SU915607A1 - Method of recording stationary holograms - Google Patents

Description

The invention relates to holography, in particular to recording media for recording stationary holograms using radiation of neodymium and ruby lasers, and can be used to record optical information and obtain holographic elements (relief holographic gratings, lenses, beam splitters, proofreaders) working in visible and near infrared spectrum.

One of the main tasks of holography, the solution of which is necessary for the successful implementation of various technical applications of holography, is the task of developing highly efficient recording media with high values of the main parameters, namely sensitivity, diffraction efficiency and resolution, as well as having not less important properties such as stability in time, short recording times, a large signal-to-noise ratio, resistance to laser radiation, etc. Required for manufacturability and ease of manufacture of the recording medium, which determines the possibility of manufacturing a large area of information carrier.

Of particular relevance is the creation of recording media for the infrared region of the spectrum that most satisfy the above requirements, since there are no effective media in the infrared region of the spectrum.

 Currently, a number of recording media that are sensitive in the IR region of the spectrum are known. These include metal films, semiconductor materials, organic semiconductors, thermoplastics.

One of the best in terms of the main parameters of the media are bismuth metal films [1]. They have a sufficiently high sensitivity of the order of 10 “ ² J / cm ² in a wide spectral range, including in the IR region.

The main disadvantage of bismuth films is the oxidation of layers in the atmosphere, which leads to a change in their physical properties.

Organic semiconductors (dimethyl-thiadiazole and methylrodanide) G2} DZ]

Infrared spectrum, high resolution (^ 2000 lin / mm in the visible. Spectrum and

1000 lin / mm in the near infrared region of the spectrum), a relatively high diffraction efficiency of ^ 5%. The gratings recorded on amorphous dimethyl-thiadiazole and methyl danide films do not require further processing; they have good signal-to-noise ratio (100). However, the technology of manufacturing films of organic semiconductor dimethylthiadiazole is quite complicated. The synthesis technology of organic semiconductor methylrodanide is much simpler and established on an industrial scale (it is used in large quantities in the manufacture of insecticides and herbicides), but in the manufacture of media for recording information by precipitating the monomer of methylrodanide on a substrate, the film surface quality is not always high, which significantly limits the achievement of high holographic recording parameters.

Thermoplastic materials (for example, polyvinylcarbaeol) have good parameters for recording in the visible region of the spectrum. When thermoplastics are sensitized with fluorene dyes, information can also be recorded in the IR spectral range £ 4]. The resulting embossed holograms have relatively high parameters: sensitivity ~ 10 ^_2 J / cm ² , resolution of 500 lin / mm, diffraction efficiency of 0.1–2%.

The disadvantages of thermoplastic materials include the need to apply electric charge and an additional process of developing a holographic recording, which is an obstacle to quickly reading information.

Holograms were also recorded on diacetate-cellulose and cellulose acetate films in the IR region at the radiation wavelength λ = 10.6 μm. However, with a high diffraction efficiency of ^ 20%, the sensitivity of these materials is low and amounts to 5 J / cm ² C5].

The closest solution to the technical essence and the achieved result is the method of recording stationary holograms [b] by placing the recording semiconductor material in the area of intersection of the light beams that form the interference pattern.

Used here semiconductor material of the type OeAzTe is used to record holograms in the spectral region of 0.8 microns. Their sensitivity is l / 1SG ² j / cm ² . Data on holographic recording by radiation of longer waves are not available.

The aim of the invention is to increase the sensitivity to recording IR holograms while ensuring high values of diffraction efficiency and resolution.

To achieve the goal in the method of recording stationary holograms by placing the recording semi-pro 915607

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Vodnikova material in the region of intersection of coherent light beams forming an interference pattern as a recording material using a semiconductor film _for ca ₁ Not _hTe where x - 5 lar MO content in CdTe HETE, while recording is performed beams with an energy density in the range from 5 · 10 '·' J / cm ² to 0.5 J / cm.

FIG. 1 shows the dependences of -10 diffraction efficiency on the spatial frequency for different waves; in fig. 2 - the dependence of the diffraction efficiency on the exposure for different spatial frequencies; , 5 in FIG. 3 - noise characteristics of the proposed material for different spatial frequencies.

The material Sa _x He ₄ _ _x Te is a solid solution for the replacement of the semiconductor compounds SyTe - NeTe, where x indicates the molar content of SyTe. It crystallizes into a cubic lattice of zinc blende type, its band gap is -5 with an increase in the content of sat in HeTe linearly changes from -0.3 eV for ΗβΤε to +1.6 eV for sat.

Sa _x Not ₁ films. _x Te were obtained by the method of rapid evaporation in vacuum from the surface of a previously synthesized 30 bulk polycrystalline material.

Since the partial vapor pressures constitute the components of the solid solution of sa _x He ₊ . _x Those are very different; in order to maintain the constancy of the molar composition of the vapor in the process of source evaporation, it is necessary to choose an evaporation temperature and volume of evaporated material that 4θ would evaporate from the surface of the source to exceed the diffusion of mercury and tellurium (the most volatile component) same source. This should be a fairly rapid layer-by-layer evaporation from the source surface.

Polycrystalline pieces of Ca ^ Hb + .TTe weighing about 600 mg were evaporated with the evaporating temperature changing in the course of evaporation in the range of 50-700 ° C. At a substrate temperature of 100–110 ° C, films uniform with a mirror surface were deposited at a speed of 200–300 A / s. To obtain large-area films in 55, glass plates, degreased and degassing in vacuum-2 · 10 mm Hg, were used as substrates. at a temperature of ^ 300 ° C immediately before film application. Tol- 60

The film thickness was determined by the deposition time and varied in the range of 0.1–7.0 μm. The area of the obtained films reached 1200 mm ² .

The holographic gratings were recorded by the radiation of a frequency laser (LTH-PCh-7) on an yttrium aluminum garnet with neodymium (A = 1.06 μm) operating in the single-pulse mode with a duration of 10 ns and a power of 1 MW, as well as in the free-oscillation mode by picosecond radiation neodymium laser (L =

= 1.06 μm) with a duration of 5 ns, as well as radiation from a ruby laser (λ = 0.69 μm) operating in the free-running mode (with a pulse duration of 300 ms).

From the dependencies (see Figs. 1 and 2), it can be seen that the maximum values of the parameters for the recorded gratings are: the diffraction efficiency of 20-.25% (when the radiation of the helium laser is restored), the resolution is of the order of 1000 lines / mm in the IR region and more than 2000 min / mm - in the visible region, sensitivity (0.5-1) xlO ^"5 J / cm ² holographic grating recorded in a time of 10 ns, 5 ps and required no subsequent processing and properties of films recorded in these lattices were not changed.. during the year.The ratio of signal / noise ratio reached 100, (FIG. 3).

From the dependence of the diffraction efficiency on the energy density of the recording beams (see Fig. 2), it follows that the recording of stationary holograms (due to the occurrence of violations of the surface layer of the recording material is carried out starting with doses of 0.5-10 ^- ^ J / cm ² , i.e. The recording sensitivity is increased by an order of magnitude, and high diffraction efficiency is provided starting with a value of not less than 5% at energy densities of recording beams of 5 -10 “^ j / cm ² , and at densities of 0.5 J / cm ² , the lattice parameters begin to degrade .

The described method allows to increase the sensitivity in the IR region of the spectrum, according to the diffraction efficiency in the IR region of the spectrum and in the visible region of the spectrum is not inferior to the known analogues.

In the material used, there is a direct fixation of the image that does not require additional processing, short recording times that allow you to quickly read information.

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Claims (2)

METHOD OF RECORDING STATIONARY ί HOLOGRAMS by placing a recording semiconductor material in the intersection of coherent light beams, characterized in that, to ensure high sensitivity to recording in the infrared region of the spectrum while ensuring high values of diffraction efficiency and resolution, use a film 'СάχΗβ ^, χΤβ, where X is the molar content of Cyte in HgTe, while the recording is carried out -. They are bunched with a density _{g of} energy in the range from 5-10 ' ³ J / cm ^g to 0.5 J / cm. : _in " one 915607 2