Table of contents

A report is given of the preliminary results of an experimental investigation of a vinyl bromide molecular maser excited by CO₂ laser radiation. This maser emits continuously at 45 wavelengths in the 2–0.2 mm range. At some of these wavelengths the output power is several milliwatts. Exact measurements (Δf/f < 10^–6) are reported of the emission frequencies of 31 lines. Information is given on CO₂ laser lines used for pumping, optimal gas pressure in the maser cavity, and polarization of submillimeter radiation relative to the polarization of the pump radiation.

An investigation was made of the parameters of an ultraviolet source emitting periodic pulses in which a dye laser was pumped by a nitrogen gas laser and the conversion was performed in new nonlinear crystals. The maximum conversion efficiency exceeding 30% was obtained for lithium iodate.

A description is given of a method for recording the transverse distribution of the gain in an active medium by illumination with a wide collimated beam. A probing laser beam is formed by using a small part of the cross section of the investigated active medium and an auxiliary resonator. A report is given of the experimental results obtained in an investigation of a transverse-discharge continuous-flow CO₂ laser.

A study was made of the possibility of using wire diffraction gratings in measurements of beam parameters of cw infrared lasers. Air cooling made it possible to increase the maximum permissible densities of laser radiation incident on the grating and yet retain a high optical quality of the beam.

It is shown theoretically that sharp absorption and total transmission lines can be formed in the energy continuum by a strong electromagnetic field.

A determination was made of the rate of transfer of energy to the last pair of molecules TF–CO₂ in the XF–CO₂ series (X = H, D, T). The exchange of energy in this pair occurred under conditions of nearly complete resonance. The rate constant was found by analyzing the changes in the characteristics of an NF₃+T₂ laser on addition of CO₂ to the gas mixture. The rate constant representing the transfer of energy from TF(ν = 1) to CO₂(00⁰0) was K_t(TF–CO₂) ≥5×10^–22 cm³/sec, i.e., it was considerably greater than the rate constant K_t(DF–CO₂) = (5–8)×10^–12 cm³/sec.

Laser emission at wavelengths of 510.6 and 578.2 nm was obtained from copper vapor at pulse repetition frequencies of 50 and 100 kHz, respectively.

Removal of absorbing microinclusions from polymethylmethacrylate (PMMA) increased considerably its ability to withstand multiple exposure to laser radiation pulses. Introduction of carbon black microparticles of 25 nm size into PMMA facilitated its damage by laser radiation. It was concluded that the processes of carbonization, resulting from local thermolysis of a polymer in the vicinity of absorbing microinclusions, played the dominant role in the damage caused by multiple exposure to laser radiation. The results of tests on methylmethacrylate and styrene copolymers were in agreement with this hypothesis.

An experimental study demonstrated that parametric oscillation could be obtained in the case of vector interaction of waves in an LiIO₃ crystal pumped with neodymium laser radiation.

An experimental investigation was made of the dependence of the difference frequency on the gain of the active medium (in which the discharge current was varied) of a ring helium-neon laser emitting at λ = 0.63 μ. The results obtained were in satisfactory agreement with the theory. These results made it possible to estimate the contribution of the homogeneous saturation of the gain profile to the dependence of the difference frequency on the output power.

Stimulated emission was obtained at λ = 10.6 μ as a result of mixing of a supersonic D+D₂+Ar stream with an O₃+CO₂+He stream. Population inversion was due to the transfer of the vibrational energy from OD molecules, formed by a chemical reaction, to CO₂.

A report is given of the measurements of thermally stimulated exoelectron emission from the surfaces of sapphire ends of laser elements before and after laser irradiation. It is shown that such irradiation does not generate new types of defect on the surface but increases the concentration of the existing defects. Analytic relationships are derived between the intensity of exoemission and the optical strength of laser elements.

An experimental investigation was made of the spectral and temporal characteristics of an electron-beam-controlled atmospheric-pressure pulse CO laser with an uncooled active mixture. The output radiation energy was 40–50 J and the stimulated emission occurred in vibrational bands from 9→8 to 15→14. The intensity of the radiation due to the 11→10 transition was considerably less than the intensities of the neighboring vibrational bands. A qualitative explanation of the experimental results was based on the partial overlap of vibrational-rotational lines of the CO molecule due to collisional (impact) broadening. A comparison was made with calculations.

An estimate is obtained of the precision of laser frequency determinations involving radiofrequency measurements of the Doppler shifts. It is shown that the method does not differ basically from that of interference fringe counting and it cannot ensure a high precision.

A description is given of the method and results are reported of the measurements of the temperature dependences of the linear expansion coefficient, temperature coefficient of the refractive index, and thermooptic constant of laser glasses and garnets (at λ = 0.63 and 1.15 μ). The results of measurements are converted to λ = 1.06 μ. It is reported that in the range 10–100°C all the measured quantities vary linearly with temperature.

Laser radiation of λ = 10.6 μ. wavelength was emitted from a supersonic stream as a result of burning of a CO+0.5O₂+He+H₂ mixture. It was established that the excited CO₂ molecules were formed as a result of a chemical reaction. A comparison was made of some of the characteristics with those of a gasdynamic CO+0.5O₂+N₂+H₂ laser.

A calculation is given of the distribution of fields and frequency spectrum of normal oscillation modes in traveling-wave resonators (ring resonators of arbitrary geometry and groups of three-dimensional resonators—in which beam trajectories do not lie in one plane).

The main developments in instrumentation for laser tracking of earth satellites and moon are reviewed. A country-by-country tabulation is given of the characteristics of laser tracking stations in operation and planned.

A brief review is given of the papers presented at the First All-Union Conference on Raman Spectroscopy, which was held in Kiev on November 18-20, 1975.

A description is given of the structure and principles underlying a new current awareness publication of the Ail-Union Institute of Scientific and Technical Information called "Nonlinear Optics and Quantum Radiophysics." The results achieved by this journal in three years of its existence are reviewed. The publication provides fast but carefully classified information on the literature on quantum electronics and on scientific and technical applications of this subject. Attention is drawn to the importance of the information content of the titles of papers published in scientific journals.

Recording and reconstruction of volume holograms by beams with Gaussian intensity distributions is analyzed on the basis of kinematic theory. Closed solutions are obtained for the general case. The application of the formulas obtained to specific cases reveals some differences compared with thin-film holography.

Methods for calculation of the output power of a carbon dioxide gasdynamic laser are discussed. The optimal conditions are found for maximum specific power on the assumption of one-dimensional flow of an inviscid gas ignoring changes in the chemical composition. The optimization is performed simultaneously with respect to the initial temperature, pressure, gas composition (carbon dioxide, nitrogen, helium, water vapor), nozzle profile, and resonator characteristics. The shape of the surface in the multidimensional space of the parameters being optimized is found. The nature of changes in the parameters near the optimal points is investigated.

The results are reported of an investigation of parameters of holographic periodic structures with modulated surface relief, methods for controlling this relief, and use of these structures in image replication. A method is proposed for constructing periodic structures with complex diffraction profiles for the fabrication of multichannel replicators.

Calculations are reported of elastic, viscoelastic, and residual stresses which appear in an optically transparent dielectric as a result of heating of a single inclusion by laser radiation. It is shown that the residual stresses may result in damage. The ray paths are considered and the induced anisotropy of a medium with thermal stresses in the vicinity of an inclusion is discussed.

A calculation is made of the gain experienced by far ultraviolet radiation in a plasma containing multiply charged helium-like ions. The populations of ionic levels are found by solving a system of rate equations, which allow for radiative decay processes and electron-ion collisions. The solutions are obtained for two cases of optically thin and optically thick plasmas. It is shown that, under steady-state conditions, the inversion density for intercombination transitions reaches 10¹³–10¹⁵ cm^–3. The use of stimulated Raman scattering of optical radiation by a plasma of this kind should result in single-pass generation of far ultraviolet radiation (λ~19–40 nm) in an active medium ~0.1–1 cm long.

The principle of operation is given and the construction is described of a compact optical delay line utilizing spherical mirrors. A delay time of 3 μsec is reported. The delay was used in multiframe shadow photography, with a ruby laser beam (1 nsec exposure), of a shock wave in air formed as a result of expansion of a laser jet.

The results are given of theoretical and experimental investigations of the influence of self-focusing in the active element on the energy characteristics of a mode-locked laser. Computer calculations of the output power for a fixed gain and laser resonator parameters are reported; allowance is made for the diffraction losses at the intracavity diaphragm. In this model the power is limited and it depends only weakly on the aperture in the diaphragm. The experimental value of the output power, ~7×10⁷ W, is in good agreement with the results of calculations.

Measurements are reported of the oscillator strengths of the absorption bands of the main glassy matrices and several industrial neodymium-doped laser glasses. The results are analyzed from the point of view of the Judd theory (1962) and represented by three parameters Ω₂, Ω₄, and Ω₆. These parameters are used to calculate the spontaneous emission probabilities and stimulated emission cross sections of the ⁴F_3/2→⁴I_11/2 and ⁴F_3/2→⁴I_11/2 transitions. A comparison is made between the values of these quantities and the published data for Nd³⁺ -activated crystals, glasses, and solutions.

The optical detection of the frequencies of incident radiation close to the fundamental frequencies of nonlinear crystals was investigated in the specific case of semiconductors CdS and CdSe. The experimental results were used to calculate the components of the nonlinear susceptibility tensor X⁰₃₃₃ and X⁰₃₁₁ of CdS and CdSe at the frequencies of ruby and neodymium lasers. Anomalously high susceptibilities were obtained for CdSe. The phenomenon of saturation of optical detection was observed for the first time and investigated. A comparison with earlier experimental results indicated that the saturation was of the same nature as the bleaching effect.

An experimental and theoretical investigation was made of the frequency tuning of a pulse electron-beamcontrolled CO₂ laser. A continuous tuning was achieved in a range of ~45 cm^–1 and the energy per pulse was ~0.1 J when the pressure in the laser mixture was 5 atm. The frequency pulling of the multimodestructure envelope of the gain lines was observed. This pulling was practically eliminated by inserting in the resonator a lens telescope or a prism, which increased the diameter of the beam on a diffraction grating. The spectral width of the radiation was ~0.05 ^–1. The results of a theoretical calculation of the tuning characteristics of the laser were close to the experimental data. A continuously tunable CO₂ laser was used in resonant excitation of visible luminescence in ethylene and optoacoustic detection of deuterated molecules HDS and NH₂D in natural isotopic mixtures of hydrogen sulfide and ammonia.

The results are given of an experimental investigation of parametric processes which govern the structure of the angular distribution of the intensity of the second Stokes and two anti-Stokes components of the stimulated Raman scattering in liquid nitrogen. The investigation was made using a collimated pump beam with a large transverse cross section. The angular structure of the first Stokes component included a highly directional peak against the background of diffuse radiation. These conditions made it possible to observe simultaneously for the first time three types of parametric generation at the second Stokes frequency. The observed angular spectra of the Raman components were explained on the basis of the theory of parametric interactions between plane waves. The reliable interpretation of the angular spectra and the high experimental precision made it possible to correct and extend the long-wavelength edge of the dispersion curve of liquid nitrogen at T = 77 °K.

A study was made of the influence of the strength of an electro-optic negative feedback, delay of the feedback signal, resonator configuration, pump energy, and the resonator Q-switching law on the stability and shape of microsecond pulses emitted by a ruby laser. It was found experimentally that the most stable microsecond pulses with a smooth top were formed by a laser with a semiconcentric resonator and the largest number of transverse oscillation modes. In this resonator the delay of the feedback signal and the mode beats, which would have resulted in a jagged pulse top, had little influence. A suitable selection of the pump parameters, feedback, and resonator Q-switching law made it possible to obtain different shapes of radiation pulses with durations from 100 nsec to several microseconds.

An investigation is reported of the amplification of resonance radiation under conditions of transient and spatially inhomogeneous excitation of a multilevel gaseous medium. Analytic expressions obtained can be used, in particular, in the design of a pulse amplifier and also of a cw amplifier in which mixing of gas streams is utilized.

A theoretical analysis is made of the interaction between a two-level quantum-mechanical system and an electromagnetic field which is frequency- and amplitude-modulated. Attention is drawn to the fact that, subject to certain general assumptions, the usual methods for population inversion in such a system—(2n + l)π pulses and adiabatic inversion methods—apply also if the pump field is of the wide-band type. Exact solutions are obtained for the nature of the time dependence of the instantaneous field frequency at which a population inversion occurs under nonadiabatic conditions.

An investigation is made of the influence of the polarization of a light wave on its emission from a corrugated section of a waveguide. It is shown that the asymmetry in the dependence of the attenuation coefficient on the direction of emission into the media adjoining a waveguide is important for E waves.

An investigation was made of a Raman laser utilizing compressed hydrogen (50-60 atm) in a cell 1 m long with an optical diameter of 70 mm. The pump source was a tunable neodymium laser with a central frequency ν_p = 9460±50 cm^–1 emitting 50 nsec pulses of radiation with a spectral width Δν_p ≲ 0.05 cm^–1. A raster focusing system was used in combination with a light guide of square 1×1 cm cross section to ensure spatially homogeneous pumping of the active region of the Raman laser. Tunable emission was obtained at the first Stokes component (ν_s = 5305±50 cm^–1, λ_s= 1.867–1.903 μ) with an energy efficiency of 10% and an output power up to 30 MW. Moreover, tunable emission was also obtained at the second Stokes component (ν_ss = 1150±50 cm^–1, λ_ss = 8.33–9.091 μ) with an energy efficiency of ~ 1% and an output energy of up to 0.5 J per pulse. The absorption spectrum of water vapor in the atmosphere was measured with a high resolution by means of this Raman laser.

An analysis is made of the principal parameters of an optical system for recording laser plasma interferograms. Methods for numerical analysis of interferograms on a computer are considered. A description is given of apparatus for high-speed interferometry with slit scanning by a streak camera with a time resolution of 10^–10 sec. The laser plasma interferograms obtained in this way are subjected to special calculation methods which increase the precision of the results. The system can be used to detect the development of a perturbation against the electron density profile in a plasma corona when the heating radiation intensity is ~5×10^–14 W/cm².

An investigation was made of the spectral, threshold, power, and time characteristics of laser diodes of planar and stripe geometry with Al_xGa_1–xAs double heterostructures. The threshold current densities in the Al02Gao8As lasers were 0.9 kA/cm² at 77°K and 6 kA/cm² at 300°K; these densities depended on the solid-solution composition in the active region. The output power of the planar diodes reached 8.2 W at 77°K and 3.6 W at 300°K; their differential efficiency was 0.5 and 0.22 at 77 and 300°K, respectively. The output power of the stripe lasers was 0.75 W per pulse and the differential efficiency was 0.26 at 77°K. The lifetime of electron-hole pairs was estimated under spontaneous and coherent emission conditions at 77 and 300°K.

A theoretical and experimental investigation was made of the interaction between two axial modes in a ring gas laser. An analysis was made of the competition between the stimulated emission regimes which were equally convenient in respect of the spectral "burning" of the Doppler line. It was found that the spatial-temporal modulation of the medium separated these stimulated emission regimes from the energy point of view. Conditions were found for the unidirectional stimulated emission with a symmetric position of the modes (relative to the center of the gain line), which appeared as narrow high-contrast power resonances.

A report is given of the principal characteristics of fluorescent screens determined directly by means of photographic and other test objects. It is shown that, under transient recording conditions, the spatial frequencies in an image decay rapidly with time. Fluorescent screens are used to show that the parameters of a converter can be predetermined by its geometric configuration and thermal properties.

A Michelson interferometer was used in an investigation of optical inhomogeneities of the active medium of an F₂ + D₂ (H₂)+CO₂ chemical laser pumped by a pulse light source. The maximum change in the refractive index was observed near the pump source: for F₂ + D₂ + CO₂ mixtures, it amounted to ~3×1O^–6 and, for F₂ + H₂ mixtures, it was approximately 3 times as large. The optical inhomogeneities were attributed to the chain chemical reaction taking place in the active medium.

A calculation is given of the efficiency of a system for pumping an active element of rectangular cross section. Allowance is made for repeated re-emission of radiation passing through the illumination enclosure and absorbed by the flashlamp plasma. The correctness of the efficiency calculations is supported by experimental results. A proposal is made for a system which should increase considerably the laser efficiency compared with the pump systems used at present.

The gain maxima are found for the stimulated scattering of light by surface waves in the range of large scattering angles. It is shown that the gain maxima appear as a result of formation of glancing (along the boundary) anti-Stokes waves and are due to a reduction in the importance of stray anti-Stokes scattering which is always present because of incomplete spatial phase matching of the interacting waves. A full analytic investigation is made near the gain maxima. The parameters of the incident light beam corresponding to a threshold minimum are obtained. It is shown that the threshold for the scattering through large angles under total internal reflection conditions is approximately an order of magnitude less than in the case when light is incident on a boundary of an optically rarer medium.