Table of contents

The problem of optical diffraction in an anisotropic dielectric medium is solved by the method of elementary solutions applying the mathematical theory of generalized functions. The results obtained are analogous to the results of the scalar diffraction theory.

Thermally induced birefringence, which depolarizes the laser radiation, appears in neodymium-doped yttrium aluminum garnet elements because of the absorption of the pumping radiation. The present paper gives a theoretical analysis of the influence of this effect on the generation of the second harmonic in the resonator under steady-state and nonstationary conditions. An expression is obtained for the nonlinear coupling coefficient corresponding to "100%" conversion. The range of losses and pumping coefficients corresponding to the "100%" conversion is identified.

A description is given of a spectroscopic method for the determination of the composition and pressure of a gas in a sealed helium-neon laser tube. The method is based on the measurement of the relative intensities of the He (λ = 501.6 and 587.6 nm) and Ne (λ = 585.2 nm) lines.

A reduction in the number of structure defects by altering the conditions during growth of GaAs crystals from the melt increased hundredfold the quantum efficiency of the radiative recombination and improved considerably the parameters of electron-beam-excited lasers. The presence of structure defects was detected by precision weighing of crystals. The dependence of the photoluminescence spectra on the density of crystals suggested that the luminescence band at ~1.35 eV was due to arsenic vacancies.

An investigation was made of the spectral energy distribution in the radiation emitted from HF and DF chemical lasers. It was found experimentally that the presence of HF in the original mixture of fluorine and hydrogen reduced the output energy of the laser and also altered the emission spectrum.

The results are given of an experimental investigation of the influence of thermal self-interactions on the second-harmonic generation in KDP, ADP (90% phase matching), and Ag₃AsS₃ (~22° phase-matching angle) crystals. The cause of the fall of the second-harmonic power was determined. It was found that at pumping powers exceeding a critical value characteristic of a given crystal the conversion efficiency fell because of the induced thermal detuning of the phase matching. The influence of birefringence was also considered.

The time of propagation of short light pulses along optical fibers of different lengths was determined. A study was made of the dependence of the passband of an optical fiber on the angle of entry of the beam into the fiber and on the fiber length. The passband decreased with increasing number of bends in the fiber. A study was made of the transmission of a sequence of spikes through a fiber.

Laser action was produced in a polymethylmethacrylate film activated with rhodamine 6F and deposited on a quartz substrate. The film was pumped with two converging second-harmonic neodymium laser beams, which formed an interference pattern. The rectangular edge of the quartz substrate acted also as a beam splitter of the pumping radiation. The output frequency of the film laser was tuned by altering the angle which the quartz plate made with the direction of the pumping radiation.

A new type of laser resonator is proposed: It is a ring resonator with a rotating field. It differs from other types of resonator by the rotation of the electromagnetic field through some angle after each pass to the active medium. This rotation ensures averaging of the transverse optical inhomogeneity in the laser resonator. Such averaging is demonstrated for a ruby laser. The proposed resonator can be used in other types of laser with inhomogeneous active media.

A study was made of the influence of the relaxation time of cryptocyanine on the shape of pulses and the width of the emission spectrum of a ruby laser operated at a low temperature under mode-locking conditions. The relaxation time was altered by the addition of quenching substances (acetone and carbon tetrachloride) to the solution of cryptocyanine. The relative quantum efficiency of the luminescence of cryptocyanine was determined as a function of the concentration of the quenching substance. The width of the laser emission spectrum was measured as a function of the concentration of the quenching substance using dye filters with an initial transmission of 3–50%. The measurements were carried out with an image converter and they showed that the duration of single pulses which passed through a filter with a 3% initial transmission was 35 psec in the presence of a quenching substance and 80 psec in the absence of this substance; the corresponding durations obtained using a filter with a 50% initial transmission were 180 and 260 psec, respectively.

A theoretical discussion is given of the characteristic features of the generation of electromagnetic radiation and of the measurement of the parameters of ultrashort laser pulses in the case when these are used to excite resonators containing electrooptic crystals.

The polarization of light scattered by a polydisperse aerosol is described by analytic average Stokes parameters. The polarization characteristics obtained in this way are of considerable practical importance in studies of the propagation of laser radiation in the atmosphere.

The Bragg diffraction of λ = 10.6 μ radiation by longitudinal acoustic waves was observed in proustite. The angular characteristics of the radiation entering and leaving the proustite crystal were determined. The number of independent resolvable elements at the exit from the crystal was 20. The ratio of the intensity of the diffracted radiation to the intensity of the incident beam was 3·10^–3.

The correlation radii of intensity fluctuations were determined for the propagation of light along short atmospheric paths. The values of the correlation coefficient were determined for the components of the fluctuation spectrum in the 100–400 Hz range. Changes in the correlation radius due to variations in the weather conditions were determined.

A new absorption line of the CH₃OH vapor, which coincided with the R(38) line of the 00⁰1–10⁰0 band of the CO₂ laser, was detected and investigated in the course of a study of an optically pumped CH₃OH laser. The absorption coefficient was 0.1 cm^–1 · torr^–1. Pumping with the R(38) line produced submillimeter radiation of wavelengths 164, 246, and 470 μ and of output power 0.1–1 mW.

An investigation was made of the influence of the condensation of water vapor, which could occur in a CO₂–H₂O–N₂ gas-dynamic laser, on the gain of the active medium. It was found that when the composition of the working mixture was CO₂:N₂ = 1:10 and it contained ~7.5% water vapor heated to a temperature of 1200–1500°K, the condensation did not affect (within the limits of the experimental error) the value of the gain at a pressure of ~20 atm. However, in the case of a CO₂–N₂–He mixture the addition of water vapor resulted in a considerable reduction in the gain in some part of the stream and this could be explained by the condensation of water vapor in the supersonic stream.

The angular structure characteristics of the expansion of multiply charged aluminum ions and nuclei were determined for the first time for a wide range of densities of radiation fluxes (10⁸–5·10¹³ W/cm²) reaching the target. The experimental results were generalized to a wide spectrum of masses and radiation flux densities and this made it possible to provide a description of the expansion of a laser plasma in vacuum. The phenomenon of "self-focusing" of beams of ions of maximum density, whose angle of expansion was 20–30° (symmetric about the normal to the target), was detected for the first time. This phenomenon and the results obtained should be useful in those cases where a sharp directionality of ion sources would be needed as, for example, in injection of ions into accelerators.

It is shown that a perturbation of an optically oriented ensemble of atoms by a nonadiabatically applied external magnetic field makes the density matrix of the ground state generally nondiagonal. The appearance of nonzero nondiagonal elements of the density matrix (i.e., the appearance of coherence) between different Zeeman states is manifested not only by the appearance of transverse components of the magnetization but also by the excitation of nonequilibrium higher-order multipole moments. In particular, if the initial state is oriented, a transverse magnetic field pulse produces an oriented nonequilibrium state. A discussion is given of the possibility of optical detection of nonequilibrium states produced in this way and of their relaxation.

An experimental study was made of the dependence of the two-photon absorption coefficient on the forbidden-band width of CdP₂ and ZnP₂ at neodymium laser radiation frequencies. It was found that this dependence was β (2ħω–E_g)^1/2, typical of the allowed–allowed transitions.

A study was made of the possibility of combining several active elements in one cataphoretic laser in order to widen the emission spectrum. Experiments were carried out using a cadmium–zinc–helium laser. It was found that this laser could emit separately or simultaneously the coherent radiation due to transitions in cadmium and zinc vapors.

An investigation was made of an optically pumped rubidium laser with its resonator filled with a nitrogen–methane gas mixture. Conditions under which the shift of the transition frequency was zero were determined for a nitrogen–methane mixture. Under these conditions the output power was 3–10^–10 W.

A description is given of a multimode laser with a resonator ensuring averaging of the output power density across an active element. The results of an experimental study are given.

A review is given of the papers presented at the Second International Conference on Lasers and Their Applications, held in June 1973 in Dresden. Brief information is given on the program and participants.

A review is given of the investigations of the properties and characteristics of Raman lasers, i.e., of oscillators and amplifiers using stimulated scattering, and of the associated processes and phenomena. The physical principles and characteristics common to Raman lasers are considered. These principles underlie various processes such as the stimulated Raman scattering, stimulated Brillouin scattering, stimulated Raman scattering accompanied by spin flip, etc. The special features of the dynamics of Raman oscillators and amplifiers are described. New properties of the stimulated scattering, typical of the "wide-band" pumping (spectrum of the exciting radiation wider than the spontaneous scattering line), are discussed. These new properties include the directional asymmetry of the gain and the threshold nature of the dependence of the gain increment of the pumping intensity. The results are given of experimental studies of the use of stimulated Raman and Brillouin scattering in the formation of light pulses, including their lengthening from tens of nanoseconds to several microseconds (Raman scattering) and Q switching (Brillouin scattering).

The anisotropy of the low-frequency electrooptical properties of lithium iodate crystals was investigated in terms of the nonlinear refractive index. A comparison of the data on the dispersion of the permittivity and of the nonlinear refractive index showed that the linear and nonlinear polarizations of lithium iodate are of different origins at frequencies of up to 10⁷ Hz.

An experimental investigation was made of the pulling of the stimulated emission frequency by a narrow molecular resonance in lasers with nonlinear absorption cells. An original method was developed for measuring the frequency stabilization coefficient. The basic dependences of the degree of pulling on the intensity of the saturating field, stimulated emission frequency, gas pressure, and transit effects were determined. A theoretical expression was obtained for the pulling of the frequency toward the center of the absorption line: This expression was in good agreement with experiment and was valid in strong saturating fields. The pulling effect was used to determine the principal spectral characteristics of the active molecular transition.

Three-photon parametric interaction of ultrashort light pulses in KDP and α-HIO₃ crystals is investigated. The study is carried out without the limitation of the given-pump-field approximation.

The active medium of a gasdynamic CO₂–H₂O–N₂ laser was investigated at high initial temperatures (up to 3200°K) for a large water-vapor content (up to 50%). The experiments were performed with a shock tube, and the mixture escaped through a slit. The method of amplification of a low-power CO₂ laser beam was used. The gain decreased with increasing H₂O concentration in the mixture, but still remained appreciable (3·10⁴ cm^–1). The corresponding component ratio was CO₂:H₂O:N₂ = 1:5:4. The experimental results were compared with the calculated data.

A description is given of the construction of an electron-beam tube with a screen made of a single-crystal semiconductor wafer in which laser radiation is excited by the electron beam. The electron-optics system, construction, and principal characteristics of this tube are described. A tube of this kind can be used in optical memory devices, color projection television, and high-speed oscillography.

An investigation was made of the dependence of the output power of a CO laser on the composition of the working gas mixture cooled by running water. It was established that the most efficient mixture was one of the composition CO:N₂:He:O₂:Xe = 1:5:24:0.04:1 kept at a total pressure of 20 mm Hg and excited with a current i =20 mA.

An approximate theory of parametric amplification and stimulated Raman scattering is developed for a pumping field which is incoherent in terms of the transverse coordinates and time. Expressions are obtained for the increments of the average field and the conditions of validity of the obtained expressions are determined. It is shown, in particular, that if the longitudinal length of the correlation between the pump radiation and the signal wave is small in comparison with the length of correlation of this radiation with the idler wave, then the employed approximation describes with sufficient accuracy the transition from the case of δ-correlated pumping (incoherent interaction) to the case when the gain achieved in a distance equal to the correlation length of the pump and idler waves exceeds unity (quasicoherent interaction). The intensity increment is then close to double the increment of the average field or the signal wave. In addition, for the indicated ratio of the correlation lengths, it is relatively easy to calculate the correlation function at a distance from the point of entry into a crystal, which is short but sufficient for an appreciable gain. Analogous conclusions hold also for stimulated Raman scattering in a pumping field with a spectral width exceeding the spontaneous-scattering linewidth.

A D₂ + F₂ + CO₂ + He pulsed chemical laser was put into operation at nearly atmospheric pressures in the mixture. The principal characteristics of the laser were the energy per pulse ~5 J, specific energy yield 1.2·10^–2 J/cm³, and pulse duration ~ 10 μsec. It was found experimentally that the CO₂ molecules inhibited the branched-chain self-ignition process. The use of photoinitiating components increased the utilization efficiency of the laser.

A theoretical analysis is given of two-dimensional focusing of light beams with Gaussian distributions of the amplitudes. The influence of the anisotropy as a method for increasing the efficiency of conversion of radiation in a nonlinear crystal is considered. The conversion at the sum and difference frequencies is discussed. An optimal ratio of the focal radii of the pump and signal beams is obtained for the axis along which rays are displaced because of the anisotropy. An estimate is made of the efficiency of conversion from λ = 10.6 μ to the visible range in a proustite crystal.

The concentration of the CN radicals in the discharge plasma of a CO laser was measured by the line absorption method. The number of the CN molecules was found to lie in the range 10¹¹–2·10¹² cm^–3 and it depended on the discharge parameters and on the initial composition of the gas mixtures. The addition of small amounts of oxygen reduced strongly the concentration of CN. The presence of CN in a discharge reduced the output power of the laser. However, under certain conditions the influence of CN on the laser action was insignificant.

An investigation was made of the spectra of Mg XI, Mg XII, Al XII, and Al XIII ions generated by laser radiation focused on solid targets. The relative intensities of the allowed and forbidden lines and of the lines beginning from self-ionized levels yielded the electron density (N_e ≈ 10²⁰ cm^–3) and temperature (kT_e ≈ 300 eV) of the radiating region. The method employed was suitable for the diagnostics of plasmas with N_e ≈ 10²³ cm^–3 provided the spectra of strongly ionized hydrogen-like and helium-like ions were observed.

A theoretical analysis is made of the physical processes in diatomic and polyatomic molecular lasers emitting in submillimeter and far infrared parts of the spectrum. The rotational relaxation is considered in detail for a system of diatomic molecules. Analytic functions are obtained for the distributions of populations of rotational levels in the presence of a source of rotationally excited molecules. Estimates obtained for the adiabatic range of the rotational spectrum indicate the possibility of building efficient lasers. The mechanisms of stimulated emission from polyatomic molecules are considered. The problems of establishing a population inversion of rotational levels of weakly asymmetric tops are discussed briefly. The laser emission due to vibration-rotational transitions is analyzed. Several specific laser action schemes are suggested for water vapor and these should make it possible to achieve high-power cw emission.

An investigation was made of a new single-frequency ruby laser producing nanosecond pulses of variable duration. The radiation was extracted from a closed resonator with an electrooptic switch. The short radiation pulses were produced by subjecting a Pockels switch to rectangular voltage pulses of amplitude equal twice the turn-on voltage. The duration and shape of the laser radiation pulses were governed by the steepness of the leading edge of the voltage pulses. ,A spatially homogeneous output radiation, equivalent to the radiation of a single-mode laser, was obtained by diffraction in a system of apertures in screens placed outside the resonator. The time and space characteristics of the laser radiation were investigated. An output power of up to 10 MW was obtained in the form of short nanosecond (1.4–7 nsec) pulses in a beam of divergence close to the diffraction limit.

It is shown that the recording and reconstruction of holograms with coherent emitting different wavelengths results in an additional restriction on the information capacity of a holographic memory. The optimal parameters, corresponding to the maximum capacity of such a memory, are deduced.

Investigations were made of the distributions of the electron and ion velocities using probe and transit-time collector methods. Experimental results were compared with a theoretical model of plasma expansion in a self-consistent electric field. It was found that at distances from the target exceeding the dimensions of the focusing region the electron and ion components interacted weakly with one another.

An investigation was made of the optical breakdown of gases by millisecond spike pulses of λ = 1.06 μ laser radiation. The breakdown in air was due to the presence of giant nanosecond spikes in the structure of millisecond pulses produced by a laser with a KGSS-3 neodymium-glass active element. Microsecond spike breakdown in argon at relatively low pressures of p < 10 atm was observed when the radiation was generated in GLS-1 glass elements. The investigation included high-speed photography, oscillography of the light produced by the spark, and measurements of the absorption of the incident laser radiation by a steady-state spark plasma. The absorption data were used in the determination of the range of temperatures and densities suitable for the experimental diagnostics of spark plasmas.

The radiation emitted from a neodymium laser, which was Q-switched by a Kerr cell, was locked by the narrow-band radiation emitted from a neodymium laser operating under free-oscillation conditions. The frequency-locking band was measured. The width of the line emitted by the Q-switched laser was reduced by a factor of 5·10³. The system employed made it possible to tune the frequency within the locking band (~40 cm^–1).

An investigation was made of the dependence of the coherent emission efficiency of a Raman laser on the width of the exciting line Δν_e. It was found that the emission efficiency remained constant up to Δν_e ≲ 2Δν_sp, where 2Δν_sp is the width of the spontaneous scattering line. The efficiency fell by an order of magnitude in the range Δν_e 10Δν_sp.

An analysis is made of nonstationary excitation of many oscillation modes in a semiconductor laser whose emission is subject to intensity pulsations (spikes). It is shown that even near the laser threshold the average emission spectrum consists of many modes if the pulsations of the intensity are sufficiently deep. An expression is derived for the width of the emission spectrum and its dependence on the pumping power.

An investigation was made of a resonance effect in a gas ring laser, which gave rise to a power peak in the opposite waves. The center of the peak corresponded to the zero value of the phase characteristic associated with the nonlinear dispersion of the medium. The theory of the effect and the results of the experiments carried out at λ = 3.39 μ were analyzed. A "methane" peak was used to measure the frequency shift of the center of the power peak relative to the center of the methane transition as a function of pressure in a helium-neon mixture.

An investigation was made of the photoluminescence spectra of cadmium sulfide and selenide single crystals (77 and 4.2°K) and of the spectra of the gain α(ħω) during excitation of the same crystals with electron beams of 20 keV energy (77°K). The experimental and calculated gain profiles were compared on the assumption of the exciton–phonon interaction between carriers. A correlation was found between the photoluminescence and gain spectra. Gains up to 70 cm^–7 were obtained for CdS crystals whose 77°K photoluminescence spectra included a strong (compared with the edge luminescence) band due to A free excitons, and there was clear evidence of transitions assisted by one or two longitudinal optical phonons. In the case of CdSe crystals grown by the sublimation of a powder in an argon stream the maximum gain and full agreement between the experimental and calculated gain profiles were obtained when these crystals were grown in the temperature range 800–900°C.

Thin films of glassy chalcogenide materials were used in pulsed recording of optical information with the aid of laser or electron beams. The information was recorded and erased using the same source but a higher intensity was used in the recording stage. The film transmission in the recording and erasing stages changed by more than 50%. Conditions suitable for recording and erasing of optical information were determined.