer film. In an advantageous refinement of the example data storage medium, there is an adhesive layer underneath the absorber layer and a partly transparent reflective layer between the polymer film and the absorber layer.

## Background
This application is the U.S. national phase of international application PCT/EP02/01951, filed in English on 25 Feb. 2002, which designated the U.S. PCT/EP02/01951 claims priority to DE Application No. 101 28 902.2 filed 15 Jun. 2001. The entire contents of these applications are incorporated herein by reference.
BACKGROUND AND SUMMARY
The invention relates to a holographic data storage medium which, for example, can be used for storing pictorial data such as photographs, logos, text and so on but also for the storage of other data.
Contained in a hologram, distributed over the area of the hologram, is optical phase information about an object, from which, when irradiated with light, and in particular coherent light from a laser, an image of the object can be reconstructed. Holograms are used in many and various ways in technology, for example in the form of largely forgery-proof identifiers. Identifiers of this type will be found, for example, on credit cards or check cards; as what are known as white light holograms, even when illuminated with natural light, they show a three-dimensional image of the object depicted. Photographically produced holograms are widespread, as are embossed holograms, in which a relief structure is embossed into the surface of a material, at which the light used to reproduce the object is scattered in accordance with the phase information stored in the hologram, so that the reconstructed image of the object is produced by interference effects.
WO 00/17864 describes a data storage medium with an optical information carrier, which contains a polymer film set up as a storage layer. The polymer film consists, for example, of biaxially oriented polypropylene. In the data storage medium previously disclosed, the polymer film is wound spirally in a plurality of layers onto a core, there being an adhesive layer in each case between adjacent layers. Information can be written into the data storage medium by the polymer film being heated locally with the aid of a write beam from a data drive, as a result of which the refractive index of the polymer film and the reflective capacity at the interface of the polymer film are changed locally. This effect can be amplified by an absorber dye which is added to the adhesive layers, which at least partly absorbs the write beam and discharges the heat produced in the process locally to the polymer film. With the aid of a read beam in the data drive, the changes in the polymer film can be registered, since the read beam is locally reflected more or less intensely at the interface of the polymer film, depending on the information written in. By focusing the write beam or read beam, information can be written specifically into a preselected position on the information carrier or read out from it.
It is an object of the invention to provide a holographic data storage medium which is inexpensive, has wide areas of application and is largely insensitive to external influences.
The holographic data storage medium according to the invention has a polymer film which is set up as a storage layer and which can be changed locally by heating. This polymer film is set up as a top layer of the data storage medium. Arranged underneath the polymer film is an absorber layer, which has an absorber dye which is set up to at least partly absorb a write beam serving to put information in and to discharge the heat produced in the process at least partly locally to the polymer film. The polymer film set up as a storage layer is preferably arranged in one layer in the data storage medium (preferably in a substantially flat arrangement), that is to say, for example, not wound up in a plurality of layers in spiral form.
Since the polymer film is set up as a top layer of the data storage medium, it can serve as the exposed outer side of the data storage medium and protects the generally relatively sensitive absorber layer located underneath. Furthermore, the changes in the polymer film which are effected by heating and using which holographic information is stored are primarily localized in the vicinity of the absorber layer, as explained in more detail further below. Therefore, this region of the polymer film provided with the stored information is likewise located in a protected zone. Undesired influences on the exposed outer side, such as scratches, therefore generally do not have any further effect and, above all, do not lead to a loss of data or to faults when putting information into the data storage medium.
The holographic data storage medium according to the invention is simply constructed, since an additional protective device can generally be dispensed with, and can therefore be produced inexpensively.
An adhesive layer is preferably arranged underneath the absorber layer, and makes it possible to stick the holographic data storage medium onto an object. If the adhesive layer is located immediately underneath the absorber layer, it simultaneously protects the absorber layer and the adjacent region of the polymer film with stored holographic information. The adhesive layer can, for example, contain an adhesive compound comprising an aqueous acrylate emulsion or can consist of functionalized poly(meth)acrylate. Other materials can also be used for the adhesive layer. One preferred thickness of the adhesive layer is about 20 μm, but other thicknesses are also possible.
In an advantageous refinement of the invention, a partly transparent reflective layer is arranged between the storage layer and the absorber layer. The reflective layer can have aluminum and preferably has a thickness in the range from 1 nm to 50 nm, other thicknesses also being possible. It is partly transparent, in order that the write beam penetrates as far as the absorber layer when information is being put in. Since the reflective layer is thin, it virtually does not hinder the discharge of heat to the polymer film. The reflective layer makes it easier to read out the stored holographic information in reflection, which represents a beneficial geometry in most applications. This is explained further below using examples. Furthermore, the reflective layer simplifies the operation of setting the focus of the write beam (see below).
It is also possible to arrange a reflective layer underneath the absorber layer. If there is an adhesive layer, this reflective layer is preferably located between the absorber layer and the adhesive layer. A layer structure of this kind permits the absorber layer to be penetrated in transmission when information is being read out of the holographic data storage medium, so that, for example, the contrast of the read-out signal is amplified if the absorption capacity of the absorber dye within the absorber layer varies in accordance with the information put in (amplitude effect; see below).
Suitable materials for the polymer film are, for example, polypropylene, polyvinylchloride, polyester, polyethylene terephthalate (PET), polyethylene naphthalate, polymethylpentene (PMP; also poly-2-methylpentene) and polyimide. The polymer film preferably has a thickness such that it is self-supporting and can carry out the protective function explained above. Suitable thicknesses lie in the range between 10 μm and 100 μm, but other thicknesses are likewise possible.
The polymer film can be oriented and is preferably biaxially oriented, for example it being pretensioned in two mutually perpendicular directions within its plane during production. This generally increases the strength of the polymer film. Furthermore, in the case of an oriented polymer film, a high energy density is stored in the film material. As a result of local heating with the deposition of a relatively small amount of energy per unit area, for example with the aid of a write beam from a writing device, which is absorbed in the absorber layer, a relatively intense material change with a change in the local properties of the polymer film can be achieved.
In addition to the absorber dye, the absorber layer preferably has a binder. The absorber dye permits local heating of the polymer film which is sufficient to change the local properties of the polymer film with a relatively low intensity of the write beam. The absorber layer can be thin and, for example, have a thickness in the range from 0.1 μm to 5 μm; other thicknesses are likewise possible. Preferred binders, which serve as a matrix for the molecules of the absorber dye are, for example, optically transparent polymers, for example of polymethyl methacrylate (PMMA) or, in the case of applications for higher temperatures, of polymethylpentene, polyether ether ketone (PEEK) or polyether imide. The absorption maximum of the absorber dye should coincide with the light wavelength of the write beam used, in order to achieve efficient absorption. For a light wavelength of 532 nm of a write beam produced by a laser, for example dyes from the Sudan red family (diazo dyes) or (for particularly polar plastics) eosin scarlet are suitable. For the usual laser diodes with a light wavelength of 650 to 660 nm or 685 nm, green dyes, for example from the styryl family (which are usual as laser dyes), are better suited.
There are various possible ways to use the local change in the properties of the polymer film, effected by local heating of the latter, for the storage of information.
In one possible way, the refractive index of the polymer film can be changed locally by heating, it being possible for optical phase information to be stored in the polymer film via the local optical path length. In this case, provision is made to transilluminate the polymer film in transmission when reading out information (it being possible for the reflective layer to be helpful, see below). It is therefore possible to store phase information locally in the polymer film, that is to say in a region provided for the storage of a unit of information, by the refractive index in this region being changed by heating (for example with the aid of a write beam from a writing device). The local change in the refractive index effects a change in the optical path length of the radiation used when reading information out of the polymer film (which transilluminates the polymer film in transmission). The optical path length is specifically the product of the geometric path length and the refractive index. Therefore, via a change in the refractive index, the local phase angle of the radiation used when reading out information can be influenced, that is to say the desired holographic information can be stored as phase information. A hologram produced in the polymer film in this way is accordingly a refractive phase hologram.
In another possible way, the surface structure or interface structure of the polymer film can be changed locally by heating, it being possible for holographic information to be stored via the local interface structure of the polymer film. In this case, therefore, the interface structure or topography of the polymer film, in particular at the interface to the absorber layer or to the reflection layer, pointing away from the exposed outer side of the polymer film, can be changed locally, for example by a laser beam serving as a write beam being focused on to the absorber layer or the interface zone of the polymer film, so that the light energy is absorbed there and converted into heat energy. In particular if the laser beam is radiated in briefly (pulsed), the material change in the polymer film leading to the local change in the interface structure is limited to a very small volume, on account of the generally poor thermal conductivity of the polymer (or of a very thin reflective layer). If the holographic information is put into the polymer film point by point, the region associated with a point typically having linear lateral dimensions of the order of magnitude of 0.5 μm to 1 μm, the height profile of the polymer film typically changes by 50 nm to 500 nm, which depends in detail on the properties and operating conditions of the write beam and the properties of the polymer film, of the absorber layer and possibly of the reflective layer. The point grid, that is to say the center spacing between two points (“pits”), typically lies in the range from 1 μm to 2 μm. In general, it is true that shorter light wavelengths of the write beam permit a closer point grid.
Mixed forms are also conceivable, in which the holographic information can be stored both by a local change in the refractive index and by a local change in the interface structure of the polymer film.
The absorber dye can be set up such that its optical properties are changed locally when it absorbs a write beam serving to put information in. In this case, it is particularly advantageous if the absorber dye changes its absorption capacity locally, that is to say by being bleached partly or completely by the write beam. By means of local variation in the absorption capacity in the absorber layer, the effect achieved in the polymer film by the changes can be reinforced, so that the signal obtained when reading out the holographic data storage medium is more intense or more contrasty than if the absorber layer does not participate in the data storage. The weighting of the individual effects (local refractive index of the polymer film, local interface structure of the polymer film, amplitude effect as a result of locally bleached absorber dye) in the read signal may be influenced or set by choosing the layer structure of the holographic data storage medium. Thus, an amplitude effect is relatively high when a locally bleached absorber layer is transilluminated when information is being read out, such as is the case when a reflective layer is arranged underneath the absorber layer.
The information to be stored can be put into the holographic data storage medium by an item of holographic information contained in a hologram of a stored object being calculated as a two-dimensional arrangement and a write beam from a writing device, preferably a laser lithograph, being aimed at the polymer film and/or the absorber layer of the data storage medium and driven in accordance with the two-dimensional arrangement such that the local properties of the polymer film are set in accordance with the holographic information. Since the physical processes during the scattering of light at a stored object are known, a conventional structure for producing a hologram (in which coherent light from a laser, which is scattered by an object (stored object) is brought to interference with a coherent reference beam and the interference pattern produced in the process is recorded as a hologram) can be simulated for example with the aid of a computer program and the interference pattern or the modulation of the local properties of the polymer film can be calculated as a two-dimensional arrangement (two-dimensional array).
As already explained further above, examples of the local properties of the polymer film which are set in accordance with holographic information are the local refractive index and the local interface structure of the polymer film.
The resolution of a suitable laser lithograph is typically about 50 000 dpi (dots per inch). Therefore, the polymer film can be changed locally in regions or pits with a size of about 0.5 μm to 1 μm. The writing speed and other details depend, inter alia, on the parameters of the write laser (laser power, light wavelength) and the pulse duration and on the properties of the polymer film and the absorber layer.
The write beam is preferably aimed at the holographic data storage medium from the side of the top layer. In this case, it is possible, for example, to put information into the data storage medium if the adhesive layer does not have good optical properties or the data storage medium is bonded to a non-transparent substrate.
If the holographic data storage medium has a partly transparent reflective layer, as explained further above, then, in order to focus the write beam, its reflection from the reflective layer can be evaluated. A comparable reflection would also occur in the case of reflection at the interface between two media with different refractive indices if no reflective layer is arranged there but, in the present case, will be reinforced considerably by the reflective layer. The evaluation can be carried out, for example, via the magnitude of the reflection, measured with the aid of a detector, it being possible for the exact focus setting to be determined, for example, with the aid of calibration measurements. If the reflective layer is very thin (about 1 nm to 50 nm, but also more or less), it can be assumed that the focus of the write beam set to the reflective layer virtually coincides with the optimum focus in the absorber layer. Therefore, when information is put in, the absorber layer can be heated virtually in an optimum way.
As mentioned, the holographic information is preferably put in in the form of pits of predefined size. The term “pit” is to be understood here more generally in the sense of a changed region and not restricted to its original meaning (hole or depression). In this case, the holographic information can be stored in a pit in binary encoded form. This means that, in the region of a given pit, the local properties of the polymer film assume only one of two possible basic forms (basic values). These basic forms preferably differ considerably, in order that intermediate forms which occur in practice and which lie close to one or the other basic form can be assigned unambiguously to one or the other basic form, in order to store the information reliably and unambiguously.
Alternatively, the holographic information can be stored in a pit in continuously encoded form, the local properties of the polymer film in the pit being set in accordance with a value from a predefined value range. If, for example, the local interface structure of the polymer film is to be set, the local maximum height change in the interface structure in the pit is therefore selected from a predefined value range. This means that, in a given pit, the interface structure of the polymer film can assume intermediate forms between two basic forms, so that the maximum height change of the intermediate form which is present assumes a value from a predefined value range whose limits are given by the maximum height changes of the two basic forms. In this case, the information can therefore be stored “in gray steps”, so that each pit is assigned the information content of more than one bit. This is correspondingly true of the setting of the local refractive index of the polymer film.
In order to read information out from the holographic data storage medium according to the invention, light, preferably coherent light (for example from a laser) can be aimed at a large area of the storage layer of the data storage medium. In this case, the light is modulated by the locally varying properties of the polymer film (for example the refractive index or the interface structure). As a reconstruction of the information contained in the irradiated region, a holographic image is registered at a distance from the data storage medium, for example by a CCD sensor which is connected to a data processing device.
In principle, the reading operation can be carried out with transmission of the holographic data storage medium, that is to say the data storage medium is transilluminated completely and the holographic image is registered behind the data storage medium. However, for this purpose all the layers of the data storage medium must have a good optical quality, that is to say not just the polymer film but also the absorber layer and an optional adhesive layer. It is therefore more advantageous to read out the information in reflection, the light used for reading being reflected after passing through the polymer film. In this case, the holographic image is produced by light which has passed twice through the polymer film and, in the process, has been modulated, for example by local variations in the refractive index and/or the interface structure of the polymer film. In principle, reading can even be carried out in reflection if there is no separate reflective layer present; the only precondition is the presence of an interface between two media with different refractive indices. However, the reflective layer mentioned between the polymer film and the absorber layer improves the reproduction of the holographic image considerably.
The term “large area” is to be understood to mean an area which is considerably larger than the area of a pit. In this sense, for example an area of 1 mm2 is large. For the scheme in accordance with which information is stored and read out, there are many different possibilities. It is conceivable to read a hologram out of the polymer film in one operation by the entire area of the region of the holographic data storage medium set up as a hologram being irradiated in one operation. In particular in the case of relatively large areas, however, it is advantageous to divide up the information to be stored in to a number or large number of individual regions (for example with a respective area of 1 mm2) and to read out the information in one operation only from a predefined individual region.
During the reading of information, as a result of the locally varying properties of the polymer film, propagation time differences of the light waves originating from various points occur, that is to say substantially periodic phase modulation (which applies in particular in the case of local setting of the refractive index or the interface structure of the polymer film). The region of the polymer film covered by the light acts in the same way as a diffraction grating, which deflects incident light in a defined manner. The deflected light forms an image of the stored object, which constitutes the reconstruction of stored holographic information.
In principle, holographic information from different types of stored objects can be used with the holographic data storage medium. For example, the information contained in images, such as photographs, logos, texts and so on, can be stored and read out. However, the storage of machine-readable data is particularly advantageous. This is carried out, for example, in the form of what are known as data pages, the holographic information contained in a hologram of a graphic bit pattern (which represents the data information) being put as explained into the polymer film serving as a storage layer. During reading, a holographic image of this graphic pattern is produced. The information contained therein can be registered, for example with the aid of a precisely adjusted CCD sensor, and can be processed by associated evaluation software. For the reproduction of images in which high accuracy is not important, a simple matt disk or, for example; a camera with and LCD screen is already in principle sufficient. During the holographic storage of machine-readable data, it is advantageous that the information does not have to be read out sequentially but that an entire data set can be registered in one operation, as explained. If, in spite of the protection by the exposed outer side of the polymer film of the regions of the data storage medium serving to store information, damage nevertheless occurs then, as opposed to a conventional data storage medium, this generally does not lead to a loss of data but merely to impairment of the resolution of the reconstructed holographic image when reading out the information. This is generally not a problem.



BRIEF DESCRIPTION OF THE DRAWINGS
In the following text, the invention will be explained further using exemplary embodiments. In the drawings:
FIG. 1 shows a schematic longitudinal section through a first embodiment of the holographic data storage medium according to the invention,
FIG. 2 shows a schematic longitudinal section through a second embodiment of the holographic data storage medium according to the invention,
FIG. 3 shows a schematic plan view of a detail of a holographic data storage medium according to the invention in accordance with the second embodiment, in which information can be stored via changes in the refractive index,
FIG. 4 shows a schematic longitudinal section through the holographic data storage medium from FIG. 3, the input of information being illustrated,
FIG. 5 shows a schematic longitudinal section through the holographic data storage medium from FIG. 3, the reading of information being illustrated,
FIG. 6 shows a schematic longitudinal section through a holographic data storage medium according to the second embodiment, in which information can be stored via the local interface structure, the reading of information being illustrated, and
FIG. 7 shows a schematic longitudinal section through a third embodiment of the holographic data storage medium according to the invention.



DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
FIG. 1 illustrates, in a schematic way and not to scale, a detail from a holographic data storage medium 1 according to a first embodiment in longitudinal section. The data storage medium 1 contains a polymer film 2 which serves simultaneously as a storage layer and as a top layer with an exposed outer side 3. In the exemplary embodiment, the polymer film 2 is self-supporting. Arranged underneath the polymer film 2 and adjacent to the polymer film 2 is an absorber layer 4 with an absorber dye. Underneath it there is an adhesive layer 6 which, in the delivered state of the data storage medium 1, is preferably covered by a film that can be pulled off or silicone paper. The terms “above” and “below” relate here and in the following text to the illustration in the figures; however, the data storage medium can also be arranged in any other orientation.
In the exemplary embodiment, the polymer film 2 is a biaxially oriented film of polypropylene (BOPP) with a thickness of 35 μm. Thinner or thicker films are likewise conceivable. Films of other materials are also suitable, as explained further above.
The absorber layer 4 in the exemplary embodiment contains polymethyl methacrylate (PMMA) as binder, to which the absorber dye Sudan red 7B is added. In the exemplary embodiment, the absorber layer is produced from a solution of 10.5% by mass of polymethyl methacrylate and 1.2% by mass of Sudan red 7B in toluene, which is applied to the underside of the polymer film 2 using a linearly engraved roll. The thickness of the absorber layer is about 0.5 μm and preferably lies in the range from 0.3 μm to 1.0 μm. However, other layer thicknesses are likewise conceivable. In order that the absorber layer 4 adheres better, before the application of the absorber layer 4 the underside of the polymer film 2 can be pre-treated in accordance with a process which is basically known.
The adhesive layer 6 in the exemplary embodiment is produced from an aqueous acrylate dispersion and has a layer thickness of 23±4 μm. Other layer thicknesses are likewise possible, and other adhesive compounds can also be used. The underside of the absorber layer 4 can be pre-treated before the application of the adhesive layer 6, in order to ensure better adhesion of the adhesive layer 6.
The absorber layer 4 and the zones of the polymer film 2 which are changed when information is put in (see below) lie in the internal region of the data storage medium 1 and are protected by the upper region of the polymer film 2 having the outer side 3 and the adhesive layer 6.
FIG. 2 is an illustration similar to FIG. 1 of a second embodiment of a holographic data storage medium, which is designated 1′ here. Just like the data storage medium 1, the data storage medium 1′ has a polymer film 2 (here made of polyethylene terephthalate), which is set up as a storage layer and top layer with an exposed outer side 3, an absorber layer 4 and an adhesive layer 6. In addition, there is a reflective layer 8 between the polymer film 2 and the absorber layer 4.
In the exemplary embodiment, the reflective layer 8 consists of aluminum vapor-deposited on the underside of the polymer film 2 with a thickness such that the result is a transmission of 50%. Preferred layer thicknesses lie in the range from 1 nm to 50 nm, but smaller or larger values are also possible. Given such a low thickness, the reflective layer 8 is partly transparent, so that a write beam aimed at the outer side 3 of the polymer film 2 (for example from a laser lithograph, see below) can pass through the reflective layer 8 in order to reach the absorber layer 4.
As already mentioned, a series of materials are possible for the individual layers of the holographic data storage medium, and the layer thicknesses can also assume a large number of values. Furthermore, additional layers are conceivable. While the polymer film 2 is self-supporting in the case of the data storage media 1 and 1′, an additional rigid carrier layer can be provided in another embodiment, for example between the absorber layer and the adhesive layer.
In the exemplary embodiment explained by using FIG. 1, the absorber layer 4 has the absorber dye Sudan red 7B, whose molecules are embedded in a matrix of an optically transparent polymer, specifically polymethyl methacrylate (PMMA), the absorber layer 4 having a thickness of about 0.5 μ. Sudan red 7B absorbs light in the wavelength range around 532 nm particularly well; this wavelength is suitable for a write beam from a laser lithograph for putting information into the data storage medium. Examples of other absorber dyes are specified further above. For example, green dyes, for example from the styryl family, are suitable, particularly for light wavelengths of 635 nm or 650 to 660 nm or 685 nm, at which the laser diodes of current DVD devices operate; laser diodes of this type can be modulated directly, which makes the generation of pulses substantially simpler and cheaper. In the future, the range from 380 to 420 nm could also be of interest if appropriate blue laser diodes can be had commercially and inexpensively. For this purpose, yellow absorber dyes should then preferably be used, such as stilbenes substituted with weak donors and acceptors, donor-substituted nitrobenzenes or coumarin dyes.
The absorber layer 4 has a preferred optical density in the range from 0.2 to 1.0; however, other values are likewise conceivable. The optical density is a measure of the absorption, here based on the light wavelength of a write beam. The optical density is defined as the negative decimal logarithm of the transmission through the absorber layer, which coincides with the product of the extinction coefficient at the wavelength of the write beam used, the concentration of absorber dye in the absorber layer 4 and the thickness of the absorber layer 4.
In the following text, using FIGS. 3 to 5, an explanation will be given as to how information can be put into a holographic data storage medium in accordance with the embodiment described using FIG. 2 and can be read out therefrom. The holographic data storage medium is designated 11 and has a polymer film 12 with an exposed outer side 13, an absorber layer 14, an adhesive layer 16 and a partly transparent reflective layer 18, see FIG. 4. In a way similar to FIGS. 1 and 2, FIGS. 3 to 5 are not to scale. The polymer film 12 here consists of biaxially oriented polyethylene terephthalate (PET) and has a thickness of 50 μm . The refractive index of biaxially oriented polyethylene terephthalate can be changed locally by heating, which is used to store information.
Within the polymer film 12, information is stored in the form of pits 20. In the region of a pit 20, the polymer film 12 has a refractive index which is different from that in the zones between the pits 20. The term “pit” is to be understood here in the sense of a changed region, that is to say more generally than in its original meaning (“hole”). In this case, the information can be stored in a pit in binary encoded form, by the refractive index assuming only two different values (it being possible for one of the two values also to coincide with the refractive index of the polymer film 12 in the zones between the pits 20). It is also possible to store information in a pit 20 in continuously encoded form, it being possible for the refractive index within the pit 20 to assume any desired selected value from a predefined value range. In clear terms, in the case of storage in binary encoded form, a pit is “black” or “white” while, in the case of storage in continuously encoded form, it can also assume all the gray values lying in between.
FIG. 3 is a schematic plan view of a detail from the data storage medium 11, which shows the arrangement of the pits 20 which are produced by the write beam from a laser lithograph (as explained further below using FIG. 4). In the exemplary embodiment, a pit 20 has a diameter of about 0.8 μm. Shapes other than circular pits 20 are likewise possible, for example square or rectangular pits, and also other sizes. The typical dimension of a pit is preferably about 0.5 μm to 2.0 μm. FIG. 3 is therefore a highly enlarged illustration.
FIG. 4 indicates in a schematic way how, with the aid of a write beam 22 from a writing device (a laser lithograph in the exemplary embodiment), a pit 20 is produced. Firstly, the write beam 22 is focused in such a way that it has its smallest cross-section approximately in the absorber layer 14. In this case, the partly transparent reflective layer 18 is of great help, since it deflects the write beam 22 back into the writing device, where the reflection is evaluated. The focusing optics of the write beam 22 are then adjusted until the position of the focus is optimized. In the exemplary embodiment, the focus 23 is in the thin reflective layer 18, which is simplest to achieve. During the focusing operation, the write beam 22 can be operated at lower power, in order to prevent excessive heating in the vicinity of the focus.
The representation of the write beam 22 and its focus 23 in FIG. 4 is very schematic. Because of the wave nature of light, the focus 23 is not shaped like a point but has a size comparable with the diameter of a pit 20, so that the write beam 22 is capable of heating relatively uniformly a region of the size of a pit 20 within the data storage medium 11. The greatest heating in this case occurs within the absorber layer 14, since it is located in the region of the focus 23 and the absorber dye absorbs the write beam 22. The heat liberated in the process is largely transferred through the reflective layer 18 to the polymer film 12 and in this way effects a local change in the refractive index in the polymer film 12 in the region of a pit 20. Since the polymer film 12 is substantially heated in the lower region, the pit 20 does not extend over the full thickness of the polymer film 12. In practice, the transition zone in the upper region of a pit 20 to the central region of the polymer film 12 is continuous, that is to say the refractive index changes gradually in this zone and is not delimited as sharply as indicated in FIG. 4.
The distance between the upper region of a pit 20 and the outer side 13 of the polymer film 12 is relatively large, so that the pits 20 produced by the write beam 22 lie in a region of the polymer film 11 which is relatively safe against external influences.
In order to put information into the polymer film 11, first of all phase information contained in a hologram of a stored object is calculated as a two-dimensional arrangement. This can be carried out as a simulation of a classical structure for producing a photographically recorded hologram, in which coherent line from a laser, after scattering at the stored object, is brought into interference with a coherent reference beam, and the interference pattern produced in the process is recorded as a hologram. The two-dimensional arrangement (two-dimensional array) then contains the information which is necessary to drive the write beam of a laser lithograph. In the exemplary embodiment, the laser lithograph has a resolution of about 50 000 dpi (i.e. about 0.5 μm). The write beam from the laser lithograph is guided over the outer side 13 of the polymer film 12 in pulsed operation (typical pulse duration of about 10 ns to 10 μs with a beam power of about 1 mW to 20 mW in order to put in a pit 20), in order to put the desired information sequentially into the polymer film 12 (or a preselected region of the polymer film 12). In the process, the write beam 22 heats the absorber layer 14 in accordance with the two-dimensional array and in this way produces the pits 20, as explained above.
FIG. 5 illustrates in a schematic way how the information stored in the polymer film 12 can be read out. For this purpose, coherent light from a laser is aimed at the outer side 13 of the data storage medium 11. For clarity, only a small section of this coherent light, preferably incident in parallel, is illustrated in FIG. 5, and is designated 24 (incident read beam). In practice, the coherent light is aimed at the polymer film 12 over a large area and covers a region of, for example, 1 mm2. This is because, in order to reconstruct the stored information, the light originating from many pits 20 must be registered. The intensity of the incident read beam 24 is too weak to change the refractive index in the polymer film 12 and thus the stored information.
Part of the incident read beam 24, which, for practical reasons, strikes the outer side 13 of the polymer film 12 at an angle, is reflected at the reflective layer 18 on the underside of the polymer film 12, so that a reflected read beam 26 originates from the reflective layer 18 and, in the process, passes through the pits 20. (The proportion of the incident read beam 24 let through by the reflective layer 18 is not shown in FIG. 5, for clarity). Since the local refractive index of the polymer film 12 is different, depending on the pit 20, the local optical path length is varied, so that phase shifts occur. The consequence of this is that spherical waves 28 originate from the data storage medium 11 in the manner of a diffraction pattern, containing the stored phase information. At some distance from the data storage medium 11, a holographic image, which is produced by interference between the spherical waves 28, can be registered by a detector.
The expenditure required for the detector and further processing of the registered holographic image depend on the type of stored object, as already explained further above. For the reproduction of machine-readable data (data pages), a CCD sensor connected to a data processing device is particularly suitable while, for pure image reproduction, a simpler detector is also expedient, in particular if the image data is not to be processed further.
Using FIG. 6, a further possible way of storing holographic information by means of a holographic data storage medium will be explained, said medium being constructed similarly to the holographic data storage medium according to FIG. 2. The holographic data storage medium designated 31 here again has a polymer film 32 with an outer side 33, an absorber layer 34, an adhesive layer 36 and a reflective layer 38.
In order to produce a pit for storing information, a pulsed write beam from a writing device (preferably a laser lithograph, as explained using FIGS. 3 to 5) is focused via the outer side 33 of the polymer film 32 and through the partly transparent reflective layer 38 onto a zone 42 which, in FIG. 6, is indicated by hatching. At the start of this process, the underside of the polymer film 32 (that is to say the interface to the reflective layer 38) and the reflective layer 38 are still flat. Since the zone 42 is located in the region of the absorber layer 34, the light energy from the write beam is converted efficiently into heat. Because of the poor thermal conductivity of the material, a significant increase in temperature occurs in a closely delimited volume, during which the interface structure of the polymer film 32 is changed locally. In this way, a pit 40 is produced, that is to say the local region in which information is stored. Each pit 40 includes a central depression 44 in the polymer film 32, which is surrounded by a peripheral, more or less annular, thrown-up portion 45. The difference in level between the lowest point of the depression 44 and the highest point of the thrown-up portion 45, that is to say the local maximum height change of the interface structure in the pit 40, is designated H in FIG. 6. H lies typically in the range from 50 nm to 500 nm. The distance between the centers of two adjacent pits 40 is preferably about 1 μm to 2 μm. In the exemplary embodiment, a pit 40 has a diameter of about 0.8 μm. Shapes other than round pits 40 are likewise possible. The typical dimension of a pit is preferably about 0.5 μm to 1.0 μm.
The information can be stored in a pit 40 in binary encoded form, by H assuming only two different values (one of the two values preferably being 0). It is also possible to store information in a pit 40 in continuously encoded form, it being possible for H for a given pit 40 to assume any desired selected value from a predefined value range.
Otherwise, the information can be put into the data storage medium 31 in a manner similar to the data storage medium 11, that is to say preferably with the write beam from a laser lithograph which is guided over the polymer film 32 in pulsed operation and in the process produces the pits 40 in a previously calculated way. In plan view, the polymer film 32 with the pits 40 then appears similar to the illustration in FIG. 3.
FIG. 6 also illustrates, in a schematic way, how the information stored in the data storage medium 31 can be read out. For this purpose, coherent light from a laser (preferably at a wavelength which is not absorbed or absorbed only slightly by the absorber layer 34) is aimed at the outer side 33 of the data storage medium 31. (Alternatively, use can also be made of a very bright LED which, under certain circumstances, even leads to more beneficial results, primarily with regard to a reduction in what is known as speckle noise). For clarity, of this coherent light, which is preferably incident in parallel (incident read beam), only a small detail is illustrated in FIG. 6, namely the incident light waves designated 46 and 47. In practice, the coherent light is aimed at the polymer film 32 over a large area and covers a region of, for example, 1 mm2. This is because, in order to reconstruct the stored information, the light originating from many pits 40 must be registered. The intensity of the incident read beam is too weak to change the interface structure of the polymer film 32 and thus the stored information.
The light waves 42 and 43 have a fixed phase Φ in relation to one another. For practical reasons, they fall on the outer side 33 of the polymer film 32 at an angle, pass through the polymer film 32 and are partly reflected at the reflective layer 38, so that reflected light waves 48 and 49 originate from the reflective layer 38 and in turn pass through the polymer film 32. For clarity, the proportion of the incident light waves 46 and 47 which passes through the partly transparent reflective layer 38 is not illustrated in FIG. 6. Since the local interface structure of the polymer film 32 varies over the pits 40, a phase shift occurs, and the reflected light waves 48 and 49 emerge with a phase Ψ, as illustrated in FIG. 6. The consequence of this is that light waves in which phase information is contained originate in many directions from the data storage medium 31 in the manner of a diffraction grating. At some distance from the data storage medium 31, a holographic image, which is brought about by interference between these light waves and constitutes a reconstruction of the stored information, can be registered by a detector.
By using FIGS. 5 and 6, two different possible methods by which a local change in the polymer film 12 or 32 can be used for storing information have been explained. Intermediate forms, that is to say both a change in the refractive index and in the interface structure of the polymer film in a pit, are likewise conceivable.
In principle, the methods explained for putting information in and reading information out can be used even when there is no reflective layer 18 or 38. For example, a write beam can also be focused without the aid of a reflective layer. When information is read out in reflection, a difference in the refractive index between two layers can be used. Furthermore, embodiments of the holographic data storage medium are conceivable in which the data storage medium is transilluminated in transmission when information is read out.
A third exemplary embodiment of a layer structure of the holographic data storage medium is illustrated in schematic longitudinal section in FIG. 7. The data storage medium designated 1′′ contains a polymer film 2 which is used as a storage layer and top layer with an exposed outer side 3. Underneath the polymer film 2 and adjacent thereto is an absorber layer 4′. A reflective layer 8′ is arranged between the absorber layer 4′ and an adhesive layer 6, on the underside (which is covered by a protective layer in the delivered state). In the exemplary embodiment, the reflective layer 8′ consists of aluminum and is so thick that it is opaque and reflects maximally.
In the case of this layer structure, the reflective layer 8′ again makes it easier to focus the write beam onto the absorber layer 4′. Furthermore, when the information put in is read out, the absorber layer 4′ is transilluminated.
If the absorber dye contained in the absorber layer 4′ can be bleached locally when information is put in (for example with the aid of a laser lithograph), a change used for storing information can be achieved not only by the local heating of the absorber dye and the local change in the polymer film 2 effected by this (as explained above), but additionally also by a local change in the optical properties of the absorber dye, namely the absorption capacity. When information is read out from the data storage medium 1′′, both effects are used in the layer structure according to FIG. 7, which results in amplification of the contrast of the read signal.
The following Table 1 lists dyes which are in principle suitable as an absorber dye for the absorber layer of the holographic data storage medium. In the first column, the wavelength (in nm) of the absorption maximum is specified; Table 1 is arranged by increasing wavelengths, if wavelengths are present. If available, the color index (CI) and a synonymous designation are also listed.







TABLE 1







Dyes which, in principle, are suitable as absorber dyes










Wave-





length
Name
Cl
Synonym














2.3.4-Triazapentamethinecyanine





Acridinium yellow



Alizarin black S



Amido yellow E



Analinee yellow



Analinee black



Analinee sulfone phthalein



Analinee violet



Anthrasol blue IBC



Antique purple

6.6′-dibromoindigo



Artisil blue GLF



Astraphloxin FF



Astrazone blue FGGL
Cl 11105



Astrazone yellow 3 GL



Astrazone red G



Benzaurin



Benzo light yellow 4GL



Benzyl orange



Bindschedler's Green



Brasilein



Brilliant indigo 4B

Ciba blue 2B



Brilliant orange RK



Bromophenol blue



Bromophenol red



Bromothymol blue



Bromoxylenol blue



Butter yellow



Caledon red XB5



Capri blue



Capri blue



Carbazolindanalinee



Carbolan violet 2R



Carthamine



Celliton fast blue-green B



Quinoline blue



Chlorantin light green BLL



Chlorantin light turquoise blue GLL



Chrome violet Gy



Cibacetyl violet



Cibanon red 4B



Cibanon red G



Doebner's violet



Epsilon blue



Fanal colors



Fluorenequinone



Yellow-orange S
Cl 15985



Green sensitizer MA2116



Haematein



Helindon orange



Helindon pink



Helio fast yellow 5GK



Heliogen green G



Hydron blue R



Hypericin



Immedial brilliant blue



Immedial yellow GG



Immedial pure blue



Immedial black



Indanthen yellow



Indanthren blue GCD



Indanthren blue RS



Indanthren bordeaux RR



Indanthren brilliant blue 4G



Indanthren brilliant green FFB



Indanthren brilliant orange GR



Indanthren brilliant violet 2R



Indanthren khaki GG



Indanthren orange 2RT



Indanthren red-brown 5RF



Indanthren red-violet



Indanthren turquoise blue 3GK



Indanthren violet RRK



Indathren yellow 5GK



Indigo yellow 3G



Indian yellow



Indra red



Irgalan brown-violet DL

o.o′-dihydroxy-azo dye



Isoviolanthrone



Juglon



Madder lakes



Lake red



Lumogen



Mauvein



Maxilon red BL



Michler's Hydro blue



Morin
Cl 75660



Muscaflavin



Muscarufin



Naphthalene green V



Neolan blue 2G



Nitramine



Oil yellow

3.2′-dimethyl-4-aminoazobenzene



Oxonine



p-Xylenol blue



Palanil pink RF



Paramethyl red



Patent blue



Patent blue V
Cl 42501



Permanent violet RL



Phenylene blue



Phthalogen blue IBN



Phthalogen blue-black IVM



Pinachrome blue



Procinyl blue R



Pseudocyanine



Rubin pigment BK



Sambesi black V



Acid fuchsine



Sulfur black T



Supracen blue SES



Thioindigo

Helindon red 2B; Algol red 5B; vat red B



Thionoultra green B



Thiopyronine



Toluylene blue



Vidal black



Violanthrone


1080
IR 26


1090
IR 5


229/345
Primuline
Cl 49000


251
BM-Terphenyl

2,2′′-dimethyl-p-terphenyl


266
TMQ

3,3′,2′′,3′′′-tetramethyl-p-quaterphenyl


275
BMQ

2,2′′′-dimethyl-p-quaterphenyl


275
p-Terphenyl

PTP


285
DMQ

2-methyl-5-t-butyl-p-quaterphenyl


295
TMI

2,5,2′′′′,5′′′′-tetramethyl-p-quinquephenyl


297
p-Quaterphenyl

PQP


302
Butyl-PBD

2-(4-biphenylyl)-5-(4-t-butylphenyl)-1,3,4-





oxadiazole


302
PBD

2-(4-biphenylyl)-5-phenyl-1,3,4-oxadiazole


303
PPO

2,5-diphenyloxazole


308
Polyphenyl 1

p-quaterphenyl-4,4′′′-disulfonic acid disodium salt


308
Polyphenyl 2

p-quaterphenyl-4,4′′′-disullfonic acid dipotassium





salt


310
QUI

3,5,3′′′′,5′′′′-tetra-t-butyl-p-quinquephenyl


313
BiBuQ

4,4′′′-bis-(2-butyloctyoxy)-p-quaterphenyl


314
BBD

2,5-bis-(4-biphenylyl)-1,3,4-oxadiazole


320
TBS

3,5,3′′′′′,5′′′′′-tetra-t-butyl-p-sexiphenyl


324
PPF

2,5-diphenylfuran


327
PBBO

2-(biphenylyl)-6-phenyl-1,3-benzoxazole


330
Furan 2

2-(4-biphenylyl)-6-phenylbenzoxazotetrasulfonic





acid potassium salt


333
a-NPO

2-(1-naphthyl)-5-phenyl-phenyloxazole


340
BBO

2,5-bis-(biphenylyl)-oxazole


340
DPS

4,4′-diphenylstilbene


341
Direct yellow 62
Cl 36900


342
Fast red violet salt LB


347
4-Hydroxyazobenzol
Cl 11800


350
Bis-MSB

p-bis(o-methylstyryl)-benzene


350
Carbostyryl 7

7-amino-4-methylcarbostyryl


350
Stilbene 1

[1,1′-biphenyl]-4-sulfonic acid, 4,4′′-1,2-ethene-





diylbis-,dipotassium salt


350
Stilbene 3

2,2′-([1,1′-biphenyl]-4,4′-diyldi-2,1-ethenediyl)-





bis-benzenesulfonic acid


352
Fast red salt PDC
Cl 37151


354
Coumarin 120

7-amino-4-methylcoumarin


354
Cristal violet lactone


354
Mordant yellow 10
Cl 14010


355
Furan 1

Benzofuran,2,2′-[1,1′-biphenyl]-4,4′-diyl-bis-





tetrasulfonic acid


355
Quinolone

7-dimethylamino-1-methyl-8-azaquinolone-2


356
Fast korinth salt Vkz.
Cl 37220


357
Celliton fast yellow G
Cl 11855


357
Fast red salt ITR
Cl 37150


358
POPOP

1,4-di[2-(5-phenyloxazolyl)]benzene


359
Disperse yellow 9
Cl 10375
N-(2,4-dinitrophenyl)-p-phenylenediamine


360
Carbostyryl 3

7-dimethylamino-4-methylquinolone-2


360
Fast granite salt
Cl 37210


362
Alizarin yellow GG
Cl 14025
Mordant yellow 1


362
Naphthochrome green
Cl 44530
Mordant green 31


366
Coumarin 2

7-amino-4-methylcoumarin


368
Walk yellow O
Cl 25135


371
Fast blue salt B
Cl 37235


372
Coumarin 4

7-hydroxy-4-methylcoumarin


372
Fast red salt RC
Cl 37120


373
Coumarin 47

7-diethylamino-4-methylcoumarin


373/487
Mordant brown 1
Cl 20110


374
Thioflavin S
Cl 49010
Direct yellow


375
Fast red salt B Tetrafluoroborate salt
Cl 37125


377
Variamine blue salt RT
Cl 37240


378
Thiazolyl blue

3-(4,5-dimethyl-2-thiazolyl)-2,5-





diphenyltetrazoliumbromide


380
1-Methoxyanthraquinone
Cl 37325


380
Coumarin 466

7-diethylaminocoumarin


380
Mordant yellow 12
Cl 14045


382
Coumarin 151

7-amino-4-trifluormethylcoumarin


382
Fast blue

Diamidino 253/50


385
Alizarin yellow R
Cl 14030
Mordant orange1, 5-(p-nitrobenzolazo)-salicylic





acid


385
Celliton fast yellow 5R
Cl 26090
7,4′-benzolazo-4-hydroxy-3-methylazobenzene


385
Pinacryptol yellow


386
Mordant orange 10
Cl 26560


388
Sudan orange G
Cl 11920
2,4-dihydroxyazobenzene


389
Chrysophenin
Cl 24895
Direct yellow 12


389
Coumarin 102

2,3,5,6-1H,4H-tetrahydro-8-methylquinolizino-





[9,9a,1-gh]-coumarin


390
Direct yellow 50
Cl 29025
Siriuslichtgebret


390
Direct yellow 8
Cl 13920


392
Supramine yellow R
Cl 18835
Acid yellow 25


393
Direct yellow 27
Cl 13950


393
Acid yellow 76
Cl 18850
Polar yellow 2G


394
Naphthol AS
Cl 37505
2-hydroxy-3-naphthanilide


395
Coumarin 307

7-ethylamino-6-methyl-4-trifluoromethylcoumarin


395
Coumarin 500

7-ethylamino-4-trifluoromethylcoumarin


395
Fast blue salt BB
Cl 37175


396
Coumarin 6H

2,3,5,6-1H,4H-tetrahydroquinolzino-[9,9a,1-





gh]coumarin


397
Brilliant yellow
Cl 24890


397
Coumarin 152

7-dimethylamino-4-trifluormethylcoumarin


400
Mesoporphyrin-IX-dimethyl ester

7,12-diethyl-3,8,13,17-tetramethyl-21H,23H-





porphin-2,18-dipropionic acid dimethyl ester


400
Mordant brown 24
Cl 11880
3-(3,5-dinitro-2-hydroxy-benzolazo)-2-hydroxy-5-





methylacetanilide


400
Acid yellow 17
Cl 18965


401
Mesoporphyrin-IX- dihydrochloride

7,12-diethyl-3,8,13,17-tetramethyl-21H,23H-





porphin-2,18-dipropionic acid


402
Thiazol yellow G
Cl 19540
Titanium yellow


403
Pyranin
Cl 59040
8-hydroxypyren-1,3,6-trisulfonic acid trisodium





salt


404
Cibachron brilliant yellow 3G-P
Cl 18972
Reactive yellow


405
1-Hydroxyanthraquinone


405
Coumarin 152A

7-diethylamino-4-trifluoromethylcoumarin


407
Flavazin L
Cl 18820


407
Supramine yellow 3GL
Cl 18900
Acid yellow 29


408
Fast light yellow D3GA
Cl 18890
Acid yellow 34


410
Coumarin 522

N-methyl-4-trifluoromethylpiperidino-[3,2-g]-





coumarin


410
Methyl red
Cl 13020
4′-(dimethylamino)-azobenzol-2-carbolic acid


410
Sulfon yellow R
Cl 22910
Acid yellow 42


412
Quinoline yellow S
Cl 47005


412
Coumarin 30

3-(2′-N-methylbenzimidazolyl)-7-N,N-





diethylaminocoumarin


412
Acid yellow 40
Cl 18950


412
Thioflavin TCN
Cl 49005
3,6-dimethyl-2-(4-dimethylaminophenyl)-





benzothiazoliumchloride


413
Mordant red 19
Cl 18735
5-chloro-2-hydroxy-3-(5-hydroxy-3-methyl-1-





phenyl-4-pyrazlolylazo)-benzosulfonic acid





sodium salt


414
Fast silk yellow G
Cl 14170
Acid yellow 65


414
Metanil yellow
Cl 13065
Tropaeolin


419
Bromocresol purple

5′,5′′-dibromo-0-cresolsulfonphthalein


422
Brilliant sulfaflavin


422
Bromophenol blue

3′,3′′,5′,5′′tetrabromophenolsulfonphthalein


423
Bromocresol green

3′,3′′,5′,5′′-tetrabromo-m-cresolsulfonphthalein


423
Coumarin 153

2,3,5,6-1H,4H-tetrahydro-8-





trifluoromethylquinolizino-[9,9a,1-gh]coumarin


423
Phenol red sodium salt


424
3,3′-Diethyl-thiacyaniniodide


424
Acid orange 63
Cl 22870


425
Coumarin 510

2,3,5,6-1H,4H-tetrahydro-9-(3-pyridil)-quinolizino-





[9,9a,1-gh]coumarin


425
Tartrazin
Cl 19140


427
Disperse orange 13
Cl 26080
1-benzolazo-4-(4-hydroxybenzolazo)-





naphthalene


427/452
Safran
Cl 75100
Saffron, Crocus


428/392
Citronin A
Cl 10316
Naphthol yellow S; 2,4-dinitro-1-naphthol-7-





sulfonic acid disodium salt


430
Curcumin
Cl 75300
Diferuloylmethane


430
Martius yellow

2,4-dinitro-1-naphthol


433
Coumarin 7

3-(2′-benzamidazylyl)-7-N,N-





diethylaminocoumarin


434/370
Auramine O
Cl 41000
4,4′-(imidocarbonyl)-bis-(N,N-dimethylanaline)





hydrochloride


436
Coumarin 314

2,3,5,6-1H,4H-Tetrahydro-9-





carboethoxyquinolizino-[9,9a,1-gh]coumarin


439
Quinoline yellow A
Cl 47000
Quinophthalone


440
Fluorol 7GA


440
Naphthyl red hydrochloride

4-benzolazo-1-naphthylamine hydrochloride


440
Palatin fast yellow BLN
Cl 19010
Acid yellow 54


442
Acridine yellow
Cl 46025
3,6-diamino-2,7-dimethylacridine hydrochloride


442
Mordant brown 33
Cl 13250


443
Celliton fast orange GR
Cl 11005
4-amino-4′-nitroazobenzene


445
Acid yellow 99
Cl 13900


446
Supranol brown 4R
Cl 26550
Acid orange 51


449
Chrysoidine G
Cl 11270


450
4′,5′-Dibromofluorescein
Cl 45370


450
Coumarin 334

2,3,5,6-1H,4H-tetrahydro-9-acetylquinolizino-





[9,9a,1-gh]-coumarin


451
Oleobrown RR
Cl 11285


452
2-hydroxy-1,4-naphthoquinone
Cl 75480
Lawson


455
Acid orange 74
Cl 18745


457
Disperse orange 25


457
Fast black salt
Cl 37190


458
Chromazurol S
Cl 43825
Mordant blue 29


458
Coumarin 6

3-(2′-benzothiazolyl)-7-diethylaminocoumarin


462
Trypaflavin

Acriflavin


465
1-Aminoanthraquinone


468
Bismarck brown R
Cl 21010
Vesuvin R


472
DASPI

2-(p-dimethylaminostyryl)pyridylmethyl iodide


472
DCM

4-dicyanmethylene-2-methyl-6-(p-





dimethylaminostyryl)-4H-pyran


475
Orange G
Cl 16230
Acid orange 10


476/418
Sudan I
Cl 12055
Sudan yellow


480
1,5-Diaminoanthraquinone


480
Pyridine 1

1-ethyl-2-(4-(p-dimethylaminophenyl)-1,3-





butandienyl)pyridinium perchlorate


482
Aurin
Cl 43800
4-[bis-(4-hydroxyphenyl)methylene]-2,5-





cyclohexadien-1-one


482
Crocein orange G
Cl 15970
Ponceau 4 GB; 5-benzolazo-6-naphthol-2-





sulfonic acid sodium salt


483
Celliton fast orange 5R
Cl 11080
4-analineo-4′-nitroazobenzene


483
Orange II
Cl 15510
Acid orange A; 4-(2-hydroxy-1-naphthalinazo)-





benzenesulfonic acid sodium salt


485
DOCI

3,3′-diethyloxacarbocyanine iodide


486
Celliton orange R
Cl 60700
1-amino-2-methyl-anthraquinone


489
Fast yellow ex.
Cl 13015
Acid yellow-R; 4-aminoazobenzol-3,4′-disulfonic





acid sodium salt


490
Astrazone orange G
Cl 48035


490
Orange ROF
Cl 15575
Acid orange 8


490
Resorcin yellow
Cl 14270
Tropaeolin O; 2,4-dihydroxy-azobenzol-4′-





sulfonic acid sodium salt


491
Fast granite GBC Base
Cl 11160
4-amino-2′,3-dimethylazobenzol


492
Acridine orange
Cl 46005
3,6-bis-(dimethylamino)-acridin hydrochloride





hydrate


492
Mordant brown 48
Cl 11300
2-(5-chlor-2,4-diaminobenzeneazo)-4,6-





dinitrobenzene


493/420
Sudan II
Cl 12140
Sudan orange, Oleo scarlet G; 1-(2,4-





dimethylbenzolazo)-2-naphthol


494
Pyrromethene 546

4,4′-difluoro-1,3,5,7,8-pentamethyl-4-bor-3a,4a-





diaza-s-indacene


494
Acid red 183
Cl 18800


494/388
Remazole brilliant orange 3 R
Cl 17757
Reactive orange 16


495
Disperse red 19
Cl 11130
4-[bis-(2-hydroxyethyl)-amino]-4′-





nitroazobenzene


496
Fluorescein
Cl 45350


497
Congo red
Cl 22120
4,4′-bis-(4-amino)-sulfo-3-naphthylazo)biphenyl





disodium salt


498
Pyrromethene 556

Disodium-1,3,5,7,8-pentamethylpyrromethene-





2,6-disulfonate-difluoroborate complex


498
Acid anthracene red G
Cl 22890
Acid red 97


500
Fast scarlet
Cl 23500
Saffrosin, benzopurpurin 4B


500
Pyridine 2

1-ethyl-4-(4-(p-dimethylaminophenyl)-1,3-





butanedienyl)pyridinium perchloratee


500
Uranine

Disodium fluorescein


500/374
Mordant brown 4
Cl 11335
2-(2,4-diamino-5-methyl-benzolazo)-4,6-





dinitrophenol


501
Rhodamine 123 hydrate


501
Acid alizarin violet N
Cl 15670
Mordant violet 5; Pontachrome violet SW


502
Celliton scarlet B
Cl 11110
Dispersions red 1


503
Celliton fast ruby B
Cl 11115
Dispersions red 13


503
Mordant black 11
Cl 14645
Eriochrome black T


503/388
Ponceau R
Cl 16150
Xylidin-Ponceau 2R


504
Allura red AC
Cl 16035


505

Cl 12100
Solvent orange 2


505
Fast red A
Cl 15620
Roccellin, Acid red 88; 2′-hydroxy-(1,1′)-





azonaphthalene-4-sulfonic acid sodium salt


505
Ponceau BS
Cl 26905
Biebrich scarlet


506/350
Cochineal red
Cl 16255
Neucoccin, Brilliant scarlet 4R,Scarlet N, Victoria





scarlet 4R


507
Benzo fast scarlet 4BS
Cl 29160
Direct red 23


507
Mercurochrome


507
Methyl orange
Cl 13025


507/354
Sudan III
Cl 26100


507/398
Toluidine red
Cl 12120


508
1-Methylaminoanthraquinone


508/376
Fast acid red E
Cl 14710
Acid red 4


508/397
Direct red 81
Cl 28160
Chlorantin light red-5BL


508/532
Cochineal scarlet PS
Cl 14900
Acid red 8


510
Brilliant crocein MOO
Cl 27290
Cotton scarlet; acid red 73


510
Cristal ponceau
Cl 16250


510
Rhodamine 110

o-(6-amino-3-imino-3H-xanthene-9-yl)-benzoic





acid


510/530
Chromotrop 2R
Cl 16570
Acid red 29


512
Chromoxancyanine R
Cl 43820
Mordant blue 3


512
Fluorescein 27

9-(o-carboxyphenyl)-2,7-dichloro-6-hydroxy-3H-





xanthen-3-one


512/356
Fabric scarlet
Cl 26900
Acid red 151


514
Chromotrop 2B
Cl 16575


514/351
Ponceau SS
Cl 27190
Fabric red G, Wool red B


514/365
Supranol red PBX
Cl 23635
Acid red 114


514/395
Eosin B
Cl 45400
Eosin scarlet


515/383
Azo rubine
Cl 14720
Mordant blue 79; Chromotrope FB


515/521
Purpurin
Cl 58205
Smoke brown G, madder purple


516
Azocarmin BX
Cl 50090
Acid red 103


516
Mordant blue 9
Cl 14855


517
Cibachron brilliant red 3B-A
Cl 18105
Reactive red


517
Eosin light blue.


517
Eosin light yellow
Cl 45380


518
Fast red B
Cl 16180
Bordeaux R


518
Helio fast ruby BBL
Cl 60760


518
Pyrromethene 567

4,4-difluoro-2,6-diethyl-1,3,5,7,8-pentamethyl-4-





bora-3a,4a-diaza-s-indacene


518/359
Oil red O
Cl 26125
Solvent red 27


519
Phenosafranin
Cl 50200
Safranin B extra


519
Pyrromethene 580

4,4-difluoro-2,6-di-n-butyl-1,3,5,7,8-pentamethyl-





4-bora-3a,4a-diaza-s-indacene


520
1-Hydroxy-4-aminoanthraquinone


520
Amidonaphthol red 6B
Cl 18055


520
Methyl eosin
Cl 45385


520/352
Ponceau S
Cl 27195


520/357
Sudan IV
Cl 26105
(Biebrich) scarlet red


521
Amaranth
Cl 16185
Azo rubine S, fast red D


521
Fast red D

Azo rubine S


521
Emodine


521
Oil red EGN
Cl 26120
Solvent red 26


521
Sudan red B
Cl 26110


522
Diiodofluorescein
Cl 45425


522
Eosin B alcohol soluble
Cl 45400


522
Sirius pink BB
Cl 25380
Direct red 75, benzo fast pink 2BL


524
1,1′-diethyl-2,2′-cyanine iodide


524
Pyrromethene 597

4,4-difluoro-2,6-di-t-butyl-1,3,5,7,8-pentamethyl-





4-bora-3a,4a-diaza-s-indacene


524
Rhodamine 6G
Cl 45160
Benzoic acid, 2-[6-(ethylamino)-3-(ethylimino)-





2,7-dimethyl-3H-xanthen-9-yl]ethyl ester,





monohydrochloride


525
Erythrosin B
Cl 45430


525
Mordant violet
Cl 43810
Eriochromcyanin RC


525
Murexide


527
Lanafuchsine 6B
Cl 18125
Acid violet


527
Mordant blue 13
Cl 16680
Eriochrome blue SE


528
Quinaldine red


528
Direct red 80
Cl 35780
Sirius red F3B


528
Mordant black 3
Cl 14640
Eriochrome blue black B


528
Rhodamine 19

Benzoic acid, 2-[6-(ethylamino)-3-(etnylimino)-





2,7-dimethyl-3H-xanthen-9-yl], perchloratee


529
Fast acid violet ARR
Cl 45190
Eriofuchsin A2R


529
SulfoRhodamine G
Cl 45220


530
DASBTI

2-(p-dimethylaminostyryl)-benzothiazolylethyl





iodide


530
Safranin T
Cl 50240
Safranine O


531/563
Carmin acid
Cl 75470
Carmine


532
Eosin alcohol soluble
Cl 45386
Ethyl eosin


532/506
Amidonaphthol red G
Cl 18050
Acid red 1, azophloxin


533/364
Sudan red 7B
Cl 26050
Oleored blueish


538
Procion red MX-5B

Reactive red 2


540
DMETCI

3,3′-dimethyl-9-ethylthiacarbocyanine iodide


540
Neutral red
Cl 50040


543
Rhodamine B
Cl 45170


544
Fuchsin S
Cl 42685


544
Para rosanalinee

Parafuchsin base


545
Formyl violet S4B
Cl 42650
Acid violet 4B


545
Parafuchsin acetate
Cl 42500
Para rosanalinee acetate


547
Bismarck brown Y
Cl 21000
Vesuvin


548
Alizarin blue black B
Cl 63615


548
Pyronin Y
Cl 45005


548/510
Eosin 10 B
Cl 45410
Cyanosin, Phloxin B


549
Bengal pink disodium salt
Cl 45440
Acid red 94


549
Brilliant benzo fast violet
Cl 27905
Sirius violet BB; direct violet 51


550
1,4-Diaminoanthraquinone


550
Phenoxazone 9

9-diethylamino-5H-benzo(a)phenoxazin-5-one


550
Pyridine 4

1-ethyl-4-(4-(9-(2,3,6,7-tetrahydro-1H,5H-





benzo(i,j)-quinolizinium))-1,3-





butadienyl)pyridinium perchlorate


552/374
Phenolphthalein


552/630
Rhodanil blue


553
New fuchsin 90 Plv.
Cl 42520
New magenta, Magenta III


553
Nil red


553
Pyronin B
Cl 45010


554
SulfoRhodamine B
Cl 45100
Xylylene red B


556/596
Alzarin red S hydrate
Cl 58005


557
DTCI

3,3′-diethylthiacarbocyanine iodide


557/360
Phenol red


558
Ethyl red

1,1′-diethyl-2,4′-cyanine iodide


560
3,3′-Diethyl-thiacarbocyanine iodide


565
Nigrosin alcohol soluble
Cl 50415


566
Sulfoncyanine 5R ex.
Cl 26360
Acid blue 113


567/629
Sulfonazo III


569
Palatinchrome black 6BN
Cl 15705
Mordant black 17


570
New fast blue 3R
Cl 51175
Meldola's blue


570
Nigrosine water soluble.
Cl 50420


570
Styryl 8

2-(4-(p-dimethylaminophenyl)-1,3-butadienyl)-3-





ethylbenzothoazolium perchlorate


570/367
Cresol red


570/407
Brilliant black BN
Cl 28440


571
Sulfonic acid blue R
Cl 13390
Anazolene sodium, acid blue 92 FG


572
Chlorophenol red


572
Sulfoncyanine black BB
Cl 26370


574
Sulfoncyanine GR ex.
Cl 26400
Acid blue 120


575
Litmus


575
Styryl 11

1-ethyl-4-(4-(p-dimethylaminophenyl)-1,3-





butadienyl)-quinolinium perchloratee


576
Rhodamine 101


576
SulfoRhodamine 101 hydrate


579
Orcein

Natural red 28


579/371
Cresol purple


580
Methylene violet
Cl 52041


582
DODCI

3,3′-diethyloxadicarbocyanine iodide


584
Janus black

Diazin black


584
Methyl violet 2B
Cl 42535


585
Brilliant blue R
Cl 42660
Brilliant indocyanine 6B


585
Styryl 9M

2-(6-(4-dimethylaminophenyl)-2,4-neopentylene-





1,3,5-hexatrienyl)-3-methyl-benzothiazolium





perchloratee


585/379
Bromocresol purple sodium salt


586
Nitrazine yellow
Cl 14890


588
Styryl 14


589
Janus blue
Cl 12210


590
Crystal violet
Cl 42555


590
Pyrromethene 650

4,4-difluoro-8-cyano-1,2,3,5,6,7-hexamethyl-4-





bora-3a,4a-diaza-s-indacene


590
Resorcinol crystal violet


592
DQOCI

1,3′-diethyl-4,2′-quinolyloxacarbocyanine iodide


592
Remazol Brilliant blue R
Cl 61200
Reactive blue 19


592
Victoria blue B
Cl 44045
Corn blue B


592/396
Thymolphthalein


594
Benzo light blue FFL
Cl 34140


594/376
Thymol blue


595
Alizarinsaphirol B
Cl 63010


595
Procion blue MX-R
Cl 61205
Reactive blue 4


596
Ethyl violet
Cl 42600


596
Cresyl violet acetate


597
Remazole black B
Cl 20505
Reactive black 5


598
Thionin acetate
Cl 52000
Lauth's violet


598/415
Sudan black B
Cl 26150
Grease black


599/374
Alizarin direct blue AR
Cl 62130


600
Alizarinsaphirol A
Cl 62055


600
Oxonol 595


601
Gallocyanin
Cl 51030


602
Indigo


602
Indigotin
Cl 73000


602
Cresyl violet perchlorate

5,9-diaminobenzo[a]phenoxazonium perchloratee


602
Acid blue 29
Cl 20460


603
Alkali blue 6B/Nicholson blue
Cl 42750


604/560
Quinaldin blue

1,1′-Diethyl-2,2′-carbocyanine chloride


605
2,6-Dichlorophenolindophenol

Tillmann's reagent


605
Analinee blue


605/388
Tetrabromophenol blue


605/642
Acid green 27
Cl 61580


606
Astra blue base 6 GLL


606
Astrazone blue GLL


606
DCI-2

1,1′-diethyl-2,2′-carbocyanine iodide


607
Celliton blue ex
Cl 64500
1,4,5,8-Tetraaminoanthraquinone


607
Pinacyanolbromide

1,1′-diethyl-2,2′-carbocyanine bromide


607
Procion blue HB
Cl 61211
Reactive blue 2


607
Trypan blue
Cl 23850
Niagara blue 3B, Diamine blue 3B


608
Indigocarmine
Cl 73015


608
Phenol blue


609/567
Alizarin
Cl 58000
1,2-dihydroxyanthraquinone


610
1,4,5,8-tetraaminoanthraquinone


610/380
Alizarin direct blue A2G
Cl 62125


611
Evans blue
Cl 23860


612/400
Bromocresol green sodium salt


614
Pinacyanol

1,1′-diethyl-2,2′-carbocyanine iodide


615
Alcian blue 8 GX
Cl 74240


615
Lissamine blue FFN
Cl 42135
Xylolcyanol FF


615
Oxazine 4

3-ethylamino-7-ethylimino-2,8-





dimethylphenoxazin-5-ium perchlorate


615
Stenacril blue RL
Cl 11075


615
Styryl 6

2-(4-(p-dimethylaminophenyl)-1,3-butadienyl)-





1,3,3-trimethyl-3H-indolium perchloratee


615
Victoria blue R
Cl 44040


615/425
Malachite green
Cl 42000


616
Azure C
Cl 52002


618
Amido black 10B
Cl 20470
Naphthol blue black 6B


618
Chicago blue 6B
Cl 24410
Diamine pure blue FF


618
Guinea green B
Cl 42085


619
Victoria pure blue BO
Cl 42595


620
1,4-dianalineoanthraquinone


622
Brilliant cresyl blue ALD
Cl 51010


622/427
Fast green FCF
Cl 42053


625/406
Erioglaucin disodium salt
Cl 42090
Alphazurin FG


625/428
Brilliant green
Cl 42040
Malachite green


626
Toluidine blue O
Cl 52040
Tolonium chloride


627
Oxazine 170

9-ethylamino-5-ethylimino-10-methyl-5H-





benzo(a)phen oxazonium perchloratee


627/582
Alizarin pure blue R
Cl 61585


628
Nil blue A perchloratee

5-amino-9-diethyliminobenzo[a]phenoxazonium





perchlorate


629
Alizarin brilliant blue RFF
Cl 62058


629
DQTCI

1,3′-diethyl-4,2′-quinolylthiacarbocanine iodide


630
Oxonol blue


630/422
Light green SF yellowish
Cl 42095
Acid green 5


630/591
New methylene blue N
Cl 52030


633
Azure A
Cl 52005


633
Wool green
Cl 44090
Lissamine green BN


635/410
Patent blue VF
Cl 42045


635/420
Methyl green
Cl 42590


637/409
Patent blue A
Cl 42080
Alphazurin A


638
Azure B Thiocyanate


638
Nil blue BX
Cl 51180
Nil blue chloride


639
HIDCI

1,1′,3,3,3′,3′-hexamethylindocarbocyanin iodide


640/594
Celliton fast blue FFR
Cl 61505


640/595
Sudan blue
Cl 61552
Calco oil blue N


642
Coelestin blue B
Cl 51050
Mordant blue 14


642/608
Alizarincyanine green G extra
Cl 61570


643
Rhodamine 700


644/595
Celliton fast blue B
Cl 61500
1,4-bis-(methylamino)anthraquinone


644/596
Oil blue N
Cl 61555
Solvent blue 14


644/607
Alizarincyanine green oleosoluble
Cl 61565


645
Styryl 20


645/522
Eosin-methylene blue

May-greenwood-dye


646
Oxazine 1

3-diethylamino-7-diethyliminophenoxazonium





perchloratee


648
Styryl 15


652/604
Sudan blue II
Cl 61554
Grease blue B, solvent blue 35


653
DTDCI

3-diethylthiadicarbocyanine


654
Rhodulin pure blue 3G
Cl 51004
Zapon fast blue 3G


655
Carbazine 122


655
Dithiazanine iodide

3,3′-diethyl-thiadicarbocyanine iodide


657
Azure II
Cl 52010


657/618
Methylene green
Cl 52020


660
Chlorophyll a
Cl 75810


660/395
Janus green B
Cl 11050
Diazine green


663
Acid black 48
Cl 65005


665
Methylene blue
Cl 52015


667
Oxazine 750


675
Cibachron turquoise blue GF-P
Cl 74459
Reactive blue


682
Methyl-DOTCI

3,3′-dimethyloxatricarbocyanine iodide


682
Rhodaminee 800


694
Copper phthalocyanine
Cl 74160
Heliogen blue B; Monastral blue B


707
1,1′-diethyl-2,2′-dicarbocyanine iodide


710
DDI

1 ,1′-diethyl-2,2′-dicarbocyanine iodide


714
Naphthol green B
Cl 10020


741
HITCI

1,1′,3,3,3′,3′-hexamethylindotricarbocyanine .





iodide


743
1,1′-diethyl-2,2′-quinotricarbocyanine



iodide


750
IR 144


760
3,3′-diethyl-thiatricarbocyanine



perchlorate


760
DTTCI

3,3′-diethylthiatricarbocyanine iodide


765
3,3′-diethyl-thiatricarbocyanine iodide


765
DNTTCI

3,3′-diethyl-9,11-neopentylenethiatricarbocyanine





iodide


780
HDITCI

1,1′,3,3,3′,3′-hexamethyl-4,4′,5,5′-dibenzo-2,2′-





indotricarbocyanine iodide


795
IR 125


798
DDTTCII

3,3′-diethyl-4,4′,5,5′-dibenzothiatricarbocyanine





iodide


810
IR 140


814
1,1′-diethyl-4,4′-dicarbocyanine iodide


815
DDCI-4

1,2′-diethyl-4,4′-dicarbocyanine iodide


830
IR 132

## Claims

1. A holographic data storage medium, comprising a self-supporting polymer film which is set up as a storage layer, which can be changed locally by heating and which is set up as a top layer of the data storage medium, and comprising an absorber layer which is arranged underneath the polymer film and has an absorber dye which is set up to at least partly absorb a write beam serving to write information and to discharge the heat produced by absorbing the write beam at least partly locally to the polymer film, wherein the holographic data storage medium further comprises a partly transparent reflective layer arranged between the storage layer and the absorber layer.

2. The holographic data storage medium as claimed in claim 1, further comprising an adhesive layer arranged underneath the absorber layer.

3. The holographic data storage medium as claimed in claim 1, wherein the reflective layer has a thickness in the range from 1 nm to 50 nm.

4. The holographic data storage medium as claimed in claim 1, wherein the reflective layer comprises aluminum.

5. The holographic data storage medium as claimed in claim 1, wherein the self-supporting polymer film is oriented.

6. The holographic data storage medium as claimed in claim 5 wherein the self-supporting polymer film is biaxially oriented.

7. The holographic data storage medium as claimed in claim 1, wherein the self-supporting polymer film comprises a material which is selected from the following group: polypropylene, polyvinylchloride, polyester, polyethylene terephthalate, polyethylene naphthalate, polymethylpentene, polyimide.

8. The holographic data storage medium as claimed in claim 1, wherein the absorber layer comprises a binder.

9. The holographic data storage medium as claimed in claim 1, wherein the refractive index of the self-supporting polymer film can be changed locally by heating, it being possible for optical phase information to be stored via the local optical path length in the self-supporting polymer film.

10. The holographic data storage medium as claimed in claim 1, wherein the interface structure of the self-supporting polymer film can be changed locally by heating, it being possible for holographic information to be stored via the local interface structure of the self-supporting polymer film.

11. The holographic data storage medium as claimed in claim 1, wherein the absorber dye is set up such that its optical properties can be changed locally when it absorbs a write beam serving to write information.

12. The holographic data storage medium as claimed in claim 1, further comprising stored holographic information.

13. Use of a data storage medium comprising a self-supporting polymer film which is set up as a storage layer, can be changed locally by heating and which is set up as a top layer of the data storage medium, and comprising an absorber layer which is arranged underneath the self-supporting polymer film and has an absorber dye which is set up to at least partly absorb a write beam serving to write information and to discharge the heat produced by absorbing the write beam at least partly locally to the self-supporting polymer film, as a holographic data storage medium, wherein the data storage medium further comprises a partly transparent reflective layer arranged between the storage layer and the absorber layer.

14. The use as claimed in claim 13, wherein the data storage medium has the features of the holographic data storage medium as claimed in claim 2.

15. The use as claimed in claim 13, wherein the refractive index of the self-supporting polymer film can be changed locally by heating, it being possible for optical phase information to be stored via the local optical path length in the self-supporting polymer film and the self-supporting polymer film is transilluminated in transmission when reading out information.

16. The use as claimed in claim 13, wherein the interface structure of the self-supporting polymer film can be changed locally by heating, it being possible for holographic information to be stored via the local interface structure of the self-supporting polymer film.

17. The use as claimed in claim 16, wherein the holographic information is stored via the local interface structure of the self-supporting polymer film to the absorber layer.

18. The use as claimed in claim 13, wherein the absorber dye is set up such that its optical properties can be changed locally when it absorbs a write beam serving to write information.

19. A method of writing information into a holographic data storage medium comprising a self-supporting polymer film which is set up as a storage layer, which can be changed locally by heating and which is set up as a top layer of the data storage medium, and comprising an absorber layer which is arranged underneath the self-supporting polymer film and has an absorber dye which is set up to at least partly absorb a write beam serving to write information and to discharge the heat produced by absorbing the write beam at least partly locally to the self-supporting polymer film, the data storage medium further comprising a partly transparent reflective layer arranged between the storage layer and the absorber layer, the method comprising calculating holographic information contained in a hologram of a stored object as a two-dimensional array, aiming a write beam from a writing device at one or both of the self-supporting polymer film and the absorber layer of the data storage medium, and driving the write beam of the writing device in accordance with the two-dimensional array such that the local properties of the self-supporting polymer film are set in accordance with the holographic information.

20. The method as claimed in claim 19, wherein the write beam is aimed at the holographic data storage medium from the side of the top layer.

21. The method as claimed in claim 19, wherein the holographic information is stored in the form of pits of predefined size.

22. The method as claimed in claim 21, wherein the holographic information is stored in a pit in a binary encoded form.

23. The method as claimed in claim 21, wherein the holographic information is stored in a pit in continuously encoded form, the local properties of the self-supporting polymer film in the pit being set in accordance with a value from a predefined value range.

24. A method of reading information out of a holographic data storage medium comprising a self-supporting polymer film which is set up as a storage layer, which can be changed locally by heating and which is set up as a top layer of the data storage medium, and comprising an absorber layer which is arranged underneath the self-supporting polymer film and has an absorber dye which is set up to at least partly absorb a write beam serving to write information and to discharge the heat produced by absorbing the write beam at least partly locally to the self-supporting polymer film, the data storage medium further comprising a partly transparent reflective layer arranged between the storage layer and the absorber layer, the method comprising aiming light at a large area of the storage layer of the data storage medium and reconstructing the information contained in the irradiated region as a holographic image which is registered at a distance from the data storage medium.

25. The method according to claim 24, wherein the light comprises coherent light.