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Acoustic Modes Transformation upon Reflection in Tellurium Dioxide Crystal

100%
Polikarpova N., Voloshinov V.
Acta Physica Polonica A
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2015
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vol. 127
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issue 1
96-98
EN
Generation of acoustic shear waves in crystals is one of the main problem of acousto-optics. Launching of the shear waves is much more difficult than the longitudinal modes because of difficulties related to acoustic contact and also because of problems arising from matching of acoustic and electric parameters of piezoelectric transducer. We obtained the transverse waves as a result of longitudinal-shear modes reflection in a crystal. Crystals having the required effect should possess a strong anisotropy of their elastic properties to realize the effective acoustic mode transformation. In this paper, one of the important cases of the acoustic waves reflection is investigated theoretically and experimentally. The research was carried out in the crystal of paratellurite.
2
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Influence of Acoustic Anisotropy on Frequency Bandwidths of Bragg Diffraction in Two Orthogonally Polarized Diffraction Orders

100%
Zakharov A., Voloshinov V.
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EN
This paper theoretically and experimentally examines a specific regime of acousto-optic diffraction during which an arbitrarily polarized incident light in a paratellurite crystal is scattered simultaneously into two orthogonally polarized diffraction maxima. We examined acoustic energy walk-off in the crystal and its influence on phase matching as well as on distribution of light energy between the two diffraction orders. This influence was theoretically considered by means of wave vector diagrams illustrating momentum conservation law during the photon-phonon interaction. We obtained expressions for mismatch parameters in the ordinary +1 and extraordinary -1 diffraction orders both depending on the walk-off angle. The obtained parameters were used in the Raman-Nath system of coupled-wave equations to calculate the diffracted light intensities and frequency bandwidths of diffraction. We measured the bandwidths in experiments carried out in the (11̅0) plane of paratellurite crystal at the walk-off angle equal to 54°.
3
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Structure of Acoustic Field in Infrared Tellurium Based X-Y Deflector

100%
Trushin A., Voloshinov V.
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EN
Theoretical investigation of acoustic field in a tellurium two-coordinate deflector was carried out. We used angular spectrum method supported by consideration to boundary conditions in approximation of a given displacement to calculate spatial distribution of the acoustic field intensity. Volumetric illustration is presented for the acoustic beam launched from YZ face of the crystal. Cross-sections of the acoustic field generated from XZ face are also presented in the work. It is shown that the strong anisotropy of acoustic properties in the Te crystal leads to principally different structure of the two fields excited from the XZ and YZ crystal faces. The acoustic field excited from the XZ face may be considered as a simple beam with a relatively high divergence. On the other hand, the field generated from the YZ face looks like superposition of two beams with relatively low divergence. Ratio of intensities of the two beams generated by longitudinal piezotransducers is equal to the ratio predicted by analysis based by plane-wave theory.
4
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Influence of Refractive Indices Dispersion on Parameters of Imaging AOTFs Operating with Non-Polarized Light

81%
Yukhnevich T., Voloshinov V., Pritulenko I.
Acta Physica Polonica A
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2015
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vol. 127
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issue 1
78-80
EN
The paper presents results on investigation of paratellurite based imaging tunable acousto-optic filters operating with arbitrary polarized light. We analyzed influence of dispersion of refractive indices in the crystal on a simultaneous satisfaction of the Bragg matching condition for ordinary and extraordinary polarized optical beams. The analysis was carried out at different optical wavelengths over the wide tuning range of the filters 400-1150 nm. Theoretical and experimental analysis of the problem proves that in a paratellurite tunable acousto-optic filter, the Bragg matching angle common for the two optical polarizations is varying in the limits up to 0.3°. This variation of the incidence angle may be as wide as a quarter of the filter angular aperture thus proving that the examined phenomenon should be considered in design of the imaging tunable acousto-optic filters.
5
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New Acousto-Optic Regime of Interaction in Media Possessing Strong Elastic Anisotropy

81%
Voloshinov V., Djakonov E., Polikarpova N.
Acta Physica Polonica A
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2015
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vol. 127
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issue 1
36-42
EN
We present results on theoretical and first experimental investigation of a new regime of acousto-optic interaction existing in acoustically anisotropic medium. We defined the new regime as "semi-collinear" or "mixed interaction" since it combined properties of the traditional non-collinear diffraction and the pure collinear interaction. The peculiar phenomenon was registered in the tellurium dioxide crystal due to the extremely strong elastic anisotropy of the material. Application of a specific cut of the crystal provided observation of the effect in the middle infrared at the optical wavelength 3.39 μm and at the acoustic frequencies limited to 300 MHz. The observed interaction was characterized by a non-collinear propagation of incident light with respect to acoustic energy flow and simultaneously a collinear propagation of diffracted radiation along the acoustic energy flow. A brief theoretical analysis of the interaction based on wave vector diagrams and two-dimensional coupled wave equations is included in the presentation. Finally, we describe in the paper, the setup and basic details of the carried out acousto-optic experiment.
6
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Quasi-Collinear Acousto-Optic Interaction in Inhomogeneous Acoustic Field

81%
Maslakov A., Trushin A., Voloshinov V.
Acta Physica Polonica A
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2015
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vol. 127
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issue 1
46-48
EN
In studying characteristics of quasi-collinear acousto-optic tunable filters, we observed a new effect not explained by existing theories. As found, at high levels of driving power corresponding to high diffraction efficiency, a transition of energy from a diffracted light beam to a non-diffracted one vanished. In addition, the increase of the acoustic power was accompanied by a significant broadening of the filter frequency bandwidth. This effect could not be described in terms of the traditional consideration of acousto-optic diffraction based on a plane wave approximation and a model of a homogeneous acoustic column. The goal of this research was to develop a mathematical model capable of a correct description of the new effects. The paper examines a case of the quasi-collinear acousto-optic diffraction taking into account the two-dimensional spatial structure of the acoustic field. We gave a theoretical description of the effect of diffracted light beam intensity saturation at high level of acoustic driving power. It was shown that this effect was caused by the diffraction distortion of the acoustic field phase fronts in the plane of the acousto-optic interaction.
7
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Regular Trends of Acousto-Optic Interaction in Terahertz Region of Electromagnetic Radiation

81%
Nikitin P., Voloshinov V., Gerasimov V., Knyazev B.
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EN
Basic problems of acousto-optic interaction in terahertz region of electromagnetic spectrum are considered. We obtained experimental results that are fitted by generalized theoretical model developed with the goals to describe the interaction in detail. Our analysis showed that crystalline germanium is one of the best materials to observe the acousto-optic interaction in the terahertz range. The carried out study proved that a germanium based acousto-optic device could be used for fast and reliable deflection of monochromatic radiation in the terahertz spectral region.
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