Table of contents

An Agat-SF linear-scan streak image-converter camera was used to record output pulses of 2.7 psec duration generated by an injection laser with an external dispersive resonator operated in the active mode-locking regime. The duration of the pulses was determined by the reciprocal of the spectral width and the product of the duration and the spectral width was 0.30.

An investigation was made of potential applications of a carbon monoxide laser (λ=5–6 μ) in surgery. It was established that the radiation emitted by this laser had better cutting and coagulating properties than CO₂ laser radiation currently used widely in medicine.

A pulse-periodic neodymium laser was made from a new crystal, which was gadolinium scandium gallium garnet activated with chromium and neodymium ions (GSGG:Cr³⁺: Nd³⁺). When the pump energy was 7.3 J per pulse, the output energy in the free-running regime was 255 mJ, i.e., the absolute efficiency was 3.5%. At the maximum pulse repetition frequency (20 Hz), which was limited by the nature of the power supply unit, the average output power was 5 W when the pump power was 145 W. The differential efficiency was 4.5%, which was 2.4 times higher than for an YAG:Nd³⁺ crystal operated under similar conditions. The diameter of the GSGG active element was 5 mm and its length was 50 mm. The differential efficiency in the Q-switched regime was 3% when the pump energy was in the range 3–7 J.

An investigation was made of various configurations and operating regimes of systems for ion extraction in a method of selective multistage laser photoionization of atoms. The factor representing separation of a substance per cycle was determined. When several impurities were introduced deliberately, this separation factor was ≥10³. The crystallization temperature decreased to 300 K when films were formed by deposition from a beam of In⁺ ions.

An investigation was made of an electrooptic Bragg modulator based on an LiTaO₃:Ag waveguide with a variable period with an apodized longitudinal structure of the electrodes. A calculation of an integral representing the overlap of the mode and electrode fields was used to determine how the length of the zone of interaction between light and a grating varied with the waveguide and electrode parameters. A prototype modulator was constructed: its control voltage was 7.2 V, the maximum depth of modulation was 97%, and the focal length was 13 mm.

An investigation was made of stimulated Brillouin scattering of light in a medium located in a hollow light pipe. The dependence of the angular distribution of the nonreversed component of the scattered radiation on the parameters of the medium and of the exciting light was determined experimentally. The main physical mechanism that determined this angular distribution was found to be the depolarization of the scattered radiation on the walls of the light pipe.

A theory of polarization-holographic recording is considered in the general case of a reaction of a photoanisotropic medium involving linear and nonlinear effects when the medium subjected to elliptically polarized light assumes the properties of a gyrotropic crystal. The matrix describing conversion of the state of polarization of a reconstructed image is obtained in the linear approximation. This matrix depends on a scalar reaction and two vector reactions of a photoanisotropic medium and also on the state of polarization of the reference and reconstructing waves. The approximation of an infinitesimally thin hologram is used to derive the equation for the characteristic ellipse of a photoanisotropic medium, which describes an elliptically polarized reference wave matched to the characteristics of the medium so as to ensure that the reconstructed image is undistorted in respect of the polarization.

A theoretical investigation is made of the absorption spectrum of guided TM modes in a four-layer planar metal–dielectric waveguide heterostnicture with narrow-gap electronic excitation of a buffer layer in the case when the electronic transition frequency is close to the frequency of a resonance between the guided TM modes in a three-layer dielectric wave-guide and a surface plasmon. It is shown that two types of singularity—dips (antiresonances) and shifted lines—may appear in the absorption spectrum of the guided TM modes of a four-layer heterostnicture. Potential integrated-optics applications of the predicted effect are considered.

The method of path integration is used to solve the problem of the influence of weak noise on nonlinear propagation of an ultrashort light pulse in an optical fiber. A calculation is made of the correlation function and pulse intensity. It is shown that the coherent properties of a pulse deteriorate in a nonlinear medium. Noise also increases the pulse duration by an amount depending on the interaction length. It follows that steady-state propagation of pulses cannot be expected in the presence of noise.

A study was made of the stimulated-emission characteristics of a longitudinally pumped laser utilizing a grazing-incidence holographic grating. Gratings with 1450 and 2500 line/mm were specially optimized for operation in the grazing-incidence regime. Measurements were made of the diffraction efficiency of these gratings for large incidence angles at a wavelength of 571.5 nm. An output power of 180 kW was achieved for rhodamine 6G with a laser line width of 0.1 cm⁻¹. Single-mode radiation with a half-width of 1.5×10⁻² cm⁻¹ was generated near the lasing threshold without using additional selective elements.

An experimental investigation was made of stimulated Brillouin scattering (STBS) in multimode quartz fiberoptic waveguides excited by a relatively narrow-band (spectral band width of less than 0.025 cm⁻¹) spatially inhomogeneous pump source. Mathematical expressions are given which characterize the development of steady-state STBS and help to explain certain properties of observed STBS. A description is given of the characteristic features manifested by STBS excited together with stimulated Raman scattering, and also of new facts associated with damage to the fiber-optic waveguides.

A direct numerical solution of reduced equations is used to study theoretically second harmonic generation in nonlinear crystals in the case of strong energy exchange. An allowance is made for the aperture effects and for diffraction. It is shown that transformation of single-mode radiation in crystals with critical phase matching is not very inferior in respect of the conversion efficiency to that in crystals with 90° phase matching, and that displacement of an extraordinary wave relative to an ordinary one prevents the reverse energy conversion. It is shown that in the case of a strong energy exchange in crystals with critical phase matching the efficiency of second harmonic generation decreases strongly even in the presence of slight spatial distortions in a transverse cross section of the fundamental-frequency beam.

A theoretical analysis is made of the process of isotopically selective excitation of atoms in the field of opposite waves when the compensation of the Doppler broadening is incomplete. The density matrix formalism for a homogeneous steady-state case is used to obtain expressions for the total probability of the excitation of resonating and nonresonating isotopes and for the selectivity of the process defined as the ratio of these probabilities. In some cases analytic expressions are obtained and these make it possible to determine the nature of the dependence of the total probability of the excitation and selectivity on the temperature of a vapor, buffer gas concentration, ratio of the Rabi transition frequencies, detuning from a resonance, and isotopic shifts. Numerical estimates are obtained of the atomic parameters for transitions in potassium and rubidium atoms. It is shown that the adopted method is more promising for the separation of the isotopes of alkali metals than is one-photon excitation.

A theoretical investigation is made of the behavior of a melt on whose surface laser radiation with a homogeneous intensity distribution is absorbed. A dispersion equation is obtained for the hydrodynamic perturbations, taking into account the vaporization pressure, thermocapillary forces, and melt viscosity. The vaporization pressure is shown to lead to an instability of the melt surface. This effect differs qualitatively from an instability of a plane sublimation front which arises only for bulk absorption of laser radiation. The time needed for the hydrodynamic instability to develop decreases rapidly with increasing temperature of the illuminated surface and become less than a millisecond when the vaporization pressure reaches 0.1 bar.

An analysis is made of the problem of propagation of a wave beam in a moving (circulating) medium under thermal self-interaction conditions. An analytic method is developed for solving the wave equation in the case of a one-dimensional collimated beam. This method is based on reduction of a nonlinear parabolic equation to a nonlinear integrodifferential equation of the Schrödinger type. Analytic solutions are obtained for the wave equation in the case of one-dimensional focusing of the beam and also for the same beam scanning a medium at a constant low velocity. The conditions for guided (self-channeled) propagation of a one-dimensional beam are considered for a model continuous-flow homogeneous medium under thermal self-interaction conditions.

A theoretical and experimental investigation was made of the interaction between counterpropagating waves in an He–Ne ring laser having a circularly anisotropic resonator. This was done for large values of the ratio of the gain to the losses when the gain saturation was comparable with the gain itself. The dependences of the counterpropagating wave intensities and of the frequency of beats (formed when a longitudinal magnetic field was applied to the active medium) on the resonator detuning in a single-mode 0.63 μ wavelength laser were obtained experimentally. Numerically found theoretical dependences were in good agreement with experiment for values of the ratio of the gain to the losses of up to 2.9.

The sensitivity of an interferometer, when a high-power laser is used, is limited by the amount of power which can be dissipated within the interferometer without causing a deterioration in its characteristics. An analysis was made of the optimization of interferometers for maximum signal/noise ratio with a given power dissipation. It is shown that the best results are obtained by recording the light reflected from an interferometer, and not transmitted through it. The detectivity threshold for small displacements associated with thermal effects is roughly 10⁻¹⁰ nm·W^1/2·Hz^−1/2 for the present-day dielectric mirror manufacturing technology.

The method of the inverse scattering problem is used to find solutions of the Maxwell–Bloch equations. It is shown that the area theorem does not apply to complex solutions.

The conditions for high-efficiency operation of a KrF electron-beam laser were determined. It was found that the amounts of Xe and O₂ impurities present in the gas mixture must not exceed 0.01%. An empirical expression was derived for determining the optimal composition of the active gas mixture. A laser output energy of 14.1 J was obtained from a 0.45-liter active volume with an efficiency η=9% (in terms of energy input to the active volume) at a gas pressure of 3 atm and for a pulse duration of ∼80 nsec. The gain and absorption of the active medium were determined (0.15 and 0.014 cm⁻¹, respectively) for a specific excitation power of 1.25 MW·cm⁻³·atm⁻¹.

An experimental and theoretical study was made of the concentration of radiation in a dye laser with an intracavity absorption cell. The phenomenon was shown to be nonlinear and was explained theoretically on the basis of a generalized model of a two-level atomic system. Good quantitative agreement was obtained between the experimental and theoretical results. Recommendations were developed for utilizing the investigated phenomenon in laser technology and nonlinear spectroscopy.

A study is made of the dynamics of a superradiance pulse in a transversely inhomogeneous active medium inside a tubular waveguide with dielectric walls. The problem is solved numerically in the approximation of a given field profile by expanding the radiation field in terms of the normal modes of the waveguide and the polarization and inversion of the medium in terms of basis functions dependent on the transverse coordinates. It is shown that an inhomogeneous transverse distribution of the field and of the initial inversion can suppress the appearance of oscillatory replicas (superradiant "ringing") of the main superradiance field and also can result in incomplete utilization of the energy stored in the active medium because of coherent dephasing of the polarization of the medium in different parts of a transverse cross section of the waveguide.

A theoretical study is made of the influence of diffraction by self-induced amplitude gratings on propagation of spatially inhomogeneous radiation in nonlinear resonant media. Dependences of the gain and absorption, and also of the distortion of the spatial spectrum on the parameters of the medium and radiation are determined. It is shown that interfering radiation is amplified and absorbed under saturation conditions less strongly than is spatially homogeneous radiation.

Unusual behavior of the amplitudes of stimulated Brillouin and stimulated thermal scattering in benzene was investigated experimentally and analyzed in the cases of simultaneous and separate excitation under wavefront reversal conditions. The influence of phase modulation of the exciting radiation on the stimulated thermal scattering gain was considered.

Investigations were made of the time-resolved spectral and energy characteristics of a C₃H₈–SF₆ laser using different active mixture pressures, chemical reaction initiation levels, and resonator parameters in both selective and nonselective lasing regimes. The measurements were performed using fast-response (≤0.5 nsec) pyroelectdc detectors. It was established that the laser pulses had a three-spike structure, resulting from lasing of the P lines in the following sequence: P₂→P₃→P₁. It was found possible to control the pulse shape and the spectral composition of the emitted radiation. An analytical model was proposed to explain the time sequence of lasing on the different vibrational transitions. An identification was made of the vibrational distributions of the laser pump reaction products for which other lasing time sequences are possible.

A quantum-mechanical problem of the reflection and transmission by a barrier on which electrons are incident in the field of a strong electromagnetic wave is considered. An expression is obtained for the modulated electron current.

It is shown that self-focusing of light beams may occur as a result of cooling of a mixture of reacting gases in the case of resonant interaction of light with atoms (or molecules) participating in chemical reactions. Estimates of the duration and degree of cooling are obtained.

An experimental investigation was made of the temperature dependences of the energy characteristics of a cw electron-beam-controlled industrial CO laser. High values of the lasing efficiency (37%) and specific output energy (113 J/g) were achieved. Rapid formation of carbon dioxide was observed in working CO mixtures in an electron-beam-controlled discharge.

An image-converter camera was used to determine the duration and shape of the output pulses of a single-pass optical parametric oscillator (OPO) composed of two KDP crystals pumped by the second harmonic of a passively mode-locked YAG:Nd³⁺ laser (the duration of the pump pulses was 25±3 psec). It was found that under weak energy exchange conditions (when the energy conversion efficiency was ≤ 5%) the duration of the OPO output pulses decreased to 20±2 psec, whereas in the case of a strong energy exchange (∼15%) the duration of these pulses increased to 28±5 psec.

Quantum chemistry methods are used to calculate the cross section for stimulated emission σ(ν) and the Einstein coefficients B(ν) for several substituted forms of oxazole, oxadiazole, naphthalene, pyrene, and other molecules. It is shown that introduction of electron-donor and phenylethynyl substituents into molecules of heteroaromatic and aromatic compounds, respectively, increases considerably both σ(ν) and B(ν) and imparts lasing ability to nonlasing compounds. A criterion is established for the oscillator strength of an electronic transition which must be satisfied if a compound is to have the lasing ability.

A four-frame system for laser diagnostics of a plasma was developed and constructed. The active medium in this system was molecular nitrogen. The system was used to study explosions of thin tungsten wires in the Triton accelerator system.

A method for narrowing the emission spectrum of a wide-band laser by a diffraction grating operating in the region of the Wood anomalies is considered. A numerical calculation is reported of the kinetics of emission by a wide-band laser. It is shown that in 1 μ sec the width of the emission spectrum may be reduced to 3.4 pm.

A self-consistent generalization is made of the correlation function of a Doppler signal to the case when a gradient of a laminar flow velocity exists in the scattering volume. Analytic results are obtained for the spectral width of the signal in the case of a linear gradient and a relatively small change in the velocity in the investigated volume.

The nature of propagation of electromagnetic oscillations in a multimode waveguide is considered and it is shown in principle that such a waveguide can be used in a fiber-optic ring interferometer in combination with an optical radiation source characterized by a short coherence length. A description is given of the apparatus and the results of an experimental investigation of such an interferometer are reported. Ways of improving further the sensitivity of this interferometer are discussed.

A model of "dagger" melting of metals by high-power light beams is considered. An allowance is made for multiple reflections of the rays from the walls of a cavity formed in a sample and the maximum depth of penetration of a laser beam into a metal is calculated. It is shown that the greatest depth of penetration and the largest ratio of the depth to the diameter are obtained if the laser beam polarization corresponds to axially symmetric magnetic modes in a metal waveguide, i.e., when the electric field vector is parallel to the side walls of the cavity.

Cadmium sulfide crystals with a disturbed surface layer about 5 μ thick were annealed by KrF* laser pulses of 10 nsec duration. This improved the crystal structure when the cadmium side was irradiated. The effect was not detectable on the sulfur side. The threshold energy density of the effect was ∼0.25 J/cm².

An investigation was made of a pulse-periodic surface (gliding) discharge of the kind used in electric-discharge excimer lasers. In contrast to a bulk discharge, the surface discharge remained homogeneous at high pulse repetition frequencies without the need to replace the gas in the discharge zone.

A determination was made of the characteristics of a YAG:Nd³⁺ laser with wavefront reversal and with frequency doubling in a DKDP crystal. The energy carried by each of the second harmonic pulses was 20 mJ and the divergence was close to the diffraction limit when the pulse repetition frequency was up to 50 Hz.

A theoretical investigation is made of the influence of diffusion of excited particles on the parameters of the process of wavefront reversal by a degenerate four-wave interaction in amplitude gratings formed in an inverted carbon dioxide gas. It is shown that the thermal motion of molecules makes the reversal efficiency and the optimal degree of saturation of the gain depend strongly on the direction of propagation of the reversed wave.

An analysis is made of the possibility of estimating reliably the service life of injection lasers from the results of accelerated tests carried out at elevated temperatures. An expression is obtained for the test acceleration coefficient under the following assumptions: the distribution of the initial parameters of the investigated lasers is described by the normal law; the distribution of failures under test is described by the logarithmic-normal law; the influence of temperature may be described by a thermally activated dependence. The efficiency of screening tests for the rejection of potentially unreliable samples is discussed and the possibility of finding an informative parameter suitable for the forecasting of service life is considered. The results obtained can be applied to accelerated service life tests on transmitter molecules.

A theoretical investigation is made of the influence of various effects on four-photon parametric upconversion in metal vapors: saturation, one-photon absorption of output radiation, two-photon depletion of pump radiation, wave detuning, and dispersion of the group velocities of the interacting waves. Estimates indicate that the simultaneous influence of all these effects can ensure a fairly efficient up-conversion of noise pump radiation, compared with the monochromatic case. The results agree well with the experimental results obtained in a study of conversion of tunable CO₂ laser radiation in sodium vapor.

A method is proposed for attaining pulsed laser emission at the wavelength of 1.3 μ from iodine atoms as a result of electron-beam-controlled excitation of hydrogen–iodine mixtures. Quasiresonant vibrational–electronic exchange between H₂ and I results in a population inversion. It is shown that a deposited energy of the order of 0.3 J·cm⁻³·amagat⁻¹ corresponds to an ultimate laser efficiency of ∼50%.

A comparison of the output parameters of an H₂–F₂ laser initiated alternately by photolysis and electron beam methods was used to find the energy ε_F^e = 4.3±0.9 eV needed to form one fluorine atom by an electron beam.

A method is proposed for the determination of the refractive index profile of few-mode waveguides. Calculations are reported of the profiles of waveguides formed by ion exchange in certain optical glasses.

The average output power of the second harmonic can be increased and the construction of a laser can be simplified by using a nonlinear crystal not only for second harmonic generation, but also as an electrooptic switch for the separation of rays with different polarizations at the fundamental frequency. By way of example, the results are given of a continuously pumped YAG laser in which a switch for unpolarized radiation is in the form of a Pockels cell and a nonlinear lithium iodate crystal cut at an angle of 29° to the optic axis. It was found that such a laser configuration could ensure 77% conversion of the fundamental frequency radiation to the second harmonic at the wavelength of 0.53 μ and with an average power of 2.4 W.

Stimulated emission from LiF:F₂⁺ was observed when this crystal was pumped at the wavelengths λ₁ = 570.6 nm and λ₂ = 578.2 nm simultaneously or by the yellow line of the copper vapor laser or with radiation from an oxazine-17 dye laser excited by a Cu laser. The average output power of the color-center laser was 23 mW with a maximum at 911 nm. The highest efficiency achieved in these experiments was 3.4% when the color centers were pumped by the yellow line of a Cu laser. The output characteristics of the color-center laser were determined for all three types of pumping.

The Doppler broadening of the absorption lines of the I₂ molecules was suppressed by a combination of the saturated absorption and molecular beam methods. Saturated absorption resonances were observed at the components of the hyperfine structure of the P(13) and R(15) branches of the ^lΣ⁺_g(X)→³Π_OU⁺(B) electronic transition in the I₂ molecules subjected to 514.5 nm radiation from an argon laser. The optical fields were separated spatially by 3.5 cm along the molecular beam. The advantages of this method of inducing narrow resonances were considered from the point of view of their reproducibility.

A theoretical investigation is made of the behavior of a gaseous mixture in the field of cw laser radiation. It is shown that thermal diffusion at radiation intensities above a certain critical value destabilizes inhomogeneous distributions of the concentration of the absorbing component and of the gas temperature, giving rise to a steady-state inhomogeneous periodic structure. A diffusion instability may explain splitting of a laser radiation beam into several components observed in the course of propagation of cw infrared laser radiation in gaseous mixtures.

A theoretical analysis is made of the relative importance of the various mechanisms of formation of a periodic microrelief on the surface of an absorbing medium subjected to pulsed high-intensity monochromatic radiation. A linear approximation in respect of the amplitude of a surface perturbation is used to find the depth of spatial modulation of the absorbed intensity as a function of the optical parameters of the medium. It is shown that hydrodynamic effects in a molten layer on an irradiated surface may play an important role in the formation of a surface relief.