Table of contents

A theoretical investigation is made of the output pulse duration and the efficiency of a CO laser pumped by ~1 μsec pulses. A study is also made of the selection of the P₉(J) and P₁₀(J) lines suitable for laser isotope enrichment. The variable parameters are the pressure and temperature of the gas, pump energy density, losses in the resonator, and losses at the selected transition line.

Detailed investigations were made of the statistical relationships between the energy and time parameters of a picosecond phosphate-glass laser operating at a repetition frequency of 2 Hz. This was done using an original measurement system based on a nonlinear-optical correlator, amplitude analyzers, and computers. Optimization of the gain saturation and bleaching of a two-component medium ensured a reproducibility of better than 0.95 in ultrashort pulse generation. The pump energy was reduced to 260 J and the coefficient representing fluctuations of the picosecond pulse energy was lowered to 0.08. The average pulse duration in a train was 8.5 psec. Stimulated Raman scattering produced pulses of τ_p = 2.6 psec duration. The duration of a single pulse selected from the initial part of a train was 6.2 psec. The spectral Q factor was Δυτ_p = 0.5, indicating the absence of phase modulation. The high stability of the laser made it possible to use its second harmonic in pumping an optical parametric oscillator in which a crystal of α-HIO₃ was used inside the resonator. The energy conversion efficiency was up to 10% for Δυτ_p = 0.7.

It is shown that selective diffusion, i.e., spatial separation of gas mixture components in the collisional regime, found only on excitation of one of the mixture components by laser radiation, is possible at extremely low laser radiation intensities.

A theory is developed of an electronic-phototransition cw chemical laser initiated by a shock wave in a dense reagent stream. Calculations are made of the population inversion behind the shock wave front in the case of photorecombination reactions. The formation of a waveguide which localizes the lasing mode in the inversion zone is demonstrated. Calculations are made of the optical gain a of the waveguide modes. In an analysis of the gas dynamics and chemical kinetics of the laser action an allowance is made for a light-stimulated chemical reaction which alters the spatial dependences of the density, temperature flow velocity, and concentrations of the reagents. The specific optical power P extracted from the stream is determined as a function of the optical losses. Various specific gas mixtures are analyzed and the three most promising for laser applications are selected: NO₂Cl–Ar, O₃–Ar, and O₃–CO. It is shown that an inversion is established for these mixtures over a wide wavelength range and the waveguide formation conditions are compatible with the inversion condition. A gain α≈10^–3cm^–1 and power ~100 kW per 1 cm² of the gas stream are predicted for these mixtures.

An investigation is made of the kinetics of evolution of a pulsed discharge and accumulation of excited XeF* excimers in an He–Xe–NF₃ mixture. A kinetic model is proposed for a pulsed gas-discharge laser. This can be used to predict the optimal mixture pressure and pulse duration and to estimate the excited excimer concentrations attainable under optimal pulsed discharge conditions.

A theoretical investigation is made of the influence of the width of a dye laser emission line on the efficiency of difference frequency generation (DFG) using pump radiation at different wavelengths. The line width must be reduced to obtain the maximum efficiency and the longer the DFG radiation wavelength, the narrower the line which is required. An experimental investigation is reported of the conversion of dye laser radiation of wavelength 590 nm and line width between 0.17 and 6.5 nm into difference frequency radiation; this was done using nitrogen laser pump radiation and a KDP crystal 3 cm long. The maximum degree of conversion was 3×10^–4.

Analytic estimates are obtained of the radiation parameters of lasers utilizing complex organic compounds. An allowance is made for the influence of reabsorption of stimulated radiation by unexcited and excited singlet molecules. It is shown that reabsorption limits the laser radiation power. A comparison is made between the stimulated emission efficiencies of laser oscillators and amplifiers. Equations are derived to estimate the limiting length of oscillators and amplifiers. Dimensionless parameters, which determine the possibility of scaling up laser systems utilizing complex organic molecules, are obtained. Examples of calculations of the radiation parameters of lasers utilizing POPOP vapor and a rhodamine 6G solution are presented.

An experimental investigation was made of the influence of spatial filtering on the brightness of the output beam from the amplifying channel of a high-power laser system in which the active elements were Nd³⁺-doped phosphate glass rods. It was found that the brightness of the output beam could be increased substantially by an appropriate choice of the parameters of a vacuum spatial filter. A beam 40 mm in diameter with a peak intensity of 3.4 GW/cm² was obtained. Small-scale self-focusing did not cause appreciable energy losses in an angle of 0.25 mrad. The possible criteria for estimating the influence of small-scale self-focusing on the brightness of the beam being amplified were considered. These criteria should be useful in the development of systems of amplifying channels with periodic spatial filtering.

A system of diagrams is proposed for the calculation of the energy and shape of a pulse emerging from a system comprising a laser amplifier and spatial filters. The calculations are based on the input energy and shape of a pulse and on the small-signal gain subject to allowance for the losses in the active medium and for nonlinear losses in spatial filtering of the output signal.

A calculation is made of the lengths of active media and operating conditions optimal from the point of view of achieving maximum efficiency and still avoiding damage to glass because of self-focusing in the emission of pulses of 0.2–0.8 nsec duration. It is estimated that the brightness which can be attained in neodymium-glass lasers is 10¹⁸–10¹⁹ W/cm^–2sr^–1.

Calculations are made of frequency and amplitude nonreciprocal effects found in a ring laser on application of a transverse magnetic field to the active medium. An analysis is made of the case of quasilinearly polarized opposite waves, which is of interest in practice. It is shown that these effects are due to the nonlinear polarization nonreciprocity found in the active medium on application of a transverse magnetic field. These effects depend on the square of the magnetic field on its orientation with respect to the electric field of the wave. Numerical estimates are made of possible errors in laser gyroscopes caused by transverse magnetic fields. It is suggested that the effects described may be used in laser spectroscopy to determine the relaxation constants of active levels.

The passage of relativistic electrons through the foil-gas-anode system in an electron-beam-controlled laser was analyzed by the Monte Carlo method. A study was made of the influence of the beam parameters, composition of the active medium, electric field in the nonself-sustained discharge, and also laser design features on the ionization homogeneity in the discharge gap and the uniformity of the electric field in it. A discussion is given of the choice of the beam energy and of the construction elements of a laser using light foils.

A theoretical and experimental investigation was made of the dependence, on the detuning of the resonator (relative to the center of the gain profile), of the intensities of the opposite traveling orthogonalmode waves. The dependences were found of the width of the detuning region within which a four-wave lasing regime exists on the ratio of the gain to the losses, pressure of the active medium, and strength of the longitudinal magnetic field applied to it. The results of an experiment, carried out using an He–Ne laser operating at a wavelength of 1.15 μ, were in satisfactory quantitative agreement with a theory in which radiation trapping is taken into account and the usual phenomenological approach is employed to describe the pressure effects.

An experimental investigation was made of the energy, space-time, and polarization characteristics of an atomic iodine photodissociation laser with a four-mirror ring resonator. The direction of lasing was governed mainly by weak reverse signals which could originate, in the absence of auxiliary mirrors, from parasitic reflections or scattering. Under flashlamp pumping, an influence of dynamic inhomogeneity waves on the lasing threshold was manifested in the space-time structure of the near-field pattern. It was established that the polarization of the emitted radiation was linear in the absence of external magnetic fields. It was shown that one can use a ring-laser oscillator for investigations on amplifying systems, and that this approach ensures suppression of amplifier self-excitation by reflection from the resonator mirrors.

An analysis is made of the dynamics of the electronic spectra of complex molecules associated with the nuclear motion, and of its manifestation on exposure of a molecule to high-power optical radiation. A model is proposed for the inhomogeneous broadening dynamics. This describes the random walk of the spectral frequency in the form of a Gauss-Markov random process and allows for the relaxation of the spectra which accompanies an electronic transition. Simple readily interpreted relationships, which describe the influence of nuclear relaxation on the stimulated emission frequency, are obtained.

A theoretical and experimental investigation was made of the high-frequency properties of Nb–Nb superconducting point contacts (SPC's) operating under nonequilibrium conditions with a high critical current I_c and low normal-state resistance R_N. The possibility of using these contacts in raetrological applications in the near infrared was studied. On exposure of these SPC's to external radiation, current steps corresponding to the harmonics of the external radiation frequency were readily observed on their current-voltage characteristics at voltages exceeding the limiting value for niobium SPC's. In this case, the frequency was subject to a capacitative limitation. Frequency multiplication up to 8×10¹²Hz (~38μ) was observed at bridges having dimensions not exceeding 50 nm. Investigations were made of the dependences of the step-like structure of the current-voltage characteristics of SPC's on the external radiation power, and frequency. The dependences of the intermediate-frequency signal amplitude and width on the bias voltage and power of the external signals on exposure of SPC's to two radiation sources were also studied. A theoretical analysis showed that, in frequency multiplication and mixing by SPC's operated under nonequilibrium conditions, allowance must be made for the action of both the selfradiation and its harmonics on the SPC.

An investigation is made of a compression wave traveling from the source of laser breakdown in a transparent insulator. It is shown that at large distances from the source the wave structure is governed by the conditions of its formation and it is related to the energy characteristics of the source and properties of matter; a study of the wave structure can give information on the wave source. An experimental investigation is reported of the space and time structure of a compression wave as a function of the distance from the source of laser breakdown and energy of the initiating radiation. A theoretical model is developed for the formation of an acoustic wave in this case. The experimental and theoretical results are compared and it is shown that they are in qualitative and quantitative agreement.

Coordinated theoretical and experimental investigations were made of the conditions for achieving high energy exchange in three-wave parametric interaction of temporally and spatially modulated picosecond light packets. An efficiency of 50% was achieved for conversion of pump energy into radiation with continuously tunable wavelengths under optimal conditions in a KDP crystal. In this case, a spatial pump-radiation profile without random amplitude-phase distortions was an extremely important factor.

Radiation emitted from a neodymium glass laser was modulated by exciting ultrasonic (20–200 kHz) longitudinal vibrations in the active element or in one of the resonator mirrors. The intensity modulation occurred at twice the ultrasonic vibration frequency, with a simultaneous increase by a factor of 2–3 in the average intensity of the spikes. The total energy emitted in a pulse remained constant. The laws governing the modulation were studied, especially its dependence on the ultrasonic amplitude and frequency, over a wide range of pump energies; these laws were independent of the type of active medium used. The mechanism of the ultrasonic modulation of solid-state laser radiation is considered.

A detailed investigation is made of the interaction between a hypersonic vibrationally excited donor gas and a carbon dioxide aerosol stream with a view to improving the energy characteristics of a gasdynamic CO₂ laser. The analysis shows that rapid (within times shorter than the relaxation time of the upper active level) mixing of the evaporating aerosol and the vibrationally excited gas is possible as a result of this interaction. For a planar flow geometry with symmetrical aerosol injection, the transverse dimension of the active medium may be 20 cm for a hypersonic nozzle with a throat cross section ~1 mm high. The conditions under which there were no gas-dynamic perturbations in the mixing zone and the active medium was optically homogeneous were determined. A CO₂ aerosol generator was developed with a solid particle size distribution function close to the optimal. An experimental investigation was made of the interaction between the streams using a system with a conical hypersonic nozzle for the air and perpendicular injection of the aerosol. The experimental results broadly agreed with the theoretical predictions. A CO₂ laser radiation gain close to the calculated value was obtained in the excited air-carbon dioxide aerosol mixing zone.

An analysis is made of the distortions of an optical wave propagating in a turbulent atmosphere containing an aerosol. Calculations are made of the spatial correlation functions and temporal frequency spectra of the fluctuations of the amplitude logarithm and phase of a plane wave using the smooth perturbation approximation. Averaging of the intensity fluctuations by a receiver aperture is discussed.

A theoretical analysis is made of the influence of the misalignment between the axes of a semiconductor laser beam and of multimode or single-mode fibers on the efficiency of coupling of radiation into the fibers. Two cases are considered: a direct contact between a laser and a fiber, and an indirect contact with a matching element in the form of a fiber segment with a square-law variation of the refractive index.

An investigation is made of the dependence of the pass band of a waveguide on the excitation conditions. Approximate equations which express the dependence of the waveguide pass band on the excitation conditions are derived using an analytic expression for the transfer function of a waveguide having a step refractive index profile. An experimental investigation was made of this dependence. This technique can be used to measure the pass band of graded-index waveguides.

It is shown that wavefront reversal may be observed in superradiance emitted from dye solutions. The saturable nature of the dependence of the gain on the pump power makes the discrimination of the uncorrelated modes of a reconstructing field less than in the stimulated scattering case.

An experimental investigation was made of the properties of a neodymium glass laser with an unstable resonator and an additional mirror which covered part of the optical beam cross section to reduce the stimulated emission threshold. The results were compared with the case of a conventional low-magnification unstable resonator. It was found that radiation with a low angular divergence cannot be obtained from a laser with an unstable resonator and additional feedback.

The results are given of preliminary experiments carried out on a gasdynamic CO₂ laser in which an N₂–CO₂–He working mixture of gases was heated in a plasmotron. A specific output energy 20 J/g and an efficiency ~1.2% were obtained for cw operation when the initial gas temperature was T₀= 1700±100°K, the parameter p_oh* had the value ≲ 0.5 atm-cm, and the total flow rate of the gaseous mixture was ~0.5 kg/sec.

An experimental study was made of the angular and polarization dependences of the diffraction efficiency of a holographic grating formed by the interference between an evanescent wave and a plane wave orthogonal to it. The reconstructing wavelength range was 488.0–676.4 nm.

The principle of formation of inhomogeneous electric fields is applied to an electrooptic KDP-type crystal. This makes it possible to use this crystal, together with polarizers, in a space-time light modulator which can perform functions of a high-speed switch and a soft-edge stop. A method used to calculate electric fields in such modulators establishes the relationship between the design parameters and the transverse distribution of light transmission. Comparison with experimental results shows that this method is in error by not more than 10%.

It is shown experimentally that for a constant total concentration C+C_N (C is the CO₂ concentration and C_N is the nitrogen concentration), the product of the small-signal gain k₀ and the saturation parameter I_s does not depend on C and I_s(C+C_N)/C. This permitted us to obtain analytic expressions for the dependence of the laser radiation power on C and time if the rate of renewal of the medium and the CO₂ dissociation and recombination rates are known. The expressions derived show fairly good qualitative and quantitative agreement with the experimental data. Recommendations are made for minimizing the reduction in the radiation power with time caused by the dissociation of CO₂.

A calculation is made of the gain experienced by an electromagnetic wave in a semiconductor subjected to magnetic field and ultrasonic fields. It is shown that the gain can be 1–500 for a wide range of the parameters. Analytic expressions are obtained for the frequency depencence of the real part of the highfrequency conductivity when the pump power, ultrasonic wavelength, and temperature of the semiconductor are varied.

Results are presented of an experimental investigation of the polarization characteristics of the radiation from single-channel GaAs injection lasers. It is shown that single-channel cw lasers operated at T=77°K emit linearly polarized radiation over a broad range of injection currents. On application of a uniaxial pressure perpendicular to the p-n junction plane, the plane of oscillations of the vector E is rotated through 90° and the pressure range in which this rotation occurs depends on the width of the emitting area.

An investigation is made of the frequency response of a ring laser operated with a variable-sign (reversible) frequency pedestal. Backscattering-induced wave coupling is observed under these conditions due to the asymmetry of the scattering in the opposite directions. An analysis is made of single- and two-mode stimulated emission.

An investigation was made of the effect of conversion of the pump radiation spectrum in a luminescent liquid (solution of rhodamine 6G in ethanol) on the output energy of neodymium glass and YAG lasers. Analyses were made of the dependences of the conversion efficiency on the luminescent liquid concentration and type of active medium. The laser output energy in the free-oscillation regime was doubled, the differential efficiency was increased by 50–130%, and the stimulated emission threshold was reduced by 10–25%. A comparison was made between the experimental measurements and the calculation results.

A theoretical analysis is made of the diffraction of a guided mode in a periodically corrugated section of a slab waveguide. The case of the Nth Bragg resonance is considered. It is shown that the amplitudes of the guided modes satisfy the coupled-wave equations. Analytic expressions are given for the amplitudes of the continuous-spectrum modes.

An investigation was made of the influence of the degree of focusing on ruby-laser third harmonic generation in thallium vapor. It was found experimentally that, as the focal length of the lens used for focusing decreases, the maximum stimulated emission signal increases and is shifted toward higher temperatures, and narrowing of the stimulated emission curve is observed.

A cylindrical waveguide with a square-law medium is used to demonstrate theoretically the possibility of optical image transmission along multimode waveguides over long distances (from hundreds of meters to a few kilometers). Expressions are derived to determine the position of the distant cross sections where the image is formed, and the number of image elements which can be transmitted to these cross sections. Requirements on the radiation source are formulated allowing for the chromatic aberrations in the waveguide.

An investigation was made of the phase diagram of the Hgs–HgGa₂S₄ system. It was shown that there is a region of HgGa₂S₄-based solid solutions. Optically homogeneous mercury thiogallate single crystals were grown and used to measure the refractive indices in the 0.55–11 μ range. A phase-matching diagram was plotted for an o + o→e frequency mixing process. This diagram confirmed phase-matched interaction in the specified wave-length range.

An experimental study was made of photosensitive metal-insulator-semiconductor structures in contact with a nematic liquid crystal. Utilization of the orientational electrooptic effect in the liquid crystal ensured a high energy sensitivity of a structure with gallium arsenide as the semiconductor. Modulation of the phase of light by π or attainment of the highest optical contrast (of the order of 100:1) was achieved when the minimum intensity of the exciting helium-neon laser radiation (λ=633 nm) was 5×10^–7 W/cm² and the switching energy was 10^–8–10^–9J/cm². Spatial resolution was at least 10–12 lines/mm. A structure of this kind could be used for coupling in and conversion of optical data, including visualization of infrared radiation.

An experminetal investigation was made of the transient self-diffraction of coherent light beams in an absorbing liquid. The measured efficiency was comparable with the calculated value. The discrepancy between the calculated and experimental results increased on increase of the energy (but not the power) of the radiation supplied to 1 cm³ of liquid. An experiment involving the construction of a laser utilizing stimulated thermal scattering is described.

The efficiency of the lasing transition and gain saturation law are found for a CO laser with a selective resonator. The selective lasing efficiency is limited by transfer of quanta by the molecules to the upper part of the vibrational spectrum, bypassing the lasing transition.

An analysis is made of the excitation of a four-photon parametric process by a noncoherent Gaussian (noise) pump field. An allowance is made for the dispersive and dissipative properties of the nonlinear medium. It is shown that this process may have a fairly high efficiency in vapors of Cd, Hg, and Zn metal atoms if rare gas fluoride excimer laseres are used as pump sources.

Measurements were made of flame propagation velocities in atmospheric-pressure fluorine-hydrogen mixtures with different compositions. It was shown that, for the same stored energy, diluting a mixture with a diatomic gas such as nitrogen, instead of with monatomic gases, or adding the polyatomic gas SF₆ sharply reduced the combustion rate and increased the threshold fluorine pressure at which combustion was converted into detonation under the conditions being studied.