Transformation of images upon dual-frequency recording and reading at sum frequencies of dynamic χ<Superscript>(2)</Superscript> holograms using spherical reference waves

The transformation properties of images reconstructed by dynamic χ⁽²⁾ holograms recorded with radiation of the sum frequency with the use of spherical reference waves are studied theoretically and experimentally. Notions of fields and zones of locrises as regions of localization of holographic images formed by reference and object beams of different frequencies at arbitrary frequency ratios of these beams and distances from the reference point source to the hologram are defined. The domains of the parameters of the reference source ensuring the formation of real and imaginary images are determined. The reconstruction of real images by dynamic χ⁽²⁾ holograms is demonstrated.     

Volume holograms as frequency-selective elements

In this paper we investigate the possibility of using thick holograms as diffraction gratings. We compare the well-known parameters of the plane diffraction grating such as dispersion, efficiency, resolution, and others, with those for volume holograms. The calculations for the case of volume holograms are based on the theory of coupled waves. Experiments were performed with volume-phase holograms in transmission, stored in dichromated gelatine layers. The investigations show that the volume hologram fulfills two functions simultaneously. It acts as a spectral predecomposer and also as a high-resolving spectral apparatus.     

Computer generated holograms using personal computers

Holography or the method of wave-front reconstruction to produce an image was introduced by D. Gabor in 1948. Normally a laser is necessary to produce holograms in the laboratory. This paper introduces the usage of the high resolution display of the IBM-PC and a graphics printer to generate holograms. The advantages of using this method are that holograms of real or fictitious objects can be made, since all objects can be represented by a collection of points and one does not need an elaborate set up to make the holograms. This method is also useful for making Fourier transform holograms, image plane holograms, spatial filters, optical elements, etc.^1,2     

Effective room-temperature broad-band recording of 3D dynamic holograms in CdF<Subscript>2</Subscript>:Ga crystals

Photochromic CdF₂:Ga crystals with bistable impurity centers were effectively used for the dynamic recording of holograms and readout over the visible and near IR spectral regions at spatial frequencies of up to 5000 mm^?1 at room temperature. The diffraction efficiency of the dynamic holograms was as high as 60% at maximum and exceeded 1% when the beams’ intensities were in the ratio 1:100. As one goes from the low temperatures (≤200 K) to 300 K, the peak diffraction efficiency of the dynamic holograms decreases approximately by a factor of 1.5, while the speed of their response and photosensitivity in the long-wavelength spectral region increases by more than an order of magnitude. For the sake of comparison, the dynamic holograms were recorded under the same conditions as the widely used electrooptical SBN crystals. Comparative analysis ascertained a unique combination of the useful features offered by CdF₂:Ga crystals in holography.     

Solar radiation concentrators paired with multijunction photoelectric converters in ground-based solar power plants (Part II)

The present work is devoted to determining the conditions of the joint operation of photoelectric converter–solar concentrator pairs, which are used in solar power plants with concentrators. Three-cascade photoconverters based on A³B⁵ materials with different distributions of solar radiation in spectral ranges are studied. Concentrators of solar radiation are designed as the Fresnel lenses with silicon-on-glass structure. Refractive lens profile fabricated on the basis of Wacker RT604 silicone rubber is characterized by significant changes in refractive index with temperature. The effect of geometric parameters of the Fresnel lenses and their operating temperature on characteristics of solar radiation concentration in specified spectral intervals have been examined. The parameters of concentrators being paired with a photoelectric converter, which may ensure the efficient functioning of the solar power plant, have been calculated.     

Modeling of the Spectral Characteristics of Reflection Holograms in Photopolymeric Materials

The dependences of the spectral characteristics of reflection holograms on various parameters are investigated for the model of multilayered thin films and in the context of the Kotel'nikov theory of coupled waves. The practically important cases of the influence of the recording layer thickness shrinkage, the Bragg angle mismatch, and the recording of multicolored reflection holograms are considered. A comparative analysis of the experimental data and the results of computer modeling is made.     

Role of recording geometry in the performance of spectral diversity filters with spherical beam volume holograms

We present experimental demonstrations of spectral diversity filters with spherical beam volume holograms for multimodal multiplex spectroscopy. Major properties of filters under diffuse-light illumination are discussed. The comparisons of spectral diversity between the transmission geometry holograms and the reflection geometry holograms are also studied. The results show that there is a trade-off between the degree of the spatial coherence of the source and the spectral diversity of the filter. We also conclude that the reflection geometry holograms have better spectral diversity and less sensitivity to the spatial coherence of the source.     

Emission of organic dyes in the case of nonlinear absorption upon excitation by the XeCl* laser

Spectral luminescent properties of eight organic dyes are studied upon excitation by focused radiation from the XeCl* laser at the pump power up to 200 MW/cm². The transmission of pump radiation by dyes is investigated as a function of the pump power. It is shown that variations in the energy, spectral, and temporal parameters of radiation of organic dyes upon high-power excitation are explained by the development of superluminescence (amplified spontaneous emission).     

Recording volume holograms on color centers in a CaF2 crystal

The conditions for preparing photochromic CaF₂ crystals, recording holograms with 532-nm radiation in them, and postexposure photothermal treatment of samples with holograms that provide the formation of holographic elements of significant thickness (about 1 cm) are considered. It is shown that the diffraction efficiency of volume holograms in such crystals in the case of reading out by radiation with wave-lengths of 532 and 632.8 nm can be as high as 10–15%. The role of the recording mechanism and the Borrmann effect in the fabrication of these holograms is demonstrated.     

Electric field selectivity and multiplexing of volume holograms in LiNbO3

Theoretical and experimental investigations of electric field multiplexing and selectivity of reflection volume holograms in LiNbO₃ are reported. Recording of at least five holograms is demonstrated. Equivalent spectral selectivity (5Ƽ.5 pm for the case of three electrically tunable holograms and (5ǁ pm for the case of five electrically tunable holograms are estimated.     

对用空间扩展宽谱光源再现的彩虹全息像的分析

用空间扩展宽谱光源再现的彩虹全息像时,整个光源只在一定的光谱的和空间的“有效宽度”内起作用,本文在此概念的基础上,研究了光源的光谱扩展和空间扩展在其单独作用和联合作用时对全息像的影响。发现当两者联合作用时,对像质的总影响几乎与它们单独作用时一样。给出了用宽谱空间扩展光源所再现的彩虹全息像的分辨率,从而提出了一个实用的狭缝宽度。     

Thick holograms: a survey

Many workers are turning away from holograms made with thin photographic emulsions and are investigating ‘thick’ holograms, with their exciting potential of high diffraction efficiency, increased information storage capacity, reduced noise, and increased spectral or angular discrimination. This article discusses the principles of thick hologram theory, and describes some of the materials which can be used as thick recording media. Advantages and limitations of thick holograms are illustrated by experimental examples. The article concludes with a survey of the existing and future applications for thick holograms.     

Effect of the spectral distribution of a chirped pulse on the interaction of the high-power laser radiation with matter

The interaction of high-power picosecond laser radiation with solid targets is experimentally studied for the first time at various spectral distributions of a chirped laser pulse. The interaction of the high-power laser radiation with the target is studied at four regimes of the experimental setup: (i) at a relatively high contrast (10³) in the picosecond (Δt ～ 25 ps) range, (ii) at a relatively low contrast (3 × 10¹) in the picosecond (Δt ～ 25 ps) range, (iii) with spectral distortions of the chirped pulse, and (iv) with a strongly modulated spectrum of the chirped pulse. The results obtained reveal a strong dependence of the atomic and nuclear processes in the laser picosecond plasma on the spectral distribution of the chirped laser pulse. The prospects for the application of the spectral interferometry of chirped pulses for the online control of the parameters of the high-power laser radiation are demonstrated.     

Influence of radiation damage on lattice vibration parameters in crystalline and vitreous SiO2

The influence of radiation damage on a number of lattice vibration parameters in two SiO₂ modifications was investigated using IR reflectance spectroscopy. The radiation kinetics of changes in spectral characteristics of SiO₂ fundamental vibrations in crystalline and glassy states were determined. The reflectivity coefficient and the frequency of degenerate vibrations as functions of dose showed minima, the locations of which were governed by the type of sample. At high neutron irradiation doses (10²¹ cm⁻²), certain characteristics of the bands had the same values for both modified materials. Features of the radiation kinetics of sample dynamic parameters were determined. It was deduced that the specific character of the observed radiation-induced changes in spectral and dynamic parameters of vibrations near degenerate modes was due to both the accumulation of radiation damage and a change in the force field surrounding bridging bonds, which is related to a change in the SiO₂ structure. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 3, pp. 354–358, May–June, 2008.     

Storage of binary electrical signals in one-dimensional holograms with extremely narrow tracks

A report is given on the results of an experiment in which binary data stored in sequentially superimposed one-dimensional holograms with extremely narrow tracks were recorded on a transported recording medium. The width of the holograms was reduced to 3 μm. Since the results obtained show the optical signal-to-noise ratio of the reconstructed image points to be only slightly inferior to that with holograms with 100 μm wide tracks, the method used can be expected to yield an areal bit density greater than 10⁷ bits/cm².     

Spectroscopic diagnostics of the laser erosion plasma of an AgGaS<Subscript>2</Subscript> polycrystalline target

Results are presented from experimental studies of the radiation emitted from a plasma produced in vacuum after irradiating a polycrystalline target by 1.06-μm laser radiation with an intensity of (3–5)×10⁸ W/cm². Plasma radiation from regions located at distances of 1 and 7 mm from the target is analyzed. It is shown that the main contribution to the plasma radiation in the 220–600 nm spectral range is made by transitions from the excited states of single-charged Ag⁺ and S⁺ ions. The atomic component of plasma radiation is represented by intense spectral lines corresponding to transitions from the Rydberg states of Ag and Ga atoms, whereas no resonance lines of these atoms are observed.     

A laser system providing tunable, narrow-band radiation from 35 nm to 2 μm

We describe a laser system that readily provides radiation tunable from 2 μm in the infra-red to 35 nm in the extreme ultraviolet spectral range. The broad spectral range is covered through a range of non-linear processes such as Raman shifting and high-order harmonic generation. Pulses with duration of tens of picoseconds are obtained. The relative bandwidth of the radiation is δλ/λ=10^-4, comparable with what can be achieved by using high-resolution monochromators at state-of-the-art synchrotron beamlines. We discuss different methods for characterising the radiation in this wide wavelength regime. We also discuss the capabilities of the system from the measured parameters. Received: 12 December 2000 / Revised version: 8 March 2001 / Published online: 27 April 2001     

Fundamental Studies of Stimulated Raman Scattering and Adaptive Optics on the Basis of Stimulated Light Scattering

Some results associated with the fundamental investigations of stimulated scattering of light in various media are reported. A number of problems of adaptive optics based on stimulated scattering is studied. Concrete results of experimental investigations of physically important characteristics of conventional (spontaneous) and stimulated Raman scattering are presented and discussed. Among them are the scattering indicatrix and the relations between the phases of laser radiation incident on a substance and stimulated scattering. These results were first obtained in the G. S. Landsberg Optical Department of the P. N. Lebedev Physical Institute of the Russian Academy of Sciences. Data on excitation sources and the radiation detection technique are systematized. The main characteristics of spontaneous Raman scattering and forward and backward stimulated Raman scattering (energy parameters, pulse duration, pulse shape, divergence, brightness, spectral width, far- and near-field intensity distributions) are presented. The results on dynamic holography, phase conjugation of light in stimulated scattering, and reconstruction and recording of information (images) with the help of amplifying dynamic holograms are presented. The physical mechanisms responsible for the interference field recording and the phase conjugation of pump radiation in stimulated light scattering are discussed. The data on phase conjugation for stimulated scattering excited by picosecond optical pulses and the results associated with the effect of excitation geometry on the optical phase conjugation in the case of stimulated scattering excited by nanosecond pulses are presented.     

Formation of the nonlinear dynamic hologram in clear organic fluids

The recording of dynamic holograms during multiwave interactions in clear organic fluids (ethanol, acetone, dioxan, etc.) is investigated. It is shown that the fifth-order nonlinearities and higher become activated along with the cubical nonlinearity under the intense laser excitation (～100 MW cm^?2) in the near-IR spectral range, which allows visualization of the IR images using different orders of diffraction.