Wide-aperture acousto-optic interaction in birefringent crystals

Regularities of the wide-aperture mode of light diffraction by acoustic waves in crystals with different values of birefringence are considered. The diffraction has been investigated theoretically and experimentally with the aim of applying it in acousto-optic filters used in processing uncollimated optical beams and images. It is proved that the main filtration parameters depend on the birefringence of crystals used in processing luminous fluxes. By the example of wide-aperture filters based on paratellurite, magnesium fluoride, and potassium dihydrogen phosphate crystals, it is shown that the choice of crystals with high birefringence may increase the maximum attainable angular aperture and throughput of devices. It is also proved that application of crystalline compounds of mercury and tellurium (characterized by high optical anisotropy) in filters increases spectral resolution and improves the quality of filtered images.     

Features of acousto-optic interaction in uniaxial gyrotropic crystals

The features of noncollinear acousto-optic interaction in gyrotropic crystals in the intermediate diffraction regime and the regime of Bragg diffraction were investigated. The dependence of the efficiency of diffraction in gyrotropic paratellurite, tellurium, and quartz crystals on the intensity of the ultrasonic wave, acousto-optic interaction length, and incident-light polarization was investigated. It is shown that the gyrotropy of the crystal is responsible for the appearance of a multiple-peak structure of the Bragg maximum. It has been established that in the case of propagation of incident and diffracted waves in the vicinity of the optical axis of the crystal, the diffraction efficiency is independent of the polarization state of the incident light. The results of theoretical calculations are in agreement with the experimental results obtained for uniaxial crystals. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 105–110, January–February, 2000.     

Conditions for obtaining backward collinear isotropic acousto-optic interaction in germanium and iodic acid crystals

The possibility of experimentally obtaining backward collinear isotropic acousto-optic interaction based on bulk ultrasonic waves and terahertz electromagnetic waves is considered. The magnitudes of the acousto-optic figure of merit and the corresponding acoustic frequencies are calculated for the basic crystallographic axes in germanium and iodic acid crystals. The acousto-optic parameters of both crystals are compared.     

Prolonged acousto-optic interaction with Lamb waves in crystalline plates

The propagation and acousto-optic interaction of Lamb modes in an anisotropic plate of tellurium dioxide (TeO2) are studied numerically and analytically. In the case of a Y-cut X-propagating TeO2 plate, the very high elastic anisotropy of the crystal greatly modifies the dispersion curves, giving rise to their multiple oscillations. The existence ranges of backward Lamb modes increase with the mode order contrary to the case of isotropic plates. The quasi-collinear light scattering by Lamb waves is considered. Owing to the structure of Lamb wave field, a simultaneous light diffraction at two different optical frequencies can take place while Lamb waves are excited only at the single frequency. It is demonstrated with the Z-cut (110)-propagating plate that a small change in the acoustic frequency can result in a significant shift in the frequency of the scattered light.     

Image scanning using acousto-optic interaction with surface waves

The scanning of a one-dimensional light intensity distribution was accomplished by employing the acousto-optic interaction of surface waves on LiNbO₃. The acoustic signal was 200 nano-seconds long with a center frequency of 100 MHz. To produce a large interaction length, the light propagates through the crystal parallel to the surface on which the acoustic surface wave is launched. The detected diffraction signal yields a temporal representation of the spatial intensity distribution.     

Measurement of acousto-optic interaction in Germanium in the far infrared

Acousto-optic interaction in a Germanium Bragg cell, which was operated as acoustic resonator, was measured at 119 m relative to 10.6 m. The figure of merit of the material was found to be approximately 20% higher in the far infrared. The performance of various acousto-optic materials in the far infrared is briefly discussed.     

Spatial structure of acousto-optic phase matching in uniaxial crystals

The spatial structure of Bragg angles and the transfer functions of an acousto-optic cell are calculated for the cases of isotropic and anisotropic light diffraction in a uniaxial crystal. Their change with ultrasound frequency is traced. The possibility of image processing by acousto-optic filtration of the spatial spectrum of an image is considered. The results of experimental visualization of the transfer functions of a calcium molybdate crystal cell are presented.     

Difference of natural waves determined in the modern and previous theories of natural gyrotropy of crystals

On the basis of exact numerical calculations, the difference of parameters of natural waves determined in the contemporary and previous theories of gyrotropy is determined. It is found that the differences correspond to the limit and, for the majority of commonly used crystals, are beyond the limits of the practically accessible accuracy of the measurement of natural-wave parameters. Because of this, experimenters are recommended to study gyrotropic crystals as before, using the previous theory of gyrotropy. The modern theory of gyrotropy, as a manifestation of spatial dispersion, should be used only in exceptional cases, for instance, in the search for the third, i.e., excitonic, natural wave.     

Effect of parametric refraction upon acousto-optic interaction

The interaction of optical and acoustic beams is studied for the case of a violated Bragg matching condition. The optical beam experiences self-action due to a cascade nonlinearity. Acousto-optic interaction can result in total reflection of the optical rays from the ultrasound beam.     

Collinear acousto-optic interaction in a single tellurium crystal

The problem of designing acousto-optic imaging filters based on tellurium crystal is discussed. The measurement and calculation results of acousto-optic properties of tellurium are presented. The collinear acousto-optic interaction in tellurium crystal is experimentally implemented for the first time at the light wavelength of 10.6 μm.     

Intermediate and Bragg acousto-optic interaction in elastically anisotropic medium

The Raman-Nath, intermediate and Bragg regimes of acousto-optic interaction in an acoustically anisotropic medium are theoretically examined in the paper. The general model of the interaction is extended over the case of an elastically anisotropic medium. Basic results of computer modeling of diffraction processes taking place in crystals are presented in the paper. The interaction of light and ultrasound is investigated in media with arbitrary elastic anisotropy in a wide range of the Klein-Cook and Raman-Nath parameters. The influence of the acoustic anisotropy on the process of light diffraction, especially on the light intensity in diffraction maxima, is also discussed.     

Overlap integral dependence on the penetration depth in abnormal guided acousto-optic interaction

A numerical analysis about the overlap integral for TE-TM polarized light is presented about abnormal guided acousto-optic interaction using mode conversion. Overlap integral dependence on the penetration depth is obtained in abnormal acousto-optic interaction.     

Particular features of detecting the acousto-optic interaction signal in visualization of scattering media

Experimental dependences of the detected acousto-optic interaction signal and of the signal-to-noise ratio on parameters of a scattering medium have been obtained using single- and three-slit diaphragms in front of the photocathode of the receiver. Under the aforesaid conditions, the visualization parameters of the absorbing object are compared. The conditions of preferable use of a multislit diaphragm are determined.     

Dislocation interaction with radiation defects in alkali-halide crystals

A mechanism of room-temperature irradiation-induced strengthening of alkali-halide crystals (AHCs) is suggested. It is shown that the deformation-stimulated luminescence is a result of the destruction of hole color centers, which strengthen AHCs, by dislocations.     

Application of acousto-optic interaction for holographic conversion of light fields

This paper represents a survey of research on the problem of acousto-optic conversion of optical images. This method of conversion permits us to retain all information that is contained in both amplitude and phase spatial modulation of a light wave. Particular attention is given to acousto-optic visualization of phase objects and registration of optical wavefronts. Information possibilities of the acousto-optic method are illustrated by numerical calculations as well as by some experiments recently performed in this area.     

Spectral characteristics of a Fabry-Perot resonator with controlled gyrotropy

The propagation of light through a system consisting of two naturally gyrotropic layers placed in a magnetic field with an isotropic layer in between is considered. The effect of gyrotropy on the interference amplification of light in a nonreciprocal Fabry-Perot resonator is studied. It is shown that, at normal incidence of light, the system offers a high controllable rotatory power and a high transmissivity and also exhibits no polarization ellipticity.     

Acousto-optic interaction in crystals with large acoustic anisotropy

The Bragg diffraction of light from a sinusoidal phase grating induced in an anisotropic medium by an acoustic wave has been studied theoretically for the case of a large acoustic energy walk-off. Based on the modified coupled-wave equations, the frequency and angular characteristics of an anisotropic diffraction in a paratellurite crystal have been calculated. It is shown that the acoustic beam walk-off significantly changes the angular and frequency ranges of acousto-optic interactions.     

Two dimensional image scanning of movies using surface acousto-optic interaction

The scanning of two-dimensional black and white movies is described by using the interaction of light with surface acoustic waves. The modulation transfer function for the image scanner is derived. Further, it is shown that the spatial resolution is limited by the surface acoustic wave transducer bandwidth rather than the physical size of the exit pupil of the scanner.