EP1166188A1

EP1166188A1 - Holographic recording material

Info

Publication number: EP1166188A1
Application number: EP00912500A
Authority: EP
Inventors: Horst Berneth; Thomas Bieringer; Johannes Eickmans; Rainer Hagen; Serguei Kostromine
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1999-03-08
Filing date: 2000-02-23
Publication date: 2002-01-02
Also published as: JP2002539475A; DE19910248A1; WO2000054111A1; KR20010103044A; AU3424700A; CA2365934A1

Abstract

The invention relates to novel holographic recording materials for use in the area of photoadressable polymers.

Description

Holographic recording material

The present invention relates to a recording material for a holographic volume memory, its production and use for the recording of volume holograms.

Holography is a process in which objects can be imaged in suitable storage materials by the interference of two coherent light beams (signal wave and reference wave) and these images can be read out again with light (reading beam) (D. Gabor, Nature 151, 454 (1948), NH Farath, Advances in

Holography, Vol. 3, Marcel Decker (1977), H. M. Smith, Holography Recording Materials, Springer (1977)). By changing the angle between the signal and reference wave on the one hand and the holographic storage material on the other hand, numerous holograms can be written into the material at one and the same sample position and finally read out again individually. As coherent

The light source is usually the light of a laser. Various materials are described as storage material, e.g. B. inorganic crystals such as LiNb0 ₃ (z. B.), organic polymers (z. BM Eich, JH Wendorff, Makromol. Chem., Rapid Commun. 8, 467 (1987), JH Wendorff, M. Eich, Mol. Cryst Liq. Cryst. 169, 133 (1989)) or photopolymers (Uh-Sock Rhee et al., Applied Optics, 34 (5), 846

(1995)).

However, these materials do not yet meet all the requirements of a holographic recording medium. In particular, they do not have sufficient stabilities of the inscribed hologram. A multiple description is generally only possible to a limited extent, since when a new hologram is written in, the hologram already written in is overwritten and thus deleted. This applies in particular to inorganic crystals that are subjected to extensive temperature treatment in order to compensate for these stability problems. On the other hand, photopolymers show the problem of shrinkage, which the holographic ones

Image properties adversely affected. Materials with high stability of the registered holograms are also known, e.g. B. from EP-A 0 704 513 and the as yet unpublished German application DE-A-19703132.

However, the high optical density of these materials does not allow the production of holographic volume memories, as are required for storing numerous holograms in a storage material.

Accordingly, there was a need for a material that is suitable for the production of sufficiently thick holographic volume memories and that enables the long-term stable storage of numerous holograms at a sample position of the storage material. With previous materials, storing numerous holograms in succession at one position led to the successive deletion of the holographically stored information: later written

Holograms addressed the same molecules that contributed to the construction of previously written holograms, so that the information from earlier holograms was lost after only a few more writing processes.

The invention accordingly relates to a recording material for a holographic volume memory, containing at least one dye which changes its spatial arrangement when a hologram is written in, and optionally at least one shape-anisotropic grouping, characterized in that it allows two or more holograms to be recorded at a sample position.

This is preferably done in that the at least one dye changes its spatial arrangement so that it can no longer be excited by the electromagnetic radiation or changes its absorption behavior, in particular reduces its sensitivity to actinic light, preferably between 10% and

100%, particularly preferably between 50% and 100%) and very particularly preferred reduced between 90 and 100%, each based on the sensitivity before writing the first hologram.

The dye can also reduce its absorption behavior, in particular its sensitivity to actinic light, by folding it in the direction perpendicular to the polarization direction of the actinic light and its longitudinal molecular axis making an angle between 10 ° and 90 °, preferably between, with the polarization direction of the actinic light 50 ° and 90 ° is particularly preferably between 75 ° and 90 ° and very particularly preferably between 85 ° and 90 °.

In this way it can be realized that writing several holograms at a sample position is successfully carried out, i.e. that the information of the early holograms is not completely erased.

This change in the excitation behavior with regard to electromagnetic radiation when writing in the hologram can be achieved in that the dye changes its spatial arrangement in the polymeric or oligomeric organic, amorphous material.

Materials of this type can be used to prevent the holograms previously written into this material from being unacceptably reduced, completely damaged or even completely overwritten when a hologram is written.

From an measurement point of view, an unacceptable weakening means that the remaining information can no longer be resolved in relation to the background noise.

The information is stored holographically. For this purpose, two polarized, coherent beams are brought to interference on the sample. By exposure to this actinic light, the dyes change their spatial position in the polymeric or oligomeric layers. Dyes that align their molecular longitudinal axis in the plane that are spanned by the two writing beams (plane of incidence) during exposure are from this

Light can no longer be excited if the polarization of the light is perpendicular to the plane of incidence. The information (hologram) written into these dyes during this writing process is secured against change when a next hologram is written. Dyes that do not come to rest completely perpendicular to the polarization direction of the light, but with it

The direction of polarization forming an angle Θ not equal to 90 ° is addressed further in the case of further hologram exposures. The likelihood of a reorientation of these dyes and in particular the sensitivity of the dyes to light decreases the closer the angle of the molecule's longitudinal axis comes to the 90 ° position.

The molecular longitudinal axis can be determined, for example, on the basis of the molecular shape by molecular modeling (eg CERIUS ² ).

The reorientation of the dyes after exposure to actinic light results, for example, from investigations into polarized absorption spectroscopy: A sample previously exposed to actinic light is placed between 2 polarizers in a UV / VIS spectrometer (e.g. CARY 4G, UV / VIS spectrometer) examined in the spectral range of absorption of the dyes. When the sample is rotated around the sample normal and a suitable polarizer position, for example in the crossed state, the reorientation of the dyes follows from the intensity profile of the extinction as a function of the sample angle and can thus be clearly determined. There are various multiplexing methods for writing several holograms, such as angle multiplexing, wavelength multiplexing, phase multiplexing, shift multiplexing, peristrophic multiplexing and others.

A measure of the sensitivity to actinic light is holographic

Sensitivity. It is calculated, for example, from the holographic growth curve, i.e. the development of the diffraction efficiency (= diffracted intensity based on the incident intensity of the reading laser) as a function of the energy deposited by the writing beams. The sensitivity is defined as the slope of the root of the diffraction efficiency according to the deposited energy, normalized to the thickness of the storage medium.

The invention relates to a recording material for a holographic volume memory that has an optical density <2, preferably <1, particularly preferably <0.3 at the wavelength of the writing laser. In this way it can be ensured that the actinic light leads to homogeneous illumination of the entire storage medium and a thick hologram can be generated. The optical density can be determined with commercial UV / VIS spectrometers (e.g. company CARY 4G, UV - VIS spectrometer).

In particular, the recording material according to the invention is a material which has an irradiated thickness of> 0.1 mm, particularly 0.5 mm, preferably> 1 mm and very particularly preferably not greater than 5 cm.

The grouping that interacts with the electromagnetic radiation is a dye. The material according to the invention consequently contains at least one dye. The electromagnetic radiation is preferably laser light, preferably in the wavelength range between 390 to 800 nm, particularly preferably in the range 400 to 650 nm, very particularly preferably in the range from 510 to 570 nm. For reading, the recording material is no longer exposed to two interfering beams as in writing, but only one beam, the reading beam. The wavelength of the reading beam is preferably longer than that of the signal and reference waves, for example 70 to 500 nm longer. However, reading with the wavelength of the writing laser is also possible and will be used in particular in the commercial use of holographic volume memories. For this purpose, the energy of the reading beam is reduced during the reading process either by reducing the exposure intensity or the exposure time, or by reducing the exposure intensity and the exposure time.

The optical density of the recording material according to the invention is set by the following two parameters

a) via the molar extinction coefficient of the at least one dye and / or b) via the concentration of the at least one dye in the polymeric or oligomeric organic material.

Dyes with low extinction coefficients are, for example, dyes with a non-polar and / or less polarizable structure. Such dyes can, for example, come from the classes of anthraquinone, stilbene, azastilbene, azo or methine dyes. Azo dyes are preferred. Azo dyes with an absorption maximum of the ππ * band which is less than or equal to 400 nm, very particularly preferably less than 400 nm, are particularly preferred.

For example, azo dyes have the following structure of formula (I) wherein

X ¹ and X ^{2 are the} same or similar,

R ^! and R ^{2 are} independently hydrogen or a nonionic substituent and

m and n independently of one another represent an integer from 0 to 4, preferably 0 to 2.

The equality or similarity of X ¹ and X ² lies in the fact that both are bound via atomic types or atomic groupings, which are either identical or of a similar electronic structure.

The Hammett constants, for example, can be used as a measure of the similarity of the electronic structure of the atom types or groups.

X ¹ and X ^{2 are} preferably -X ^r -R ³ or X ^{2 '} -R ⁴ ,

wherein

X ^{1 '} and X ^2' for a direct bond, -O-, -S-, - (NR ⁵ ) -, -C (R ⁶ R ⁷ ) -, - (C = O) -, - (CO- O ) -, - (CO-NR ⁵ ) -, - (S0 ₂ ) -, - (S0 ₂ -0) -, - (S0 ₂ -NR ⁵ ) -, - (C = NR ⁸ ) - or -

(CNR ⁸ -NR ⁵ ) - stand, R ³ , R ⁴ , R ⁵ and R ⁸ independently of one another for hydrogen, C, - to C ₂₀ alkyl, C ₃ - bis

C ₁₀ cycloalkyl, C ₂ to C ₂₀ alkenyl, C ₆ to C ₁₀ aryl, C _r to C ₂₀

Alkyl- (C = O) -, C ₃ - to C ₁₀ -cycloalkyl- (C = O) -, C ₂ - to C ₂₀ -alkenyl-

(C = O) -, C ₆ - to C ₁₀ -aryl- (C = O) -, C, - to C ₂₀ -alkyl- (SO ₂ ) -, C ₃ - to C, ₀ - cycloalkyl- (SO ₂ ), C ₂ to C ₂₀ alkenyl (SO ₂ ) or C ₆ to C ₁₀ aryl

(SO ₂ ) - stand or

X ^r -R ³ and X ^{2 '} -R ^{4 can represent} hydrogen, halogen, cyan, nitro, CF ₃ or CC1 ₃ ,

R ⁶ and R ⁷ independently of one another for hydrogen, halogen, C, - to C ₂₀ -alkyl, C, - to C ₂₀ -alkoxy, C ₃ - to C ₁₀ -cycloalkyl, C ₂ - to C ₂₀ -alkenyl or

C ₆ - to C _{] 0} aryl.

Nonionic substituents are to be understood as halogen, cyano, nitro, C 1 -C ₂₀ -alkyl, C 1 -C ₂₀ alkoxy, phenoxy, C ₃ -C ₁₀ cycloalkyl, C ₂ -C ₂₀ alkenyl or C ₆ - to C ₁₀ -aryl, C, - to C ₂₀ -alkyl- (C = O) -, C ₆ - to C _I0 -aryl- (C = O) -, C, - to C ₂₀ -

Alkyl- (SO ₂ ) -, C _r to C ₂₀ -alkyl- (C = O) -O-, C _r to C ₂₀ -alkyl- (C = O) -NH-, C ₆ - to C, ₀ - Aryl- (C = 0) -NH-, C _r to C ₂₀ -alkyl-O- (C = O) -, C to C ₂₀ -alkyl-NH- (C = O) - or C ₆ - to C ₁₀ -Aryl-NH- (C = O) -.

The alkyl, cycloalkyl, alkenyl and aryl radicals can in turn be replaced by up to 3

Residues from the series halogen, cyano, nitro, C, - to C ₂₀ -alkyl, C, - to C ₂₀ -alkoxy, C ₃ - to C ₁₀ -cycloalkyl, C ₂ - to C ₂₀ -alkenyl or C ₆ - bis C ₁₀ aryl can be substituted and the alkyl and alkenyl radicals can be straight-chain or branched.

Halogen is to be understood as fluorine, chlorine, bromine and iodine, in particular fluorine and

Chlorine.

The recording material according to the invention is preferably polymeric or oligomeric organic, amorphous material, particularly preferably a side chain polymer, likewise particularly preferably a block copolymer and / or a graft polymer. The main chains of the side chain polymer come from the following basic structures: polyacrylate, polymer methacrylate, polysiloxane, polyurea, polyurethane, polyester or cellulose. Polyacrylate and polymethacrylate are preferred.

The block copolymers consist of several blocks, at least one of which contains the copolymer systems described above. The other blocks consist of unfunctionalized polymer scaffolds, which serve the purpose of thinning the functional block in order to set the required optical density. The extension of the functional block is below the light wavelength, preferably in the range of less than 200 nm, particularly preferably less than 100 nm.

The block copolymers are polymerized, for example, via free-radical or anionic polymerization or via other suitable polymerization processes, possibly followed by a polymer-analogous reaction or by

Combination of these methods. The uniformity of the systems is in a range less than 2.0, preferably less than 1.5. The molecular weight of the block copolymers obtained by radical polymerization reaches values in the range of 50,000, values greater than 100,000 can be set by anionic polymerization.

The dyes, in particular the azo dyes of the formula (I), are covalently bound to these polymer skeletons, generally via a spacer. For example, X ¹ (or X ² ) then stands for such a spacer, in particular with the meaning X ¹ - (Q '-T'-S ¹ -,

in which

X ^{1 has} the meaning given above, Q ¹ for -O-, -S-, - (NR ⁵ ) -, -C (R ⁶ R ⁷ ) -, - (C = O) -, - (CO-O) -, - (CO-NR ⁵ ) -, -

(SO ₂ ) -, - (SO ₂ -0) -, - (S0 ₂ -NR ⁵ ) -, - (C = NR ⁸ ) -, - (CNR ⁸ -NR ⁵ ) -, - (CH ₂ ) _p -, p- or mC ₆ H ₄ - or a double-bonded radical of the formulas

stands,

i stands for an integer from 0 to 4, where for i> 1 the individual Q ^{1 can have} different meanings,

T ^{1 stands} for - (CH ₂ ) _p -, where the chain can be interrupted by -O-, -NR ⁹ -, or -OSiR ^{, 0} ₂ O-,

S ^{1 stands} for a direct bond, -O-, -S- or -NR ⁹ -,

p represents an integer from 2 to 12, preferably 2 to 8, in particular 2 to 4,

R ^{9 represents} hydrogen, methyl, ethyl or propyl,

R '° represents methyl or ethyl and

R ^D to R ^{8 have} the meaning given above.

Preferred dye monomers for polyacrylates or methacrylates then have the formula (II) wherein

R represents hydrogen or methyl and

the other radicals have the meaning given above.

Particularly preferred monomers of the formula (II) are, for example:

The polymeric or oligomeric organic, amorphous material according to the invention can carry formanisotropic groups in addition to the dyes, for example of the formula (I). These are also covalently bonded to the polymer frameworks, usually via a spacer.

Shape anisotropic groupings have, for example, the structure of the formula (III)

where Z represents a remainder of the formulas

(Illb) says what

A represents O, S or NC, to C ₄ alkyl,

X ^{3 stands} for -X ^{3 '} - (Q ² ) _j -T ² -S ² -,

X ^{4 stands} for X ^{4 '} -R ¹³ ,

X ^{3 '} and X ^4' independently of one another for a direct bond, -O-, -S-, - (NR ⁵ ) -, - C (R ⁶ R ⁷ ) -, - (C = O) -, - (CO -O) -, - (CO-NR ⁵ ) -, - (SO,) -, - (S0 ₂ -O) -, - (SO ₂ - NR ⁵ ) -, - (C-NR ⁸ ) - or - (CNR ⁸ -NR ⁵ ) - stand,

R ⁵ , R ⁸ and R ¹³ independently of one another for hydrogen, C, - to C ₂₀ alkyl, C ₃ - bis

C ₁₀ cycloalkyl, C ₂ to C ₂₀ alkenyl, C ₆ to C ₁₀ aryl, C _r to C ₂₀ alkyl (C = O), C ₃ to C _I0 cycloalkyl (C = O) -, C ₂ - to C ₂₀ -alkenyl- (C = 0) -, C ₆ - to C _I0 -aryl- (C = O) -, C, - to C ₂₀ -alkyl- (SO ₂ ) - , C ₃ - to C ₁₀ - Cycloalkyl- (S0 ₂ ) -, C ₂ - to C ₂₀ -Alkenyl- (SO ₂ ) - or C ₆ - to C, ₀ -Aryl- (SO ₂ ) - or

X ⁴ -R ¹³ can stand for hydrogen, halogen, cyan, nitro, CF ₃ or CC1 ₃ ,

R ⁶ and R ⁷ independently of one another are hydrogen, halogen, C, - to C ₂₀ -alkyl, C, - to C ₂₀ -alkoxy, C ₃ - to C ₁₀ -cycloalkyl, C ₂ - to C ₂₀ -alkenyl or - to C, ₀ aryl stand,

Y for a simple bond, -COO-, OCO-, -CONH-, -NHCO-,

-CON (CH ₃ ) -, -N (CH ₃ ) CO-, -O-, -NH- or -N (CH ₃ ) -, R ", R ^12, ^R:> are independently hydrogen, halogen, cyano, nitro, C, - to C ₂₀ - alkyl, C, - to C ₂₀ alkoxy, phenoxy, C ₃ - to C ₁₀ cycloalkyl,

C ₂ - to C ₂₀ -alkenyl or C ₆ - to C, ₀ aryl, C, - to C ₂₀ -alkyl- (C = O) -, C ₆ - to C ₁₀ -aryl- (C = O) - , C, - to C ₂₀ -alkyl- (SO ₂ ) -, C, - to C ₂₀ -alkyl-

(C = O) -O-, C, - to C ₂₀ -alkyl- (C = O) -NH-, C ₆ - to C ₁₀ -aryl- (C = O) -NH-, C, - to C ₂₀ -alkyl-O- (C = O) -, C, - to C ₂₀ -alkyl-NH- (C = O) - or - to C ₁₀ -aryl-NH- (C = O) -,

q, r and s independently of one another represent an integer from 0 to 4, preferably 0 to 2,

Q ² for -O-, -S-, - (NR ⁵ ) -, -C (R ⁶ R ⁷ ) -, - (C = O) -, - (CO-O) -, - (CO-NR ⁵ ) -,

- (SO ₂ ) -, - (SO ₂ -O) -, - (SO ₂ -NR ⁵ ) -, - (C = NR ⁸ ) -, - (CNR ⁸ -NR ⁵ ) -, - (CH ₂ ) _p -, p- or mC ₆ H ₄ - or a double-bonded radical of the formulas

stands,

j represents an integer from 0 to 4, where the individual Q 'may have different meanings for j> 1,

T ^{2 stands} for - (CH ₂ ) _p -, where the chain can be interrupted by -O-, -NR ⁹ -, or -OSiR ¹⁰ ₂ O-,

S ^{2 stands} for a direct bond, -O-, -S- or -NR ⁹ -,

p represents an integer from 2 to 12, preferably 2 to 8, in particular 2 to 4, R ^{9 represents} hydrogen, methyl, ethyl or propyl and

R ^{10 represents} methyl or ethyl.

Preferred monomers with such shape-anisotropic groupings for polyacrylates or methacrylates then have the formula (IV)

wherein

R represents hydrogen or methyl and

the other radicals have the meaning given above.

Particularly preferred shape-anisotropic monomers of the formula (IV) are, for example:

The alkyl, cycloalkyl, alkenyl and aryl radicals can in turn be substituted by up to 3 radicals from the series halogen, cyano, nitro, C 1 -C ₂₀ -alkyl, C 1 -C ₂₀ alkoxy, C ₃ -C ₁₀ -cycloalkyl, C ₂ - to C ₂₀ -alkenyl or C ₆ - to C ₁₀ -aryl can be substituted and the alkyl and alkenyl radicals can be straight-chain or branched.

Halogen is to be understood as meaning fluorine, chlorine, bromine and iodine, in particular fluorine and chlorine.

In addition to these functional building blocks, the oligomers or polymers according to the invention can also contain building blocks which are used primarily to lower the percentage of functional building blocks, in particular dye building blocks. In addition to this task, they can also be responsible for other properties of the oligomers or polymers, e.g. B. the glass transition temperature,

Liquid crystallinity, film-forming property, etc.

For polyacrylates or methacrylates, such monomers are acrylic or methacrylic acid esters of the formula (V)

wherein R represents hydrogen or methyl and

R ^{14 represents} optionally branched C 1 -C ₂₀ -alkyl or a radical containing at least one further acrylic unit.

Polyacrylates and polymethacrylates according to the invention then preferably contain, as repeating units, those of the formulas (VI), preferably those of the formulas (VI) and (VII) or of the formulas (VI) and (VIII) or of the formulas (VI), (VII) and (VIII)

wherein the radicals have the meanings given above.

Several of the repeating units of the formula (VI) and / or of the repeating units of the formulas (VII) and / or (VIII) can also be present.

The quantitative ratio between VI, VII and VIII is arbitrary. The concentration of VI is, depending on the absorption coefficient of VI, between 0.1 and

100%) based on the respective mixture. The relationship between VI and VII is between 100: 0 and 1:99, preferably between 100: 0 and 30:70, very particularly preferably between 100: 0 and 50:50.

The dyes of the formula (I) or the dye monomers of the formula (II) have a short-wave main absorption band (π-π * band) and a longer-wave secondary absorption band (n-π * band). The molar extinction coefficient ε of this n-π * band is in the range 400 to 5,000 * 10 ³ cm ² / mol. With an assumed dye molecular weight of 400 g / mol, oligomers or polymers with an irradiated thickness of 0.1 mm have an optical density <2 if they are <1.6% (for ε = 5,000) to <20% (for ε = 400) on such dyes.

The polymers and oligomers according to the invention preferably have glass transition temperatures T _g of at least 40 ° C. The glass transition temperature can be determined, for example, according to B. Vollmer, Grundriß der Makromolekularen Chemie, pp. 406-410, Springer-Verlag, Heidelberg 1962.

The polymers and oligomers according to the invention have a weight average molecular weight of 5,000 to 2,000,000, preferably 8,000 to 1,500,000, determined by gel permeation chromatography (calibrated with polystyrene).

Graft polymers are prepared by free radical attachment of dye monomers of the formula (II) and, if appropriate, additionally of formanisotropic monomers of the formula (IV) and / or if appropriate additionally of monomers of the formula (V) to oligomeric or polymeric basic systems. Such basic systems can be a wide variety of polymers, e.g. B. polystyrene, poly (meth) acrylates,

Starch, cellulose, peptides. The radical attachment can follow by irradiation with light or by using radical generating reagents, e.g. B. tert-butyl hydroperoxide, dibenzoyl peroxide, azodisobutyronitrile, hydrogen peroxide / iron (II) salts. The intermolecular interactions of the structural elements of the formulas (VI) with one another or between the formulas (VI) and (VII) with one another are adjusted by the structure of the polymers and oligomers in such a way that the formation of liquid-crystalline order states is suppressed and optically isotropic, transparent non-scattering films, foils, Slabs or cuboids can be made. On the other hand, the intermolecular interactions are still strong enough to cause a photochemically induced, cooperative, directed reorientation process of the photochromic and the non-photochromic side groups when irradiated with light.

Preferably, interaction forces occur between the side groups of the repeating units of the formula (VI) or between those of the formulas (VI) and (VII), which are sufficient for the photo-induced configuration change of the side groups of the formula (VI) to produce a so-called cooperative Realignment of the other side groups ((VI) and / or (VII)) causes.

Extremely high values of optical anisotropy can be induced in the optically isotropic amorphous photochromic polymers (Δn to 0.4).

Due to the influence of actinic light in the polymers or oligomers

Order states are generated and modified, thus modulating the optical properties.

Polarized light is used as the light, the wavelength of which lies in the region of the absorption band, preferably in the region of the long-wave n-π * band of the repeating units of the formula (VI).

The polymers and oligomers can be prepared by methods known from the literature, for example according to DD 276 297, DE-A 3 808 430, Macromolecular Chemistry 187, 1327-1334 (1984), SU 887 574, Europ. Polym. 18,

561 (1982) and Liq. Cryst. 2, 195 (1987). Films, foils, plates and cuboids can be produced without the need for complex orientation processes using external fields and / or surface effects. They can be opened up by spin coating, dipping, pouring or other technologically easily controllable coating processes

Apply the underlay, put it between two transparent plates by pressing or flowing it in, or simply prepare it as a self-supporting material by pouring or extruding. Such films, foils, plates and cuboids can be abruptly cooled, i. H. by a cooling rate of> 100 K / min, or by rapid removal of the solvent also from liquid-crystalline polymers or oligomers which contain structural elements as described.

Preferred is a manufacturing process of the holographic volume storage in which a step by a conventional injection molding process is included in the range up to 300 ° C, preferably up to 220 ° C, particularly preferably 180 ° C.

The layer thickness is> 0.1 mm, preferably> 0.5 mm, particularly preferably> 1 mm. A particularly preferred preparation process for layers in the millimeter range is the injection molding process. Here, the polymer melt is pressed through a nozzle into a shaping holder, from which it can be removed after cooling.

A preferred method of producing the recording material or the polymer according to the invention comprises a process in which at least one monomer is polymerized without a further solvent, preferably free-radically polymerizing, and particularly preferably initiated by free-radical initiators and / or UV light and / or thermally .

The process is carried out at temperatures between 20 ° C. and 200 ° C., preferably between 40 ° C. and 150 ° C., particularly preferably 50 ° C. and 100 ° C. and very particularly preferably around 60 ° C. In a particular embodiment, AIBN is used as the radical starter.

It has often proven to be advantageous to use a further, preferably liquid, monomer. At the reaction temperatures, this means liquid monomers which are preferably olefinically unsaturated monomers, particularly preferably based on acrylic acid and methacrylic acid, very particularly preferably methyl methacrylate.

The proportion of the monomers of the formula (II) in the copolymers is preferably 0.1 to 99.9% by weight, particularly preferably 0.1 to 50% by weight, very particularly preferably 0.1 to 5% by weight. %> and in the best case 0.5 to 2 wt .-% o.

The method of holographic data storage is, for example, in LASER

FOCUS WORLD, NOVEMBER 1996, page 81 ff.

When writing a hologram, the polymer films described above are irradiated by two coherent laser beams of a wavelength which causes the required light-induced reorientations. One beam, the object beam, contains the optical information to be stored, for example the intensity curve, which results from the passage of a light beam through a two-dimensional, checkerboard-like pixel structure (data page). In principle, however, light that is diffracted, scattered, or reflected by any two or three-dimensional objects can be used as an object beam. The object beam is brought to interference on the storage medium with the second laser beam, the reference beam, which is generally a flat or circular wave. The resulting interference pattern is memorized in the storage medium as a modulation of the optical constants (refractive index and / or absorption coefficient). This modulation penetrates the entire irradiated area, in particular the thickness of the

Storage medium. If the object beam is now blocked and the medium only with exposed to the reference beam, the modulated storage medium acts as a kind of diffraction grating for the reference beam. The intensity distribution resulting from the diffraction corresponds to the intensity distribution which started from the object to be stored, so that it can no longer be distinguished whether the light comes from the object itself or whether it results from the diffraction of the reference beam.

Different multiplexing methods are used to store different holograms at a sample position: wavelength division multiplexing, shift multiplexing, phase multiplexing, peristrophic multiplexing and / or angle multiplexing and / or others. Angle multiplexing changes the angle between the storage medium in which a hologram was saved at the current angles and the reference beam. After a certain change in angle, the original hologram (Bragg-Mismatch) disappears: the incident reference beam can no longer be transferred from the storage medium to the reconstruction of the

Object to be distracted. The angle from which this occurs depends crucially on the thickness of the storage medium (and on the modulation of the optical constants generated in the medium): the thicker the medium, the smaller the angle by which the reference steel has to be changed.

Another hologram can be written in this new angular configuration. Reading out this hologram works again exactly in the angular configuration between storage medium and reference beam in which it was also written.

By successively changing the angle between the medium and the writing beams, several holograms can thus be written into the same location on the storage medium.

The polymer systems described in this patent now have the great advantage that when writing a subsequent hologram, those in the storage medium deposited information of the previous holograms is not deleted and that more than 5 holograms, preferably more than 50, particularly preferably more than 100, very particularly preferably more than 500 and extremely preferably more than 1000 holograms can be written at one location on the storage medium. The objects to be stored are data pages that are transmitted by a

Liquid crystal displays are generated. These data pages have 256 x 256 pixels, preferably 512 x 512 pixels, particularly preferably 1024 x 1024 data pixels.

Another object of the invention is a recording material for a holographic volume storage consisting of a polymeric or oligomeric organic, amorphous material which contains at least one group which interacts with electromagnetic radiation and optionally at least one shape-anisotropic grouping, characterized in that it has an optical density < 2, preferably <1, very particularly preferably <0.3. The recording material can be a self-supporting film, or preferably in one

Multi-layer structure can be used for data storage. This multilayer structure is, for example, a sandwich in which the actual recording medium is surrounded by at least one substrate. The substrate can be transparent media with high optical quality, for example glass plates, quartz plates or plates made of polycarbonate.

High optical quality is understood to mean that the scattering efficiency, ie the quotient between light scattered on this sandwich and the incident light, is not less than 10 ^"4 , preferably not less than 10 °, very particularly preferably not less than 10 ^{" 6} . To determine this quotient, the sample can be exposed to the beam of a HeNe laser. The detection takes place via a CCD camera. Examples

example 1

Manufacture of monomers:

a) 4- (2-Hydroxyethyloxy) benzoic acid

138 g of p-hydroxybenzoic acid and 0.5 g of KI are placed in 350 ml of ethanol with stirring. A solution of 150 g KOH in 150 ml water is added dropwise. 88.6 g of ethylene chlorohydrin are added dropwise at 30 ° -60 ° C. in the course of 30 minutes. The

The reaction mixture is stirred under reflux for 15 h. The solvent is then completely distilled off first under normal pressure and then in vacuo. The residue is dissolved in 1 liter of water and acidified with HCl. The precipitate is filtered off and recrystallized from 1.8 l of water. The product is dried and recrystallized twice from ethanol. The yield is 46 g (25%> Th.). Mp

179.5 ° C.

b) 4- (2-methacryloyloxyethyloxy) benzoic acid

45 g of 4- (2-hydroxyethyloxy) benzoic acid, 180 ml of methacrylic acid, 10 g of p-toluenesulfonic acid and 10 g of hydroquinone are stirred in 150 ml of chloroform on

Reflux heated. The water formed during the reaction is separated on the water separator. The reaction mixture is diluted with 150 ml of chloroform, washed several times with 100 ml of water and dried over Na ₂ S0 ₄ . The desiccant is filtered off and the chloroform is distilled off on a rotary evaporator to two thirds. The product precipitates, is suctioned off and extracted twice

Isopropanol recrystallized. The yield is 28 g (45%> of theory). Mp 146 ° C. c) 4- (2-methacryloyloxyethyloxy) benzoic acid chloride

25 g of 4- (2-methacryloyloxyethyloxy) benzoic acid, 80 ml of thionyl chloride and 0.5 ml of DMF are stirred at room temperature for 30 minutes. Excess thionyl chloride is then distilled off first in a moderate vacuum and then in a high vacuum.

The resulting acid chloride, with almost quantitative yield, now slowly crystallizes out at room temperature.

Elemental analysis: C ₁₃ H ₁₃ ClO ₄ (268.7) Calc .: C58, ll; H4.88; C113.19; Found: C58.00; H4.90; C113.20.

d) 4-pivalinoylamino-4 ^' aminoazobenzene

36 g of 4,4'-diaminoazobenzene and 62 g of triethylamine are placed in 400 ml of THF. A solution of 23.2 g of pivalic acid chloride in 100 ml of THF is slowly added dropwise. After stirring for 2 h at room temperature, the reaction mixture is mixed with

Water added. The precipitate is filtered off and dried. 42 g of the product are obtained. Further purification is carried out by chromatography (silica gel; toluene / ethyl acetate 1: 1). The yield is 8 g. Mp 230 ° C.

e) 4-Pivalinoylamino-4 '- [p- (2-methacryloyloxy-ethyloxy) bezoylamino] azobenzene lg 4-Pivalinoylamino-4'-aminoazobenzene is placed in 10 ml of N-methyl-2-pyrrolidone (NMP) at 50 ° C and added to the solution of 1 g of 4- (2-methacryloyloxyethyl oxy) benzoic acid in 1 ml of NMP at 50 ° C. The reaction mixture is stirred at this temperature for 1 h, cooled, and 200 ml of water are added. The

The precipitate is filtered off, stirred in 30 ml of methanol at room temperature, filtered off from the mother liquor and dried in vacuo. The yield is 1.2 g. Mp 194 ° C. λ _mm = 378 nm (DMF) ε = 37000 l / (mol.cm) Example 2

a) 32 g of N-benzoyl-p-phenylenediamine were concentrated in a mixture of 210 ml of glacial acetic acid, 75 ml of propionic acid and 31 ml. Hydrochloric acid submitted at 3-5 ° C. 50 g of nitrosylsulfuric acid (approx. 40 percent) were added dropwise at this temperature for 1 hour.

b) 16 g of m-toluidine were dissolved in 130 ml of glacial acetic acid. The diazotization from a) dripped in at 0-5 ° C. for 2 h. The mixture was stirred at room temperature overnight. The precipitated dye was filtered off and suspended in 550 ml of water.

The pH was raised to 8.4 with soda. The dye was suctioned off again, washed with isopropanol and dried. 27 g (54.4% of theory) of the dye of the formula were obtained

UV / VIS in dimethylformamide: λ _ma = 416 nm.

c) 5 g of the dye from b) were dissolved in 20 ml of N-methylpyrrolidone at 50 ° C. 3.5 g of the acid chloride of the formula

were added. The mixture was stirred at 50 ° C. for 1.5 h. Finally, 20 ml of water were added and the precipitated dye was filtered off with suction. It was stirred with 50 ml of isopropanol, suction filtered and dried. 6.2 g (73.4%> of theory) of the dye monomer of the formula were obtained

UNNIS in dimethylformamide: λ _max = 386 nm.

The dye monomers from the following table were prepared analogously.

Example of graft polymers

8.7 g of the starch Perfectamyl A 4692 (86.3%) from Avebe, Foxhol, NL, were dissolved in 60 ml of water at 86 ° C. For this purpose, a mixture of 1.5 g of a 1% by weight aqueous FeSO ₄ solution and 6.1 g of a 3% by weight aqueous H ₂ O ₂ solution was added. The mixture was stirred at 86 ° C. for 15 min. Thereafter, a solution of 1.4 g of the dye monomer of the formula were simultaneously at this temperature for 90 min

in 12.5 g of methyl methacrylate and 4.1 g of a 3% by weight aqueous H ₂ O ₂ solution. After a further 15 minutes at this temperature, 0.105 g of t-butyl hydroperoxide were added and stirring was continued at 86 ° C. for 1 hour. The fine yellow dispersion was filtered through a 100 μm polyamide filter.

The dispersion was diluted 1:10 with water, spread on a glass plate and dried. The transparent, slightly yellow film on the glass plate was irradiated with polarized light, cold light lamp KL 500 from Schott, (spot diameter 6 mm) for 10 min. Between the crossed polarizers, the illuminated spot could be seen brightly in a dark environment.

Example 3

Production of holographic materials by block polymerization

A solution of 1 mol%> of a monomer of formula (II) or of Example 2 and 0.052 grams of 2,2'-azoisobutyronitrile in 10 grams of methyl methacrylate was rinsed in a glass ampule with dry argon for 30 minutes. The ampule was sealed with a rubber stopper and annealed at 60 ° C for 7 days. The result was a transparent polymer cylinder. The polymer cylinder could be isolated by breaking the ampoule and removing the glass fragments. Another storage for 2 weeks at 60 ° C served to remove the residues of methacrylic acid methyl ester and to dissolve the internal stresses in the polymer block.

The PAP cylinder obtained in this way was cut into disks with a diameter of 17 mm and a thickness of 1.9 mm in the precision engineering workshop and then polished. These discs have the optical according to the invention

Densities at the essential wavelengths: OD (532 nm) and OD (568 nm)

A copolymer with 10 mol% of the azo dye is produced analogously. Analogously, copolymer is produced from 1 mol% of the other monomers and 99 mol% of the methacrylic acid methyl ester.

Example 4

A polymer from Example 3 is applied from a solution by means of spin coating to a 150 μm thick glass substrate. The layer thickness in the middle on the

The measuring point lying on the substrate is 600 nm. The height of the refractive index n of the polymer layer is determined for the three spatial directions x, y (layer plane) and z (layer normal) using the prism coupling method. For this purpose, the base of a prism is brought into close contact with the polymer layer. The angles at which the polarized light from a laser couples into the layer and passes through it in a waveguide fashion provide information about its refractive index at the light wavelength. Every coupling is evident as a signal dip at a detector in reflection.

If the polarization of the laser is selected perpendicular to the plane of incidence (s-polarization), the refractive index in the direction of polarization can be determined. Depending on the For the substrate, the values for n _x and ri _y can be determined. The index of the weakly refractive substrate, the index of the prism and the laser wavelength (λ = 633 nm) are included in the calculations. With polarization in the plane of incidence (p-polarization), the value for n _z can be determined. For this, one of the two spatial directions x or y must coincide with the plane of incidence. In addition, the value of the refractive index of the direction chosen in this way (n _x or n _y ) is included in the calculation.

The refractive indices n _x , n _y and n _z are determined on the sample before, during and after several exposures and deletions. The exposure happens through

Irradiation onto the polymer layer in a vertical incidence with laser light of wavelength λ = 514 nm. The light intensity is 200 mW / cm ² . The light is linearly polarized in the x direction. The orientation anisotropy induced in this way in the xy plane is deleted with polarization in the y direction.

This can easily be checked by measuring the refractive indices n _x n _y and n _z at λ = 633nm. For this purpose, for example, the sample is measured untreated, after 200 s, exposure, after 500 s exposure and after 5000 s exposure.

Still further information can be obtained by measuring the refractive indices n _x n _y and n _z at λ = 633nm after the first deletion and second deletion, and after a second or further exposure for 5000 s.

The level of the refractive index of each spatial direction is a measure of the average number of chromophores oriented in this direction, because it correlates with the inducible polarization and this is mainly composed of the high molecular polarizabilities along each molecular axis. Since n _x and n _{y are} originally identical, there is a macroscopically isotropic distribution in the xy plane. The smaller value for n _z indicates the planar molecular orientation, which was created by the manufacturing process. The first exposure successively leads to an orientation distribution with a reduced number of chromophores lying in the x direction. The depletion of this direction takes place on average in equal parts in favor of the other two spatial directions y and z, which can be seen from the increasing values for n _y and n _z . A birefringence n _y -n _x in the film plane can be almost completely deleted. However, the number of chromophores oriented in the z direction increases with each new exposure or deletion process. These are therefore no longer available for a further (subsequent) writing process.

Example 5

A polymer from a monomer according to Example 2 is in the form of granules. It is placed on a glass support and heated to approx. 180 ° C. The polymer melts at this temperature. There are spacers on the glass substrate, e.g. made of Mylar film or glass fibers and another cover glass. This sandwich glass-polymer-glass creates layers in the range from 20 to 1000 μm.

Example 6

A 500 μm thick polymer film, prepared by the method from Example 5, is examined in a holographic structure. An SHG serves as the writing source

Nd: YAG laser (532 nm). In the beam path of the object beam is a spatial light modulator that creates a data mask of 1024 x 1024 pixels. The intensity ratio of the reference to the object beam is 7: 1, the total power density falling on the sample is 200 mW / cm ² . By superimposing the reference and object beams polarizing perpendicular to the planes of incidence, which fall onto the sample at an angle of 40 ° to one another and expose the sample for 30 seconds, a hologram is written, which is then only exposed to the reference beam (exposure time 10 Milliseconds) is read out. Changing the angle of the reference beam from 0.25 ° violates the Bragg condition and the original hologram is no longer visible. A new hologram is written under this new angle configuration. This pre walk is repeated 100 times. After each writing process, in addition to the hologram just written, all previously written holograms are read out by setting the corresponding reference angle. Even after the 100 writes have been completed, the information is retained in all holograms.

Claims

claims

1. Recording material for a holographic volume memory, containing at least one dye that changes its spatial arrangement when writing in a hologram, and optionally at least one shape-anisotropic grouping, characterized in that it allows two or more holograms to be recorded at a sample position.

2. Recording material according to claim 1, characterized in that the at least one dye changes its spatial arrangement so that it is

Absorption behavior changed, in particular its sensitivity to actinic light reduced, preferably between 10%> and 100%, particularly preferably between 50% and 100%) and very particularly preferably between 90 and 100%), each based on the sensitivity before writing of the first hologram.

3. Recording material according to claim 1, characterized in that the at least one dye changes its spatial arrangement so that it changes its absorption behavior, in particular reduces its sensitivity to actinic light, in particular in that it is in the direction perpendicular to the polarization direction of the actinic light works and its molecular axis along with the polarization direction of the actinic light comes to an angle between 10 ° and 90 °, preferably between 50 ° and 90 °, particularly preferably between 75 ° and 90 ° and very particularly preferably between 85 ° and 90 °.

4. Recording material according to one or more of claims 1 to 3, characterized in that it has an optical density <2, preferably less than or equal to 1, very particularly preferably less than or equal to 0.3 in a wavelength range from 390 to 800 nm, preferably from 400 to 650 nm, very special preferably from 510 to 570 nm and most preferably from 520 to 570 nm.

5. Recording material according to one or more of claims 1 to 4, characterized in that it has a radiated thickness of> 0.1 mm, preferably> 0.5, particularly preferably> 1.0 mm, very particularly preferably not greater than 5 cm Has.

6. Recording material according to one or more of claims 1 to 5, characterized in that it contains predominantly polymeric or oligomeric organic material.

7. Recording material according to one or more of claims 1 to 6, characterized in that the optical density of the recording material is adjusted, preferably via the concentration of the at least one

Dye.

8. Recording material according to one or more of claims 1 to 7, characterized in that the optical density is adjusted via the molar extinction coefficient of the at least one dye.

9. Recording material according to one or more of claims 1 to 8, characterized in that it is polymeric or oligomeric organic, amorphous material, preferably side chain polymers and / or block copolymers and / or graft polymers.

10. Recording material according to one or more of claims 1 to 9, characterized in that the electromagnetic radiation is light in the wavelength range of lasers, preferably between 390 to 800 nm, particularly preferably between 400 and 650 nm, very particularly preferably between 510 and 570 nm.

11. Use of the recording materials according to one or more of claims 1 to 10 for recording, preferably angle-dependent recording of at least three, particularly preferably more than 100, very particularly preferably more than 500 and extremely preferably more than 1000

Volume holograms, at a location of the storage material.

12. Use of the recording materials according to one or more of claims 1 to 10 for reading, preferably angle-dependent reading, of volume holograms.

13. Holographic volume storage, characterized in that a recording material according to claims 1 to 10 is included.

14. Holographic volume memory according to claim 13, characterized in that the recording material contains one or more self-supporting objects of any shape, preferably a self-supporting sheet-like structure, particularly preferably a self-supporting film, wherein in a multilayer structure, preferably at least one substrate layer is contained.

15. A method for producing the holographic volume memory according to at least one of claims 13 or 14, characterized in that a step is included in which by a conventional injection molding process in the range up to 300 ° C, preferably up to 220 ° C, particularly preferably 180 ° C. is being worked on.

16. Polymers with chemically bound dyes of the formula (I)

wherein

X ¹ and X ^{2 are the} same or similar, characterized in that they have the same or similar Hammett constants, and

R ¹ and R ² independently of one another represent hydrogen or a nonionic substituent and

m and n independently of one another represent an integer from 0 to 4, preferably 0 to 2, where

X ¹ and X ^{2 are} preferably -XNR ³ or X ^{2 '} -R ⁴ , and

X ^r and X ^{2 '} for a direct bond, -O-, -S-, - (NR ⁵ ) -, -C (R ⁶ R ⁷ ) -,

- (C = O) -, - (CO-O) -, - (CO-NR ⁵ ) -, - (SO ₂ ) -, - (SO ₂ -0) -, - (S0 ₂ -NR ⁵ ) - , - (C = NR ⁸ ) - or - (CNR ⁸ -NR ⁵ ) -,

R ^3, R ^4, R ⁵ and R ⁸ are independently hydrogen, C, - to C ₂₀ - alkyl, C ₃ - to C, ₀ cycloalkyl, C ₂ - to C ₂₀ -alkenyl, C ₆ - to C, ₀ -aryl, C, - bis

C ₂₀ alkyl (C = O) -, C ₃ - to C, ₀ -cycloalkyl- (C = O) -, C ₂ - to C ₂₀ - alkenyl- (C = O) -, C ₆ - to C _10- aryl- (C = O) -, C, - to C ₂₀ -alkyl- (SO ₂ ) -, C ₃ - to C ₁₀ -cycloalkyl- (SO ₂ ) -, C ₂ - to C ₂₀ -alkenyl- (SO ₂ ) - or C ₆ - to C ₁₀ -aryl- (SO ₂ ) - stand or

X ^r -R ³ and X ^{2 '} -R ^{4 can represent} hydrogen, halogen, cyan, nitro, CF ₃ or CC1 ₃ , R ⁶ and R ⁷ are independently hydrogen, halogen, C, - to C ₂₀ - alkyl, C, - to C ₂₀ alkoxy, C ₃ - to C, ₀ cycloalkyl, C ₂ - to C ₂₀ -alkenyl or C ₆ - to C, ₀ -aryl.

17. Polymer according to claim 16, characterized in that at least one monomer of formula (II) is included

wherein

R represents hydrogen or methyl and

the other radicals have the meaning given above.

18. A method for producing the recording material according to one of claims 1 to 10 or the polymers according to one of claims 16 and 17, characterized in that the at least one monomer is polymerized without further solvent, preferably free-radically polymerized, and particularly preferably by free-radical Starter and / or UV light and / or thermally initiated.