Knowledge of the velocity of sound waves in a medium allows one to characterize many aspects of the medium. It enters directly into determination of the adiabatic compressibility, the adiabatic bulk modulus, and the acoustical dispersion. Its variation is associated with anisotropic behavior. This anisotropy is evaluated in the recently developed resonant ultrasonic spectroscopy (RUS) technique from which one can evaluate elastic moduli of anisotropic samples.

The paper examines regular trends of light diffraction by ultrasound propagating in media possessing anisotropy of elastic properties. The analysis is carried out on base of the single crystals of tellurium dioxide TeO₂, calomel Hg₂Cl₂ and tellurium Te. The particular crystalline media have been chosen due to the extremely large angles between phase V and group V_g velocities of the acoustic waves in the materials. In X-Y planes of the crystals, the obliquity angle may exceed the value φ > 45°. It is shown that the strong anisotropy of the elastic properties influences on the process of light and sound interaction. In the case of Bragg regime of light diffraction, the diffracted beam intensity I₁ and the acoustic frequency bandwidth of diffraction Δf in the anisotropic crystals differ from the corresponding efficiency and the bandwidth in glass materials. The paper considers features of the acousto-optic interaction originating from the presence of the elastic anisotropy.

A review is presented of conventional eikonal theory, applied to acousto-optics, and of a new, generalized eikonal theory, specifically developed for Bragg diffracted rays. Examples of application of the latter are Bragg diffraction imaging and strong interaction with curved wave fronts of sound.

Optically isotropic media which are susceptible to acoustically induced birefringence can be used as acousto- optic polarization converters. A comparative study between fused silica and dense flint shows that at normal light incidence 52% of the light can be converted from linear to circular in the case of fused silica and only 20% in the case of dense flint. In each case the conversion appears at moderate sound amplitudes and at frequencies which are typical for the intermediate regime of diffraction. Applying oblique light incidence, most interesting effects can be obtained with fused silica at high sound frequencies which are typical for the Bragg regime of diffraction and in the neighborhood of the Bragg angle. The possibility is shown to use an AO cell fabricated of fused silica as a laser-beam splitter, converting a linearly polarized beam of light partially into a circularly polarized beam and a linearly polarized beam, the light intensity of the two beams being equal. In addition, it is seen that the temporal light intensity modulations which can be observed in the near field of the light diffracted under these specific conditions, can be understood from the polarization changes taking place.

An overview is presented of the key results in the field of acousto-optic bistability in the past two decades. It is shown that the basic acousto-optic bistable device may be described as a nonlinear dynamical system which satisfies a quadratic map. Thereafter, details are presented of several analytical methods, computer modeling approaches, including the SPICE circuit modeling technique, and experiments that have been used to understand the phenomenon. Extensions to logical and digital applications are also discussed.

We review the role of acousto-optic (AO) Bragg modulators in spatial filtering. For lowpass spatial filtering, we use the Bragg-scattered beam, whereas for highpass filtering, we employ the forward scattered beam. Using the forward-scattered beam results in cross-derivative operation applications when two orthogonally oriented AO Bragg modulators are used. Using the Bragg-scattered beam, we propose suppression of beam fanning countered in nonlinear optics. In most cases our theory is verified by experimental results and computer simulations.

It is shown that two types of acousto-optic diffraction (isotropic and anisotropic) are not independent. Speaking generally, the existence of one type testifies that the other type is possible also, though with less efficiency. The values of Raman-Nath parameter both for isotropic and anisotropic diffraction were calculated. The dependence of each Raman-Nath parameter value on every photoelastic constant is demonstrated. It is indicated that the divergent beam can interact in the "forbidden" direction in crystal, where acousto-optic figure of merit is equal to zero due to the crystal symmetry. The coefficient determining Raman-Nath parameter was calculated in the vicinity of Euler angles defining the "forbidden" [110] direction in paratellurite crystal. The results of experimental investigation of a collinear diffraction in paratellurite crystal are presented which proved the existence of this type of acousto-optic interaction with the efficiency up to 15%.

An acousto-optic generator based on the effect of optical heterodyning is investigated theoretically and experimentally. The condition for self-excitation of oscillations in this system is determined, its dependence on parameters of acousto- optic interaction and feedback circuit is analyzed. The possibility of single-mode and multimode regimes of operation is shown. Preliminary results of experimental investigations of the generator with a paratellurite acousto-optic cell are presented. Experiments on active mode locking by means of an external harmonic signal are described as well.

A number of possible configurations of acousto-optical tunable filter (AOTF) with a quasi-collinear geometry of interaction in the paratellurite crystal are observed. A theoretical examination of the AOTF resolution improving problem in the case of quasi-collinear geometry of acousto-optical interaction is presented. The analysis of interaction of light and sound in different planes of the paratellurite crystal is carried out. Devices with spherical angles of sound equal to 85.5° and 88° in the plane (110) are calculated. Some new and original configurations of AOTF are described. Possible angle apertures of sound and light in all these kinds of devices are observed and the frequency dependence, figure of merit dependencies are presented.

Brillouin scattering experiment has been carried out in the oxide crystal materials. A new wide-band component in the Brillouin spectrum has been observed in the SLAO sample. This completes typical the Brillouin spectrum in a solid state, where Rayleigh lines, stokes and anti-stokes optical signals are usually observed. This newly discovered spectral component is distributed uniformly in frequency, independent of the light power incident on a crystal and dependent on the light wavelength applied, what suggests absorption origin the phenomenon. The absorption-like channel in a scattering process should be interpreted as the sea of frequencies from where some specific values of Brillouin frequencies are seen.

This paper presents analytical solutions to the three- dimensional acousto-optic interaction problem. The analytical results are presented for safely combined applications of ultrasound and laser radiation in medicine.

Photoacoustic spectroscopy method has been applied to study nonradiative processes in the excited states of Ce³⁺ and Cr³⁺ ions in YAG crystals. A comparative analysis between photoacoustic and absorption spectra has been performed.

A model is presented for the acousto-optic interaction of a focused Gaussian laser beam with a profiled sound column in the Bragg regime. Expressions for the spectral distribution of the first diffraction orders are derived on the basis of a successive approximation method originally introduced by Aggarwal to study plane light wave diffraction by continuous plane ultrasonic waves [Proc. Ind. Acad. Sci. Sec. A 31, 417 (1950)]. It is shown that sharp images of the sound field in the first diffraction orders only occur in the focal plane of the laser beam after the sound column. The quality of the resulting images is investigated as a function of the initial beamwidth of the laser, the focal distance and the distance of the focusing lens from the sound column.

In this work there is presented a description of the Gaussian light beam diffraction on the planar ultrasound wave in the Raman-Nath region by the complex optical rays method. The case of the perpendicular light beam incidence (i.e. its axis relatively to the direction of propagation of the ultrasound beam fulfilled the acoustics buffer of Δz width was considered. Final analytical formulae gives a possibility analyze the influence of such parameters as: a size and position of the Gaussian beam waist, a laser-screen (detector) distance, a position of the ultrasound beam and Raman-Nath parameter value on diffraction pattern. It has been proved that in some cases the diffraction beams have a fine structure. The light beam deflection contribution to the diffraction pattern was taken into account. Obtained analytical formulas were illustrated by some graphs of the light intensity distributions in beams diffracted on ultrasound wave propagated in fused quartz.

In this paper the split-step Fourier method is used to find a solution to the rotation-cylindrical acousto-optic interaction problem. The numerical results are applied to practical examples which could help to answer the safety question during a combined application of ultrasound for selective tissue excision and Nd:YAG-laser for coagulation of bleeding tissue in surgical therapy.

The paper contains results of experimental investigations of the pressure field distribution in the vicinity of underwater sources of non-continuous radiating surface. Two sources were examined, each in form of 16-element array. The arrays are composed of circular piezoceramic pistons of the same dimensions and radiating properties. The elements of the first source are pistons of 25-mm-diam and resonant frequency equal to 600 kHz. The second of examined sources is using piezoelements of 10-mm-diam and resonant frequency of 1.5 MHz. Shown and characterized is the impact of the discontinuity of radiating surface on the nonlinear distortion process in the vicinity of the multi-element source.

Acousto-optic phase processor (AOPP) is a new and powerful acousto-optic device designated for measurements of phase difference of radio-signals. It can be used for detecting and recognizing of radio-sources. The main parameter, which decides of its usefulness in application, is accuracy of phase difference measurement. This paper is focused on factors affecting phase measurement accuracy.

The first part of this paper presents theoretical analysis of the response of typical photoacoustic cell excited with a laser pulse absorbed by the sample located inside the cell and causing changes of temperature in the whole system. Pressure response curves provide information about optical and thermal properties of the sample. System of 1D heat conduction differential equations for each region of the cell has been solved. Changes of solid sample temperature, resulting from absorption of a laser beam warm up gas surrounding the sample. Changes of gas temperature are transferred into changes of its pressure, in result of thermodynamic processes in the gas filling photoacoustic cell and are detected with a microphone in a typical photoacoustic experiment. In the second part of the article a review of application of wavelet analysis for PT signal filtering is presented. The wavelet method is compared with Fourier transform and signal subtraction and seems to be very promising.

We propose a novel synchronous switch for telecommunication networks at a 1.5 μm wavelength. This switch is based on the acousto-optic interaction. In this paper, we discuss about the switch's constraints to be applicable in a network, and present an acousto-optic cell architecture using planar phased array piezoelectric transducers.

Wavelets described for the first time by Haar have been rediscovered once more some years ago thanks to efforts of large community of scientist mainly belonged to a so called applied mathematicians. However, what seems especially interesting, wavelet theory, very sophisticated from mathematical point of view, quickly has been moved to applications. From application areas we should mention signal and image compression, signal filtering, signal denoising, and transient signal analysis. The paper examines different types of wavelets. The main purpose is to find the best fitting to noised peaks measured in the low-level optical-signals Brillouin scattering experiments where single photon counting method is applied.

The article presents the numerical system that allows to analyze as well as to design the acoustic, multielements ultrasound heads. The system enables the modeling of complex acoustic heads that consists of arbitrary number of simply transducers. It allows to investigate theoretically of these heads as well as to calculate the spatial distributions of acoustic field. Also the diverse presentation module of acquired field characteristics is presented.

Preliminary results concerning a hydrogen sensor based on a multilayer structure in a Surface Acoustic Wave dual-delay line system are presented. The sensor material consists of two layers performed in two different vapor deposition processes. The first one is a 720 nm CuPc layer, the other one -- a 20 nm thin palladium film. This structure was formed in a one of the dual-delay line system on a LiNbO₃ Y-cut Z-propagation substrate. In such a multilayer structure can detect hydrogen in a medium concentration range (from 0.25% to 3% in nitrogen), even at room temperature. The sensor has a very good sensitivity, stability and is entirely reversible. The response and recovery times are very short (approximately 200 s - 800 s), which is very important from the practical point of view.

The previously tested MRI methods quantitative measurement of mechanical properties required a synchronization between MRI acquisition pulses and mechanical stimulation. Two new unsynchronized methods: (1) with B_o static field gradient G_o and (2) with a B₁ radio-frequency field gradient G₁ are proposed. The methods are usable without any a- priori knowledge of the intensity, direction and frequency of the mechanical waves. A specifically modified SPAMM sequence has been used, operating on a 0.2 T MRI system. The proposed methods are sufficient fast (acquisition time less than 5 seconds) for a routine clinical use.

Unexpected rise of longwave band magnitude observed in photoacoustic (PA) spectrum obtained for the YAG:Cr laser material is discussed. Explanation of this phenomenon is proposed based on comparison of measured and calculated photoacoustic signal dependence on modulation frequency. Finite lifetime of excited level has been taken into account for this reason. Contribution of PA signal generated after absorption of sample luminescence by walls of measuring cell has been considered.

The amplitude of near field modulation of light diffraction by two ultrasound beams, simply depends on phase between two sound beams. This paper presents suggestion for measurement of this phase.

There is considered theoretically the competition near the resonant acousto-optical (AO) conditions of two mechanisms which influence to the diffraction efficiency η_d variation, when the thickness L of the sample (the length of interaction) is changed: (1) the enhancement of η_d due to increase of L, and (2) degradation of η_d due to the increase of optical absorption α_L in crystal. It is shown that: (1) when changing the length of interaction L the maximum diffraction efficiency η_d is changed and shifted in wavelength's scale, reaching the maximum value at defined L which depend on the particular interaction geometry; (2) for particular considered in present work crystals the variation of L is more critical to the wavelength λ change for GaAs as compared to InP; (3) when realizing the optimized geometry of AO interaction closed to resonant condition at frequency 2.5 GHz, the diffraction efficiency in GaAs crystals can reach 8% and in InP 3.5% per 1 mW of conducted electromagnetic power (correspondingly 8000 and 3500% per 1 W of RF power) when the thickness of samples is about 4 mm.