Table of contents

Experiments on luminescence and lasing were used in a study of the population inversion kinetics in high-pressure lasers pumped by an electron beam and utilizing the 3p–3s transitions of neon. The optimal active-medium compositions were established and explained qualitatively for a wide range of specific excitation powers. The special features and advantages of using different quenching agents were identified.

A numerical investigation was made of the temporal characteristics of high-power radiation and of the field structure of a laser generating series of pulses at repetition frequencies in the kilohertz range. Lasers with plane and unstable resonator geometries were considered. The lasing was found to be unstable in both cases. The reasons for this instability are discussed.

A description is given of a theoretical model of gain saturation in neodymium glasses based on the minimum of the standard deviation from experimental data. It is shown that it is undesirable to search for active medium parameters on the basis of this minimization. The feasibility of using multipass systems to select a theoretical model is examined.

An investigation was made of saturation of the gain in GLS21 and OPS3106 phosphate neodymium glasses. It was found that the gain may be accurately described by the Franz-Nodvik equation in which the saturation energy density W_s depends on the type of glass and the energy density and does not depend on the polarization of the radiation. The efficiency of energy extraction from the active medium was found to be around 60% and it was found that this may be increased at least to 70%. It was established that for a pulse duration τ_p = 1–30 nsec, W_s does not depend on τ_p, whereas when τ_p < 1 nsec, it decreases slowly with decreasing τ_p. Empirical formulas were derived to calculate the radiation energy and its extraction efficiency.

A cw dye laser capable of generating both single- and double-frequency radiation with a high output power (P⋍1W) was made and investigated. A simple system for active stabilization of the laser, was based on an external passive Fabry-Perot etalon with a drift in the lasing frequency of less than 3 MHz/h. Electronic discrete-continuous tuning in a range of 200 GHz was provided by using galvanometers to rotate intracavity Fabry–Perot etalons.

Numerical calculations of the kinetics of secondary processes occurring during photolysis of iodides (RI) are made using published values of the rate constants. It is shown that in the case of insufficient time resolution and a large number of photolysis-inducing pulses these processes may have a considerable influence on the relative values of the quantum yield Ô_I*^rel(λ) measured by kinetic spectroscopy methods. A report is given of measurements, under conditions avoiding the influence of such secondary processes on Ô_I*^rel(λ), of the values of this yield at λ = 266 nm for the following iodides RI:CF₃I, C₂F₅I, C₃F₇I, CF₃CFICF₃, C₄F₉I, (CF₃)₃CI, CH₃I, C₂H₅I, C₃H₇I, and CH₃CHICH₃. The rate constants of deactivation of I(²P_1/2) atoms by alkyl iodide molecules are determined.

Experimental and theoretical investigations were made of mode locking in a two-mode linear gas laser. It was found that locking can be suppressed by a transverse spatial shift between the modes. In the limit of large spatial shifts a two-mode laser can be regarded as two quasi-independent single-mode lasers.

The temperature dependences of the pump intensity I_th corresponding to the lasing threshold were determined in the range 4.2 K≤T≤300 K for CdS single crystals with different levels of losses in the case of one-photon pumping with nitrogen laser radiation. The temperature dependence I_th(T) was nonmonotonic. An analysis of the dependences I_th(T) was made using the available theoretical treatments and a comparison of the experimental and calculated subthreshold emission spectra indicated competition between three lasing mechanisms, which changed with temperature, took place under the experimental conditions. These mechanisms were exciton-phonon, exciton-exciton, and exciton-electron inelastic scattering. In particular, the fall of I_th recorded under certain conditions on increase in temperature could be attributed to spectral degeneracy of two or three of these mechanisms.

An investigation was made of the physical processes occurring in the active medium of a pulsed CO₂ laser and responsible for variation of the laser frequency during a pulse. The processes considered were inhomogeneous deposition of the input energy, influence of free electrons, and self-interaction of the laser radiation. It was found that free electrons and the self-interaction provided the main contribution to the frequency variation. Some of the results differed from those described in the literature. The reasons for the discrepancy are discussed.

An experimental investigation was made of the amplitude- and phase-frequency characteristics of an optical-signal amplifier based on a cw CO₂ laser. The efficiency of such an amplifier was governed not only by the frequency of amplitude modulation of the input radiation, but also by such parameters of the laser system as the output power and the degree of spatial overlap of the controlling and controlled optical fields in the active medium.

New capabilities of an "optical boiler" pumping system, characterized by a high lasing efficiency and a high density of the stored energy, were predicted theoretically and confirmed experimentally. A record lasing efficiency of ~ 2.85% for single pulses was achieved in a pumping system with YAG:Nd rods distributed around a flashlamp when the output energy from one rod was 300 mJ. An increase in the efficiency in excess of 3% was forecast.

A report is given of the construction and of the results of an investigation of a XeCl laser (λ = 308 nm) with an output energy 1J and an output power ~40 MW.

Radiation tunable in the 1.08–1.25 μ spectral range (from a laser utilizing an LiF crystal containing F₂⁻ color centers) was converted into radiation tunable in the 1.2–1.6μ range as a result of stimulated Raman scattering in Ba(NO₃)₂ and KGd(WO₄)₂ crystals. The conversion efficiency was 60% and 30%, respectively.

An investigation was made of the optical inhomogeneity of the active medium in a fast-flow closed-cycle CO₂ laser with a transverse hf capacitative discharge and a 5-liter active volume. A lateral-shear interferometer employing a pulse-periodic copper bromide vapor laser was used in the measurements. Optical inhomogeneity of the wedge type in the flow direction and of the positive lens type in the transverse direction was found to be present at the start of the discharge, and there was a 2-mm-thick layer at the electrodes. The inhomogeneity was considerably smoothed out toward the end of the discharge zone along the flow direction. The gain and gas temperature distributions in the active medium were measured in the discharge current direction. The results obtained prove that the active medium homogeneity in a laser with an hf capacitative discharge is higher than that when a self-sustained discharge is pumped by a dc current.

The development of a numerical model of a fast-flow CO laser with an unstable resonator is reported. The results of calculations of selective lasing due to a specific transition in a medium having a homogeneous refractive index at various pumping rates are presented by way of an example. Distributions of the output radiation intensity in the resonator, determined in the diffraction approximation, and the energy characteristics are compared with the results obtained using the constant-gain model.

An experimental investigation was made of the kinetics of changes in the planar texture of an absorbing cholesteric liquid crystal under the action of pulsed (nanosecond) laser radiation. An analysis was made of the possible mechanisms of light-induced changes in the texture under the action of a laser wave. An irreversible change in the transparency of a cholesteric liquid crystal in the irradiation zone was attributed to the formation of a confocal texture induced by pulsed heating above the phase transition temperature and rapid cooling of the investigated hysteretic mixtures of cholesteric liquid crystals.

Experimental and theoretical studies were made of mechanisms of the influence of the gas pressure on isotopically selective multiphoton dissociation of CF₃Br by pulsed CO₂ laser radiation. The dissociation yields and selectivity were determined at three different frequencies [9P(18), 9P(24), and 9P(32) lines of a CO₂ laser] corresponding to preferential excitation of ¹³CF₃Br. A simple four-level model is proposed to describe these dependences and take into account rotational relaxation and intermolecular vibrational exchange. As a result of these processes, the rotational and vibrational bottleneck is overcome. A sharp drop in the dissociation selectivity when a specific gas pressure is exceeded is due to an explosive increase in the multiphoton dissociation yield of the nonresonant isotopic component (¹²CF₃Br) due to its vibrational self-heating.

A theoretical analysis was made of the evolution of an electron avalanche in a laser radiation field with an arbitrarily time-dependent power density. The electron diffusion equation in the energy space was used to determine the distribution function. The avalanche growth rate averaged over a pulse was determined for an arbitrary time dependence q(t). It was found that when the laser pulse duration was greater than the electron-atom energy relaxation time, the growth rate depended strongly on the pulse time profile.

It is found that when a two-frequency pump wave is used in an expanding laser plasma, three nonlinear scattering regimes are feasible. A nonlinear interaction between the incident and reflected waves, in the zone where the plasma flow velocity is close to the velocity of sound, may substantially reduce the efficiency of utilization of multifrequency pumping to suppress stimulated Brillouin scattering.

The profile of pulses emitted by a TEA CO₂ laser with an unstable resonator changed as a result of interaction of laser radiation with the surface of a metal in the presence of a breakdown plasma. This influence of a target on laser operation and its possible applications in laser processing of materials are analyzed.

A study was made of resonant excitation of surface plasmons at an interface between a metal and a nematic liquid crystal under conditions of self-interaction of light. The experiments yielded optically bistable characteristics of the intensity of the radiation transmitted by the system in the field of low-power cw laser radiation.

An analysis is made of the interaction between two mutually coherent plane waves in a medium whose refractive index varies by an amount proportional to the local exposure up to a selected time. It is found that the parameters of the process depend on a single self-similar variable, the product of the depth and the input exposure: zE²dt. Analytic and numerical studies are made of the properties of the self-similar solution for various ratios of the wave intensities at the entrance to the medium.

A quantum theory of coherent four-photon spectroscopy of electron resonances in molecular systems is developed. A model allowing for real properties of the dispersion of perturbations modulating electron transitions in complex molecules is considered. New relationships are established between the characteristics of spectra of one-photon absorption and the law governing the dispersion of a signal obtained in steady-state four-photon spectroscopy, conditions for excitation of this signal, its dispersion, etc. It is shown that the theory agrees with the available experimental data.

The dynamics of the self-interaction of picosecond laser pulses in semiconducting crystals was investigated for the first time. A "nonlinear lens" method was analyzed theoretically allowing for diffraction and then this method was used in direct measurements of the nonlinearity of the anisotropy of the refractive index of CdS single crystals excited with picosecond light pulses.

A theoretical investigation is made of the influence of linear amplification as a result of stimulated Brillouin scattering in a multimode fiber waveguide. Calculations are made of the threshold of such scattering and of the efficiency of conversion of a pump wave into a Stokes wave under steady-state and transient conditions. The theoretical results are shown to agree well with experimental results obtained under small-gain conditions.

A new modification of the generalized method of moments is used to derive a system of differential equations which describe the behavior of a Gaussian beam in a nonlinear medium. This modification is used in an analysis of an asymmetry and frequency shifts of saturated absorption resonances and dispersion due to light-induced aperture and lens-like properties of the medium.

A theoretical investigation is made of the stability of a plane electromagnetic wave traversing a plasma of a non-self-sustained discharge in a relaxing gas. It is shown that an overheating instability of the plasma leads to an absolute instability of an electromagnetic wave in the presence of small-scale perturbations. The angular distribution of the instability increment is obtained. Its anisotropy is attributed to a transverse (relative to an electric field) nature of the overheating instability.

An experimental investigation was made of pulsed laser heat treatment of annealed tungsten and tungsten–molybdenum–cobalt high-speed cutting steels. The results indicated that saturated austenite did not form during thermal cycles of duration typical of free-running solid-state lasers. The observed increase in microhardness of the surface layer was due to the high density of dislocations formed by laser heating. A model of an α→γ transition in this class of steels subjected to pulsed laser heating was proposed and analyzed theoretically. The model allowed for the kinetics of the austenitic transformation and microplastic deformation.

An analysis is made of the process of stimulated Brillouin scattering in the case when the length of a speckle element of a wide-angle pump field is of the order of the attenuation length of hypersound and the diffraction laws for the pump and signal fields differ because of a frequency shift. An equation for the structure of the conjugated wave is obtained and solved for increments and conjugation quality as a function of the profile of the angular spectrum of the pump.

A model of equalized parameters of a breakdown zone is used in a numerical estimate of the coefficient of transparency of paths in an atmosphere with a background aerosol content for a collimated and focused CO₂ laser beam. The calculated transparency coefficient is compared with the available experimental data.

Picosecond spectroscopy was used to investigate an intermolecular hydrogen bond between an impurity center and a solvent. The proposed method for determination of the spectral dependence of the rotational relaxation time of molecules was used to find the inhomogeneous broadening of the spectra of dye solutions governed by the impurity-solvent interaction. The influence of the microstructure of the environment on the rotation of molecules in binary solvents was observed. An investigation was made of the influence of temperature on the rate of formation and dissociation of complexes in an excited state.