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The specific manifestation of the amplification of backscattering due to surface waves, caused by angular misorientation of the optic axes of the lidar transmitter and detector, was investigated theoretically and in model experiments. This effect limits the accuracy of the internal reference method with normalization to the spontaneous Raman scattering signal, widely used in lidar experiments. Measurement errors may also arise as a result of nonlinear optical interactions caused by random focusing of the probe beam by surface waves.

An experimental investigation was made of the emission spectra of a laser plasma which appeared on the surface of distilled water and of aqueous solutions of NaCl and FeBr2 during a time interval of 0.2–8 μs after the action of a YAG:Nd3+ laser pulse. The intensity of the continuous spectrum and the temperature of the plasma fell at a rate characterized by a time constant ~ 2 μs, whereas the intensity maximum in the line spectra of the elements depended on the energy of the relevant excited state, so that the kinetics of the emission spectrum obtained above the surface of water was basically similar to the kinetics of the radiation emitted by a plasma jet formed above the surface of a solid.

Conditions are analyzed for the stability of compensation for nonlinear distortions, by means of wavefront reversal for the four combinations of polarizations of opposite waves. It is shown that the most stringent requirements on the reflectivity of the wavefront reversal mirror are satisfied for linearly polarized waves. Problems of stability of polarization states of opposite pump waves in a medium with cubic nonlinearity are considered.

Equations describing the propagation of an elliptically polarized Gaussian beam, focused in a nonlinear medium of finite length, are derived. Allowance is made for the beam inhomogeneity, nonlinearity, diffraction, and polarization state. These equations are required for measurements of the nonlinear polarization of the medium. By using these, it is possible to explain the discrepancy between certain experimental results of measurements of the nonlinear polarizability. In particular, in the case of deep focusing of the radiation in the sample, the parameters of the polarization ellipse at the exit from the medium are identical to those at the entrance. Moreover, the combined effect of diffraction and nonlinearity amounts to nonlinear rotation of the ellipse as a whole through a certain angle which is half the conventionally used axial angle of calculated within the geometric-optics approximation. Examples are given of the use of these results to explain the scatter of the published measurements. Results are also given of original experiments to measure the nonlinear precession of elliptically polarized laser radiation and these confirm the validity of the calculations.

A description is given of a new experimental method for the suppression of strong and scalar (polarized) types of stimulated scattering of light and the excitation of tensor (depolarized) types. This method is based on elongation of the nonlinear interaction region in the direction of the electric vector of the exciting wave. The results are given of experiments in which the new method was used to study the temperature dependence of the shift of the stimulated scattering in the wing of the Rayleigh line when the stimulated Brillouin scattering was suppressed. Simple formulas are given for the design of such experiments. The advantages and capabilities of the proposed method are discussed.

An analysis is made of the conditions for efficient nonlinear interaction during propagation of four concurrent waves in a cubic medium. It is found that the evolution of the energy distribution between the waves depends on their phase relationships. An investigation is made of the influence of thermal nonlinearity on the time dependence of the four-photon scattering process. Possible variants of the application of this effect in physical research are described.

The coherent anti-Stokes Raman scattering (CARS) method was used for the first time in the visible range to resolve the structure of a Raman band due to the scattering by valence vibrations by liquid water at 21°C. An automated spectrometer with a resolution of 0.5 cm−1 was based on a YAG:Nd3+ laser with amplifiers and on a dye laser.

A theoretical analysis is made of an axial image-multiplication system and some requirements realting to optical elements in such a systemt are specified. The quality of images obtained by this method is estimated in the specific case of the technological processes used in the manufacture of integrated circuits. Experimental results are reported on the generation of sets of images of drawings of integrated circuits.

Interaction between spatial components of stimulated Brillouin scattering associated with secondary scattering of angular components of the optical pump radiation by shared hypersonic waves results in specific spatial selection and disrupts wavefront reversal. In this case, an important part is played by the phase matching between the interacting waves. Theoretical and experimental investigations of this type of interaction are presented for a particular type of laser beam having a regular transverse structure. It is demonstrated that mode solutions exist for the equations describing the amplitudes of planar components of the Stokes wave. These relationships are confirmed by experimental measurements.

An experimental investigation was made of stimulated Raman scattering, in compressed hydrogen, of radiation from an electric-discharge wide-band pulse-periodic electron-beam controlled XeCl laser with a divergence of 10??4?10??5 rad, an energy per pulse up to 0.5 J, and a pulse repetition frequency ? up to 600 Hz. Under specified experimental conditions the energy efficiency of conversion to the first (353 nm), second (414 nm), and third (499 nm) Stokes components was 45, 40, and 28%, respectively. The efficiency of stimulated Raman scattering conversion decreased in the pulse-periodic regime on increase in ?, so that at ? = 500 Hz and 20 Hz the efficiency of conversion to the second and third Stokes components was 50% of the corresponding values for single pulses. A theoretical interpretation of the results obtained was developed. The main reason for the observed behavior was a reduction in the gains of the higher Stokes components because of heating of the scattering medium.

The results are given of a numerical calculation of the time structure of an echo pulse obtained in the course of laser sounding of the upper layer of the ocean in the presence of large surface waves. The calculations are carried out rigorously in a narrow range of the parameters of the problem and an allowance is made for diffraction, but in the case of more general calculations the geometric-optics method is used.

An analysis is made of the polarization interaction of laser radiation with stimulated Raman scattering and stimulated Brillouin scattering (STBS) waves in Raman- and STBS-active media.

The factors limiting the precision of measurements by the internal standard method are considered in the case of laser sounding of the upper layer of seawater across a rough water surface. Numerical modeling is used to show that, near the depth of focusing of the probe radiation by surface waves, the use of the internal standard method may result in unpredictably large errors because of the dispersion of the refractive index in seawater. The influence of such dispersion is important in dynamic and static measurements in situ.

An experimental investigation was made of the conversion efficiency and energy balance in stimulated Brillouin scattering (STBS) in various liquids and numerical solutions were obtained of a system of nonlinear equations describing approximately the conversion of pump radiation into STBS light in the presence of two-photon absorption. The experimental results and those obtained by an approximate theoretical calculation indicated that the influence of two-photon absorption was strongest near the STBS threshold. When the efficiency of conversion of pump radiation into STBS light was high, the influence of two-photon absorption decreased because of effective weakening of the field in a cell.

An analysis is made of the problem of compensation for phase distortions in a medium with time-dependent fluctuations of the permittivity (or phase velocity). The calculations are made using Green's function which allows for fluctuations of the medium within the limits of the geometric-optics method. Allowance is only made for fluctuations whose magnitude is determined by the integral along the beam trajectory. Using these assumptions, estimates can be made of the efficient utilization of wavefront reversal systems for focusing radiation in transiently fluctuating media.

A study was made of the influence of microbending of fiber waveguides on their total losses, depending on the numerical aperture of the guide. Measurements were made also of the total losses in fiber waveguides before and after assembly of an optical cable. The total losses of guides with a numerical aperture of ~0.30 were not affected significantly by cabling.

An analysis is made of steady-state generation of electromagnetic oscillations in an optical resonator excited by an external monochromatic beam when the resonator is filled with a substance characterized by a sufficiently strong temperature dependence of the refractive index and by considerable absorption at the excitation frequency.

An analysis is made of the general case of a nondegenerate system for CARS (coherent anti-Stokes Raman scattering) spectroscopy in the case of remote measurements. A system of equations is derived for the interacting fields: it allows for stimulated Brillouin scattering and for enhancement of pump radiation by stimulated Raman scattering. The constant field approximation and realistic experimental conditions are used in estimating the magnitude of the signal which should be observed.

The Kirchoff integral is used to calculate the intensity of an echo signal reaching a detector after double passage of probe radiation across a stochastically perturbed water surface with a narrow spectral energy distribution.

The components of the nonlinear susceptibility tensor chi/sup(/sup 3/)/sub 1221/ were determined by a method eliminating the contribution of the slow part of the nonlinearity. A comparison with an interferometric method made it possible to demonstrate a considerable contribution of the slow part of the nonlinearity in the measurements of n/sub 2/ under conditions of hard focusing of radiation in a sample. This comparison also showed that allowance for the slow part of the nonlinearity is essential in calorimetric measurements of n/sub 2/ in the case of pulse durations typical of Q-switching conditions.

The first Soviet low-loss fiber-optical cable is described. The ten-fiber cable has the lowest optical losses of 8 dB/km at the wavelength of 0.9 μ and 5 dB/km at the wavelength of 10.6 μ.

An analysis is made of the possibility of using the CARS method for remote measurements by excitation of an intense return wave in stimulated Brillouin scattering in the medium which is being probed. The results are reported of a model (laboratory) experiment on such remote probing, carried out using a neodymium glass laser (second harmonic) and a dye laser pumped by the second harmonic.

Two interference methods were developed for measuring geometric parameters of quasi-Gaussian beams. In these methods, the radius of curvature of the wavefront, radius of the diffraction-limited divergence, and radius and position of the beam constriction were determined by measuring the distances between the maxima or minima in an interference pattern. There was no need to plot the sensitivity curve of the photographic film. Moreover, the proposed methods provided easy means for qualitative and quantitative analysis of the wavefront aberrations.

A study was made of additional optical losses in the range from – 195 °C to + 85 °C observed in a fiber-optic cable containing different types of waveguides. The use of waveguides with noncrystallizing primary and fluoroplastic secondary claddings made it possible to ensure that the additional losses in this cable were less than 1 dB/km at temperatures in the range from – 120 °C to + 85 °C.

A parametric phase-reversing amplifier of sound is described. Its operating principles and estimates of the parameters are given. An actual amplifier is described: its active medium is a liquid containing gas bubbles and it is pumped by an alternating electric field. The phenomenon of two-pulse electroacoustic echo is analyzed from the point of view of parametric reversal of acoustic wavefronts.

Measurements were made of the energy, space, and time characteristics of radiation from a laser with a long (273 m) resonator. Stable self-locking of the longitudinal modes was observed in this laser. A mechanism accounting for the self-mode-locking in lasers with long resonators is proposed.

A study was made of the influence of some chemical compounds on the luminescence spectrum of phytoplankton. It was found that the intensity of the pigment luminescence decreased strongly in the region of 650 nm and that the integrated intensity of the signal decreased threefold on introduction of 0.01% HgCl2 into an aqueous medium containing phytoplankton.

An analysis is made of variants of systems which can extend the range of conditions under which the CARS method can be used. An analysis is made of the efficiency of such systems from the point of view of the condition for spatial phase-matching in four-wave interactions.

An investigation was made of the influence of temperature on the luminescence spectrum of blue-green single-cell algae in water. It was found that the relative intensity of the maxima changed by 30% when temperature was increased from 0 to 23 ?C. This dependence could be used for remote determination of the temperature of water.

Conditions are found for ensuring compensation of nonlinear distortions of elliptically polarized beams by wavefront reversal. It is shown that, in contrast to the case of linear polarization, there are several ways of achieving such compensation and they reduce to wavefront reversal which conserves the polarization structure and is characterized by near-unity reflection coefficients as well as additional rotation of the polarization vectors.