CH671473A5 - - Google Patents

Description

DESCRIPTION The present invention relates to a method for recording and reading information in the form of holographically generated optical changes in a recording material which contains at least one radiation-sensitive compound which has at least one inhomogeneously broadened absorption band in the UV and / or visible and / or IR spectral range .

The recording of data or image information in

The form of interference patterns (referred to as hologram) with the aid of coherent laser light beams on radiation-sensitive materials is known to the person skilled in the art as holography and is described, for example, in Optical Holography, by P. Hariharan, Cambridge University Press 1984, in particular on pages 1-2. If the hologram is then illuminated in a second step with coherent laser light from the same direction from which the reference wave fell during the recording, diffraction at the interference patterns produces two deflected light beams, one of which is a spatial, real image behind the hologram and the other another creates a spatial virtual image in front of the hologram. The virtual image can be observed directly with the eye, and its view changes with the position of the observer in the same way as the view of the object itself. With a fixed geometric arrangement, this method allows only one image to be recorded per surface element of the recording material.

It is also known, for example, according to US Pat. No. 4,101,976 that radiation-sensitive compounds having at least one inhomogeneously broadened absorption band in a material (matrix) change into a new, photochemically or photophysically changed state at low temperatures by irradiation with laser light of narrow bandwidth. These optical changes should expediently be narrow-band in order to ensure the desired high spectral resolution. It is thus possible to burn in a large number of mutually independent structural holes at the same geometric location within the inhomogeneously broadened absorption band of a radiation-sensitive connection and then to detect it again at the corresponding wavelengths. In this way, information can be stored in digital form (often referred to as bits = binary numbers) by assigning individual bits to a spectral hole at a specific point in the material, so that a very large amount of information is stored in a specific volume of the material becomes. The photochemism of this type of optical bleaching only detects those molecules that absorb at the laser frequencies used; the remaining molecules in the material absorbing at other frequencies remain unchanged because they do not participate in the photo-induced reaction.

The above US Pat. No. 4,101,976 (column 4, lines 27-30) also shows that the information can also be recorded holographically.

Furthermore, it is known, for example from Chemical Physics Letters 94 (1), pp. 485-488 (1983), to change such spectral holes generated by suitable laser light under the influence of an electrostatic field (Stark effect) in such a way that their absorption depth decreases and theirs spectral width is expanded. The same effects can also be achieved if an electrostatic field created during the burning of the spectral hole is subsequently changed or broken down. In addition, according to Molecular Physics 45, p. 97 and p. 133 (1982), it is also known that magnetic fields have a similar influence on spectral holes, and that, for example, according to Optical Communications 51, p. 412 (1984), spectral holes under the influence of pressure (as hydrostatic pressure or as sound waves) change their shape accordingly. The spectral holes are restored if the same field strength that was already present during the recording is set during the detection. In this way, several bits in the form of photochemical holes can also be recorded at one point in a matrix, a laser with a fixed wavelength being used according to this reference.

It has now been found that several holograms appear as

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Have spectral holes stored in a suitable recording material if, under the influence of variable external fields, several different holograms are recorded at the same location in the recording material and at the same laser wavelength and then read. It is surprising that the recorded holograms can be made visible again with good selectivity by simply reconstructing the original field strengths, although the spectral holes only change their shape and depth due to the influence of different external fields. This is all the more surprising since the same molecules for different information which have been recorded in different external fields can be used as storage material (recording and reading) without the burned-in holes completely disappearing; the various information can thus be registered and read independently of one another.

The invention accordingly relates to a method for optically recording and reading information in a recording material which contains at least one radiation-sensitive compound which has at least one inhomogeneously broadened absorption band in the UV and / or visible and / or IR spectral range and which under the action of narrow-band laser light with at least one frequency lying within this absorption band and under the influence of an externally adjustable electrostatic, magnetic or pressure field undergoes a change in the absorption behavior, whereby by changing other field strengths of the electrostatic, magnetic or pressure field causes further changes in the absorption behavior and additional information can therefore be recorded, but these changes can be read again when the field strengths are restored at the time of the recording, characterized in that the information in For m recorded and read by holograms.

An electrostatic field is preferred as an externally adjustable field.

Radiation-sensitive compounds which absorb in the UV and / or visible and / or near IR spectral range, but very particularly in the visible and / or near IR spectral range, are particularly suitable.

The near IR spectral range is the range between 0.78 | i.m and 2 (xm.

The radiation-sensitive compound can be used in the recording material (matrix) in question according to the invention, for example in an amount of 0.001 to 30% by weight, based on the recording material, preferably of 0.01 to 10% by weight, but in particular of 0, 01 to 0.5% by weight. The optimum concentration depends in particular on the compound used, the thickness of the recording material and the laser frequency used to produce the hologram.

Through the action of narrow-band laser light of a certain frequency, certain molecules of this radiation-sensitive compound experience a change in the absorption profile of the inhomogeneously broadened band affected by the laser frequency through the process of the photophysical or photochemical hole burner. Information bits can therefore be recorded with a laser of a specific frequency at different values of the field applied externally (electrostatic, magnetic or pressure field) and later read again by adjusting the field strength corresponding to the recording process. Changes in the absorption behavior of the radiation-sensitive compounds can also be physically coupled with changes in the refractive index of the recording material, and the diffraction efficiency of the holograms can be influenced by the two effects.

The lifetime of such radiation-induced information bits is generally of the order of years at low temperature, so that this information can be regarded as stable.

Examples of compounds which are suitable according to the invention and which can undergo photophysical or photochemical reactions by selective irradiation are substances which, for example, according to Phys. Bl. 41 (1985), No. 11, pp. 363-369 can be converted after one or two photon processes, with proton transfer or tautomerization reactions in particular for one-photon processes and, for example, for two-photon reactions Photochemical decomposition and photoionization come into question. An example of a proton transfer reaction is the molecule quinizarin, the intramolecular hydrogen bridge of which opens under suitable radiation and forms an intermolecular bridge to the matrix. As a result, a spectroscopic shift by a few hundred wave numbers can be generated, so that the resulting photoproduct lies in absorption outside the inhomogeneously broadened absorption band of the starting substance. An example of a photo-tautomerization is phthalocyanine, an example of a photochemical reaction dimethyl-s-tetrazine.

Radiation-sensitive compounds which are suitable according to the invention are e.g. Porphine derivatives, such as phorophyrin, deuterized porphyrin, tetraphenylporphyrin, 7,8-dihydroporphyrin (chlorin), furthermore porphyrazines, such as unsubstituted or substituted phthalocyanines, furthermore quinizarin, a-diketones, such as benzil, camphorylquinone or biac Oxazines, such as the iminium perchlorate of 3,7-bisethylamino-2,8-dimethylphenoxazine, compounds which can be photochemically converted by cis-trans-isomerization, such as maleic acid, fumaric acid or crotonic acid, and also tetrazines, such as dimethyl -s-tetrazine or diphenyl-s-tetrazine, spiropyrans, isoimidazoles, azirines, and compounds which are known to those skilled in the art as laser dyes.

Particularly preferred compounds are porphine derivatives, porphyrazine, quinizarin, a-diketones, tetrazines or compounds which can be photochemically converted by cis-trans isomerization.

Spectrally pure laser sources are expediently used to record the information in the recording material in accordance with the invention. The energy radiation is directed and, if necessary, focused onto the surface of the recording material to be marked in accordance with the shape of the information to be applied, a spectral change occurring at the irradiated points.

Examples of such laser sources are solid-state pulse lasers, such as alexandrite lasers, ruby lasers or frequency-multiplied Nd: YAG lasers, pulsed lasers with additional devices, such as pulsed dye lasers or Raman shifters, and further continuous wave lasers, which may include pulse modifications (Q switch, mode -Locker), for example based on CW Nd: YAG laser with frequency multiplier, continuous dye laser or CW ion laser (Ar, Kr), also pulsed metal vapor lasers, such as Cu vapor lasers or Au vapor lasers, or semiconductor lasers low spectral bandwidth, especially so-called single-mode lasers.

Continuous-wave lasers are preferred, such as those listed in the table below, in addition to other commercially available lasers according to the invention.

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TABLE

ylrt / representative

Commercial example

Main wavelength (secondary wavelengths) [nm]

Pulsed laser with additional device such as

• dye laser

CW laser (with pulse modification cation)

• Nd: YAG (Q switch, 2 <d)

• Argon (mode-locked)

• Helium neon

Pulsed metal vapor laser

• Cu steam laser

• Au steam laser

• Mn vapor laser

• Pb steam laser

Semiconductor diode laser

Semiconductor diode laser array

CW dye laser

Lambda Physics FL 2002

Lasermetrics (9560QTG)

Spectra-Physics 161

PMS LSTP 0010

about 300-1000

532

514.5 / 488

632.8 / 543.8 / 594.1 / 612/1152

Plasma Kinetics 751

Plasma kinetics

(Oxford Laser CU 25

Sharp LT-020 MC Spectra Diode Labs, Inc. 502-2410-H1

STANTEL type LF 100

510, 578

628 534, 1290 723

780

905

Coherent CR-699-21 approx. 400-900

The recording material (matrix) that can be used according to the invention can be high-molecular organic material of natural or artificial origin, glass, ceramic glass or a frozen liquid.

If the recording material is a high-molecular organic material, it can e.g. are natural resins or drying oils, but also modified natural substances, for example oil-modified alkyd resins or cellulose derivatives, such as cellulose esters or cellulose ethers, and especially fully synthetic organic polyplastics, i.e. plastics that are produced by polymerization, polycondensation or polyaddition. The following may be mentioned from the class of these plastics: polyethylene, polypropylene, polyisobutylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetals, polyacrylonitrile, polyacrylic acid and poly-methacrylic acid esters or polybutadiene, and copolymers thereof, in particular ABS or EVA; Polyesters, especially high molecular esters of aromatic polycarboxylic acids with polyfunctional alcohols; Polyamides, polyimides, polycarbonates, polyurethanes, polyethers of polyphenylene oxide, polyacetals, the condensation products such as formaldehyde with phenols, the so-called phenoplasts, and the condensation products of formaldehyde with urea, thiourea and melamine, the so-called aminoplastics; the polyaddition or polycondensation products of epichlorohydrin with diols or polyphenols known under the name "epoxy resins" and also the polyesters used as coating resins, both saturated, e.g. Alkyd resins, as well as unsaturated, such as maleate resins. It should be emphasized that not only the uniform compounds, but also mixtures of poly-plastics, as well as mixed condensates and copolymers, e.g. butadiene-based ones can be used, s High molecular weight organic materials in dissolved form are also suitable as film formers, e.g. Linseed oil varnish, nitrocellulose, alkyd resins, phenolic resins, melamine resins, acrylic resins and urea-formaldehyde resins, it being possible for the films obtained therefrom to be used, for example on transparent supports or between two transparent supports.

The addition of the radiation-sensitive compound considered according to the invention to the high-molecular organic material to be processed into shaped articles is carried out according to methods known per se, for example in such a way that such a compound is optionally in the form of masterbatches, this substrate using extruders, rolling mills , Mixing or grinding devices. The radiation-sensitive compounds can also be added before the final polymerization or crosslinking into a mixture of monomers, prepolymers, saturated or unsaturated oligomers and / or multifunctional monomers, optionally with the addition of polymerization initiators, so that these compounds during the polymerization or Cross-linking can be built into the matrix chemically or physically. The material obtained is then brought into the desired final shape by methods known per se, such as calendering, pressing, extrusion, brushing, casting, extruding or by injection molding. It is often desirable to incorporate so-called plasticizers into the matrix materials in order to produce non-rigid moldings or to reduce their brittleness before they are deformed. As such, e.g. Serve esters of phosphoric acid, phthalic acid or sebacic acid. The plasticizers can be incorporated into the polymers before or after the radiation-sensitive compound has been incorporated.

To produce films, the matrix materials and the radiation-sensitive compound, optionally together with other additives, are finely dispersed or dissolved in a common organic solvent or solvent mixture. You can do this by dispersing or dissolving the individual components for yourself or several together, and only then bringing all the components together. The homogenized mixture is then applied to a transparent substrate by methods known per se and baked or dried, and the film obtained is then irradiated according to the invention.

If the recording material (matrix) is glass or ceramic glass, then these are glasses and ceramic glasses which are well known to the person skilled in the art and are described, for example, in the Ullmann encyclopedia of techn. Chemie, 4th edition, vol. 12, pp. 320-323 and 361-364. Examples include silicate glasses, two-component silicate glasses, borate, phosphate, borosilicate, aluminosilicate and lead glasses. Glasses, 55 which e.g. produced by melting at low temperature by the sol-gel process can also be used according to the invention.

The recording material considered according to the invention can also be a frozen liquid which is liquid, for example, at room temperature, but is solid and transparent at a lower temperature. The radiation-sensitive compound is expediently dissolved in the liquid in question, for example at room temperature, whereupon a solid recording material, for example in the form of a thin film, is produced by cooling the solution obtained below the freezing point of the liquid used.

Examples of suitable liquids are alcohols, such as ethanol, ethers, n-alkanes, ketones, esters or amides.

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The recording material in question according to the invention can also be a mixture of the liquids specified above with one another or one or more of these liquids with a high-molecular organic material specified above.

Recording materials which are particularly preferred for the process according to the invention are amorphous transparent materials.

Very particularly preferred materials are e.g. Polyacrylates, such as polymethyl methacrylate, polyethyl methacrylate, poly-methyl or polyethyl acrylate, polycyanoacrylates, such as a-methyl, a-ethyl or a-isobutyl-cyanoacrylate, polyethylene, polypropylene. Polystyrene, polyvinyl acetals, such as polyvinyl butyral, polyvinyl carbazoles or polyvinyl alcohols.

The setting of the laser during recording and reading to a selected point on the recording material is carried out according to methods known to the person skilled in the art, for example by means of deflection by means of movable mirrors, movable prisms, electro-optical elements or by means of displacement of the recording material.

A wide variety of recording types can be obtained by the process according to the invention. Examples include: characters, data, images, bit patterns, and a wide variety of information.

The invention will be explained in more detail below with reference to drawings 1, 2, 3a, 3b, 3c and 3d. The following show:

1 shows a schematic illustration of a storage device that is suitable according to the invention, including the means for writing and reading the information,

2 is a perspective view of the storage medium and the electrode arrangement,

3a shows the absorption behavior of the material as a function of the applied field strength before it is exposed to the laser light,

3b shows the absorption behavior of the recording material as a function of the applied electric field strength after it has been exposed to exposure to laser light at a fixed frequency in a certain electric field C.

3c shows the absorption behavior of the recording material as a function of the electric field strength after it has been exposed to irradiation with the same fixed laser frequency at two different electric field strengths C and D,

3d shows the holographic diffraction efficiency of the recording material as a function of the field strength after it has been subjected to a holographic exposure at two different field strengths C and D with the same fixed laser frequency.

When the information is recorded as holograms, the diffraction efficiency of the hologram generated in the recording material depends on the field strength. Figure 3d shows the diffraction efficiency of two holograms recorded at field strengths C and D. The maxima at the field strengths C and D represent holographically stored information which stands out clearly and with a good signal / noise ratio from the zero line.

4 shows a schematic illustration of a recording device which can be used according to the invention.

An optical storage device to which the electric field strength is applied is shown schematically in FIG. 1. The optical information storage device contains a laser light source which operates stably at one or more fixed frequencies and whose line or lines are narrow-band with respect to the inhomogeneously broadened absorption band. The light intensity of the laser must be able to be adapted to the requirements of the storage material during the writing and reading process. If the laser 1 operates at more than a fixed frequency, an optical filter is used to select the desired laser frequency. The laser beam generated is structured holographically by a suitable structure 2. The devices for the spatial deflection of the laser beam are not shown and are of a common design. The storage medium 3 is in an electrical field by applying an external voltage 7 to a set of suitably constructed transparent electrodes 4. When laser light of fixed frequency is irradiated, the storage medium 3 experiences a permanent or temporary change in absorption, which is largely reduced to the value before the irradiation by a change in the electric field strength, but essentially in the originally recorded form when the electric field strength is restored reappears. The optical filter 5 and a detector circuit 6 are used only during the reading process.

2 shows a perspective illustration of the recording material (storage medium) in the form of a film, to which an electric field can be applied by two electrodes, and the electrode arrangement. This film has a dimension of 20 mm x 10 mm x 50 yy. and is arranged between two transparent glass plates 9, each carrying an electrode for generating the electric field. These glass plates serve as carriers for the electrically conductive and optically transparent electrodes 4 which are vapor-deposited on the inside. The concentration of the radiation-sensitive compound is selected such that an optical density of approximately 1 results in the maximum of the inhomogeneously broadened absorption band. A narrow-band, frequency-stabilized dye laser with a frequency in the region of the inhomogeneous band width is used for writing. With an irradiation intensity of, for example, 0.2 mW / cm 2, absorption changes in the size of 0.3 optical density units can be achieved within a few seconds in the storage medium which is in a cryostat at the temperature of the liquid helium. The storage properties of the storage medium are significantly influenced by the choice of its operating temperature. The available storage capacity increases at lower temperatures. The storage properties also depend on the type of (polymer) film. For example, chlorine in a polymethyl methacrylate film shows an approximately 5 times smaller storage capacity than a polyvinyl butyral film. Substances or centers with good storage capacity are characterized by the fact that the difference in the dipole moments and / or the polarizabilities between the ground state and the excited electron state used is as large as possible in such substances.

The recording material is written according to the information to be stored in each case at a fixed laser frequency with gradually changing field strengths applied from the outside, each recording and reading process being carried out with the field strength remaining constant.

When the laser light hits the storage medium in the applied field at a fixed frequency within the inhomogeneously broadened absorption band, the laser creates a narrow spectral hole. Molecules or centers are recorded that absorb the laser light of the fixed frequency in this field of a certain size. The selection of these molecules affected by the bleaching process is determined, among other things, by the size of the field strength applied. The change in the absorption behavior generated in the storage material can be either permanent or limited in time. Further information storage processes can be carried out according to the same principle after changing this electrical field.

An important property of the storage method according to the invention is that in the recording material with a laser of fixed frequency in the dimension of the outer field

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of which several holograms can be saved. The number of holograms that can be recorded at a fixed wavelength depends on the electrical dielectric strength of the material, which limit the possible storage area of the material. The limits of this dielectric strength are shown in Figures 3a, 3b and 3c with A and B and are in the order of magnitude of ± 5 x 105 V / cm. The range that can be used for the electric field strengths is thus between A and B. Furthermore, the change in the field strength is decisive, which leads to a largely disappearance of the change in absorption. From the example of chlorine in a polyvinyl butyral film at the temperature of the liquid helium, it follows that an electrical field strength range of approximately 2 × 104 V / cm is sufficient for the storage of a hologram. With a film layer thickness of 50 | x, this corresponds to a change of 100 V in the applied voltage. This means that in the permissible range between A and B, information of the order of 50 holograms can be stored for each laser frequency.

The absorption change generated by the narrow-band laser light can be called up again by irradiating light of suitable frequencies at the points of opposite absorption changes.

The memory device shown in FIG. 1 can be used to read the data. The intensity of the narrow-band laser 1 of fixed frequency is reduced by more than a factor of 100 compared to the writing process. The laser light 8 strikes the storage material in the electrical field. The transmitted light represents a measure of the change in the absorption behavior achieved in the writing process and, after passing through the optical filter 5, which has the task of suppressing interfering light, is registered in the detector as a function of the electric field strength. 3a shows the absorption behavior of the storage medium before it is exposed to the writing process with laser light. 3b shows the absorption behavior of the sample at a fixed wavelength as a function of the applied electric field strength after it has been exposed to the laser light at the electric field strength C. 3c shows the absorption behavior of the sample at a fixed wavelength as a function of the applied electric field strength after it has been exposed to the laser light at the electric field strengths C and D. The minima at positions C in FIG. 3b, at positions C and D in FIG. 3c represent stored information.

Other devices than those shown in FIG. 1 can also be used for storing and reading. For example, the optical filters can be dispensed with.

The inventive method described so far works with a single fixed laser wavelength. The principle shown can also be applied to information storage processes, the recording material being described simultaneously or preferably successively in accordance with the information to be stored at a plurality of fixed laser wavelengths which originate from one or more lasers.

Thus, several discrete laser frequencies (frequency multiplex method) can be combined, for example, with the Stark effect, so that at each laser frequency, by further varying the Stark voltage, a further increase in the information density or a simpler recording of the information about the tension that can be achieved.

It is also possible to use a plurality of diode lasers (semiconductor lasers), each with a different, fixed frequency, which record at the same point on the storage medium, with each diode at its frequency by varying the externally applied field, for example the Stark voltage, can record different information (a different hologram).

According to the invention, it is also possible to use recording materials composed of a matrix which by definition contains radiation-sensitive compounds and which have at least one inhomogeneously broadened absorption band, the matrix consisting of a polymer material or a wax which can also be found at room temperature in the interior of electronic devices, for example up to about 60 ° C. , remain solid and chemically stable without deleting the information recorded at low temperatures.

A polymer matrix can also be used as recording material, in which the radiation-sensitive compound by definition, which has at least one inhomogeneously broadened absorption band, is chemically bound to the polymer matrix or incorporated into the polymer chain, e.g. Anthracene built into polystyrene [cf. Vlauer, P. Remmp, L. Monnerie, Y. Yang, R.S. Stein, Polymer Communie., 26, (1985), pp. 73-76].

Finally, matrices containing a radiation-sensitive substance according to the definition can also be used as recording materials, in which the molecules of the radiation-sensitive compound are geometrically aligned by means of suitable production techniques. This can e.g. by adsorption or chemical bonding on a smooth surface or phase boundary, by adsorption or bonding on the surface of small platelets which are introduced into the matrix in a parallel arrangement, coating according to the Langmuir-Blodgett technique [in chemistry in our time, no. 9 (1975), pp. 173-182], by aligning the radiation-sensitive connection in an externally applied (eg electrical) field during the production of the storage medium, or by mechanically stretching the matrix with the homogeneously distributed radiation-sensitive connection.

By aligning the molecules in parallel, not only can the spectral holes be broadened, but also an effective spectral shift of the center of gravity can be achieved under the influence of the field, especially the Stark effect.

The following examples illustrate the invention.

example 1

An optical recording medium (see Fig. 2) is manufactured by the following procedure:

0.37 mg chlorine [7,8-dihydroporphyrin, synthesized according to the instructions in U. Eisner and R.P. Linsteadt, Journal of the Chemical Society 4 (1955), p. 3742] are dissolved in 2 ml of methylene chloride (Merck, UVASOL). 600 mg of polyvinyl butyral with a molecular weight of 38,000-45,000 (Polyscience Inc., Warrington, Pennsylvania 18978, USA) are dissolved in 10 ml of methylene chloride (Merck, UVASOL). The two solutions are mixed well in a 4 cm diameter crystallizing dish and then left to stand at room temperature until the solvent has evaporated. A rectangular piece of 1 x 2 cm in size is cut out of the colored plastic plate of approx. 0.2 mm thickness remaining at the bottom of the bowl and fixed as follows:

2 glass plates (10 X 24 x 1 mm) [(9), Fig. 2], which are vapor-coated on one side with an electrically conductive, optically transparent film made of tin dioxide, become a sandwich with a lateral offset of approx. 5 mm - Stacked together so that the plastic is in the middle and is in contact with an electrode on both sides. The entire sandwich is then bonded under pressure at 100 ° C. for 12 hours, the thickness of the plastic film being set to 0.2 mm by distance gauges in the press.

The two electrodes [(4), FIG. 2] are contacted with wires [(7), FIG. 2], and then the whole sandwich on one

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insulated support mounted on a vacuum flange with electrical feedthroughs.

An apparatus with the following main components is used for optical recording and reproduction (see FIG. 4):

- A bath cryostat (11) for liquid helium with two perpendicular pairs of windows and vacuum connection for working with reduced helium pressure;

A dye laser (2), excited by an argon ion laser (1) at 488 nm, with tuning unit and frequency stabilization (line width less than 1 MHz, model CR-599-21 from Coherent, Palo Alto, CA. 94304, USA), equipped with the DCM laser dye from Exciton, Overlook Station, Dayton, OH 45431, USA;

- A detection device consisting of a residual light amplifier (16) and a commercially available video camera (17) with monitor and video recording device (not shown).

For the recording of a hologram, the holder with the recording material is installed in the cryostat (11) so that it comes to rest between the windows; the cryostat is closed in a vacuum-tight manner and cooled to about 4 ° Kelvin by filling in liquid helium. The temperature is then reduced by a further 2 ° Kelvin by pumping out gaseous helium at 1066 Pa.

The output beam of the dye laser (2) is set to 635 nm and stabilized, weakened to a power of 1 microwatt, then expanded with a beam telescope (3) with a magnification factor of 7 and with a cube beam splitter (5) into two partial beams of the same power [Object beam (7) and reference beam (6) called] divided. By deflection with adjustable mirrors (S2, S3, S4), the two partial beams are directed approximately perpendicularly onto the recording plate (10) in the cryostat (11), so that they intersect at an angle of 10 ° on the latter. The entire beam can be interrupted by a first electrically operated flap (4) between the telescope (3) and the beam splitter (5), the object beam (7) by a further flap (8) after the beam splitter. For the recording of a first hologram, a voltage of −500 V is initially applied to the electrodes of the recording plate with the laser beam interrupted, a first image [a slide with a black and white line drawing (9)] is placed in the object beam, and then both laser beams released by opening the flaps for 20 seconds. Then the voltage is increased by 200 V to -300 V,

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placed a second image in the object beam and exposed again for 20 seconds. This process is repeated at -100 V, +100 V and + 300 V.

To reproduce the individual images, the laser is attenuated to approximately 0.1 microwatts at the same wavelength, but only the reference beam (6) is released. This is now diffracted on the recording plate (10) and can be imaged on the residual light amplifier (16) via a lens (13) with a focal length of 25 cm. In the focal point after the lens, disturbing stray light is blocked by a pinhole (14) with a diameter of 1 mm. By applying the voltage between -500 V and + 300 V used in the recording, the 5 recorded images are optionally displayed separately on the video camera (17).

In the present example 1 (chlorine in a polyvinylbutral film), the irradiation with light in the frequency range of 15 600-16 000 cm-1 leads to the process of photochemical hole burning. The molecule chlorin performs a photo reaction under the influence of light, whereby the new photo product generated absorbs in the range of 17 100-17 600 cm-1. This photoreaction is reversible, and the stored information can be erased with good efficiency by irradiation with light in the spectral range from 17 100-17 600 cm-1 or into another absorption band of the photoproduct. The stored information is also completely deleted when the storage medium is warmed up to room temperature.

Example 2

The procedure and apparatus are analogous to Example 1, but instead of chlorine, a solution containing 0.35 mg of oxazin-4 - perchlorate (laser quality, Eastman Kodak, Rochester, NY 14692) in 2 ml of methylene chloride is used to prepare the recording material used. The dye laser is set to 620 nm for recording and playback.

Example 3

The procedure and apparatus are analogous to Example 1, but instead of chlorine, a solution with 0.35 mg of cresyl-violet (laser quality, Eastman Kodak, Rochester, NY 14692) in 2 ml of methylene chloride is used for the production of the recording material . The dye laser is set to 620 nm for recording and playback.

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3 sheets of drawings

Claims (10)

671 473 1. A method for the optical recording and reading of information in a recording material which contains at least one radiation-sensitive, in the UV and / or visible and / or IR spectral range at least one inhomogeneously broadened absorption band having compound under the action of narrow-band laser light with at least a frequency within this absorption band and under the influence of an externally adjustable electrostatic, magnetic or pressure field undergoes a change in the absorption behavior, whereby by changing other field strengths of the electrostatic, magnetic or pressure field further changes in the absorption behavior are effected and additional information is therefore recorded can, but these changes can be read again when the field strengths are restored at the time of recording, characterized in that the information is recorded in the form of holograms and g be read. 2. The method according to claim 1, characterized in that an electrostatic field is used as an externally adjustable field. 2nd PATENT CLAIMS 3. The method according to claim 1, characterized in that the recording material is high molecular weight organic material of natural or artificial origin, glass, ceramic glass or a frozen liquid. 4. The method according to claim 3, characterized in that the recording material is an amorphous transparent material. 5. The method according to claim 3, characterized in that the high molecular weight organic material is a polyacrylate, a polycyanoacrylate, polyethylene, polypropylene, polystyrene, a polyvinyl acetal, polyvinyl carbazole or a polyvinyl alcohol. 6. The method according to claim 1, characterized in that the radiation-sensitive compound undergoes a change in the absorption profile of the inhomogeneously broadened band touched by the laser frequency through the process of the photophysical or photochemical hole burner. 7. The method according to claim 1, characterized in that the radiation-sensitive compound absorbs in the UV and / or visible and / or near IR spectral range. 8. The method according to claim 7, characterized in that the radiation-sensitive compound absorbs in the visible and / or near IR spectral range. 9. The method according to claim 1, characterized in that the radiation-sensitive compound is a porphine derivative, a porphyrazine, quinizarin, an a-diketone, an oxazine, a compound which can be photochemically converted by cis-trans isomerization , a tetrazine, a spiropyran, an isoimidazole, an azirine, and a laser dye. 10. The method according to claim 1, characterized in that the radiation-sensitive compound is present in an amount of 0.001 to 30 wt .-%, based on the recording material (matrix).