RU2229154C2 - Recording medium to write phase three-dimensional holograms and phase three-dimensional hologram - Google Patents

Abstract

FIELD: three-dimensional holography. SUBSTANCE: invention is related to polymer recording media and can be used to create systems for information storing, processing and transmission, for formation of holographic optical elements. Recording medium to write phase three-dimensional holograms presents composition of clear polymer material that is polycarbonate in which phenanthraquinone is capable of experiencing photographic addition to its polymer chain or copolymer including links of such polymers or mixture of polymers and low-molecular substance containing polymers or copolymers of above-mentioned classes and 9, 10-phenantraquinone replaced with hydrogen or hydrocarbon substituents. Invention also describes phase three-dimensional holograms recorded on above-mentioned medium that presents polymer material containing alternating layers made of polymer with photographic additions to it in various concentrations of phenanthraquinone groups with different refractive indices. EFFECT: generation of high-stability holograms. 2 cl, 1 dwg, 1 tbl _

Description

The invention relates to three-dimensional holography, polymer recording media and can be used to create systems for storing, processing and transmitting information, holographic optical elements.

Known recording medium, which is a solution of phenanthrenquinone in a glassy carbocarbon polymer, which is used polymethylmethacrylate [1. A.P. Popov, A.V. Veniaminov, V.F. Goncharov. RF patent No. 2035764, priority 6.09.1991]. When the medium is exposed to an interference field (recording a hologram), phenanthrenone quinone is restored and attached to macromolecules in the form of phenanthrene groups [2. O.V. Bandyuk, N.S. Shelekhov, A.P. Popov, M.Ya. Danilova. Solid-phase reduction of phenanthrenquinone in a polymer matrix. / Adj Chemistry, 1988, vol. 61, No. 4, pp. 946-948]. In the same way, phenanthrenquinone interacts with other polymers and low molecular weight substances [3. A.V. Veniaminov and H. Sillescu Forced Rayleigh scattering from non-harmonic gratings applied to complex diffusion processes in glass-forming liquids Chem. Phys. Lett. 1999, v. 303, No. 5-6, p. 499-504 (1999)]. In the photochemical reaction, a relatively weak diffracting structure (holographic lattice) arises, which practically does not introduce distortions into the recorded wavefront. Following this, the lattice is significantly (up to two orders of magnitude in diffraction efficiency) enhanced due to the natural diffusion of phenanthrenquinone in polymer glass [1, 4. A.V. Veniaminov, V.F. Goncharov, A.P. Popov. Amplification of holograms due to diffusion destruction of antiphase periodic structures. / Wholesale. Spectrum. 1991, vol. 70, issue 4, pp. 864-868], and the diffraction efficiency reaches the required values, approaching 100% close to 100% for both transmission and reflection holograms. The hologram thus obtained is physically based on the spatial modulation of the concentration of the photoreaction product — phenanthrene groups attached to the macromolecules. Frozen large-scale motions of macromolecules in a glassy state provides high stability of holographic gratings. Unlike photopolymerizable compositions, the medium under consideration does not contain significant amounts of monomers and it does not exhibit any noticeable shrinkage. Using this medium, holographic spectral filters (selectors) and demultiplexers were created and successfully tested [5. A.P. Popov, I. Novikov, K. Lapushka, I. Zyuzin, Yu. Ponosov, Yu. Ashcheulov, A. Veniaminov. Spectrally selective holographic optical elements based on thick polymer medium with diffusional amplification - J. Opt. A: Pure Appl. Opt. 2000, v. 2, No. 5, p. 494-499; 6. J.E. Ludman, J.R. Riccobono, N.O. Reinhand et al. Very thick holographic nonspatial filtering of laser beams Opt. Eng. 1997, v. 36, No. 6, p. 1700-1705; 7. N. Reinhand, Y. Korzinin, I. Semenova. Very selective volume holograms: Manufacturing and applications J Imaging Sci. Techn. 1997, v.41, No. 3, p.241-248]; the medium is considered as promising for the creation of optical memory systems [8. G.J. Steckman, I. Solomatine, G. Zhou et al. Characterization of phenanthrenequinone-doped poly (methyl methacrylate) for holographic memory Opt. Lett. 1998, v.23, No. 16, p.1310-1312].

However, this environment has the following disadvantages:

1. Diffusion of PMMA macromolecules, responsible for the stability of the diffraction efficiency of holograms, is slow, but was nevertheless found in long-term experiments [9. A.V. Veniaminov, Yu.N. Sedunov, A.P. Popov, O.V. Bandyuk. Post-exposure behavior of holograms under the influence of diffusion of macromolecules. / Wholesale. Spectrum. 1996, vol. 81, No. 4, p.676-680], and the actual diffusion coefficients are higher than could be expected from the extrapolation of the values obtained from measurements above the glass transition temperature [10. A.V. Veniaminov, H. Sillescu: Polymer and Dye Probe Diffusion in Poly (methyl methacrylate) below the Glass Transition Studies by Forced Rayleigh Scattering. Macromolecules, 1999, v. 32, p. 1828-1837]. Accordingly, the expected service life of holographic optical elements will be years instead of decades according to previously made estimates. In addition, in the absence of a reserve for stability, the possibilities for modifying the material are narrowed by the introduction of various kinds of additives (for example, to improve the mechanical and optical properties), which can have a plasticizing effect and thus accelerate diffusion, and therefore degradation of holographic gratings; the requirements for the concentration of residual monomer or solvent capable of plasticizing the material, as well as directly participating in the photoaddition reaction of phenanthrenquinone or initiating photopolymerization, are being tightened.

2. In order to avoid deformation of the material and the corresponding distortion of the holograms recorded in it, as well as accelerated aging by the diffusion mechanism, the maximum temperature of operation and storage of the medium should be significantly (tens of degrees) lower than the glass transition temperature of the polymer, which for PMMA (atactic) 95- 105 ° C; this entails restrictions on the scope.

3. Polymethyl methacrylate is susceptible to thermal decomposition (depolymerization) at temperatures lower than 150 ° C [11. Yu.I. Matveev, A. A. Askadsky. High Molecule. Comp., 1993, v. 35, p. 50]) lower, than the temperature of a viscous flow (180-190 ° C [12. A. V. Veniaminov, Yu. N. Sedunov. Diffusion of phenanthrenquinone molecules in polymethyl methacrylate (holographic measurements). / Vysokomol. Soed. Ser. A, 1996, v. 38, No. 1, pp. 71-76]), which reduces the manufacturability of the fabrication of the material and, therefore, holographic optical elements and optical memory based on it by molding from lava.

4. Water is able to penetrate into PMMA and its related polymers and dissolve in them in macroscopic amounts (1.5-2%), changing the optical and physicochemical properties of the polymer. The optical heterogeneity of the material that occurs when the humidity of the environment changes, leads to out-of-phase and distortion of the reconstructed wave front of the holographic element, and to a change in diffraction efficiency (see drawing).

The aim of this invention is to increase the durability and stability of the parameters of volume holograms recorded on a recording medium, as well as this medium itself. The medium for recording volumetric phase holograms based on phenanthrenquinone in polymethylmethacrylate using the principle of diffusion amplification is considered as a natural prototype.

This goal is achieved by the fact that as a polymer material in which a photochemically active agent is dissolved - phenanthrenquinone with the general formula:

,

,

where R ₁ -R _{8 is} hydrogen or hydrocarbon substituents, a polycarbonate is used, such that phenanthrenquinone is capable of experiencing photoaddition to its polymer chain, or a copolymer comprising units of such polymers, or a mixture of polymers and low molecular weight substances, including polymers or copolymers of these classes.

A hologram recorded in such a medium due to the photochemical addition of phenanthrenquinone molecules to macromolecules and enhanced by diffusion of the remaining unattached phenanthrenquinone physically consists of a polymer material including layers with different refractive indices formed by a polymer with phenanthrene groups photochemically attached to it in different concentrations, which correspond to the distribution of light intensity in the recorded interference pattern. There is no doubt that the technical effect will be achieved at any real concentrations of PF. An increase in the concentration of PF allows you to increase the dynamic range of the medium, that is, record more holograms or more effective holograms (which does not apply to the technical effect of the present invention), however, the compatibility of PF with the polymer (solubility) is not unlimited and very high concentrations (for example, 50%) are not realizable in practice. At high concentrations of PF, incomplete dissolution of it in the polymer, thermodynamic instability, and precipitation of crystals are possible. In addition, with an excessive content of PF, the efficiency of the photochemical reaction decreases. Due to the following advantages of polycarbonate (PC) over polymethyl methacrylate (PMMA), holograms recorded in a PC-based medium are more stable than similar holograms recorded in a PMMA-based medium, as the following example shows.

1. The glass transition temperature of the PC is 140-150 ° C or more, depending on the specific formula, against 95-105 ° C for PMMA; Owing to this, the PC-based material does not deform at higher temperatures, and the diffusion of macromolecules in it, which is responsible for the long-term stability of the holographic lattice, is slower than in the case of PMMA.

2. Thermal decomposition (depolymerization) of PC occurs at temperatures above 300 ° C [13. C. Puglisi, L. Sturiale and G. Montaudo. Thermal Decomposition Processes in Aromatic Polycarbonates Investigated by Mass Spectrometry Macromolecules, 1999, v. 32, p. 2194-2203] (softening start temperature 200 ° C), while PMMA already at 150 ° C [11] (softening at 180 ° FROM). In addition to better PC stability, this allows mass production of optical parts from PC by extrusion, while PMMA has to be polymerized in bulk, which is orders of magnitude less efficient.

3. PC significantly absorbs moisture than PMMA (0.2-0.3% [14. Encyclopedia of polymers edited by V. A. Kabanov et al. M: Soviet Encyclopedia, 1974] versus 1.5-2% ), due to which the holograms made on its basis are more resistant to changes in environmental humidity.

Polycarbonate has good optical and mechanical properties, allowing it to be used for the production of polymer optical elements. In recent years, a huge number of compact discs, precision optical, electrical and other parts have been made from polycarbonate, which greatly contributed to optimizing the properties of the material and perfecting the technology of its mass production.

Example 1

, отсюда вычислялись характерные времена роста дифрагированного сигнала τ₁ (диффузионное усиление голографических решеток) и его ослабления τ₂ (диффузионная деградация) и, далее, соответствующие им коэффициенты диффузии ФХ (D₁=Λ²/(4π²τ₁)) и макромолекул (D₂=Λ²/(4π²τ₂)). Замедление деградации голограммы (то есть уменьшение соответствующего ей коэффициента диффузии макромолекул D₂) по сравнению с материалом-прототипом и составит положительный эффект.This example illustrates the higher stability of holographic gratings recorded in a polycarbonate-based material compared to a similar material based on PMMA. Samples of the medium are made of injection polycarbonate (polybisphenol-A-carbonate), which serves as the basis for CDs. This material and phenanthrenquinone are separately dissolved in dichloromethane, the solutions are combined in a proportion that provides the desired ratio of phenanthrenquinone to polymer, which in various experiments was 0.2, 0.5, 3, and 10% by weight, and then dried in the form of a film. To impart the required optical quality, the film is pressed between two polished glasses at 220 ° C. For comparison, samples of a medium based on polymethyl methacrylate were similarly prepared, however, in this case, the pressing temperature was 140 ° C. The diffraction gratings were recorded on two samples with two flat beams of continuous neodymium laser in a reflective scheme (recording beams incident on the medium from different sides). Next, one of the recording beams was blocked and the dynamics of the diffraction intensity of the other beam weakened by 10,000 times was monitored to avoid photochemical erasure of the recorded grating during measurements. The obtained time dependences of the light diffraction intensity were analyzed similarly to what was done in [9], following the diffusion amplification model and Kogelnik formulas for volume phase holograms:

, from this we calculated the characteristic times of growth of the diffracted signal τ ₁ (diffusion amplification of holographic gratings) and its attenuation τ ₂ (diffusion degradation) and, further, the corresponding diffusion coefficients of the PC (D ₁ = Λ ² / (4π ² τ ₁ )) and macromolecules (D ₂ = Λ ² / (4π ² τ ₂ )). Slowing down the degradation of the hologram (i.e., reducing the corresponding diffusion coefficient of macromolecules D ₂ ) in comparison with the prototype material will be a positive effect.

The table shows the calculated diffusion coefficients D _1, D ₂ corresponding to the growth (development) and degradation of the grating, the development time (τ ₁ ) and the estimated time of degradation of the grating - the conditional life (τ ₂ ) for reflective and transmission diffraction gratings with a spatial period, respectively 0.18 and 1 μm, in phenanthrenequinone-based media using polycarbonate (new medium) and polymethylmethacrylate (prototype): PC / PMMA.

In a medium with diffusion amplification, diffusion determines both growth (diffusion of unreacted phenanthrenquinone) and hologram destruction (diffusion of macromolecules). The PC shows at least an order of magnitude slowed down diffusion of macromolecules, which corresponds to an increase in the hologram lifetime by an order of magnitude as well.

For the experiment used low molecular weight, injection, PC (average molecular weight of 18,000); it is obvious that when using a higher molecular weight polymer, the effect can be even more pronounced. When PMMA is replaced by polycarbonate, the effective diffusion of phenanthrenquinone, which is responsible for post-exposure amplification (manifestation) of holograms in a PC does not slow down, and due to this, the amplification process in a PC does not take longer than in a prototype environment.

The table shows the average values over the entire range of concentrations of PF. The spread of values is from 20 to 50% of the given values. Within the considered concentration range, no systematic concentration dependence of the amplification or degradation rates of holographic gratings (or diffusion coefficients) was revealed.

Example 2

This example demonstrates a higher stability of polycarbonate compared to polymethyl methacrylate. PC and PMMA samples containing 0.5% PF by weight each were prepared similarly to that described in Example 1. Further, reflective holographic gratings were recorded on the samples of both materials and a change in the light diffraction intensity on such gratings was observed at 100 ° C. The same samples of both materials were kept at 200 ° С for two hours, after which holographic gratings were also recorded on them, the change in the light diffraction intensity on which was then observed at 100 ° С. No effect of aging at 200 ° С was detected. material based on PC, while the change in the diffraction efficiency of gratings in a PMMA-based medium was accelerated as a result of the same treatment by about 40 times as compared with a control sample, which indicates a significant plasticization of the material by low molecular weight products of thermal degradation of PMMA.

Claims (2)

1. A recording medium for recording phase three-dimensional holograms, which is a composition of a transparent polymer material and substituted 9,10-phenanthrenquinone of the general formula

where R ₁ -R _{8 is} hydrogen or hydrocarbon substituents, characterized in that the polymer material is polycarbonate, such that phenanthrenquinone is capable of experiencing photoaddition to its polymer chain, or a copolymer comprising units of such polymers, or a mixture of polymers and low molecular weight substances, including polymers or copolymers of these classes. 2. A phase three-dimensional hologram recorded on a medium according to claim 1, which is a polymeric material comprising alternating layers with different refractive indices, characterized in that the alternating layers are made of polymer with phenanthrene groups photoconnected to it in various concentrations.