Table of contents

A new modification of the method of passive Q switching in a semiconductor laser with an isotypic saturable absorber was proposed and implemented. An increase in the power and repetition frequency of ultrashort pulses and a reduction of their duration were achieved by transferring a major fraction of excited carriers from the absorber to an amplifier with the aid of an electric field. Ultrashort pulses of 5 psec duration with a repetition frequency in excess of 18 GHz and a peak power in excess of 10 W (power density 4×10⁸ W/cm² in the active medium) were generated in a multicomponent AlGaAs/GaAs injection heterolaser.

An analysis is made of the basic principles and methods of construction of integrated optical circuits (IOC) for data processing, which are optical waveguide processors in the integrated form. A classification is provided of IOC in accordance with the nature of the input connections to optical components and in accordance with their intended function. An analysis is made of the current status of research and development of analog IOC for handling analog and digital signals, IOC for computing technology, and switching IOC. A detailed analysis is made of IOC with different functions in data processing: spectrum analyzers and correlators, analog-digital converters, circuits for identification of data sets and for encoding of signals, threshold and multistable circuits, logic and arithmetic units, and switching arrays. Descriptions are given of IOC for optically controlled data handling: bistable purely optical logic circuits, multivibrators, flip-flops, and optical transistors. The ultimate performance and trends in development of optical waveguide processors are considered as well as the problems of compatibility of such IOC with electronic microcircuits.

An analysis is made of various phase-matched nonlinear laser devices utilizing ZnGeP₂ crystals with the chalocopyrite structure. The coefficients in the Sellmeier formula for the refractive indices of the crystal are given. Tuning curves of an optical parametric ZnGeP₂ oscillator are obtained for the case of pumping with two erbium laser lines.

A single-frequency pulse-periodic YAG:Nd³⁺ laser was constructed. Its divergence was ∼5×10⁻⁴ rad and the peak output power was ∼1 GW in the case of nanosecond pulses. These pulses were generated utilizing stimulated Brillouin scattering for compression of an amplified pulse from a master oscillator.

A pulsed single-frequency YAG:Nd³⁺ crystal laser was constructed and investigated. Resonance reflectors were used in this laser as the resonator mirrors, whereas the other components were of conventional nature. Single-frequency operation was retained at 25% excess of the rate of pumping above the threshold. A calculation was made of the frequency dependence of the Q factor of the resonator.

An experimental investigation was made of the influence of a longitudinal magnetic field on the power and noise of He–Ne laser radiation utilizing a transverse microwave (λ = 0.63 µ) discharge. The laser radiation power increased in the presence of the magnetic field. The maximum increase in the output power produced by a field of H = 34.3 Oe reached 35% for the TEM_00q radiation mode and 20% for the TEM_33q mode. The field increased also the laser radiation noise in the range 1–20 kHz.

Current pulses were used to modulate directly the radiation emitted by a mesastripe (GaAl)As heterojunction laser with two isolated injection sections. This made it possible to generate single pulses of duration down to 8 psec with a peak power up to 1.2 W.

A theoretical investigation is reported of the evolution in space and time of a small-scale perturbation against the background of a smooth beam entering a pulsed CO₂ amplifier. The ranges of the transverse frequency, longitudinal coordinate, and time in which the perturbation growth is exponential are determined. It is shown that the wavefront instability can be suppressed by amplification of the main beam and by the attenuation of sound.

An investigation was made of the emission spectra of a neodymium phosphate glass laser during various stages of formation of ultrashort pulses. The kinetics of the spectrum of free lasing with passive mode locking was observed first. Considerable changes in the spectrum were observed for successive free-lasing spikes, which made it impossible to achieve self-stabilization of the ultrashort pulse duration. The spectrum of ultrashort pulses varied with the point of selection of a pulse in a train. The results were explained allowing for the simultaneous influence of burning of spectral holes in the population inversion and phase self-modulation on the operation of a laser with passive mode locking.

Theoretical and experimental investigations were made of the feasibility of controlling the amplitude and frequency characteristics of a YAG:Nd³⁺ ring laser by self-diffraction of opposite (counterpropagating) light waves on gratings of the absorption coefficient and refractive index induced in nonlinear absorbers. These absorbers were unpumped YAG:N³⁺ crystals or crystals of LiF containing F₂⁻ centers. It was established that in the absence of an offset between the centers of the gain and absorption lines the competition between the opposite waves in the ring laser was reduced. In the presence of an offset an amplitude nonreciprocity was observed and it was proportional to the difference between the frequencies of the opposite waves. However, when fast-response nonlinear absorbers were used, suppression of one of the opposite waves could be weak even in the case of a large offset. The distortions of the amplitude and frequency characteristics of a rotating ring laser were shown to be small in the presence of nonlinear absorbers with a short relaxation time and a low initial absorption coefficient.

The absolute quantum efficiency of the luminescence emitted by gaseous xenon in the vacuum ultraviolet range was determined as a function of the concentration of the gas and the luminescence wavelength. The main channel for decay of Xe₂* excimers after excitation right up to the ionization limit was radiative. The possibility of using xenon-based mixtures as active media was analyzed.

The composition dependences of the absolute quantum efficiency of the luminescence of the Xe₂Cl* trimer, emitting in the blue-green part of the spectrum, were determined for Cl₂–Xe mixtures excited at the wavelength of 137.2 nm. A high (up to 100%) efficiency of trimer formation observed under optical excitation conditions makes media of this kind promising for laser applications.

A description is given of a nonabsorbing spatially inhomogeneous amplitude filter designed for the transformation of laser beam profiles without introducing small-scale irregularities of the beam amplitude and phase. Experiments carried out using an He–Ne laser showed that it was possible to form beams with a flat top carrying 33% of the power of the original Gaussian beam. A filter of this kind could also be used to produce other beam profiles, for example, one with a dip on the axis.

A surface channel discharge was used as the source of ultraviolet radiation for pulse-periodic photoionization of CO₂ laser mixtures. This source was sufficiently powerful to ensure a volume discharge at pressures of ∼5 atm necessary for continuous tuning of the emission frequency. Experiments on the use of this source in a laser showed that it could be used at pressures up to 3 atm and in this range the input energy density was 500 J/liter, the output energy density was ∼30 J/liter, and the actual output energy in the form of laser radiation was 2.3 J.

A longitudinal continuous discharge in two independent supersonic gas streams, which were subsequently mixed, was used for nonequilibrium electronic excitation of components undergoing reactions and emitting chemiluminescence. Formation of XeCl excimer molecules as a result of mixing of excited He:Xe = 95:5 and He:HCl(Cl₂) = 99:1 streams was deduced from the XeCl* fluorescence spectra (B→X and C→A bands). The steady-state concentration of the XeCl molecules in B and C states determined in the mixing region was ∼10¹⁰ cm⁻³ when the pump power was 50 W, so that the efficiency of conversion of the input electrical energy into the excimer fluorescence was ∼1%.

A theoretical investigation is made of stimulated four-photon parametric scattering in a medium of two-level atoms pumped by high-intensity ultrashort pulses. A simple dependence of the gain on the phase mismatch, pumping duration, and length of the interaction region is obtained. The spectral and angular distributions of the scattered radiation are considered and the features of these distributions associated with the transient nature of the process are discussed.

An analysis is made of new applications of multilayer corrugated structures. Waveguide polarizers made of multilayer structures make it possible to suppress more effectively the diffraction of TM modes and at the same time enhance diffracted TE modes. A numerical analysis is reported of the influence of variation of the corrugation period, parameters of the waveguide structures, profiles of corrugation grooves, and the effect of resonant intermode coupling on the characteristics of a waveguide grating polarizer.

The example of a semiconductor interferometer with a thermooptic nonlinearity was used to demonstrate experimentally the decisive role of the ratio of the duration of an exciting pulse to the relaxation time of the nonlinearity in establishment of steady bistable operation of a nonlinear system with a feedback loop. A change in the spatial distribution of the intensity of the output signal during switching of the bistable element was recorded.

Theoretical and experimental investigations were made of the direction of energy transfer in the case of transient self-diffraction of waves incident on a nonlinear medium from opposite sides. It was found that, in spite of the different behavior of the intensities of the waves inside the nonlinear layer, the conditions governing the direction of energy transfer were the same for the concurrent (parallel) and opposed (antiparallel) geometries. The experimental results confirmed the theoretical predictions.

An optical interferometer with a wavefront-reversing mirror is considered. This mirror contains a layer with a time-dependent refractive index. The dependence of the phase shift of the beams returning to the input of the interferometer on the rate of change of the refractive index is determined.

A theoretical study is reported of the self-interaction of light beams during their propagation in weakly absorbing media. An analytic solution is obtained for thermal self-focusing of a light beam with a parabolic intensity distribution. The Ehrenfest theorem is used to obtain an expression for the shift of a light beam in a moving medium in the case of an arbitrary dependence of the velocity of this medium on the coordinate along the beam.

An investigation is reported of the self-interaction of a strong electromagnetic wave near the temperature of a structural phase transition in a ferroelectric. It is shown that in the infrared range of wavelengths the thermal self-interaction is dominated by the direct interaction of critical phonons with an electromagnetic wave.

An experimental investigation was made of the influence of the reflection conditions and of the characteristics of the incident radiation on the amplification of light in the course of its reflection by an excited dye solution. A strong dependence of the reflection coefficient on the angle of incidence was observed and its maximum occurred near the critical angle of total reflection. The amplitude and width of the reflection peak depended on the parameters of the ambient media, as well as on the spectral composition and energy of the incident radiation.

An experimental investigation was made of the energy characteristics of an antiresonant ring cavity containing a dye solution, as used in systems for generation of ultrashort light pulses. It was found that collisions of light pulses increased the reflection coefficient by a factor of 1.5–2 and enhanced the nonlinearity of the bleaching of the solution.

The results are given of analytic and numerical investigations of the process of self-interaction of partly coherent pulses in fiber waveguides. The attention is concentrated on identification of the optimal compression regimes. It is shown that the parameters of compressed pulses can be stabilized by spatial filtering of the spectrum in a grating compressor.

An analysis is made of the possibility of utilizing resonance photodissociation of van der Waals complexes (with a binding energy of <0.1 eV per molecule), and resonance desorption and acoustodesorption of adsorbed molecules bound to the surface by the weak van der Waals interaction in generating fluxes of cold atoms and molecules.

Theoretical and experimental investigations were made of the dependences of the delay time of plasma formation in a gas near the surface of a solid and of the energy density released at the target up to the moment of breakdown on the intensity of microsecond CO₂ laser radiation, subject to suitable allowance for the pulse profile. The appearance time of the optical breakdown was found to be determined both by the time needed to heat the target surface to the temperature of advanced evaporation and by the time needed to form a plasma in the gas. The plasma formation times were determined experimentally for the optical breakdown near the surfaces of targets made of graphite and tungsten grids. A study was made of attenuation of radiation by a breakdown plasma as a function of the intensity of laser radiation, as well as of the nature and pressure of the gas.

A considerable difference was found between the dependences of the optical damage threshold of the surface of zinc selenide on the area of the irradiated spot when single CO₂ laser pulses were used and when the surface was exposed repeatedly to such pulses. Electron microscopy was used to identify the characteristic types of damage. The experimental results were explained on the basis of the probabilistic nature of the presence of defects with a lower evaporation threshold in the irradiation zone using a theory of thermoelastic interaction of pulsed laser radiation with the surfaces of solids.

The problem of a volume hologram converting a reference speckle field into a plane wave is considered. The angular distribution and the total intensity of a plane wave are calculated for distortions which appear because of the amplitude inhomogeneity of cross gratings and which propagate close to the plane wave direction. The total intensity is found to be proportional to the product of the angle between the signal and reference waves and the divergence of the reference speckle wave.

An investigation is made of the statistical properties of an optical field with a speckle structure in multimode fiber waveguides. Asymptotic formulas are obtained for the spatial correlation function of the field. This function is used to obtain expressions for the statistical average density of dislocations in the wavefront of the field distributed over a transverse cross section of a waveguide with an arbitrary refractive index profile. It is shown that the dislocation density is an oscillatory function of the transverse coordinate. A study is also reported of the dependence of the dislocation density on the refractive index profile and on the conditions of excitation of a waveguide.

Experimental and numerical investigations were made of the propagation of laser absorption waves in metal capillaries subjected to CO₂ laser pulses. The dependence of the velocity of propagation of a plasma front on the initial pressure of air in a capillary was determined. It was found that in a wide range of parameters the time needed for the formation of a layer of an optically opaque plasma was governed by the total energy of a pulse from the beginning from its action to the moment of appearance of screening and was not greatly affected by the pulse profile or by the gas pressure.

Crystals capable of second harmonic generation can be used effectively as analyzers and polarizers of laser radiation in the visible and infrared parts of the spectrum. Experimental results show that the extinction coefficient of a system comprising a polarizer in the form of a Glan prism an an analyzer representing a KDP crystal capable of second harmonic generation reached 6×10⁻⁹.

The problem of optical pumping of vacuum ultraviolet lasers is considered from the point of view of the properties of optical cylindrical concentrators in the range of wavelengths when all materials suffer from a low reflectivity. The losses due to escape of radiation through the ends and reflecting walls are determined and the maximum efficiency of a concentrator is found. The available data on the optical constants are used in an analysis of the dependence of the concentrator efficiency on the material used as the reflecting coating. The role of the roughness of the reflecting surface is considered and the requirements in respect of the dimensional tolerances in the fabrication of concentrators are formulated. The systems for optical pumping of transitions in hydrogen-like ions, resulting in generation of radiation in the 20–150 nm range suggested earlier in the literature, are considered as examples.

A simple model of pumping is used to predict the relationships governing the spatial distribution of a population inversion in active elements made of GLS22 phosphate glass as a function of the neodymium concentration and of the pump field on the surface of an element.

A study was made of an injection laser for a monolithic integrated-optics module based on a system of strongly coupled waveguides, in which a resonator mirror is formed by two combined diffraction gratings in the form of slots with vertical walls. The resujts indicated that such a reflector can ensure selection of longitudinal modes and reduce the width of the angular distribution of laser radiation. It can also be used to provide optical coupling to other components of a monolithic integrated module.