Effect of UV radiation on the diffraction efficiency of holograms when recording in additively colored KCl crystals

We have shown that the increase in diffraction efficiency of holograms recorded in additively colored crystals as a result of preliminary UV irradiation may be due not only to an increase in the concentration of F centers but also to radiolysis of impurity hydroxyl ions, which are always present in nominally pure crystals. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 1, pp. 85–87, January–February, 2008.     

A study of M center formation in additively colored KCl

Additively colored crystals of KCl were cooled rapidly from a high temperature and then exposed to light absorbed by the F band. The rate of growth of the M band was initially low and increased markedly during the first part of the irradiation giving rise to what is called a “delay period” in the M center formation. During this delay period it was observed that 1. the quantum efficiency of F center fluorescence decreases by a factor of 3 or 4, and 2. the ability to convert F centers to F′ centers is reduced by about a factor of 3. These effects are interpreted as arising because of an appreciable decrease in the average nearest neighbor F center separation during this period. Results are also presented concerning the kinetics of M center formation, oscillator strengths of the M center transitions, the degree of polarization of the M center fluorescence, and the transfer of energy from an excited F center to an M center.     

Diffusion of water in additively colored potassium iodide crystals

The diffusion of water into additively colored potassium iodide has been studied in the range 15–45°C. Penetration depths, measured by decrease in the F-band absorption, increase with $\text{t}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$. The diffusion coefficient, D = 0·58 exp (?6496/T) cm² sec^?1 agrees very well with that determined by other workers. The Henry's law constant, $\text{K =}\text{C}{}_0\text{p}{}_{\mathrm{w}}\text{= 1·3 × 10}{}^9\text{exp}\text{(+4882/T)}\text{cm}{}^{\mathrm{?3}}\text{torr}{}^{\mathrm{?1}}$ implies a water concentration of C₀ ? 10¹⁷ molecules per cm³ in the surface of KI crystals in equilibrium with an environment at 25°C and 35 per cent relative humidity. The large C₀ makes penetration very rapid. Diffusion occurs by interstitial migration of water molecules with an entropy of activation of 9.4 cal/mol deg and an enthalpy of activation of 12·9 kcal/mol.     

Transient absorption induced by flash-light excitation in additively colored KCl: Na

Transient bands occuring between 600–1100 nm on flash-light illumination in the F-band near room temperature were investigated. Identified as the F′-andF′_A-bands, they varied substantially on repeated flashing: the F′_A-band intensified because of the F-F_A-conversion, while the F′-band attenuated as a result of the F-center bleaching.     

Some luminescent properties of additively colored KBr · Ag crystals

The luminescent characteristics of additively colored KBr · Ag crystals are investigated. In particular, the decay of the phosphorescence, the flash of emission due to IR light in relation to the silver concentration, and the temperature quenching of the steady luminescence are discussed. It is shown that the investigated crystals have a complex system of shallow and deep traps. The thermal activation energy for nonradiative transitions in the B centers is found. It is concluded that the luminescence is produced by an electron-recombination mechanism.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 81–85, November, 1973.     

Paramagnetic susceptibility of additively colored CdF2:In photochromic crystals

The paramagnetic susceptibility K _para of CdF₂:In crystals with metastable indium centers has been measured in darkness after photobleaching the crystals in visible light in the temperature interval 4–300 K. For crystals cooled in darkness to liquid-helium temperature K _para is wholly determined by the accompanying impurity Mn²⁺ with magnetic moment J=5/2. Illumination of the crystals leads to the appearance of an induced signal δ K _para due to the formation of centers with J=1/2. The results of the experiments indicate the absence of paramagnetism in the deep state of the indium center and its existence in the shallow (donor) state, i.e., they confirm the two-electron (negative-U) nature of the deep indium level in CdF₂. Fiz. Tverd. Tela (St. Petersburg) 39, 1205–1209 (July 1997)     

Electron-trapping centers in additively colored alkali halide crystals doped with divalent impurities

A study has been made of the temperature dependences of the dielectric loss and structure-sensitive conductivity of additively colored KCl single crystals having a Sr²⁺ impurity. The optical absorption spectra were recorded before and after heat treatment of the colored crystals. A model for Z-centers is proposed on the basis of the results.Translated from Izvestiya VUZ. Fizika, No. 10, pp. 26–29, October, 1969.In conclusion the author thank Professor E. K. Zavadovskaya for suggesting thistopic and for discussion of the results.     

Transformation of color centers during hologram recording in an additively colored CaF2 crystal

When holograms are recorded on color centers in calcium fluoride crystals, these centers undergo spatial redistribution in the crystal bulk, which is accompanied by their transformation. The nature of this transformation has been investigated by optical spectroscopy and confocal scanning microscopy. It is shown that, under the recording conditions we used, the degree of center aggregation increases in both minima and maxima of the interference field in which the recording performed. The enhanced aggregation in field minima is caused by the increase in the concentration color centers, while the additional aggregation in maxima is determined by the specific conditions of hologram recording: the wavelength and power density of recording radiation and the crystal temperature.     

Anti-stokes emission in an additively colored KCl caused by excitation with a Nd: YAG laser

Abstract

We have observed the quadratic laser power dependence of two anti-Stokes emission bands at 15100cm^?1 and 14000cm^?1 in an additively colored KCl when excited with a Nd:YAG laser. The cross section of two photon absorption to cause the 14000cm^?1 band is estimated to be 4×10^?40cm⁴sec. We have observed that emission intensities are dependent on temperature in the range between 4. 2K and 130K. They are enhanced by means of optical bleaching and also with the increase of the F concentration. From a qualitative analysis of these observations, we propose that these emissions are correlated to the loose aggregation of the F centers.     

Thermal polarization properties of thick anisotropic diffraction holograms recorded in polymer-dispersed liquid crystals

The diffraction and polarization properties of thick anisotropic holographic gratings recorded in polymer-dispersed liquid crystals are studied experimentally and theoretically. Such gratings are anisotropic and sensitive to temperature variations and also exhibit a strong dependence of the diffraction properties on the incident radiation polarization because of the presence of liquid-crystal molecules. The dependences of the diffraction efficiency and diffracted beam polarization orientation on the diffraction grating temperature and incident beam linear polarization are obtained for the case of Bragg incidence. The same dependences are derived using the known experimental temperature curves of the liquid crystal permittivity. The experimental data are in agreement with the theoretical calculations. The feasibility of controlling the diffraction characteristics of the grating in a wide temperature interval is demonstrated.     

Two-level model of recording and reading of volume phase holograms in photorefractive crystals of BSO-type

A two-level model of optical transitions in crystals of BSO-type has been proposed for the effect of readout beam on the dynamic holographic grating to be taken into account, and an expression for diffraction efficiency representing the generalized formula by Vinetskii and coworkers [1–3] has been obtained.     

Reflection-type polarization holograms in bacteriorhodopsin films for low-light recording

Reflection-type polarization holograms with phase-conjugated readout are very useful for low-light recording with bacteriorhodopsin (BR) films. The dependence of reflection-type holograms with parallel and orthogonal recording beams on their intensity ratio (1:1-1:20) was investigated. It was found that for orthogonally polarized beams the phase-conjugated signal depends significantly less on the beam intensity ratio than predicted by coupled-wave theory. This finding is of particular relevance for recording of very low object-beam intensities with BR films, e.g., in interferometry, where signals with a high signal-to-noise ratio, owing to the different polarizations of the scattered light and the signal, and with low dependence of the diffraction efficiency on the ratio between the reference and object-beam intensities are obtained. With this asymmetric recording process, holograms were recorded successfully in BR films with a good signal-to-noise ratio at exposures (from the object side) as low as 50muJ/cm(2) . These exposures are in the range of those typically used for silver halide films.     

Nondestructive read-out holograms recording in photochromic salicylideneaniline

The plane wave holograms were recorded with the 488 nm line in salicylideneaniline and nondestructive read-out was by the 632.8 nm line. The 0.8% diffraction efficiency was achieved.     

数字化合成全息图自动记录系统研究

从合成全息术的编码原理出发,采用了液晶空间光调制器、步进电机控制的可移动狭缝和一维移动平台等设备以及计算机数字多媒体技术、软件编程技术设计出一套数字化合成全息自动记录系统。该系统能够改善传统全息图手工制作效率低、操作不准确产生误差等缺陷,提高了合成具有视差、动感、颜色以及不同景深等特殊效果全息图的自动化水平。实际应用该系统合成了含有40幅照片信息的全息图。     

Fourier holograms recorded and decoded in polychromatic light

This paper describes a recording and reconstruction method applied to two-dimension Fourier holography, in which the illumination at the recording stage is spatially coherent and temporally incoherent. The various chromatic components of the information to be recorded in the hologram are spread along a direction orthogonal to the entrance slit of a spectroscope that behaves as scanning pupil performing a chromatic coding. The message, both spatially and temporally coded, can be reconstructed by using a conventional process, the light source being still polychromatic.