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An investigation was made of the visible radiation emitted by planar metal–barrier–metal structures as a result of decay of plasma oscillations. A method was found for increasing the intensity of the output radiation using a barrier in the form of a multilayer insulator consisting of different oxides evaporated consecutively. It was found experimentally that the efficiency of emission by these structures was twice that of structures with a simple barrier. The rise time of an optical response of such metal–barrier–metal structures to a single short voltage pulse was at least 4 nsec. The output radiation intensity increased under the additional action of a microwave field of frequency up to 1.2 GHz. This property could be used for the purpose of fast-response visualization of microwave fields with a sensitivity threshold of ~1 mW/cm2.

An analysis is made of the evolution of high-power laser pulses in the case of coherent two-photon interaction with resonant media. It is shown that pulses of frequencies ω0 and ωs satisfying the equalit ω0±ω0=ω21 (ω21 is the resonance frequency of the medium) experience splitting into separate subpulses followed by a reduction in their duration and increase in their power. The efficiency of this process depends on the initial ratio of the amplitudes E0 and Es. It is shown that such effects can be observed in paramagnetic acoustic resonance.

A theoretical investigation was made of the propagation of a high-power light pulse in a semiconductor under interband absorption conditions. A self-consistent system of equations was obtained for the field and the medium allowing for nonequilibrium particle relaxation processes. Allowance was also made for the influence of a strong pulse field on the intensity of such processes. Analytic and numerical investigation of various interesting cases permit comparison between theory and experiment.

A theoretical investigation is made of the coherent interaction between high-power optical radiation and excitons in impurity-doped molecular crystals. A self-consistent system of equations is obtained for the medium and the optical field. It is shown that, under certain conditions, the distances over which coherence effects are observed, decrease sharply. An analysis is made of the specific conditions for the experimental observation of these effects.

A numerical analysis is made of a self-consistent system of equations describing resonant two-photon interaction between light and a medium. The radiation pulse duration is assumed to be short compared with the phase relaxation time (coherent interaction). Allowance is made for the transverse structure of the fundamental-frequency and third-harmonic pulses. It is found that under certain conditions, the resultant self-focusing increases the efficiency of energy transfer from the pump pulse to the third-harmonic radiation.

A diffusion expansion is obtained for the integrals of Coulomb collisions between nonequilibrium electrons which are responsible for relaxation of the particle distribution functions and polarization induced by interband interaction of a high-power optical pulse with semiconductors and insulators. An analysis is made of the effect of Coulomb collisions on the coherence of the interaction between the field and the medium.

This part of the review deals with coherent effects in the interaction of ultrashort light pulses with media characterized by degenerate transitions, including semiconducting media (in the direct band-band transition region), and with media exhibiting two-photon resonances. It is shown that the self-induced transparency can appear under such conditions and the properties of this effect are studied. A review is made of experimental investigations of the coherent bleaching of various media. The paper ends with a list of the most urgent problems requiring clarification.

A theoretical analysis is made of the influence of a transverse inhomogeneity of a plane wave on third harmonic generation under conditions of coherent two-photon interaction with resonant media. It is found that self-focusing filaments are formed in a distance equal to the two-photon absorption length and that the harmonic generation efficiency is enhanced considerably under these conditions.

A theoretical investigation is made of the evolution of a high-power light pulse in a semiconductor under interband interaction conditions for an arbitrary relationship between the effective masses of electrons in the bands. A self-consistent system of equations for the pulse field and medium are derived and some properties of the system are considered.

The threshold characteristics of semiconductor lasers are considered as a function of the doping level and the temperature. Use is made of a model of the transitions from a parabolic conduction band to an impurity acceptor band with a Gaussian distribution of the density of states. The gain and the spontaneous recombination rate are calculated. The dependences of the threshold current, the quasi-Fermi levels, and the laser oscillation frequency on the impurity concentration and the temperature are obtained.

A theoretical, investigation is made of the laser gain associated with interband transitions in heavily doped semiconductors. Analytic expressions are obtained for the gain and quasi-Fermi levels considered as a function of the impurity concentration, temperature, and pumping power.

A theoretical analysis is made of the nonequilibrium dissociation of molecules under the action of laser radiation whose frequency coincides with the frequency of one of the vibrational modes of a molecule. Equations are obtained for the relationship between the dissociation rate constant and the vibrational temperature, on the one hand, and the laser radiation flux density, on the other. It is assumed that the characteristics of the molecules and the gas temperature are known. The vibrational states of molecules are considered in the harmonic oscillator approximation and also making allowance for the anharmonicity.

A theory is given of the resonant interaction between an ultrashort coherent light pulse and a semiconductor, which occurs when the pulse duration is less than the polarization or phase memory relaxation time. It is shown that, under certain conditions, a stationary 2? pulse can form. Numerical estimates of the velocity of propagation of a stable pulse are obtained for a typical semiconductor.

A theoretical analysis is made of the problem of obtaining a negative differential resistance in the currentvoltage characteristic of metal–barrier–metal–barrier–metal junctions and the feasibility of using these to develop a tunable oscillator is examined. Calculations are made of the maximum lasing power and gain.

Electromagnetic oscillations of 180 kHz frequency tunable in a range of 30 kHz were generated in a metal–barrier–metal–barrier–metal (MBMBM) structure characterized by a negative differential resistance. Such structures are potential tunable sources of electromagnetic radiation ranging from the radio to the optical frequencies.

An analysis is made of the influence of third harmonic generation and parametric interaction on twophoton coherent effects which occur during propagation of high-power light pulses through resonant media. It is shown that third harmonic pulses can be generated in this way.

A theoretical investigation is reported of the influence of the electron-phonon interaction on the long-wavelength edge of the gain band of semiconductors. A numerical study is made of the specific case of a CdS crystal. It is shown that this interaction allows us to explain some of the experimentally observed effects.

An analysis is made of some aspects of defect formation in laser semiconductor crystals under conditions of capture of nonequilibrium carriers by the resonance level of a deep center. Calculations are made of the resonance level width GAMMA/sub n/ with respect to electron autoionization for the cases of acceptor and donor centers. A numerical investigation is made by computer of the dependence of GAMMA/sub n/ on the captured electron energy and on various center parameters. A comparison is made with the experiment for the case of a donor center. Analyses are also made of some aspects of the defect formation kinetics. Functions describing the increase in the stimulated emission threshold and the laser service life are determined and a comparison is made with some experimental results.

An experimental investigation was made of the two-photon absorption in GaAs using laser radiation of 2ω= 1.50, 1.75, 1.89, and 2.34 eV energies at room temperature (the for jidden band width of the semiconductor was Δ = 1.43 eV). An anomalous rise in the absorption was observed at the band edge and this was interpreted theoretically as the influence of a deep impurity level in the middle of the forbidden band.

It is shown theoretically that self-induced transparency may occur during propagation of a laser radiation pulse in the case of two-photon interaction with small-radius excitons. An experimental method for the observation of this effect is suggested.

A theoretical investigation is made of the interaction between an electron and a barrier in metal–barrier–metal junctions in a high-frequency electromagnetic field. Using the second harmonic as an example, it is shown that harmonic generation does not take place over the whole length of the metal wire but in a region near the barrier.

An analysis is made of the influence of the phase modulation and Stark shift of levels on the coherence of light pulses propagating in media with a two-photon resonant interaction. An analytic solution is obtained for the case of two pulses, each carrying the same number of photons. The case of arbitrary numbers of photons in light pulses is also discussed.

An analysis is made of the mechanism of nonradiative resonant electron capture accompanied by the transfer of energy to a lattice atom. This mechanism may be responsible for the motion and formation of defects in semiconductors as a result of injection of excess carriers. The process of dissociative capture of an electron by a molecule is used as the model of the defect-forming capture process. An approximate expression is obtained for the probability of the displacement of atoms in laser crystals of the gallium arsenide type.

A self-consistent system of equations is obtained for the field and medium (semiconductor) in the propagation of high-power light pulses under interband absorption conditions. Allowance is made for the relaxation processes. It is shown that a sufficiently strong pulse field may "suppress" the polarization relaxation processes, increase the coherence time, and thus facilitate the appearance of the self-induced transparency in semiconductors.

A study was made of light emitted as a result of decay of surface plasma oscillations in metal–oxide–metal structures. An absolute increase in the intensity of this light and its control were achieved by using a medium external to the metal film. This medium was a liquid crystal forming a domain structure in a static electric field. The arrangement provided a convenient means for investigating the processes of radiative decay of surface plasmons.

A theoretical analysis is made of the interaction of radiation with a semiconductor crystal under the Gunn oscillation conditions. It is shown that the reflection coefficient of a domain may differ considerably from the reflection coefficient of a crystal as a whole. A method for amplitude modulation utilizing this effect is suggested. The plasma and magnetoplasma reflections are analyzed.

A theoretical analysis is made of the dependences of the Fermi level and absorption coefficient on the field in optical transitions occurring in doped semiconductors. The distribution of the intensity of the optical field in a semiconductor crystal is obtained under saturation conditions.

Collisions of heavy particles (in particular, collisions which are accompanied by charge exchange) can be described over a wide energy range in the quasi-classical (parametric) approximation. This investigation consists in assuming that the coordinates of the nuclei are stipulated time functions rather than dynamic variables. Under these conditions the problem of charge exchange reduces to solving a system of equations in nonstationary perturbation theory for the probability amplitudes of the states.

An increase in the efficiency of light emission (by over an order of magnitude) was achieved for plasma oscillations in a thin silver film of a gold–aluminum oxide–silver (Au–Al2O3–Ag) structure by altering the permittivity of a nematic liquid crystal adjoining the silver film.

An experimental study was made of the amplification of surface plasma oscillations due to a negative differential resistance of an Au–Al2O3–In2O3–Al2O3–In2O3–Al2O3–Ag structure resulting from resonance tunneling of electrons in a periodic potential field of a complex insulator barrier in this metal–barrier–metal structure.

A theoretical analysis is made of the dependence of the quasi-Fermi levels on the impurity concentration and nonequilibrium carrier density in heavily doped semiconductors. The influence of the degree of doping, pumping, and temperature on the behavior of the spontaneous emission is discussed. It is assumed that the conditions are of the kind encountered in semiconductor lasers.

The results are given of a study of the dispersion of E1 polaritons in an LiIO3 crystal. The dispersion of the polaritons was deduced from the angular dependence of the wave vector of the exciting radiation in the crystal. It was found that the dispersion curves of the E1 polaritons could be determined in the range of the polariton wave vectors from zero to ~105 cm–1.

A theoretical analysis is made of the possibility of inversion of the population of the vibrational levels of a molecule by external pumping which depends exponentially on time. The nature of the population distribution is deduced and the inversion conditions are obtained.

Equations are obtained for the change in the total energy of an ultrashort coherent light pulse traveling across a semiconductor under two-photon interband resonance conditions. It is shown that the absorption of such a pulse may be several orders of magnitude less than the absorption of a weak incoherent pulse.

It is shown experimentally that an injection laser beam can be deflected quite effectively by an acoustooptic deflector. The maximum deflection obtained (~40') corresponds, for the divergence of the investigated beam, to 8 resolvable positions a hologram memory. A deflection by ~6° is possible if an ultrasonic cell contains a TeO2 crystal.

A review is given of the current status of the self-induced transparency effect. The McCall–Hahn theory (2π pulses) is considered and its generalization to the case of phase modulation of radiation pulses, degeneracy of transitions, and two-photon resonance is discussed. The relationship with the theory of nonlinear waves, obeying the Korteweg–de Vries equation, is pointed out. The possibility of similar coherent effects in direct interband transitions in semiconductors is discussed. A summary is given of the experimental results demonstrating a strong fall in the absorption and a considerable slowing down of light pulses, typical of the self-induced transparency. Possible physical applications of the effect, based on these properties, are discussed.