Table of contents

Single crystals of gadolinium vanadate doped with neodymium ions have been grown by the Czochralski method. The absorption and luminescence spectra of the neodymium have been measured. The absorption near 0.8 μm is higher than 70 cm⁻¹. The lifetime of the neodymium ions is 90 μs. Laser action has been achieved on the transitions ⁴F_3/2 → ⁴I_13/2, ⁴I_11/2. The differential efficiency of the lasing near 1.06 μm is 54%.

This review examines some questions concerning the capabilities of interference and polarization-interference correlation diagnostics of the amplitude-phase characteristics of random optical fields for the purpose of identifying these fields and then studying the corresponding objects. The diagnostics of random phase objects is discussed separately in the cases in which the phase dispersion of the inhomogeneities is less than and greater than one. The outlook is promising for the use of the correlation dimensionality of chaos in a field as a diagnostic parameter. It is also shown that the use of interference principles for a parallel processing of large data files can substantially increase the speed of processing systems.

It is predicted theoretically that the efficiency of self-mode locking can be raised by means of a bleachable shutter in the main cavity or an auxiliary cavity. The laser emits a stable train of ultrashort pulses under these conditions. The theory is based on a fluctuation model of the operation of a cw solid-state laser with a linear auxiliary cavity. The increase in efficiency involves a broadening of the region of parameter values of the system in which self-mode locking occurs, a significant decrease in the threshold pump intensity, and a reduced sensitivity of the operation to the phase mismatch of the lengths of the cavities. It is shown, for the first time, that a stable train of double ultrashort pulses can be generated by a system with a shutter in the auxiliary cavity. It is also shown that a self-mode locking is possible in the case in which there is a phase mismatch of the cavity lengths and there is no phase self-modulation in the main cavity.

The photophysical properties of some new and also some known complex organic molecules which emit in the wavelength interval 340–410 nm have been studied in a wide range of organic solvents. Specifically, these molecules are based on phenyl-, furyl-, and thienyl-oxazoles and oxadiazoles. Density-matrix methods are used to study the properties of a broad spectrum of excited singlet and triplet electronic states. There are relationships among the structure, fluorescence spectra, and emission properties of the complex molecules forming a quasihomologous series. The method of a priori structural modeling of active complex molecules is useful for achieving quantum-mechanical control over the properties of the excited states and the transitions.

The anomalous emission (λ~146 nm) from a Kr–Xe mixture observed in a previous study is interpreted as emission in the course of optical collisions. A kinematic model is constructed which explains the dependence of the emission intensity on the composition and temperature of the gas mixture.

A physical model and a method for solving the appropriate equations have been developed for the photodissociation of an optically dense medium in the presence of several cylindrical sources of radiation of finite length. The sources are symmetrically located with respect to the axis of the chamber containing the working material. The brightness temperatures and radiating surface areas of the sources can be time-varying. The cross section for photodissociation of the working material is an arbitrary function of frequency and time. The computations can provide for the case in which a filter, whose transmission coefficient can depend on the wavelength of the radiation in an arbitrary way, is placed between the sources and the working medium. A diffusely reflective chamber wall can also be considered. Results of calculations of the spatial distribution of active particles are presented for iodine laser-fusion amplifiers with a single source of radiation and with several different sources.

When IR laser radiation that is intensity-modulated at a frequency of 1.1 GHz is incident on a conducting target in a rarified gas at a pressure of 0.1 torr, microwave modulation of the current pulses generated in the erosion plasma is observed. A microwave signal with a voltage amplitude of 2 V is obtained at a laser intensity of 100 GW/cm². The efficiency of the conversion of laser energy to the microwave band at an intensity of 10 GW/cm² is 2.5 · 10⁻⁷.

The effect of pulses of laser radiation at a wavelength λ = 1315 nm with durations in the range 0.5–0.7 ns on the laser damage resistance of high-reflection, antireflection, and polarizing coatings and quarter-wave plates made from SiO₂ is measured and discussed. The study includes various impact geometries and radiation polarizations. It is shown that for high-reflection coatings the damage resistance depends strongly on whether the coating is at the entrance or exit surface, whereas for antireflection and single-layer coatings there is essentially no such dependence. The threshold for destruction of polarizing coatings depends on the polarization of the radiation. These results are explained within the framework of a mechanism according to which the microscopic absorbing inhomogeneities which initiate the destruction are concentrated predominantly at the boundary between the coating and substrate.

The absorption of laser radiation by a spherical microtarget is analyzed with the ponderomotive force included explicitly in the gasdynamic equations. The analysis is carried out for the experimental conditions at the ISKRA-4 apparatus, in which the wavelength of the heating pulse is 1.315 μm, and the pulse duration is 0.3 ns (the intensity of the radiation at the surface of the target is 10¹⁴–10¹⁵ W/cm²). The calculations predict a pulsation in the reflection coefficient of the plasma for the laser radiation with a characteristic period of 8 ns. The results obtained on the absorption of laser radiation are in fairly good agreement with calculations based on the SNDP method, in which the distortion of the density profile under the action of the ponderomotive force is included in the model. This agreement validates the absorption model used in the SNDP program. Inclusion of a finite electron thermal conductivity in the equations along with the ponderomotive force sharply decreases the absorption coefficient. When a limitation factor of ~ 0.03 is used, the limitation on the thermal conductivity is found to have a decisive effect on the laser energy absorbed by the target.

Photoionization of a gas by a laser pulse propagating under conditions of a coherent two-photon interaction with the atoms (or molecules) of a medium is discussed. It is shown that the small yield of electrons for small photoionization cross sections remains small even in a strong field when the cross section is large. The reason is an ionization-induced broadening of an intermediate level. As a result, an extremum appears in the ionization yield as a function of the cross section. It is also shown that the two-photon self-induced transparency for the field of the pulse at this transition can significantly decrease the energy cost of ionizing the gas.

The propagation of Gaussian pulses through an isotropic medium with anomalous frequency dispersion and spatial dispersion of the cubic nonlinearity is discussed in the aberrationless approximation. Ranges of the parameters of the light and medium in which various propagation regimes are realized are identified.

The problem of propagation of a light beam with speckle in a photorefractive crystal with diffusive photoresponse is solved analytically. While the angular spectrum of the beam remains Gaussian, the beam is deflected, with a rate of rotation proportional to the square of the divergence angle.

The problem of controlling the transmission of optical radiation through a randomly inhomogeneous medium is investigated for the case in which complete a priori information on the statistical properties of the propagation channel is available. An optimal control algorithm is found for adaptive-optics systems for an arbitrary ratio of the observation time interval to the coherence time of the propagation channel. Both cw and pulsed probe regimes are discussed. An estimate is obtained for the efficiency of this optimal algorithm for the steady adaptation state.

Algorithms for reconstructing the wavefront and for cancelling phase distortions of the field of an adaptive-optics phase-conjugating system have been developed. It is assumed that there is a measurement noise and that there are errors in the control by the phase corrector. A statistical approach based on calculus of variations and matrix calculus is used. A priori information about the statistical characteristics of the measured wavefront, the measurement noise, and the control errors is used to calculate the phase distribution to be reconstructed and the correcting phase distribution. In addition, equations are derived for orthogonal modes of the Karhunen–Loéve type which minimize the error in the correction of the phase distortions of the field for a given number of modes. These orthogonal modes are realized without approximation error by a phase corrector with prespecified response functions. Also presented and discussed are the results of calculations of the residual reproduction and correction errors for the cases of 3, 7, and 19 channels of measurement by a Hartmann receiver and for the same numbers of actuators, as a function of the amplitude of the measurement noise and the control errors.

A fast single-component objective with a corrector has been developed for focusing laser light down to a diffraction-limited spot. It has an aperture ratio of 1:1.61. For the first time, a method involving sintering and hot molding of glasses has been used to produce an aspherical corrector that can cancel a wave aberration of 352 wavelengths.

The Schuurmans theory of selective specular reflection is generalized to the case of reflection from a medium composed of multilevel atoms. The reflection spectrum given by this theory is demonstrated. In this theory, which is linear in the field, the reflection linewidth is a nonlinear function of the density of the atoms. The reason is that the Doppler broadening and the collisional broadening make nonadditive contributions to the linewidth. The results of numerical calculations show the limits of applicability of the approximate expressions of the Schuurmans theory for interpreting experiments. The Schuurmans theory is also generalized to the case of selective specular reflection from a two-component medium consisting of working and buffer atoms. The case of an additional narrowing of the reflection line (due to the wings) is discussed.

Comment on V P Torchigin 1991 Quantum Electron.21 1144.

Response to A A Maĭer regarding V P Torchigin 1991 Quantum Electron.21 1144.