In the present paper, Fresnel phenomena occurring in the near field of light diffracted by a plane ultrasonic wave are examined for parameters in the Raman-Nath, Bragg, near-Bragg, and intermediate diffraction regime. First, the basic equations of the theoretical model are presented. Next, some remarkable results obtained over the last three years are summarized, such as the possibility of reconstructing the time-history of the sound wave from the modulation profile of the diffracted light intensity under Raman-Nath conditions and the good agreement between theory and experiment in the intermediate diffraction regime. Finally, new results relevant to the Bragg and near-Bragg regime are presented. Throughout the paper, the very high sensitivity of the light intensity with respect to several diffraction parameters is emphasized and demonstrated.

Scanning acoustic microscopy (SAM) is a method to detect and characterize typical elastic discontinuities, which are connected with mechanical defects or electronic failures on modules and chips, actors, packages, and micromechanical tools. As the SAM can `look'' under the surface of the specimen it is able to reveal hidden structures from the inner part of the probe. Direct interpretation of the monitor image is difficult, especially when the object of investigation is unknown, as three types of contrast mechanisms have to be considered separately for all thin layers of the specimen. Additionally, each elementary layer is more or less defocussed and the superposition of all reveals a highly complicated structure on the monitor screen.

The determination of the actual vibration distribution of an ultrasonic transducer radiating into a liquid is identified as one of the major unresolved questions of precision ultrasonic science. Direct measurement of the surface vibration distribution using optical interferometry is not possible due to the piezo-optic effects of the radiating ultrasonic beam on the liquid through which the optical interferometer beam must travel. An analysis is presented which relates the actual vibration distribution to that which would appear to be measured. The possibility of inverting this process to retrieve the original distribution is identified.

The interaction of light waves and acoustic vibrations of the lattice manifests in a variety of phenomena. The non-equilibrium phonons in solids are created in two ways: using ultrasonic techniques, the coherent waves of relatively low frequencies as compared to kT/h are generated, and using thermal pulse techniques, the waves with random phases in a wide frequency range with the central frequency of order kT/h are injected. The interaction of waves of the latter type with a light propagating in the surface optical waveguides is the subject of the present lecture. Depending on the lifetime of the phonons, the ballistic and diffusive propagation cases should be distinguishable. Here we consider the diffusive propagation case only, describing the phenomena in terms of the lattice temperature.

The acousto-optic correlator is a well developed tool for performing pattern recognition. By cascading several one-dimensional correlators in parallel, it is possible to implement two- dimensional image correlation using only one acousto-optic device. We review the development of acousto-optic correlation and pattern recognition systems, and describe recent developments which have made image correlation practical. Computer simulations of image correlation and modifications to the existing architectures are discussed.

The phase-vector analysis enabled us to study the vectorial behavior of the light diffracted in the Fraunhofer plane by two adjacent antiparallel beams of progressive ultrasonic waves. It predicts also the vector angle, usually neglected, in addition to the light amplitude. Interesting frequency shifts superposed in some cases to a frequency modulation have been found if the ultrasonic frequency ratio F1/F2 equals m/n, with m, n small integers and m does not equal n. We present the results of the improved research, carried out by analyzing the light beam interacting with several wavelengths (Lambda) 0 equals m(Lambda) 1 equals n(Lambda) 2, to avoid the effects of the distortions of the diffraction lobes occurring if one wave (Lambda) 0 only is considered.

The reconstruction processes in acoustical tomography have to satisfy several conditions. First, account has to be taken of refraction. Second, account has to be taken of scattering (which is linked to the refraction process). Third, diffraction occurs. Fourth, the sampling of wave fronts by transducers of finite size produces averaging effects which reduce resolution. Fifth, the refractive and scattering effects create a noise problem which limits time of flight measurement resolution. Sixth, the reconstruction times should be less than 1 minute for many applications. These factors are discussed in relation to the conditions found in soft tissue.

Light diffraction by ultrasound waves is discussed in the wide range from weak acousto-optic interaction to strong acousto-optic interaction in terms of numerical simulations and experimental investigations for normal incidence. Particular emphasis has been placed on the complex nature of the diffracted light amplitude. The paper is intended as a contribution towards a unified representation of the general phenomenon.

Acousto-optic research in Belgium started in 1942 by R. Mertens, at the Rijksuniversiteit, Gent and was continued by O. Leroy at the Katholieke Universiteit Leuven Campus, Kortrijk since 1972. Methods and results, used in solving light diffraction problems caused by single (progressive and standing), superposed, parallel, anti-parallel, and crossing ultrasonic beams are discussed. Optical near- and far-field are mentioned from which inverse calculations were possible.

We obtained a general expression for an electric field amplitude of a diffracted light beam. With the help of this expression one can calculate the intensity of the diffracted light at a different distance from an acoustic transducer. It is shown that diffraction characteristics are essentially dependent on a divergency of the acoustic beam. The central frequency of transmission curve is shifted relative to 2 equals 0 corresponding exactly to the satisfaction of the Bragg condition. The optimum relationship between the interaction region length and the acoustic beam radius is found.

Recently, there appeared in acousto-optics (AO) a tendency to develop the optical information processing technology based on AO spatial light modulators, which are very promising in relation to very fast analog signal processing and algebraic data processing with digital accuracy. The best widely distinguished way to win many other marketing counterparts lies in the performance of AO interactions in guided wave structures with highly developed planar technology. In contrast to numerous developments devoted to guided wave AO devices the collinear ones facilitate multichannel or 2-D-devices to increase their throughput and processing gain. We discuss general backgrounds of the guided wave AO devices, especially in the case of the collinear wave propagations. Some applications similar to the multichannel collinear AO Bragg cell on LiNbO for 2-D-beam scanning, AO spectrum analysis, 2-D- Fourier signal processing, frequency multiplexing/demultiplexing, and digital vector-matrix multiplication are presented.

Semiconductor crystals exhibit very high figures of merit for acousto-optic applications at photon energies close to their band gaps. In semiconductor superlattices one can also exploit a Fabry-Perot effect whose resonances occur near the stop bands. These periodic structures allow light retrodiffraction by ultrasonic waves. It is shown that the use of semiconductor crystals and superlattices as interaction materials permits the conception of fast broadband acousto-optic deflectors and modulators.

The proposal of application of acousto-optical methods for nondestructive evaluation in the layered system described by O. Leroy and J. M. Claeys and the reconstructing of an ultrasonic field method used by Y. Nishida et al., have been reviewed. A suggestion is made to adapt the Nishida et al.'s, method of measuring the intensities in given light diffraction orders in pairs: I₊₁ + I_-1, I₊₁ - I_-1, I₊₂ + I_-2, I₊₂ - I_-2, ... to evaluate Raman-Nath parameters and phase shift between UW components for the layered system similar to that described by O. Leroy and Claeys.

The nature of the first moment ensemble averages of the scattered light fields from an acousto- optic (AO) device in the Bragg regime under the influence of noise is investigated. The intensity profile of the diffracted light at the output has coherent and incoherent contributions from the deterministic and random parts of the interaction impulse response. The light beam profile is distorted due to the imperfections in the sound profile resulting from the bonding between the transducer and the AO device, random sound scatterers, etc. We compute the dependence of the signal-to-noise ratio of the first order light on the mean square values of the distributions of the imperfections and scatterers. The dependence of the diffracted light on the optical imperfections in the AO interaction region is also discussed.

Anisotropic Bragg diffraction of light on ultrasound propagating along (110) axis or close to the axis in TeO₂ is examined. Special attention is devoted to close to collinear scattering in paratellurite with a long length of interaction. The investigated case of the diffraction is characterized by a collinear orientation of optical and ultrasonic group velocity vectors resulting in the interaction length up to several centimeters and extremely narrow frequency bands of Bragg scattering.

Results of the theoretical and experimental investigation of an additional phase shift effect, which arises during propagation of a light beam through an acoustic field, are presented. Some consequences of the effect, namely, a light polarization change and a polarization nonreciprocity are considered as well.

In the report an experimental apparatus for photoacoustic imaging is described. Results of testing measurements and investigation of ion-implanted silicon wafer were presented. Obtained results show possibilities of photoacoustic imaging of ion-implanted regions in semiconductors with good resolution. Strong dependence of the resolution on frequency was demonstrated.

A method is proposed to describe the diffraction phenomena that occur when an inhomogeneous plane wave is incident onto a stress-free solid-vacuum boundary with periodic roughness. Theoretical results for several samples show that this method predicts a minimum in the reflection coefficient near the fundamental resonance frequency, corresponding to Rayleigh wave generation. This dip is clearly observed experimentally, but failed to show up in previous treatments of the problem which always used homogeneous plane waves.

Binary holographic phase gratings, also known as Dammann gratings, can be electronically synthesized by using the acousto-optic effect. We review the field of digital phase grating optics, and discuss some of their modern applications. We present the underlying grating theory and describe an approach to realizing these gratings in an acousto-optic device. Potential applications include Fourier domain signal processing, matched filtering, optical interconnects, and switches for digital optical computing.

Condition of the surface where acousto-optic interaction occurs defines the nature of the process in many respects. Specifically, the light scattering on the rough changing in time surface loses its coherence, that leads to efficiency of known interference and holographic methods of small acoustic perturbation registration decreases. Results of theoretical and experimental investigations of acoustic modulation, both space and frequency spectra of the light scattered by essentially incoherent means on the rough chaotic moving surface, are presented. It is shown that the magnitude of sound modulation of the scattered light energetic pattern is defined not only by the interface condition, but also by the light characteristics. Further, the possibility of coherent combination frequency Bragg scattering is considered. Such processes occur as a result of acousto-optic interaction on a statistically rough surface with the typical sizes of roughness much larger with respect to the wavelength of both light and sound. In case of commensurable wavelengths of optic and acoustic fields, we arrange the phenomenon with similar phase conjunction of optic radiation on sound stimulated chaotic moving rough surfaces.

The characterization of layered media, for example in semiconductor technology, can be one important field for future application of acoustic microscopy. Opaque layers can be evaluated in a nondestructive way without the need of edges. The measurements require pads of 40 $CCL 40 micrometers ². This leads to a spatial resolution of the same magnitude. For further applications it seemed to be of technological interest to expand this method on buried layers. Thickness measurements are based on the comparison of surface acoustic wave (SAW) speed evaluated using the V(z)-option of the acoustic microscope with theoretically predicted values. We used a mathematical model for the description of sound propagation in multilayered structures by Thomson and Haskell to calculate the SAW-speeds for a given system of layers. The evaluation of SAW-speed from measured V(z)-curves with high accuracy was performed by means of FFT-algorithm. By comparing calculated SAW-speed values with results from measurement it was possible to verify the theoretical approach.

Double ultrasonic beam acousto-optical modulators require high precision driving electric signals for stable control of frequency ratio and phase shift. The high precision digital synthesis method has been developed for the generation of high quality periodic signals. Maximum frequency range of synthesized waveforms is determined by the speed of available random access memory (RAM) and an available D/A converter. A computer-based digital function generator can generate any arbitrary type of signal in the frequency range determined by the speed of RAM and the D/A converter. Frequency stability is determined by the quartz clock of the D/A converter and is in the order of 1/10⁷. Periodic waveforms can be synthesized, stored, and then played continuously by looping through the RAM buffer.

The pulsed signal analysis methods and their applicability to photoacoustic spectroscopy are discussed. Advantages and limitations of classical non-stationary signal analysis tool -- short- term Fourier transform and newly introduced time-frequency distributions -- are outlined. The examples of pulsed photoacoustic signal analysis with the above-mentioned methods applied are presented.

The photoacoustic (PA) cell containing the sample of material under investigation is considered as one among the most important parts of the photoacoustic spectroscope. Examples of newly designed cells for liquids and solids investigation are presented. The special photoacoustic cell for laser beam intensity measurement, together with its preliminary test results, is described.

The idea of high resolution pin scanning microscopy is presented. A comparison between a scanning head of classical acoustical microscopy and the pin one are described. Construction details of the pin scanning system and some results obtained are shown and discussed.

The preliminary results of investigations of the influence of gated ultrasonic wave on PCB nematic molecules oriented by the method of light diffraction are presented.

A method is developed for photodeflection spectroscopy of flowing gyrotropic media, having circular dichroism bands. Particular cases of collinear and transversal geometry of excitating and probing beam interaction are discussed. Probe beam deflection angles are defined, and their magnitudes are analyzed depending on modulation frequency (Omega) , interaction time t, elipticity of excilating beam, velocity of sample translation movement V_(chi ), as well as a value of reduced coordinate (chi) /(alpha) (where (alpha) is a Gause beam radius). It is shown, that there is no influence of gyrotropic effects on the angular dependence magnitude in the case of interaction collinear geometry. Application of right- and left-circular polarized excitated radiation in the case of transversal geometry of interaction leads to the appearance of two deflection angles (phi) _+/- of the probe beam. The deflection angles difference (Delta) (phi) equals (phi) ₊ -(phi) _- may reach quite measurable values (10^-3 - 10^-4 radn) and depends on movement velocity V_chi, modulation frequency (Omega) , heating time of gyrotropic sample t, and on the circular dichroism parameter (gamma) " equals Im(gamma) . A method of defining of an image part of gyration complex parameter (gamma) " on the basis of the spectroscopy photodeflection method is presented.

The photoacoustic effect in absorbing gyrotropic media at the contrary interaction of two elliptically polarized plane monochromatic light waves was investigated. It was determined that the PA response essentially depends on the value of gyration parameter real part amenable to the specific rotation of polarization plane. Negligible variations of the (gamma) ' value can lead to increase of PA signal amplitude by several orders without change of contrary light waves intensity. The characteristic extremum was discovered on graphic dependence of the PA signal amplitude at circular dichroism parameter, which is determined on the one hand by the rate of the volumetric energy dissipation change; on the other hand it is connected with the redistribution of the dissipative energy due to the multipath interference of the interacted modes and also their polarization state. We propose a method of control of generated PA signal amplitude and phase characteristics connected with the possibility of influence by external magnetic field on the energy dissipation of electromagnetic waves.

Photoacoustic spectra of malachite green adsorbed on silica gel were investigated at high dye concentrations. The measurements were carried out for two markedly differing layer thicknesses of dyed silica. The ratio of maxima of two characteristic dye bands at (lambda) equals 620 nm and (lambda) equals 425 nm was chosen as an indicator of concentration dependent changes in the shapes of the photoacoustic spectra investigated. The comparison of experimental data with the theoretical model implies that the changes observed in the shape of the spectrum result first of all from the mechanism of the signal generation in inhomogeneous medium.

Formulae for the differential scattering cross section and the scattering cross section of unit volume of a random turbulent medium have been derived using the von Karman correlation function of the acoustic refractive index fluctuations. The differential scattering cross section has been studied in dependence on scattering angles, mean scale of inhomogeneities, and the wavelength. The elastic mean free path of acoustic waves in turbulent media has been estimated in dependence on k (DOT) a and the mean square fluctuation of the medium refractive index for acoustic waves.

Infrared absorption (IR) and Fourier transformed photoacoustic spectra (FTIR PAS) of the europium dibenzoylmethane complexes are compared in the 400 - 1400 and 2400 - 3400 cm^-1 regions. A close similarity has been found between the IR and FTIR PAS spectra in the whole spectral range examined, in respect of both line positions and intensity ratios. Vibration frequencies in the PAS and IR spectra and their interpretation are given.

Studies in pressure and temperature effects on non-equilibrium superquick processes occurring within condensed media allow us to get much more correct information about mechanisms of intermolecular relations during the molecule media transfer from natural position up to the more strongly packed one. This is proven by experimental results on effective influence of pressure upon vibrational relaxation of benzene, carbon bisulfide, carbon dioxide, tetrachloridemethane, and methane. The main purpose of the paper is to conduct experimental studies of the pressure and temperature effects on vibrational relaxation processes of liquid brombenzene within the range of ultra high frequencies (UHF). These studies are accessible as yet to optical Brillouin spectroscopy in total with low-frequency ultrasound techniques.

The usage of high pressure measuring techniques increases the possibility of studying and more common interpretation of condensed media molecular processes. Nowadays, ultrasonic techniques are widely used in studying liquids under high pressures, various temperatures, and frequencies. However, the present techniques for measurements allow us to conduct studies within a relatively narrow range of pressures (100 to 500 MPa) and frequencies (1 to 30 MHz) that hinder the registration of thermodynamic and visco-elastic parameters of liquid media with densities comparable with the solid state. In connection with this the authors of the paper tried to develop acoustic measurements experimental techniques in the direction of higher frequencies (to 100 MHz) and pressures (to 1000 MPa). The authors give a brief description of more important technical units of the developed high pressure acoustic equipment.

The solution of the main problem of high frequency (up to 10 GHz) acousto-optics (sound attenuation and restriction of the bandwidth) may consist in the utilization of the multielement electroacoustical transducers which ensure automatic tuning at Bragg angle in wide frequency band. The current presentation describes the consideration of different types of new high frequency multielement transducers, the theoretical advantages of the diffraction efficiency and bandwidth of acousto-optic interaction as compared with the case of the one element transducer.

An acousto-optical measurement method is described which was used to conduct proof of principle experiments for a novel acoustic pulse system. The pulse theory the Localized Wave pulse is discussed and the system explained and described. The results of the experiments confirm the Localized Wave theory. 2.