FR2607307A1 - METHOD FOR OPTICALLY RECORDING AND READING INFORMATION - Google Patents

Abstract

THE OBJECT OF THE INVENTION IS A PROCESS FOR THE OPTICAL RECORDING AND READING OF INFORMATION IN A RECORDING MATERIAL 10 WHICH CONTAINS A PHOTOSENSITIVE COMPOUND PRESENT, IN THE ULTRAVIOLET, VISIBLE OR INFRARED, AN ABSORPTION BAND ENLARGED IN A NON-HOMOGENEOUS WAY, COMPOUND WHICH, UNDER THE ACTION OF A NARROW-BAND LASER LIGHT AND INCLUDING AT LEAST A FREQUENCY LOCATED IN THE SAID ABSORPTION BAND AND UNDER THE ACTION OF AN ELECTROSTATIC FIELD CREATED BY THE ELECTRODES 20 AND ADJUSTABLE FROM THE OUTSIDE, SUBJECTS A MODIFICATION OF ITS ABORPTION BEHAVIOR, OTHER MODIFICATIONS OF THE BEHAVIOR ON ABSORPTION THAT MAY BE CAUSED BY ADJUSTING THE FIELD INTENSITY TO OTHER VALUES, AND, THUS, INFORMATION ADDITIONAL MAY BE RECORDED, THESE MODIFICATIONS MAY HOWEVER BE READ AGAIN WHEN RESETTING FIELD INTENSITIES. THIS PROCESS IS CHARACTERIZED IN THAT THE INFORMATION IS RECORDED AND READ IN THE FORM OF HOLOGRAMS.

Description

The present invention relates to a method for recording and reading

  information in the form of optical modifications created by holography in a recording material which contains at least one photosensitive compound having at least one non-uniformly enlarged absorption band in the ultraviolet and / or

the visible and / or infra-red.

  Registration, on photosensitive matters

  In the form of interference data (or "holograms"), data or video information, by means of coherent light beams from a laser, is a known method which the specialist calls "holography". he

  is described for example in Optical Holography, by P. Hari-

  haran, Cambridge University Press 1984, especially pages 1 and 2. If, in a second step, we illuminate

  the hologram with a coherent beam of light

  from a laser and arriving on the hologram in the same direction as that of the incident reference wave during the shooting, then two light beams are formed by diffraction in the interference patterns. deviated, one of which creates, behind the hologram, a real spatial image and the other creates, in front of the hologram, a virtual spatial image. The virtual image can be observed directly with the eye: the visual perception that it gives to the observer varies with the position of the latter as that which the object itself gives. This process

  allows, for a fixed geometrical arrangement, that the

  recording of a single image per surface element of

the recording material.

  It is further known, for example by

  US Pat. No. 4,101,976, for passing photo

  responsive to at least one inhomogeneously expanded absorption band, which are in a material (matrix), at low temperatures, by exposure to low bandwidth laser light, in a new state, photochemically or photophysically modified . It is good that these optical modifications are narrowband to ensure the desired high spectral resolution. It is therefore possible to create, within the absorption band, non-homogeneously enlarged, of a photosensitive compound, at the same geometrical location, with different

  wavelengths, a large number of inde-

  pendents from each other, then detect them again at the corresponding wavelengths. In this way, it is possible to store information in digital form (often in the form of "bits", ie binary numbers) by assigning a bit to each of the spectral holes in a specific location of the matter, of

  so that we can accumulate a very large amount of information

  in a given volume of matter. The photo-

  chemistry of this kind of optical whitening affects only the molecules that absorb at laser frequencies put

  stake; the other molecules, those that absorb to

  very frequent, remain unaltered in the material because

  that they do not participate in the photo-induced reaction.

  In US Patent 4,101,976, mentioned above,

  above it is further stated in column 4, lines 27 to 30, that the recording of information may also be

performed by holography.

  Furthermore, it is known, for example from Chemical Physics Letters 94 (1), pages 483-487 (1983), that such spectral holes created by appropriate laser light

  can be modified by an electrostatic field.

  that (Stark effect) so that their depth of ab-

  sorption decreases and their spectral width increases.

  Identical effects can also be achieved by later modifying or deleting an applied electrostatic field during the creation of the spectral hole. Moreover, it is known from Molecular Physics 45, ns 1, pages 113-127 (1982), that magnetic fields exert an analogous effect on spectral holes, and that, for example, according to Optics Communications 51, pages 412 -416 (1984), spectral holes change shape under the effect of pressure

  (hydrostatic pressure or sound waves). Spectral holes

  traux are reconstituted when, during the detection,

  the same field strength is applied as when

  tration. In this way one can also record in a matrix in one place several bits in the form of

  photochemical holes; according to this document of the

  a fixed wavelength laser is used.

  That being so, the present inventors have found that several holograms can be stored in the form of spectral holes in a recording material

  appropriate if one records, under the effect of ex-

  different holograms at the same place in the recording material and at the same time

  same laser wavelength, then read.

  It is surprising then that the recorded holograms can again be made visible with good separating power by simply reconstructing the primitive field strengths, although the spectral holes change only in shape and depth under the effect of different external fields. This is all the more surprising since molecules of the same type can be used as storage materials (for recording and playback) for different information that has been recorded with different external fields, without the created holes disappearing completely; the different pieces of information can be recorded and read independently

each other.

  The present invention therefore relates to a

  method for optical recording and reading of

  training in a subject matter containing

  least a photosensitive compound having, in the ultra-

  violet and / or the visible and / or infra-red, at least one inhomogeneously broadened absorption band composed, under the action of a narrow band laser light and having at least one frequency located in said absorption band and under the action of an electrostatic field, magnetic or externally adjustable pressure, undergoes a change in its absorption behavior, other changes in the absorption behavior may be other values of the electrostatic, magnetic or pressure field strength and, thus, additional information that can be recorded, but these changes can be read again when the field strengths are reconstructed at the time of recording, characterized in that the information is recorded and read under

the form of holograms.

  It is good that the adjustable field of the outside

  As photosensitive compounds, those which absorb in the ultraviolet and / or in the visible and / or in the near infra-red, but especially in the visible and / or near, are particularly appreciated. infrared. By "near infra-red" we mean the region

which ranges from 0.78 μm to 2 μm.

  In the recording material (matrix)

  which can be envisaged according to the invention the photo-

  The sensitizer may be, for example, in an amount of from 0.001 to 30% by weight, preferably from 0.01 to 10% by weight, but more preferably from 0.01 to 0.5% by weight, based on recording. The optimal concentration depends in particular on the compound involved,

  the thickness of the recording material and the frequency

  laser that is used to create the hologram

  gram. Under the action of a narrow-band laser light of a certain frequency certain molecules of this photosensitive compound undergo, in the photophysical or photochemical hole creation operation, a modification in the absorption profile of the band, enlarged

  in a non-homogeneous way, which is affected by the laser frequency.

  Information bits can therefore be recorded with a laser of a specific frequency, for different

  values of the field applied from the outside (electrostatic field

  tick, magnetic field or pressure field), and be replayed later by adjusting the field strength

  at a value corresponding to that of the transaction

  tration. Changes in the absorption behavior of the photosensitive compounds can also be physically combined with changes in the refractive index

  of the recording material, and the performance of diffract

  Holograms can be influenced by both effects.

  The dimensions of the surface irradiated by the

  laser can range from a few micrometers to several

  meters. Small area holograms are read at

medium of optical instruments.

  The lifetime of such photoinduced information bits is generally of the order of a few years at low temperature, so that this information can

to be considered stable.

  The compounds which can be used according to the invention

  that can give photophysical or photochromic reactions

  under the effect of selective irradiation are

  compounds which can be converted, for example according to Phys. B1. 41 (1985), No. 11, pp. 363-369, by a one or two-photon process, the one-photon processes being predominantly proton transfer or tautomerization reactions and the two-photon processes being by

  example of photochemical decompositions or a photo-

  ionization. The change of the position or the orientation of molecules of the photosensitive compound in the matrix, for example the indirect reorientation of matrix molecules

  neighboring countries, is also covered by the concept of

  As a molecule capable of giving a proton transfer reaction, mention may be made, for example, of

  that of quinizarin, including the intramolecular hydrogen bridge

  the eyepiece opens under the effect of a suitable radiation and

  generates an intermolecular bridge with respect to the matrix.

  A spectroscopic displacement of a few hundred units, in the frequency expressed by the number of waves, can thus be created, so that the photoproduct formed is, as regards its absorption, outside the band of inhomogeneously expanded absorption of the starting compound. Examples of molecules that can give a phototautomerization include that of phthalocyanine, and as examples of molecules that can give a reaction

  photochemical will be that of dimethyl-s-tetrazine.

  The photosensitive compounds which can be envisaged according to the invention are especially derivatives of porphine, such as porphyrin, deuterated porphyrin,

  tetraphenyl-porphyrin, 7,8-dihydro-porphyrin (chlo-

  rine), also porphyrazines, such as phthalo-

  substituted or unsubstituted cyanines, quinizarin, e-diketones,

  such as benzine, camphorquinone or diacetate.

  oxazines, such as iminium perchlorate derived from bis (ethylamino) -3,7-dimethyl-2,8-phenoxazine,

  such as dimethyl-s-tetrazine or diphenyl

  nyl-s-tetrazine, spiropyrans, iso-imidazoles, azirines and compounds called "laser dyes"

by the skilled person.

  It is also possible to envisage compounds that

  can be photochemically transformed by an iso-

  cis-trans, such as maleic acid, fumaric acid,

or crotonic acid.

  The derivatives of porphine, porphyrazines, quinizarin,

ç-diketones and tetrazines.

  In order to record the information in the recording material that can be used according to the invention, it is useful to use sources of laser radiation of a

  high spectral purity. Energy radiation, corresponding to

  depending on the shape of the information to be applied, is then directed, and possibly focused, on the surface of the recording material to be marked, which has the effect of producing a spectral modification in the affected areas.

by radiation.

  Laser sources of this kind will be, for example, pulsed lasers with solid bodies, such as the Alexandrite laser, the ruby laser or the Nd: YAG lasers with frequency multiplication, the pulsed lasers with an auxiliary device, such as pulsed lasers. to dyes or lasers with stimulated Raman effect, permanent lasers, which may have pulse changes (resonant cavity, phase lock), for example based on a laser CW Nd: YAG frequency multiplier, lasers dye lasers or CW (Ar, Kr) ion lasers, pulsed metal vapor lasers, eg copper vapor laser or gold vapor laser, or semiconductor lasers with low

  spectral band, more specifically so-called "single" lasers.

  In the solid-state and gas lasers mentioned above it is advantageous to use auxiliary devices to reduce the bandwidth, for example prisms, arrays and standards,

  inside the laser resonator.

  Continuous-mode lasers, such as those mentioned in the following table, are preferred, although it is also possible to use in the process

  of the invention, other commercial lasers.

Board

Wave length

  Type / Representative Examples of Main / On-Line Trade

Main / LON

secondary wavelengths) (nm ..

Pulsed lasers at disposal

  auxiliary tif, e.g. Lambda Physik dye laser approx. 300-1000

FL 2002

CW lasers (with modification

  pulse cation) to Nd: YAG (resonant cavity Lasermetrics 532 te, 2u) (9560QTG) Argon (Spectra-Physics lock 161 514.5 / 488 phase) phase) 632.8 / 543.8 // Helium- neon PMS LSTP 0010 6328/5438

594.1 / 612/1152

  Metallic Vacuum Pulsed Lasers Cu Plasma-Kinetics 751 510 Steam Laser. 578 Au Plasma-Kinetics 628 Steam Laser Mn Oxford 534, 1290 Steam Laser Pb JLaser CU 25 723 Semiconductor Laser Diodes Sharp LT-020TM 780 Conductors Spectra Diode Labs, Inc.

502-2410-41

  Semiconductor laser diodes STANTEL 905 conductors Arrangement Typ LF 100 Dye lasers with Coherent CR-699-21 approx. 400-900 The recording material (matrix) that can be envisaged in the process of the invention can be a high molecular weight organic material,

  of natural or artificial origin, glass,

  ceramic or a frozen liquid. Macromolecular organic materials which may be considered as recording materials include natural resins or drying oils, or modified natural substances, for example oil-modified alkyd resins or cellulose derivatives, such as esters. or ethers of the

  cellulose, or, more particularly, plastics

  completely synthetic organic materials, that is plastics which have been prepared by polymerization, polycondensation or polyaddition. Among these plastics there will be mentioned in particular: polyethylene,

  polypropylene, poly-isobutene, polystyrene, poly-

  (vinyl chloride), poly (vinylidene chloride), poly (vinyl acetals), polyacrylonitrile, poly (esters)

  acrylates), poly (methacrylic esters) and poly-

  butadiene, as well as copolymers thereof, more specifically

  ABS and EVA copolymers; polyesters, between

  macromolecular esters derived from poly-

  aromatic carboxylic and polyols; polyamides, polyimides, polycarbonates, polyurethanes,

  polyethers, such as poly (oxy-phenylene), poly-

  acetals, the condensation products of formaldehyde with phenols. products called "phenoplasts", and the condensation products of formaldehyde with urea, thiourea or melamine, a so-called

  aminoplasts, polyaddition products or poly-

  condensation of epichlorohydrin with diols or polyphenols, products which are known as "epoxy resins", and also polyesters used as resins for paints and varnishes, and among these as well as saturated ones such as alkyd resins than unsaturated resins, such as maleic resins. It should be noted that not only isolated compounds but also mixtures of

  plastics as well as co-condensates and co-poly-

  mothers, such as those based on butadiene.

  One can also consider, as a leaflet

  genes, macromolecular organic matter in the state

  dissolved, for example, linseed oil varnish, nitro-

  cellulose, alkyd resins, phenolic resins, melamine resins, acrylic resins and urea / formaldehyde resins; the films (films) obtained from these materials may be used for example

  on transparent supports or between two trans-

  parents. To add the photosensitive compound to

  use according to the invention to the organic matter macro-

  For example, such a compound, possibly in the form of a masterbatch, is added to this substrate using extruders, rolling mills, mixers or grinders. . The addition of the photosensitive compounds can also take place before the final polymerization or crosslinking in a mixture of monomers, prepolymers, saturated oligomers

  unsaturated and / or multifunctional monomers, possibly

  in the presence of polymerization initiators, such that these compounds are solidly incorporated in the matrix, chemically or physically, during the polymerization or crosslinking. The desired final form is then given to the obtained material by known methods, such as calendering, compression molding, transfer molding, coating,

  casting, extrusion molding or injection molding.

  When you want to make non-rigid molded objects or

  when we want to reduce their fragility, it is often

  It is desirable to incorporate substances known as "plasticizers" into the matrix material before molding. These substances include esters of phosphoric acid, phthalic acid or sebacic acid. Plasticizers may be incorporated into the polymers before or after

photosensitive compound.

  To make films (films)

  disperses finely or dissolves the materials

  kill the matrix and the photosensitive compound, optionally with other additives, in an organic solvent, or

  organic solvent mixture, common. We can then dis-

  Persist or dissolve the various components in isolation or by associating several, and then join together all the components. After that, the homogenized mixture is applied to a transparent substrate, then cooked or dried, using known methods, and the film obtained is then

  irradiated according to the invention.

  The dried film can also be

  brought, before the irradiation, onto another trans-

  parent or be attached between two support plates. If the material constituting the matrix is sufficiently solid

  it is also possible to directly apply trans-

  parents, which makes the transparent support plates superfluous. The glass or glass-ceramic which may constitute the recording material (matrix) may be chosen from glasses and glass-ceramics which are well known to those skilled in the art and which are described for example in Ullmann's work entitled " Enzyklopadie der techn Chemie ", 4th edition, volume 12, pages 320 to 323 and 361 to 364. Silicate glasses, two-component silicate glasses, borate, phosphate, borosilicate and aluminosolicates, and lead glasses. Glasses that have been manufactured at low temperature by the process

  sol-gel can also be used in the con-

form to the invention.

  The recording material which may be envisaged according to the invention may also be a frozen liquid, more specifically a material which is, for example

  liquid at room temperature but which, at a

  lower erase, is solid and transparent. In this case it is good to dissolve the photosensitive compound in the liquid in question, for example at room temperature,

  then cool the resulting solution in a suitable bowl.

  in a thin layer, below the freezing point of the liquid used, so as to obtain a solid recording material, for example in the form of

a thin film.

  Suitable suitable liquids include alcohols, such as ethanol, also glycols, glycerol, ethers, nalcanes, ketones, esters or amides, as well as mixtures of these liquids. The recording material to be used according to the invention may also be a mixture of the above-mentioned liquids, with each other, or with one or more of

  these liquids with one of the macromo-

  leculars that have been mentioned above.

  We very much appreciate the transparent materials

  amorphous annuities as recording materials to use

  in the process according to the invention.

  The subjects that we recommend all

  In particular, polyacrylates such as poly (methyl methacrylate) and poly (ethyl methacrylate) are especially suitable. poly (methyl acrylate) or poly (ethyl acrylate), poly (cyanacrylates), such as poly (methyl, ethyl and isobutyl) -decanacrylates, polyethylene,

  polypropylene, polystyrene, polyvinyl acetals.

  such as poly (vinyl butyral), poly (vinyl carbazoles)

or polyvinyl alcohols.

  The setting of the laser during recording and reading on a selected location of the recording material is carried out by methods known to those skilled in the art, for example by deflection by means of

  movable mirrors, mobile prisms or electro-

  optical, or by displacement of the recording material.

  The method according to the invention makes it possible to obtain the most diverse types of recording, for example signs, data, images, drawings

  bits as well as the most diverse information.

  The following description will make it easier to understand

  with the annexed drawing opposite, how the invention can be realized. Here is what can be seen in the various figures of this drawing: FIG. 1 diagrammatically represents a storage device that can be used according to the invention, with the means used for writing and reading

some information.

  Figure 2 is a perspective representation of the storage medium and electrode arrangement.

  Figure 3a shows how the absorp-

  tion of the material as a function of the intensity of the applied field, before this material is exposed to laser light. Figure 3b shows how the absorption of recording material varies with the intensity of the applied electric field after this material has been

  exposed, in a given electric field C, to a ray-

a fixed frequency.

  FIG. 3c shows how the absorption of the recording material varies as a function of the intensity of the electric field after it has been exposed, for two different intensities C and D of the electric field, to

  laser radiation having the same fixed frequency.

  Figure 3d shows how the holographic diffraction efficiency of the recording material varies with field strength after said

  subject matter has been submitted for two different field intensities

  C and D, to a holographic irradiation with the

same fixed laser frequency.

  When the information is recorded in the form of holograms, the diffraction efficiency of the created hologram in the recording material depends on the intensity of the field. Figure 3d shows the diffraction efficiency of two holograms that were recorded at field strengths C and D. The field strength maxima C and D represent the information stored by holography; this information stands out clearly, and

  with a good signal-to-noise ratio, from the zero line.

Z6073O7

  Figure 4 schematically represents a

  Recording apparatus usable according to the invention.

  Figure 1 schematically represents a

  optical storage device to which the

  electric field tensity. The optical apparatus for storing the information comprises a laser source which operates in a stable manner with one or more fixed frequencies and whose line or lines are narrow-banded with respect to the broadly expanded absorption band. not homocene. The intensity of the radiation emitted by the laser must be able to be adapted to the conditions of the memory material during the write operation and the read operation. When the laser 1 operates with more than one fixed frequency an optical filter serves to select the desired laser frequency. The laser beam 8 created is holographically structured by a suitable device 2. The devices used to deflect the laser beam in space are not shown and are of a conventional type. The memorizing medium 3 is in a

  electric field by applying an external voltage

  7 to a set of transparent electrodes 4 of con-

  appropriate ception. As the effect of the fixed frequency laser beam, the curing medium 3 undergoes a modification of its absorption, permanent or of a limited duration, which, under

  the effect of a variation of the intensity of the electric field.

  It is practically reduced to the value which it had before the irradiation, but which, when the electric field strength is restored, appears again, essentially, in the form originally recorded. The optical filter 5 and a detector assembly 6 are not used

  than during the course of the proceedings.

  FIG. 2 is a perspective view of the recording material (storage medium) in the form of a film to which an electric field is applied by two electrodes, and this figure shows the arrangement of the electrodes. The film has dimensions mm x 10 mm x 5 cm and is placed between two transparent glass plates 9, each of which carries an electrode to create the electric field. These glass plates serve as supports for the electrodes 4 which are optically transparent and which are electroconductive on the metallized inner face under vacuum. The concentration of photosensitive compound is chosen so that there is an optical density of about 1 at most of the inhomogeneously enlarged absorption band. For writing, a narrowband stabilized frequency dye laser is used whose frequency is in the range of inhomogeneous bandwidth. For an irradiation intensity which is, for example, 0.2 mW / cm 2, it is possible to reach, in the storage medium which is in a cryostat at the temperature of liquid helium, within a few seconds, absorption modifications. of the order of 0.3 optical density unit. The recording properties of the memorizing medium are many

  influenced by the choice of its operating temperature

  ment. The lower the temperature, the higher the memory capacity that can be achieved. In addition, the storage properties depend on the nature of the film (polymer). For example, chlorin in a poly (methyl methacrylate) film has a storage capacity about half as much as in a poly (vinyl butyral) film. The substances or centers which have a good storage power are furthermore indicated by the fact that the difference in the dipole moments and / or the polarizabilities between the ground state and the excited electronic state used

It is as big as possible.

  On the recording material, in accordance with the information to be memorized, each time is written at a fixed laser frequency, with a field intensity applied from the outside and varying in degrees, each of the recording and reading operations being carried out

  with constant field strength.

  When the fixed frequency laser light, the frequency of which is located in the non-homogeneously enlarged absorption band, holographically reaches the storage medium in the applied field, it creates a narrow spectral hole. Molecules or centers are then reached, which absorb, in this field of a given intensity, the frequency laser light.

  fixed. The selection of these molecules affected by the process

  of "fading" depends, among other things, on the intensity

  applied field. The change in behavior at the

  sorption, created in the recording material, may be permanent or limited in time. After having modified this electric field one can, according to the same principle,

  carry out other information recording

tions.

  An important property of the recording process

  accordance with the invention is that it allows

  memorize in the recording material several holograms

  grams with a fixed frequency laser in the outer field dimension. The number of holograms that can be recorded at a fixed wavelength depends on the dielectric strength of the material, which limits the possible recording range of the material. The terminals of this dielectric strength are represented by A and B on Figures 3a, 3b and 3c and they are of the order of +5 x 105 V / cm. The usable range for the intensity of the electric field is therefore from A to B. In addition, the variation of the intensity of the field which leads to a complete disappearance of the absorption variation is of paramount importance. When, for example, chlorine is used in a film of poly (vinyl butyral) at a temperature of

  liquid helium it is found that an interval of the inten-

  the electric field of about 2 x 104 V / cm is sufficient for

  the recording of a hologram. In the case of a film

  ca 50 m thick this corresponds to a variation of 100 V of the applied voltage. It is therefore possible to record, in the permissible range from A to B, information in the order of 50 holograms

for each laser frequency.

  By sending a light of appropriate frequencies

  When the absorption variation is in opposite directions, it is possible to call again the absorption modification created by the narrow-band laser light. To read the data we can use

  the recording apparatus shown in FIG.

the intensity of the narrow-band, fixed-frequency laser 1 is lowered by a factor greater than 100 with respect to the recording operation. The laser light 8 reaches the recording material in the electric field. The light that passes through is a measure of the change in absorption behavior that was produced during

  writing, that is to say during the registration operation.

  is lying; this light, after passing through the filter

  optics 5, whose role is to eliminate the para-

  site, is recorded in the detector according to the intensity of the electric field. Fig. 3a shows the absorption behavior of the storage medium (recording material) before it has been subjected to

  the recording operation by means of laser light.

  FIG. 3b shows the absorption behavior of the specimen at a fixed wavelength as a function of the intensity of the applied electric field, after said

  test piece was exposed to laser light under a

  electric field tensity C. Figure 3c shows the absorption behavior of the specimen at a fixed wavelength as a function of the intensity of the applied electric field, after this specimen has been exposed to the laser light under the electric field strengths C and D. The minimums at locations C in Figure 3b and

  places C and D in FIGS.

  memorized formations. Figure 3d shows the holographic yield. For the writing (recording, storage) and the reading it is also possible to use other apparatus than that of FIG. 1. It will be possible, for example, to do without

optical filter.

  The process according to the invention which has been heretofore exposed works with a fixed and single laser wavelength. But it is also possible, following the same principle, to write on the subject of recording, in

  same time or, better, successively, in accordance with the

  formations to memorize, with several wavelengths

  fixed lasers from one or more lasers.

  It is thus possible to combine several discrete laser frequencies (frequency multiplexing method), for example with the Stark effect so as to obtain, for each laser frequency, a further variation of the Stark voltage, a further increase in the quantity.

  information or a simpler recording of information

on the voltage.

  It is also possible to use several laser diodes

  semiconductor lasers each having another frequency

  quence, which record at the same location on the storage medium, each diode that can record at its frequency by variation of the field applied from the outside, for example of the voltage Stark, different information

(a different hologram).

  According to the invention, it is also possible to use recording materials consisting of a matrix containing a photosensitive compound according to the definition, which has at least one absorption band.

  in a non-homogeneous way, this matrix being con-

  polymer or wax which remain solid and chemically stable even at the temperature prevailing inside electronic devices, for example at a temperature of up to 60 C, without the information recorded at low temperature

- be erased.

  As a recording material one can

  also use a polymer matrix in which the

  photosensitive form meets the definition, which presents

  at least one absorption band widened in a non-homo-

  gene, is chemically bonded to the polymer matrix or is

  embedded in the polymer chain, such as, for example,

  thracene incorporated in polystyrene [see Vlauer, P. Remmp, L. Monnerie, Y. Yang, R.S. Stein, Polymer Communic.,

26 (1985), pp. 73-767.

  Finally, we can use as

  registration, matrices that contain a pho-

  compatible with the definition and in which the

  The lecules of this compound are geometrically oriented by appropriate preparation techniques. This result can be achieved for example by adsorption or chemical union to a smooth surface or a phase boundary, by adsorption or surface bonding of small plates which are introduced into the matrix by being arranged parallel to each other, by coating. according to the method of Langmuir-Blodgett (method described in No. 9 (1975) of "Chemie in unserer

  Zeit 'pages 173-182), by orientation of the photosensitive compound

  in a field (e.g. an electric field) applied from the outside during the preparation of the recording medium, or by mechanical stretching of the matrix containing the photosensitive compound distributed therein

homogeneously.

  By orienting the molecules parallel to themselves one can realize, under the action of the field applied from the outside, especially of the Stark effect, not only an enlargement of the spectral holes but also an effective spectral shift of the center.

of gravity of the band.

  The following examples illustrate the invention.

EXAMPLE 1

  An optical recording medium is prepared

  (see Figure 2) operating as follows.

  In 2 ml of methylene chloride (Merck, UVASOL) 0.37 mg of chlorine (i.e., 7,8-dihydro-porphyrin), prepared according to the indications of U. Eisner and RP Linsteadt, are dissolved. Journal of the Chemical Society 4 (1955), pages 3742-3749). In 10 ml of methylene chloride (Merck, UVASOL) 600 mg of poly (vinyl butyral) having a molecular weight of 38,000 to 45,000 are dissolved (Polyscience Inc., Warrington, Pennsylvania 18978, USA). The two solutions are thoroughly mixed in a 4 cm diameter crystallizer, and the mixture is allowed to stand at room temperature until the solvent has evaporated. In the colored plastic plate which remains at the bottom of the crystallizer, which plate is about 0.2 mm thick, a rectangular piece of 1 cm × 2 cm is cut out in its middle and fixed in the

following way.

  By assembling. with a side shift of about mm, two glass plates (10 x 24 x 1 mm) [(9), Figure 2j which each bear, on one of their faces, a film of tin dioxide, optically transparent and electroconductive, applied by vacuum vaporization,

  a sandwich material is manufactured such as the plastic material

  tick is in the middle and that each of the faces thereof is in contact with an electrode. The entire sandwich material is then bonded to OOC for 12 hours under pressure, the thickness of the plastic film being adjusted to 0.2 mm in the press by means of spacer gauges. The two electrodes [(4), FIG. 27 are

  equipped with contact wires [(7), Figure 27, and then

  The sandwich material is mounted on an insulating support.

  For optical recording and reproduction an apparatus is used which comprises the following main elements (see figure 4): - a cryostat bath (11) for liquid helium, equipped with two windows parallel to each other and connected to the vacuum so that one can work with helium under reduced pressure; a dye laser (la), excited by an ion laser

  argon (1) at 48 nm, with tuning and stabilizing unit

  Frequency range (line width: about 1 MHz, CR-599-21 model from Coherent, Palo ALto, CA 94304, USA), equipped with a DCM laser dye from Exciton, Overlook Station, Dayton, OH 45431, USA; a detection device which consists of a residual light amplifier (16) and a commercial video camera (17) with screen and recording apparatus

video (not shown).

  To record a hologram, a slide holder is mounted with the recording material in the cryostat (11) so that the recording material is placed between the windows and the cryostat is closed.

  hermetically and cooled to about 4 K per

  liquid helium production. Then we lower the

  temperature, an additional 2 K, extracting from the

  gaseous lium until its pressure is

1,000 Pa.

  The beam coming out of the dye laser (la) is adjusted to 635 nm and stabilized, it is weakened to a

  power of 1 gW, then it is expanded, by means of a teles-

  cope (12) of a magnification factor 15 and is separated, by means of a cubic separator (13) into two partial beams of the same power, namely the object beam (14) and the reference beam (15). By deflecting them with the aid of adjustable mirrors (S2 'S3, S4) the two

  partial beams in such a way that they are almost

  to the recording plate (10) in the cryostat (11) and which intersect on this plate, making an angle of 10 between them. The total beam can be interrupted by a first electrically actuated valve (18), which is placed between the telescope (12) and the beam splitter (13), and the object beam (14) can be interrupted by another flap ( 19) placed after the beam splitter. To record a first hologram, the laser beam is interrupted by applying to the electrodes (20) of the recording wafer (10).

  a voltage of -500 V from a voltage source (21), a first

  first image (one-slide (22) with black and white line drawing) in the object beam, then the two beams are released

  lasers by opening the valves (18) and (19) for 20 seconds.

  The voltage is then raised from 200 V to -300 V, a second image is placed in the object beam and irradiated again for 20 seconds. This operation is repeated at -100 V, +100 V and +300 V. To reproduce the various images on

  weakens at about 0.1 gW the laser beam of the same

  wave, but this time only the reference beam (15) is released. This is then diffracted on the recording plate (10) and it can, by opening the valve (25), through a lens (23) of 25 cm focal length. to form an image on the residual light amplifier (16). At the object focus of the lens the parasitic scattered light is stopped by a diaphragm (24) 1 mm in diameter. By applying the voltages used during the recording, ie the voltages going from -500 V to +300 V. one reproduces separately, with the choice, with the

  means of the video camera (17), the five recorded images.

  In the present Example 1 (chlorine in a poly (vinyl butyral) film) irradiation with wavelength light in the range of 625 to 640 nm produces the photochemical creation of holes. The chlorine molecule then undergoes, under the effect of light, a photochemical reaction generating a photoproduct which absorbs in the range of 560 to 580 nm. This photochemical reaction is reversible and the stored information can be erased very effectively by irradiation with light of wavelength in the spectral range from 560 to 580 nm or

  in another absorption band of the photoproduct. An efface

  Complete memorized information can also occur when the recording medium is warmed to room temperature.

EXAMPLE 2

  The operating mode and the apparatus are

  to those of Example 1, with this difference being

  sometimes used to prepare the recording material

  no longer chlorine but a solution of 0.35 mg of oxazine perchlorate 4 (laser grade, Eastman Kodak Company, Rochester, NY 14692, USA) in 2 ml of methylene chloride. For registration and reproduction

  the dye laser is set at 620 nm.

EXAMPLE 3

  The operating mode and the apparatus are

  to those of Example 1, however, to prepare the recording material. instead of chlorine, a solution of 0.35 mg of Cresyl Violet (laser grade, Eastman Kodak Company, Rochester, NY 14692, USA) in 2 ml of methylene chloride was used. For

  recording and for reproduction the color laser

rant is then set at 625 nm.

EXAMPLE 4

  A recording medium is prepared by operating as in Example 1 but using, instead of chlorine, 0.5 mg of phthalocyanine (Fluka, Switzerland). The recording (creation of holes) is performed at a laser wavelength of 690 nm, the imaoe being replaced in the

  test beam with an open diaphragm, and all the

  the signal being picked up with a photomultiplier

er.

EXAMPLE 5

  A linear low density polyethylene pellet (0.5 g), which is in a flat bowl, is

  heated on a hotplate to a temperature above

  than the glass transition point, in this case 180 C

  A solution consisting of 0.35 mg is added dropwise

  chlorine (prepared according to Example 1) and 2 ml of

  chloromethane, at the same time that the polyethylene is stirred with a spatula to disperse the chlorine in the soft pellet. The polyethylene obtained is hot-molded using a spatula to form a flat disc (0.5 mm thick), then cooled rapidly.

  at room temperature. In this disc we cut a mortar

  which is fixed between two electro-

  as in Example 1. The recordings were

  The procedure is as in Example 1 at a laser wavelength of 635 nm, and the image is replaced, in the

  test beam, by an open diaphragm.

EXAMPLE 6

  A polystyrene pellet (type 144C013, BASF) (0.5 g), which is in a flat bowl, is heated, on a hot plate, to a temperature above the glass transition point, in this case at 190 ° C. A solution consisting of 0.35 mg is added dropwise

  chlorine (according to Example 1) and 2 ml of dichloro-

  methane, at the same time that the polystyrene is kneaded with a spatula to disperse the dye in the soft pellet. The polymer is then molded hot by means of the spatula to form a flat disk 0.5 mm thick and then cooled to room temperature. In this disc is cut a piece, which is fixed, as has been described in Example 1, between two electroconductive glass plates. The recording (creation of holes) is carried out according to Example 1 at a laser wavelength of 635 nm, the image in the test beam is replaced by a simple diaphragm, and any

  the intensity of the signal is captured by means of a photomulti

plicator.

EXAMPLE 7

  A silicate glass sample is made by the sol-gel process from a solution of 0.6 g of oxazine-4 perchlorate (Kodak, Rochester, NY 14692) in 10 ml of tetraethoxysilane (Fluka, Switzerland). ), 3, 7 ml

  of distilled water, 11.4 ml of ethanol and 0.1 ml of chloroacid

  Hydrogen (monomolaire). 2.5 ml of this solution is then poured into a cylindrical glass dish (2 cm in diameter), then this well is enclosed with a wide beaker used as a glass bell in such a way that

  the solvents evaporate slowly at room temperature

  ature. After 4 weeks, the mixture is solid: the pellet obtained is then removed from the cuvette.

  glass and keep it for another 2 months at

  ambient temperature. We sand and polish the pellet thus obtained to bring it to an optical standard, then place

  in the cryostat the specimen resulting from this treatment.

  The recording is performed as in Example 1 but without electrodes fixed on the test piece. The recording and reproduction of the information can thus be performed under zero voltage, the laser being adjusted

at 620 nm.

EXAMPLE 8

  The recording medium, the apparatus and the procedure are similar to those of Example 2, but two independent series of five images are recorded, one at a laser wavelength of 619 nm, the others with laser at a wavelength greater than 0.02 nm. Thus, at a radiation location, a total of 10 different images are stored. The reproduction (reproduction) of each of the 10 stored images is performed at the corresponding Stark voltage and wavelength.

  were used for registration.

Claims (16)

  1. Method for recording and playback   optical information in a recording   which contains at least one photosensitive compound   both in the ultra violet and / or the visible and / or infrared   red, at least one non-homogeneously enlarged absorption band composed, which under the action of a narrow-band laser light and having at least one frequency located in said absorption band and under the action of an externally adjustable electrostatic, magnetic or pressure field undergoes a change in its absorption behavior, while other changes in the absorption behavior can be caused by adjustment to other values of the intensity of the electrostatic, magnetic or pressure field and, thus, additional information   may be registered, these changes may   read again during the re-establishment of   field of registration at the time of registration,   in that the information is recorded and read in the form of holograms.   2. Method according to claim 1,   terized in that one uses, as an adjustable field of the ex-   interior, an electrostatic field.   3. Process according to claim 1,   characterized in that the recording material is a macromolecular organic material of natural or artificial origin, glass, glass-ceramic or a frozen liquid.   4. Process according to claim 3,   in that the recording material is a material transparent amorphous. 2 7   5. Process according to claim 3,   in that the macromolecular organic matter   is a polyacrylate, a poly (cyanacrylate), polyethylene   lene, polypropylene, polystyrene, a poly- (vinyl-   acetal), poly (vinylcarbazole) or poly (vinyl alcohol).   6. Process according to claim 1,   characterized in that the photosensitive compound undergoes, during the photophysical or photochemical creation operation of holes, a modification affecting the absorption profile of the non-homogeneously enlarged band affected by the laser frequency.   7. Process according to claim 1,   in that the photosensitive compound absorbs   the ultraviolet and / or the visible and / or the near infra-red.   8. Process according to claim 7,   in that the photosensitive compound absorbs   the visible and / or near infra-red.   9. Process according to claim 6,   characterized in that the photosensitive compound is a derivative of porphine, a porphyrazine, quinizarin, a C-diketone, an oxazine, a tetrazine, a spiropyran,   an iso-imidazole, an azirine or a laser dye.   10. The process according to claim 1   in that the photosensitive compound is present in an amount of from 0.001 to 30% by weight with respect to   recording material (matrix).   11. A method according to claim 1   characterized in that the recording material is in the form of a film, to which an electric field can   be applied by two electrodes.   12. Process according to claim 11,   in that the film is placed between two transparent glass plates, each of which has an electrode for create the electric field.   13. Method according to claim 1, characterized in that the recording material is written in accordance with the information to be memorized, each time with a fixed laser frequency, under a field, applied from the outside, of which the intensity varies by degrees, the recording operation and the reading operation being performed   each time under a constant intensity of the field.   14. Process according to claim 1,   in that we can recall the change of absorp-   created by narrow-band laser light, irra-   with a light of frequencies appropriate to the   places of opposite absorption modification.   15. Process according to claim 1,   characterized in that written on the recording material, in accordance with the information to be memorized, simultaneously or successively, with several laser wavelengths   fixed, which come from one or more lasers.   16. Process according to claim 15,   terized in that one writes successively on the matter of recording.