Table of contents

A correlation method was used to study experimentally a transient interaction of picosecond pulses with a gallium arsenide Fabry–Perot resonator. A nonlinear shift of the peak of a pulse was observed as well as its instability and splitting associated with the optical bistability effects.

An experimental determination was made of the maximum efficiencies of conversion of neodymium laser radiation into the second (efficiency 90%) and third (81%) harmonics.

Photoinduced birefringence was detected experimentally in an LiF crystal with F₂ color centers. A theoretical explanation of this effect is proposed.

The dependence of multiphoton infrared absorption by SF₆ molecules, cooled in a supersonic pulsed jet, was investigated in the collisionless excitation regime in the range of energy densities from 0.1 to 10 J/cm². A study was also made of the dependence of the yield resulting from dissociation of SF₆ molecules at T = 300 K on the intensity (duration) of exciting CO₂ laser pulses. The dependences of the ratios of the absorbed energy to the dissociation yield on the excitation radiation frequency were obtained for different pulse intensities.

An experimental investigation was made of a new method for controlling the duration of ultrashort pulses in the widest possible range (for pulses shorter than the resonator length) from the axial period to the reciprocal of the width of the gain band of the active medium. The method ensured complete reproducibility of all the parameters of the output radiation. A ruby laser with a saturable absorber in the resonator emitted pulses of ∼35 psec duration when pulses of ∼1.5 nsec duration were injected from outside into the resonator (the reduction in the pulse duration thus exceeded a factor of 40). The width of the emission spectrum was then close to the limit for a pulse with an exponential envelope.

An experimental investigation was made of the specific characteristics of wavefront reversal (WFR) and selfdiffraction of light from dynamic gratings induced near the fundamental absorption edge of cadmium sulfide. As a result of the thermal shift of the band gap E_g = 2.42 eV relative to the laser photon energy ℏω = 2.331 eV, it was possible to achieve resonant modulation of the refractive index and to optimize the conditions for maximizing the WFR and self-diffraction efficiencies. An investigation was made of the dependence of the reflection coefficient of the reversed wave on the degree of excitation and on the thickness and temperature of the samples. It was found that efficient WFR in terms of energy can be achieved at the fundamental absorption edge of direct-gap semiconductors.

An investigation was made of the reflection of laser light from a plasma formed by laser radiation obliquely incident on a planar target. It was observed that when the power density of the heating radiation was increased to 3×10¹⁵ W/cm², reflection in the specular direction and backward into the aperture of the focusing objective increased. Various features observed experimentally in the energy and spectral characteristics of the scattered light were analyzed.

A semiempirical model is used to calculate the watt-ampere characteristics and phase diagrams of heterojunction lasers with spatially inhomogeneous injection. Experimental results were reported of a study of the region of "smooth" turn-on, bistability, and self-modulation in two-component (GaAl)As stripe heterojunction lasers capable of operating continuously at room temperature. The experimental results are compared with calculations, and with similar characteristics of cooled two-component homojunction lasers.

A method is proposed for the determination of the optimal concentration of an active impurity from the point of view of maximizing the population of the upper active level in both cw and pulsed regimes at a low optical density of the laser active medium. It is shown that the dependence of the population on the concentration changes qualitatively with the law governing concentration quenching of the luminescence. For example, if decay of the excited state takes place in the kinetic limit (if the rate of nonradiative relaxation is linear with respect to the concentration of energy acceptors and does not depend on the donot concentration), concentration quenching of the luminescence does not limit the concentration of active particles in the active element The proposed method is illustrated by calculating optimal concentrations of neodymium tons in a YAG crystal for cw and pulsed regimes.

A new mechanism is suggested for phase-matched second harmonic generation using the quadrupole nonlinearity of a liquid crystal and resulting from an anomalously strong scattering of light by fluctuations of molecular orientation. An analysis is made of the structure of the tensors representing the regular and fluctuation-induced nonlinear susceptibilities and a calculation is reported of the relative efficiency of the fluctuation mechanism, which is estimated to reach a few percent.

It is shown that materials with different physical properties are characterized by different widths of the linear part of the dependence of the charge reaching the slit of a mass-spectrograph monitor on the number of laser pulses. This difference and the change in the ratio of singly and doubly charged ions in the analytic part of a mass spectrograph are determined by the shape of the craters formed as a result of the interaction of laser radiation with the investigated material.

Measurements were made of the accuracy of wavefront reversal in four-wave interaction between light and hypersound. When the radius of the signal wave beam in the nonlinear interaction zone was substantially smaller than the radii of the pump beams, the reversal accuracy was ∼0.7 for reflection coefficients substantially greater than unity.

An analysis is made of the construction, operating principle, and possible applications of analog spatial light modulators performing the function of a rotating slit and intended for optical data processing systems. A report is given of the characteristics of prototype modulators in which liquid crystals are used and a theoretical analysis of their operation is made. Ways of extending the functional potentialities of these devices by combined power supply systems are considered.

An investigation was made of the size dependences and spatial fluctuations of the laser damage thresholds of different transparent polymers subjected to radiation of wavelengths 1.06 and 0.69 μ interacting with zones the volumes of which were spread over a wide range. A correspondence was established between the size (volume) dependences and the dependences of the damage probability on the intensity of the incident radiation. It was concluded that the absorbing defects played a decisive role in the processes of laser damage occurring in transparent polymers.

An experimental study was made of the "induced" absorption in germanium accompanying the combined action of CO₂ and Nd lasers. Measurements were made of the rate of recombination of carriers excited by the Nd laser radiation. It was found that surface recombination plays an important role even at moderate radiation intensities. A theoretical model is proposed for the combined effects.

An experimental investigation was made of some features of the formation of temperature and concentration fields in chemically active systems interacting with laser radiation due to a feedback between "chemical" and thermal, and also between concentration and thermal degrees of freedom of the system, which occurs during laser irradiation. Nonlinear optical effects (self-focusing and defocusing) during propagation of laser radiation in media having a slow-response chemical nonlinearity were observed. Strong enrichment of the gas mixture in the laser beam by one of the components was also observed.

An analysis is made of the kinetics of physical processes in a hydrogen-iodine active medium. It is shown that, in principle, it is possible to achieve a population inversion due to the I^*(²P_1/2)–I(²P_3/2) spin–orbit transition in atomic iodine as a result of near-resonant transfer of hydrogen vibrational energy to I^*(²P_1/2) (VE process). A necessary condition for inversion is that at T = 300 K the mixture should contain more than 10% of the vibrationally excited hydrogen H₂(ν = 2) relative to the ground-state H₂(ν = 0). Some typical features of a hydrogen–iodine system are noted and its potential usefulness is demonstrated.

Theoretical and experimental investigations were made of the feasibility of effective time compression of light pulses as a result of stimulated Brillouin scattering of a light beam in gases. An optimal focusing geometry and a specific excess above the scattering threshold made it possible to achieve time compression by a factor of 20–30 and the duration of the Stokes pulse was then an order of magnitude less than the decay time of hypersound. Stimulated Brillouin scattering in argon at various pressures, corresponding to relaxation times in the range from 1 to 8 nsec, was used to convert pump pulses of 20 nsec duration into Stokes pulses of 1 nsec duration. The energy efficiency of the process was in excess of 80% and the angular divergence was not affected.

An experimental investigation was made of the energy characteristics of a pulsed electron-beam-controlled atmospheric-pressure CO₂ laser utilizing CO₂–N₂–H₂O mixtures as a function of the gas mixture composition, of the electric field strength, and of the specific pump power. The energy parameters of the laser were calculated for the experimental conditions. Qualitative and quantitative agreement was obtained between the calculated and experimentally measured data.

A one-dimensional model of a continuous optical discharge burning in a radiation cone close to a refractory target is investigated analytically and numerically. Formulas are obtained for the characteristic parameters of such a discharge. It is found that, for discharges burning in a stream of gas, in addition to a lower threshold power, there is also an upper limit and the transparency of the jet decreases with increasing power and gas pressure. For a sufficiently fast gas flow rate in the opposite direction to the beam the jet becomes unstable and splits into layers.

An experimental investigation was made of the physical conditions under which the effect of laser radiation on the pyrolysis of 1,2-dichloroethane was greatest. It was established that laser radiation could ensure high values of the pyrolysis efficiency (50–60%) at temperatures 150–200 °C less than those usually employed in purely thermal pyrolysis. It was established experimentally that pyrolysis produced intermediate products which absorbed strongly laser radiation. A study was made of the influence of diffusion processes on the degree of pyrolytic conversion. The experimental dependences were accounted for on the basis of a kinetic analysis.

The lasing characteristics of alcohol solutions of rhodamine dyes (R6G, RB, R110), coumarin 47, and mixtures of these with and without inhomogeneous broadening of their electronic spectra were investigated using flashlamp and laser excitation. It was found that changes in the structure of the solvate shells of the dye molecules influenced the populations of their triplet states and the efficiency of electronic excitation transfer in two-component systems.

A theoretical investigation is made of the stability of steady-state reflection of light pulses from an interferometer rilled by a transparent medium with a Kerr nonlinearity. An instability is predicted for steadystate reflections of waves characterized by different amplitudes. Stability is expected only in narrow regions near extrema of a hysteretic dependence of the transmission coefficient on the incident wave amplitude. The results of numerical calculations predict development of stochastic reflection regimes.

An experimental study was made of the photodetachment of rhodamine ions deposited in the form of layers of different thickness on a tungsten substrate. The radiation source was a laser emitting ultrashort pulses at the wavelengths of 1.06, 0.53, or 0.26 μ. In the case of a submonolayer the formation of rhodamine ions was a thermal process.

The problem of the output power of a laser utilizing multistage (cascade) transitions is solved using a model of a nonbranching cascade. It is shown that the multistage nature of the transitions results in a completely different distribution of the output power between the transition lines of a cascade than would follow from estimates of the unsaturated population inversion and losses. In the case of a cascade of transitions with similar parameters the distribution of the power between the lines (considered as a function of the line number) is approximately quadratic with a maximum at the center of the cascade, whereas the integrated power is proportional to the cube of the cascade "length".

An investigation was made of multiphoton absorption of pulsed CO₂ laser radiation by CF₃I molecules cooled in a supersonic jet. Vibrational excitation of CF₃I was investigated as a function of the energy density in the range 0.05–1.0 J/cm² and of the frequency of the exciting radiation. Multiphoton absorption spectra were recorded and the changes in these spectra due to an increase in the energy density were studied. An investigation was made of the role of the intensity (duration) of the exciting pulses in the multiphoton absorption process. The spectral dependences of the energy density corresponding to the dissociation threshold were obtained and the fraction of the molecules interacting with laser radiation was determined.

The results are given of an experimental investigation of the relaxation processes in a transverse-discharge copper vapor laser excited by pulse trains. A mathematical model is used to analyze the experiments numerically. The most important processes which determine the operation of the laser in different regimes are revealed. The method based on excitation by pulse trains is shown to be an effective technique for investigating the physical processes in metal vapor lasers.

Locking of longitudinal modes in a cw solid-state laser by the use of a saturable absorber was demonstrated experimentally for the first time. A study was made of the dependence of the nature of lasing on the density of the absorber.

An analysis is made of the process of heating of a photothermoplastic carrier with a glass base by CO₂ laser radiation. A report is given of the experimental results obtained in recording microholograms of design drawings developed by laser radiation of 3 W power. Laser development improved the quality of the reconstructed image.

Strong ultraviolet radiation and easily ionizable impurities made it possible to achieve stable self-sustained discharges using voltage (pump) pulses of 2 μ sec minimum duration and specific deposited energy of at least 200 J/liter in discharge gaps up to 25 cm filled with CO₂–N₂–He mixtures with the molecular gases representing up to 50% of the total content. The minimum voltages required from a pump source to initiate a stable discharge did not exceed 255 kV.

A mechanism is proposed for low-frequency self-modulation of the radiation emitted by a solid-state ring laser. This mechanism is based on the fine structure of the gain profile. A model of a laser with two closely spaced gain profiles is used to find the conditions of instability of unidirectional lasing. A numerical solution of a system of equations describing this situation confirms the correctness of the conclusions of this analysis and it shows that the processes described by the proposed model of a solid-state ring laser are indeed observed experimentally.

Quasi-cw operation of color center lasers was achieved and the duration of the output pulses was ∼200 μ sec in the case of a LiF:F₂⁺ crystal and ∼400 μsec in the case of LiF:. These lasers were used in intracavity spectrum analyzers of ∼10⁻⁷cm⁻¹ sensitivity in the wavelength range 880–960 nm and ∼7×10⁻⁸cm⁻¹ in the range 1.12–1.19 μ.

An investigation was made of the interaction of metals in air with ultraviolet radiation of the wavelength 308 nm and intensity up to 3×10⁹ W/cm². The plasma formation threshold was found to depend strongly on the degree of laser cleaning and preliminary preparation of the target surfaces. The target material had a decisive influence on the dependence of the efficiency of energy deposition on the laser radiation intensity. Conditions for low-threshold breakdown of air by ultraviolet laser radiation were analyzed.

An analysis is made of the density of the distribution of the laser strength over the surface of lithium niobate. It is shown that distributions of this kind are polymodal due to the presence of defects of several different types with different damage thresholds. The distribution of the laser strength on the surface of one sample, representing defects of one kind, can be described by the Weibull law. The overall (net) distribution is a random mixture of such partial contributions. In the case of a small dispersion of the weights of the partial distributions, the overall distribution can be described also—with some approximation—by the Weibull law.

An experimental investigation was made of a detector of submillimeter radiation utilizing a difference frequency generated as a result of stimulated scattering by polaritons in a crystal of lithium niobate. When the pump pulse duration was 2τ_p = 18 nsec and the cross-sectional area of the pump beam was Q_p = 0.17 cm², about 4×10⁵ photons with frequencies in the range 25–35cm⁻¹ were detected in a solid angle Ω = 10 msr for the signal/noise ratio of 5. The experimental results were in qualitative agreement with theoretical estimates obtained allowing for the finite apertures of the interacting waves.

It is shown that the matrix methods can be used to determine the parameters of the transformation of Hermitian–Gaussian beams in a square-law medium with simple astigmatism. Formulas are obtained for the transformation of the general form of such beams. The proposed method is used to calculate the spatial structure of the radiation in a plane-mirror resonator which is filled completely by an inhomogeneous medium.

An investigation was made of the time and space characteristics of the spectrum and of the brightness temperature of a plasma formed near the surface of glass during some technological processes. It was found that when the energy of the incident radiation was 10⁶–10⁷ W/cm², an air spectrum appeared first and this changed in 6–8 μ sec to the emission spectrum of glass. In the same time the maximum brightness temperature of the plasma decreased from 7×10³ to 2×10³ K.

An investigation is made of fluctuations of the intensities of optical harmonics generated under resonant conditions by the field of randomly modulated pump radiation. An experimental study is reported of the dependence of the relative variance of the intensity of the third harmonic on the average pump radiation intensity under conditions of a three-photon resonance involving the 3s –5p transition in sodium vapor. The results indicated the possibility of suppressing fluctuations of the harmonic intensity under saturation conditions. A theory explaining this suppression effect is put forward.

Theoretical and experimental studies were made of the diffraction efficiency of amplitude–phase holograms which appeared as a result of stimulated Brillouin scattering pumping consisting of reference and signal waves of the same frequency. Variation of the temperature of the scattering substance was used to vary the frequency of the Stokes radiation used to reconstruct the holograms.

A description is given of the construction and characteristics of a stabilized tunable cw CO₂ laser. Optimization of the laser resonator with the aid of the polarization properties of diffraction gratings made it possible to achieve a tuning range 9.17–10.96 μ for a discharge gap ∼0.35 m long and an output power of ∼1.5 W for the strongest transitions in the single-mode regime.

An investigation was made of the reversal of an optical wavefront by a four-wave interaction with hypersound in the absence of wave detuning. A relatively simple system ensured that the reflection coefficient R of a signal wave was much greater than unity (this coefficient could be up to R =17).

An investigation was made of the optical breakdown in sodium silicate and lead silicate glasses subjected to neodymium laser radiation at the fundamental frequency and to the second, third, and fourth harmonics of this radiation. It was found that the optical breakdown threshold of both glasses decreased by a factor of SO when the photon energy became greater than half the band gap of each glass. This effect was attributed to two-photon ionization of intrinsic centers in the glass matrix. It was found that the breakdown threshold corresponded to the formation of a critical concentration of charged particles in the focal region.

Quasi-cw pyrotechnic lasers were constructed from Gd₃Ga₅O₁₂, KGd(WO₄)₂, KLu(WO)₂, La₃Ga₅SiO₁₄, and Lu₃Al₅O₁₂ crystals with high Nd³⁺ ion concentrations.

An investigation was made of the process of excitation of HgCl₂, HgBr₂, and HgI₂ molecules by electron impact producing B²∑⁺_1/2 states of HgCl*, HgBr*, and HgI*. The maximum values of the cross sections for dissociative excitation were found at low electron energies; the values of these cross sections were σ =(6 ± 3)×10⁻¹⁸, (7.5 ± 3)×10⁻¹⁷, and (1.2 ± 0.6)×10⁻¹⁷ cm² for HgCl*, HgBr*, and HgI*, respectively. The role of such dissociative excitation in lasing was analyzed.

An investigation was made of the linear and nonlinear optical properties of new neodymium yttrium aluminum borate crystals. These crystals were found to be suitable for use as multifunctional laser media and as nonlinear media capable of efficient frequency conversion of laser radiation.

Dynamic holograms were formed in Z-cut LiNbO₃:Fe crystals. Two beams with the "ordinary" polarization and mutually orthogonal electric field vectors were used for the first time to record a grating. The conditions for the occurrence of the normal and anisotropic diffraction were determined. An estimate was obtained of the component β₂₂ of the photogalvanic effect tensor.

An investigation was made of the quality of reconstruction of the signal wavefront in a single-pass system for compensation of phase distortions accompanied by frequency up-conversion. It was found that the best resolution and contrast were achieved when the reconstructed field was observed in the optimal focusing plane and the image of an inhomogeneous medium was transferred to the center of a nonlinear converter. The efficiency of the parametric process was enhanced by two-photon excitation of the 3s–4s transition in sodium vapor. The converter resolution was 13 lines/mm. The dependence of the contrast in the reconstructed field on the parameters of the compensation system was determined.

An investigation was made of perturbations of the dominant mode in a single-mode fiber waveguide. A theoretical and experimental study was made of the phase nonreciprocity of the opposite waves excited at a local inhomogeneity in the waveguide.

An experimental study was made of the characteristics of an argon ion laser stabilized in respect of the discharge current (up to 400 A) and output power. The laser had a sectioned discharge tube 10 mm in diameter and a cold arc cathode. The current was stable to within 0.02% and the radiation power to within 0.04%. The current-voltage characteristics of the discharge were linear and the output radiation power increased right up to the currents at which a high-frequency plasma noise began to develop. The high stability of the current made it possible to increase the output power of the laser because the high-frequency plasma noise appeared only at high values of the discharge current.

An experimental investigation was made of an XeCl laser pumped by electron-beam pulses of τ_0.5=2 μ sec duration. An output energy at the λ =308 nm wavelength was 5 J/liter when dielectric mirrors were used and the corresponding efficiency (measured relative to the input energy) was ∼3%. When the pump power was reduced, it was found that the output radiation included a considerable contribution of infrared radiation due to transitions in xenon when the mixture contained a buffer gas (argon).

An experimental study was made of an N₂O waveguide laser with a BeO discharge tube with a diameter 2 mm. The dependences of the output power of the laser radiation on the density of the pump current and on the rate of circulation of gas mixtures of different compositions were determined. The maximum power near the 10.8 μ wavelength was 95 mW when the average pressure in the active medium was 2.9 kPa (the composition of the mixture was 4% Xe, 12% N₂O, 26% N₂, and 58% He).

Self-diffraction of cw laser radiation was observed and investigated in the transparency range of single-crystal CdS plates at temperatures T = 293 and 77 K. The parameters of such a light-induced diffraction grating were determined. The grating period was found to be governed by the wedge angle of the crystal plate and its formation altered greatly the optical properties of the plate.

An experimental investigation was made of initiation of a nonself-sustained bulk discharge with a plasma cathode in the active medium of a CO₂ laser of 480 cm³ volume at pressures up to 0.5 atm. A combined preionization system, consisting of a plasma cathode resulting from a sheet discharge and a circuit for generating a short self-sustained bulk discharge, ensured an initial electron density of 2×10¹³ cm⁻³. The nonself-sustained energy deposition in the active medium reached 340 J·liter⁻¹·atm⁻¹, the output radiation energy was 48 J·liter⁻¹·atm⁻¹, the efficiency was 15%, and the gain was 0.033 cm⁻¹.