Table of contents

A strong optical nonlinearity is typical of semiconductors. A large contribution to the nonlinearity comes from the influence of free carriers on the refractive index and the carrier density itself depends on the intensity either because of photoelectric absorption or because of stimulated emission. In semiconductor lasers this gives rise to a number of effects, such as self-focusing, nonlinearity of the optical losses with associated emission dynamics anomalies, bistable operation in compound resonators and amplifiers, frequency self-modulation, and nonlinear scattering by electron density waves. Self-stabilization of single-frequency emission, which makes it possible to increase the intensity of coherent radiation emitted from a semiconductor laser, has the same physical basis as the aforementioned effects.

The amplitude and polarization are found for the first coherent radiation pulse generated in time-separated fields with the aid of resonant levels exhibiting a hyperfine structure. It is shown that such hyperfine splitting of the resonant levels does not alter qualitatively the conclusion that it should be possible to observe narrow structures in the intensity of such a pulse under conditions of scanning of the frequency of the exciting pulses. This feature is important because of possible technical applications of such narrow structures. The polarization properties of the first coherent radiation pulse generated in time-separated fields depend strongly on whether one or all hyperfine components of each of the resonant levels participate in the formation of a pulse.

The paraxial approximation for the scalar wave equation is used to study the spatial coherence of optical fields in media with an overall quadratic refractive index profile and an arbitrary regular longitudinal inhomogeneity. Analytic expressions are obtained for the parameters describing the spatial coherence of fields in such media, particularly for the correlation radius and the width of a partly coherent beam generated by a variety of light sources. It is shown that for certain distributions of the longitudinal inhomogeneity there is no change in the coherent properties of the field because of a matching effect. This effect is proposed as a method for ensuring a matched contact between two different graded-index waveguides. A study is made of the influence of the degree of coherence on the focusing region of the beam and it is shown that, in principle, it is possible to focus a paraxial beam with a finite initial width in a region smaller than the wavelength. It is shown that variation of the longitudinal inhomogeneity distribution can be used to control coherent properties of the radiation. The results obtained can be used in fiber-optic communication lines, integrated optics, and coherent optical data processing.

Equations are derived for the motion of particles in a free-electron laser subject to an allowance for the inhomogeneity of electromagnetic wave and undulator fields. A study is made of the influence of the inhomogeneity of these fields on the laser gain. An analysis is made of the conversion of the energy of a particle beam into radiation when initial conditions of particle injection into the laser undulator are modulated. It is shown that a suitable selection of the modulation depth and phase can increase the average energy lost from the beam.

Experimental and calculated data are used in an analysis of the characteristics of a pulsed chemical DF–CO₂ laser under free-running and amplification regimes. A deviation of the distribution of the populations of the vibrational states of the CO₂ molecule from the Boltzmann law was observed in the course of amplification of a saturating 150-nsec pulse. The role of a "hot" R 23 (01¹1–11¹0) transition and the influence of rotational relaxation on the kinetics of lasing of individual vibrational–rotational lines, on the output radiation pulse profile, and on the output energy were considered. The calculated and experimental values of the unsaturated gain and of the output energy in the free-running regime were in good agreement when the degree of initiation (dissociation) was far from the lasing threshold.

An analysis is made of some processes that occur under conditions of accumulation of population inversion due to the ⁴I_13/2–⁴I_15/2 resonant transition in Er³⁺ ions in ytterbium–erbium (Yb–Er) glasses of various compositions. Methods of measuring the parameters of direct and reverse excitation energy transfer between Er³⁺ and Yb³⁺ ions are also studied. It is found that, under certain conditions achieved in practice, appreciable bleaching of the medium should be observed at the frequency of the pump radiation, particularly under conditions of high-intensity reverse transfer of excitation energy from Er³⁺ to Yb³⁺ ions. This is typical of glasses having a low rate of intracenter relaxation of Er³⁺ ions. It is also shown that nonsteady-state rate equations that assume a linear relationship between the rate of interionic transfer and the ground state population of the acceptor consistently describe the energy characteristics of the excitation processes of Yb–Er glasses. In this case, it is not necessary to introduce in the calculation model additional excitation losses that increase nonlinearly with the pump radiation.

The operation of an electron-beam-controlled CO₂ laser with a non-self-sustained discharge is considered. A numerical investigation is made of the influence of gasdynamic perturbations arising in the electric discharge chamber and of heating of the medium on the output radiation power in the pulsed and pulse-periodic laser operating regimes. The optimal pulse repetition frequencies are determined for different values of the discharge input energy.

Equations describing a transient degenerate four-wave interaction in a resonant medium are derived and solved numerically. The approximation of a "following" nonlinear polarization state is used to determine the range of values of the parameters of the medium and the radiation field in which the efficiency of a transient four-wave interaction is higher than that of the steady-state process. It is found that amplification of weak radiation as a result of transient energy exchange can only be achieved in the four-wave interaction for different pump wave intensities.

A discussion is given of the fundamental principles underlying the construction of high-power multibeam gas-discharge lasers with diffusive cooling. An analysis is made of the constructional features of the main systems of the multibeam CO₂ laser Iglan-3. The experimental dependences are given of the laser output power on the discharge current, the working gas pressure, and the composition and circulation velocity of the laser mixture. Laser output powers of 4.6 and 3.5 kW respectively were obtained on using exit mirrors of ZnSe and KCl. The gain and saturation intensity of the active medium obtained by different methods were analyzed. The laser resonator efficiency was estimated for different exit mirrors. The electrooptic laser efficiency was found to be 14% and the energy efficiency 10%. Experimental data on the laser radiation beam divergence and on the intensity distribution in different cross sections of a focused beam are presented.

A theory of Rayleigh light scattering is developed for photorefractive media of the strontium barium niobate (SBN) type with a diffusion mechanism of formation of optical inhomogeneities. The photoinduced increase in the scattering intensity is considered to be the result of spontaneous recording of noise phase holograms in an inhomogeneous crystal. The angular structure and the time dependence of this scattering intensity are determined. It is shown that as a result of holographic effects the scattering indicatrix may be essentially asymmetric. Theoretical calculations made for an SBN crystal show good agreement with the experimental results.

For the first time an experimental and theoretical investigation was made of the interaction of two linearly and orthogonally polarized modes in a CO₂ laser utilizing a discrete vibrational–rotational transition. The influence of the field characteristics of the modes of a phase–anisotropic resonator and of the active medium on the intermode competition was considered. Stable two-mode lasing was obtained when the intermode separation was varied from 0.3 to 70 MHz, the widest two-mode lasing range being 80 MHz.

An experimental study was made of the characteristics of multiphoton dissociation of CF₃Br molecules when ¹³CF₃Br is excited under collisional conditions. For the first time, measurements were made of the selectivity of multiphoton excitation of a natural mixture of ¹²C and ¹³C isotopes, and its dependences on the excitation frequency and buffer pressure were determined. It was observed that the selectivity of excitation of ¹³CF₃Br molecules in the low-frequency wing of the ν₁ band is governed by the absorption at the 3ν₃ overtone and its thermal bands, and the dissociation selectivity is governed exclusively by the conditions of excitation of the molecules in the ν₁ band. The optimum regime for selective dissociation of CF₃Br in terms of energy consumption matched to the parameters of existing CO₂ lasers was determined. At a radiation energy density of 2.6 J/cm² the energy consumption is ∼ 260 eV per ¹³C atom. This regime may be used as the first stage in laser enrichment of carbon isotopes.

The energy balance of a laser thermonuclear reactor is considered and it is shown that the energy of the reaction products absorbed by the focusing optics of the reactor considerably exceeds the energy absorbed from the laser pulse. The x-ray spectrum of the target emission is calculated and used to find the minimum distances from the center of the chamber to the optical system. Variants of the gas shield are analyzed. The laser radiation brightness required to ignite the reaction is used to obtain a relationship between the minimum focal length and the optical strength of the material employed for the optics. It is shown that thermonuclear neutrons incident on the focusing system generate considerable thermal stresses and deformations.

A computer solution of a system of equations is used to study bleaching of a moving polydisperse aqueous aerosol by a Gaussian laser radiation beam. An analysis is made of the influence of the beam power, aerosol velocity, and its microstructure on bleaching by cw and pulsed irradiation. An estimate is made of the error introduced by using analytic bleaching models. A comparison is made with the experimental data.

The change in the photosensitivity of CdS:Cu crystals caused by photochemical reactions was used to record a holographic grating. A phase grating was obtained having a diffraction efficiency controlled by the intensity of the readout beam.

Pumping with XeCl* laser radiation (at a wavelength of 308 nm) was used to study lasing of molecules of several complex organic compounds in the form of pure vapors. Stimulated emission from PPF, PBD, BBD, and para-methoxy-PPD molecules was observed for the first time. Measurements were made of the dependence of the lasing output energy on the pump radiation energy. The energy efficiency of lasing of pure PPF vapor was found to be several times higher than the corresponding efficiencies for p-QP and POPOP.

It is shown experimentally and theoretically that the threshold intensity for stimulated Raman scattering (STRS) due to rotational transitions depends strongly on the polarization of the pump radiation. The threshold for rotational STRS is lowest for circularly polarized radiation and increases sharply for linearly polarized radiation. The results of investigations of the energy characteristics of rotational STRS on the degree of ellipticity of the pump radiation are presented.

The possibility is investigated of raising the efficiency of particle interception in the method of resonant photoionization of atoms by laser radiation in a closed hot cavity, located in vacuum, and subsequently employing an electric field to extract the ions formed through a small aperture in the wall. It is shown that for realistic laser radiation parameters (pulse duration ∼ 15 nsec, repetition frequency 10 kHz), the cavity geometry can be chosen in such a way that the interception efficiency exceeds 50%. The possibility is demonstrated of completely extracting the ions formed by photoionization from the cavity.

In a -switched YAG:Nd³⁺ laser utilizing a three-mirror resonator a reproducible structure of regular fluctuations was obtained with a period corresponding to the reciprocal of the width of the lasing spectrum. When the optical lengths of the partial resonators were not submultiples of the total length, random intensity fluctuations over the entire duration of the giant lasing pulse were observed.

An analytic expression is derived for the efficiency of harmonic generation in focused beams allowing for the second-order Kerr effect. A specific analysis is made for the case of the third harmonic. The results show good agreement with known experimental data.

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.

Results are presented of experimental investigations of the efficiency and spectral composition of the radiation from a pulsed atmospheric-pressure electron-beam-controlled laser containing ¹³C¹⁶O₂ and ¹²C¹⁸O₂ carbon dioxide isotopes in the active mixture. It was found that the operating efficiency of a laser utilizing these isotopes is similar to that of a laser utilizing the ¹²C¹⁶O₂ molecule and the input energy is governed by the presence and number of impurities in the active mixture.

Phenomenological representations and the results of an experimental study of the emission from an Ar⁺ laser with passive mode locking were used to analyze the nature of hysteresis of the output power near the threshold. It was found that hysteresis and passive mode locking were inseparable because both effects were due to the same processes of saturation of amplification and absorption.

A mathematical model is proposed of emission from a multichannel laser regarded as a system of N identical sources with field distributions differing in respect of the phase. A study of far-field distributions of the intensity and of the radiation energy is used to formulate certain general conclusions. The example of a pair of ideal radiators which are not phase locked and have elliptic or rectangular apertures is used to analyze the characteristics of the angular divergence of the radiation.

The results are reported of calculations of the tropospheric transmission (under summer conditions) of radiation from lasers utilizing seven carbon dioxide isotopes. The absorption by various atmospheric gases is analyzed.

The rod-in-tube method was used for the first time in the Soviet Union to construct fiber waveguides with a pure quartz glass core, formed by the axial deposition technique, and a fluorine-doped quartz cladding formed by the technique of plasmachemical deposition inside a quartz jacket tube. In the case of a fiber waveguide with a numerical aperture of 0.18 the optical losses ranged from 3 dB/km at the wavelength of 0.85 μ to 1.4 dB/km at 1.5 μ. The results of an investigation of the radiation-optical stability of these fiber waveguides indicated that they were not inferior (in respect of this characteristic) to the best foreign devices. The high radiation optical stability was due to the purity of the waveguide materials.

A report is given of the development of a laser interferometer for monitoring the uniformity of the wall thickness in microspheres used as shell targets in laser fusion experiments. The sensitivity is better than 7 nm and the spatial resolution is 3 μ.

The structured nature of the flow of an erosion plasma formed as a result of laser interaction with metals was detected experimentally. The structure was interpreted as an analog of the optical caustics.

The range of compositions of the working solution of a gas generator that can be cooled to – 50 °C is determined. It is shown that in the temperature range between – 5 and – 40 °C, the concentration of singlet oxygen at the surface of the solution does not depend on its temperature and is 90 ± 20%.

Lasing in XeCl, XeF, and KrF excimer molecules in mixtures without a buffer gas was obtained for the first time by pumping with a fast electric discharge. Lasing in XeCI molecules was observed in CCl₄:Xe = 1:(400–4000) mixtures at pressures of 0.1–0.55 atm.

An investigation is made of the oscillation modes and natural frequencies of a resonator with a self-pumped wavefront-reversing mirror (SWM). An integral equation describing the transverse mode structure is derived for a resonator with an SWM and a Gaussian profile of the reflection coefficient. The parameters of the lowest oscillation mode are also found for this resonator. The advantages of a resonator with an SWM are identified and it is suggested that resonators of this kind may find extensive applications in systems for the formation of highly directional optical radiation.

An experimental investigation was made of the transfer characteristics and signal readout efficiency of devices utilizing surface acoustic waves. The investigation was carried out using a strip optical waveguide interferometer. A prototype of this interferometer was made from a YZ-cut lithium niobate substrate. Electrodes were used for electrooptic correction of ihe initial phase shift between the optical waves in the interferometer arms and an opposed-comb transducer was employed to excite acoustic waves. The results should be useful in the development of signal

It was established that the action of high-power laser radiation on the surface of Ge caused a surface shift of the periodic structure formed by such radiation. An explanation was provided of this shift and calculations indicated that for some angles of incidence of the interacting radiation the shift should vanish.

A bistable semiconductor device constructed from a layer GaSe crystal had switching times not exceeding 2 ×10 ⁻¹¹sec. The short recovery (switching-off) time of the bistable device was clearly related to the stimulated process of recombination in the strongly excited semiconductor.

An investigation was made of the spectral, temporal, and spatial characteristics of the radiation emitted by a YAG:Nd laser with a wavefront-reversing Brillouin mirror, obtained in the resonator stability range. The radiation pulses were found to be shortened while the energy was practically unaffected (it was at least 80% of the initial value).