Conditions for the suppression of spatial harmonics at a two-frequency acoustooptic interaction in the Raman-Nath mode

It is demonstrated that the diffraction of a plane light wave by an acoustic wave of fundamental frequency in the Raman-Nath mode with admixture of the second acoustic harmonic may be accompanied by a considerable change in the higher diffraction orders with numbers ±2, ±3, etc. Conditions for the selective suppression of the orders are obtained in the weak and strong interaction modes. Results of a numerical simulation are presented.     

Highly effective acoustooptic diffraction of light by multifrequency sound using a nonaxial deflector

The subject of investigation is multiple-beam Bragg diffraction of light, i.e., the formation of a highly effective multiple-beam field representing a superposition of equidistant monochromatic acoustic waves with determinate phases and amplitudes using a nonaxial TeO₂ deflector. It is shown theoretically and experimentally that the anisotropic character of interaction considerably changes the basic parameters of multiple-beam diffraction (compared with the isotropic case): the net diffraction efficiency grows to 100%, and the frequency band expands noticeably. A modulator splitting the initial laser radiation into five beams of equal intensity with a net efficiency approaching 100% is designed.     

On the possibility of extending the dynamic range in acoustooptic analysis of the spectrum of radio signals

A method is proposed to suppress nonlinear distortions arising in the acoustooptic analysis of the spectrum of radio signals. The method is based on the polynomial nonlinear correction of an electric signal before it comes to a piezoelectric transducer. The necessary form of the correction is determined in a wide range of parameters of the acoustooptic interaction. The results of numerical simulation are presented.     

Resonant acousto-optical interaction under realistic conditions of a broadened absorption line

A theory of the resonant acousto-optical interaction has been constructed for spectral line broadening of arbitrary character. Account is taken of the strongest of the mechanisms of resonant photoelasticity, associated with the potential-deformation interaction of light and sound. It is shown that when inhomogeneous broadening is present the maximum efficiency of the acoustooptical interaction over the optical absorption length is not not reached at exact resonance, as in the case of homogeneously broadened lines, but at some separation from it, at a distance of about the half-width of the absorption line. It is shown that a combined study of the diffraction efficiency of the acousto-optical interaction and the optical absorption coefficient at near-resonant frequencies would make it possible to obtain information on the contributions of homogeneous and inhomogeneous broadening in a real resonance and thus assess the quality of the material. Fiz. Tverd. Tela (St. Petersburg) 39, 1354–1357 (August 1997)     

Theory of Acousto-Optic Filtering of Radiation in the Multifrequency Near-Field Zone of a Plane Piezoelectric Transducer

Acoustical Physics - A theory of acousto-optic filtering is developed based on Bragg diffraction of a plane light wave in the near field of radiation from an acoustic transducer excited by an...     

Inverse acoustooptic problem: Coherent summing of optical beams into a single optical channel

A highly efficient summing of mutually coherent beams (channels) into a single beam with the same divergence and aperture (an inverse acoustooptic problem) is realized via diffraction in a Bragg cell. The multibeam field to be converged is formed as a result of the diffraction (splitting) of a single laser beam. Theoretical and experimental evidence is obtained for the fact that the repeated diffraction can provide a highly efficient (up to 100%) reconstruction of beam with initial parameters. The experiments are performed with a single-mode laser radiation at 0.63 μm and multimode radiation at 0.96 μm. The virtually attained summing efficiency is on the order of 70%. The factors that act to diminish the experimental efficiency below the predicted value, the ways to raise the efficiency, and possible applications of the results of this study are discussed.     

The diffraction of electromagnetic waves by sound in conducting crystals

The diffraction of electromagnetic waves by sound in conducting crystals is investigated. It is shown that in such crystals a significant contribution to the scattering of electromagnetic waves can be made by electron waves which are generated by a sound wave and accompany it. An estimate shows that in the ‘hydrodynamic’ case ql 1 (where q is the wave number of the sound and l is the electron mean free path) the contribution from an electron density wave to the scattering of electromagnetic waves in the infrared and millimeter ranges in substances with a low electron effective mass (of the type of InSb) can be comparable to the contribution from the lattice deformation waves, or may even exceed it. The results of a concrete calculation of the first and second order intensities of Raman-Nath diffraction in a semiconductor are presented.     

Extension of the angular scanning range of the acousto-optic deflector with a two-element phased-array piezoelectric transducer

The acousto-optic deflector with a two-element phased-array piezoelectric transducer is studied at an almost limiting diffraction efficiency. Significant broadening of the working acoustic frequency band (and angular scanning range) relative to the well-studied low-efficiency regime is theoretically predicted and experimentally demonstrated. For the off-axial deflector based on paratellurite (TeO₂), a radiation wavelength of 1.06 μm, and a two-element transducer with a total length of 6 mm, the working frequency band is 17–48 MHz (with the lower frequency determined by the electromechanical properties of the transducer) at an efficiency of no less than 94% of the maximum value.     

Modification of the parabolic approximation in the theory of ultrasonic-beam diffraction in a strongly anisotropic crystal

A modification of the parabolic approximation of the diffraction theory is based on the approximation of the wave surface with allowance for the shape of the angular spectrum of the ultrasonic beam. It is demonstrated that such an approach is more accurate in the analysis of the acoustic field at a relatively high diffraction divergence and/or high acoustic anisotropy. An acoustic field is simulated in paratellurite, which is a leading acoustic material with anomalously high acoustic anisotropy.     

Acousto-optic diffraction with allowance for the influence of the acousto-optic cell boundaries

The influence of the dimension of an acousto-optic cell in the plane orthogonal to the plane of acousto-optic diffraction on the acoustic field structure and, consequently, on acousto-optic diffraction is studied theoretically and experimentally. A method is suggested for approximate calculation of the acoustic field with regard to the acoustic column reflection from the crystal faces. Based on this method, the influence of the acousto-optic cell dimensions is analyzed in a wide range of ratios between the height of the piezoelectric transducer and the height of the crystal. A region of acoustic power concentration is predicted to arise both for parallel faces and for slight wedging. A number of statements are demonstrated with paratellurite used as an interaction medium. The results may be useful in designing acousto-optic devices.