Table of contents

A study was made of a method for remote detection of low concentrations of hydrocarbons by four-photon spectroscopy of the Kerr effect due to the Raman scattering. The minimum detectable concentration of benzene in water was found to be 30 ppm. Ways of improving on this value are considered. It is suggested that the method can be used for fast remote identification of oil pollution of the high seas.

Stimulated radiation as a result of the ²P_1/2→²P_3/2 transition in the chlorine atom (formed by photodissociation of the ICl molecule) was generated for the first time. A study was made of the dependence of the laser radiation (λ = 11.35μ) energy on the pump energy and on the ICl pressure. Measurements were made of the gain g ≈ (2.5±0.5)×10⁻³cm⁻¹ and of the laser radiation energy E ≈ 1 mJ. The results demonstrated the important role played by the processes of chemical "clearing" (depopulation) of the lower active level and of the recombination of atoms in the course of population inversion and recovery of the active medium by the time of arrival of the next pulse. Estimates were obtained of the rate constant of the spin-orbit relaxation of the Cl*(²P_1/2) atoms because of interaction with CF₂Cl₂,H₂,D₂,Cl₂,O₂, and rare gases.

Laser deposition of Au from triphenyl complexes RAuL of univalent gold on some semiconductor and insulator substrates was realized experimentally. A metal deposit of ~1μ transverse size was observed in a laser projection microscope.

An experimental study was made of the maximum field intensity and input energy that can be achieved in continuous electron-beam-controlled discharges in nitrogen and in active mixtures of CO₂ and CO lasers. It was found that the maximum field intensity was governed by the specific input energy and by the degree of inhomogeneity of the pumping. In the case of CO laser mixtures the reduced input energy was 3–4 times higher than in electron-beam-controlled CO₂ lasers because of the low proportion of the energy consumed in heating a gas (δ ≈ 0.25).

The method of nonlinear four-wave interaction spectroscopy was used to record the spectra of acoustic resonances of seven liquids active in stimulated Brillouin scattering (STBS) at frequencies corresponding to the backscattering of laser radiation in neodymium glass. These measurements made it possible to determine in the same experiment the STBS gain and the decay time and velocity of propagation of hypersound in the liquids.

An investigation was made of GaAs and CdS semiconductor lasers excited by several closely spaced and simultaneously acting fast-electron beams. A change in the direction of emission of light resulted in a considerable shortening of the light pulses compared with the pump pulses. This was attributed to the existence of two different lasing thresholds for mutually perpendicular electromagnetic oscillation modes.

Theoretical and experimental investigations were made of the frequency-selective and nonselective properties of a waveguide laser resonator with a circular channel and a diffraction grating. A study was made of the fundamental waveguide mode EH₁₁ corresponding to a resonator with "mode filtering," for example, when one of the reflectors is a spherical mirror matched to the waveguide. It was found that losses in a waveguide laser with a diffraction grating can be described quite accurately as the losses in an equivalent resonator with a tilted plane mirror. The grating formula was found to relate the angle of tilt of the mirror to the frequency detuning. General scaling relationships were obtained for the tilt angles and the distances between the end of the waveguide and the diffraction grating mirror. An analytic method was proposed and developed for the calculation of the losses in a waveguide laser with a diffraction grating, and with a plane or a spherical reflector in the Gaussian mode approximation. Investigations were made of lasers with a diffraction grating, with a grating and an intracavity lens, and with a grating and collimator. These cases covered practically all the important types of gas lasers emitting the fundamental waveguide mode.

An experimental investigation was made of resonant nonlinear four-wave frequency mixing processes involving cw laser radiation in sodium vapor. It was found that, in spite of an increase in absorption, the use of resonant atomic nonlinearities can substantially improve the frequency conversion efficiency in the cw regime. The results of the measurements were compared with the theoretical conclusions. Ultraviolet radiation was generated at the sum frequency (λ_s = 268 nm) with the proportionality factor C=W_s/W₁W₂W₃≈2W⁻²

It is shown that abrupt and complete transfer of the power of strong (pump) radiation from the exit of one waveguide to the exit of another is possible as a result of a small change in the power of a weak (control) signal of different frequency applied to the entry of one of the waveguides.

Generalized parameters are proposed for the description of the dispersion characteristics of channel waveguides. It is shown that the use of these parameters facilitates greatly the solution of the dispersion equation and makes it possible to describe the results by a single family of curves applicable to all the modes. The usefulness of this representation is demonstrated by a calculation of the effective refractive indices, of the sequence in which modes appear, and of the range of existence of waveguides with a given number of modes. The results of these calculations are tested experimentally for LiNbO₃:Ti waveguides.

A study was made of double heterostructures fabricated by liquid phase epitaxy and emitting at wavelengths in the range 1.06–1.6μ. The maximum values of the external efficiency reached 10% at the wavelength of 1.06μ and 5% at 1.3μ. A study was made of the homogeneity of the emission pattern by visualization of the distribution in the near-field zone with the aid of an infrared television microscope. This revealed dark spots formed as a result of ageing of the heterostructure. It was found that when a certain dose was reached, the radiation defects stabilized the output power of heterostructures over a considerable operating period. Accelerated life tests estimated that the service life should be at least (60–100)×10³h.

A theory is developed of stimulated scattering of nonmonochromatic radiation whose spectral width is much greater than the spontaneous scattering line width or the frequency shift of the Stokes wave. It is shown that scattering of nonmonochromatic incident radiation under coherent conditions may take place as efficiently as for monochromatic pump radiation. The results apply to various types of stimulated scattering, in particular, to stimulated thermal scattering and stimulated scattering in media which are in thermodynamic nonequilibrium.

An investigation was made of the spatial and temporal coherence of a pulsed dye laser with a resonator containing a grazing-incidence diffraction grating. A two-frequency lasing regime was realized with a continuously variable spectral interval between the laser emission lines. It is shown that such a laser is promising for holographic interferometry and holographic formation of relief contours.

A study was made of an anomalously wide continuous tuning range of the emission frequency of an injection laser with an external resonator operating under conditions of self-stabilized single-frequency lasing. The self-stabilization was observed for a large number of lasers with different structures, both at room and liquid nitrogen temperatures. A study was made of the influence of the power, degree of coupling with the external part of the laser, resonator length, and pass band of a selective component on the continuous tuning range. In the self-stabilization regime this range was 10-30 times greater than the corresponding range for a laser operating under conventional conditions. A nontrivial feature of hopping between longitudinal laser modes at the limit of the tuning range was observed. This feature was explained on the basis of a theory proposed by Bogatov, Eliseev, Okhotnikov, Rakhval'skii, and Khairetdinov [Sov. J. Quantum Electron. 13, 1221 (1983)].

An analysis is made of the interaction of radiation with a two-level medium at a high particle density. An explicit allowance is made in the interaction Hamiltonian for the interaction between dipoles induced by a resonance field. A semiclassical description is used to obtain a system of equations describing the propagation of a pulse in the active medium. The equations contain nonlinear terms allowing for the interaction in question. An approximate solution of the equations is obtained for the case of amplification of a weak noncoherent pulse describing pulse compression in the amplifying medium. The theory is compared with experimental results.

A study was made of the parameters of the output radiation of lasers in which aqueous micellar solutions of dyes were excited by flashlamp pumping. The efficiency and photostability of such solutions were considerably poorer than alcohol solutions. It was found that the addition of cyclooctatetraene (COT) to aqueous micellar solutions of dyes was accompanied by a strong increase in the output radiation energy. Aqueous micellar solutions of rhodamines containing COT were characterized by a high photostability when excited with light of λ > 450 nm and the output energy was much higher than that obtained from alcohol solutions. It was found that the relative efficiency of lasing of aqueous micellar solutions of dyes with COT (compared with alcohol solutions) increased on increase in the resonator length and on increase in the pulse duration. The divergence of the radiation emitted from a laser utilizing aqueous micellar solutions was an order of magnitude less than in the case of alcohol solutions. The positive effect of the COT additive was demonstrated for a number of phosphors of different classes emitting in the spectral range 500–650 nm.

An experimental investigation was made of four-wave frequency mixing of YAG laser radiation in paraterphenyl vapor under two-photon resonance conditions. An experimental estimate was made of the nonlinear susceptibility ⁽³⁾≈10⁻³¹ cgs esu. This value is comparable with the quasiresonant susceptibilities of alkali metal atoms and is considerably greater than the resonant susceptibilities ⁽³⁾ of the simplest molecules of the NO and CO types. The present paper is the first on nonlinear mixing of radiation frequencies in dye vapors.

The methods of coherent states and integrals of motion are used to describe propagation of arbitrary Gaussian beams in focusing and defocusing nonlinear (quadratic) media exhibiting absorption or amplification. Analytic expressions for the beam parameters are obtained by purely algebraic procedures, i.e., without calculation of the relevant integrals. An operator theory of perturbations is used to find corrections to the beam path and width as a result of its nonparaxial propagation. The problem of propagation of arbitrary Gaussian beams in a quadratic medium is investigated in the case when the absorption (amplification) axis is shifted relative to the axis of a waveguide.

A method suggested for the formation of non-Gaussian laser beams is based on the use of a multilayer dielectric exit mirror with its transmission dependent smoothly on the coordinates. A technique for the fabrication of such mirrors by "half-shadow" evaporation in vacuum is described. Fabrication of mirrors with a transmission minimum on the laser resonator axis is reported. Various intensity distributions (including one which is nearly uniform) are obtained. It is shown that for mirrors of this kind the TEM₀₁ mode is loaded more strongly than the TEM₀₀ mode, which ensures a higher mode stability than in the case of a laser with homogeneous mirrors.

A study was made of intermolecular phototransfer of a proton in solutions of 3-methoxybenzanthrone in benzene and in tetrahydrofuran (THF) with toluenesulfonic acid or 3-fluoroacetic acid. The elementary constants were determined in the case of THF solutions. An analysis was made of the possibility of using proton phototransfer in construction of efficient fluorescence light concentrators and dye lasers.

A study was made of the characteristic features and of a range of conditions under which the active medium in a gas-discharge laser operating at near-atmospheric pressure can be preionized by means of radioisotopes. The feasibility of this method was demonstrated in the case of a TEA CO₂ laser with preionization by a rays from plutonium sources with a protective coating. Specific input energies up to 400 J·liter⁻¹·atm⁻¹ and output energies up to 20–25 J·liter⁻¹·atm⁻¹ were obtained. A spark-free operation of a self-sustained volume discharge was realized reliably in a wide range of pressures and compositions of the gas mixture in the laser.

A numerical (computer) solution of a system of equations is used to study a new method for selective interaction of short pulses of laser radiation with pigmented biological tissues. The method is based on preferential absorption of the laser radiation energy by the pigment particles, compared with the much weaker absorption in the surrounding biotissues. An analysis is made of thermal and thermochemical processes in layer biotissues subject to an allowance for the granular structure of the pigmented layer and it is shown that denaturation of microregions may occur around individual pigment particles

An analysis is made of resonant absorption of an electromagnetic field due to a transition between excited, initially practically vacant energy states of molecules. Such absorption is manifested by an explosion and it occurs when the intensity of the field being absorbed exceeds a certain threshold value. The dependences of the threshold characteristics of such explosive absorption on the laser beam diameter and laser pulse duration are obtained. It is shown that at the moment of absorption the vibrational temperature of the system becomes different from the translational temperature. An analysis is made of the dynamics of explosive absorption in a vessel containing a gas, and also of the characteristics of such absorption in nonequilibrium systems.

It was found experimentally and theoretically that an increase in the pulse repetition frequency increased the crater depth in laser drilling and reduced the specific energy consumption. A comparison of the maximum depths of welds and craters obtained by drilling and of their dependences on the laser radiation parameters demonstrated that the mechanisms of the maximum penetration of a pulse-periodic CO₂ laser beam into a metal were identical for drilling and welding. The screening influence of a plasma jet decreased as the crater depth increased and this led to a nonmonotonic variation in the rate of growth of a crater on increase in the number of pulses. It was found experimentally that the use of pulse-periodic CO₂ lasers for cutting metals makes it possible to obtain high-quality cuts at low workpiece velocities of 1–3 mm/sec.

A theoretical and experimental investigation was made of the modes of a two-frequency helium-neon laser tuned by a strong axial magnetic field, for which the Zeeman broadening of the gain profile of the active medium exceeds the Doppler broadening.

An analysis is made of the influence of constraints relating to the profile of a flexible mirror on the quality of compensation of nonlinear distortions of light beams which are scanned and have a specific transverse distribution. The effects of propagation across thick and thin nonlinear layers are considered. Studies are made of the problems of control of the focusing and tilt of the wavefront of the scanning beam and of the influence of restrictions on the aberration modes when adaptive systems are tuned using the peak intensity or the beam width. It is shown numerically and analytically that it is desirable to use beams with a specific transverse distribution when restrictions are imposed on the wavefront profile.

An investigation was made of the conversion of XeCl laser radiation (λ∼3O8 nm) by stimulated Raman scattering (STRS) in compressed gases. Eleven Raman scattering lines in the ultraviolet and visible parts of the spectrum were obtained in hydrogen, methane, and a mixture of these. It was found that by altering the experimental conditions (gas pressure, pump power, focusing) the energy distribution of the converted radiation over the STRS lines could be controlled. Calculations are made of STRS cross sections of various gases.

The Kirchoff integral is used to calculate the intensity of an echo signal reaching a detector after double passage of probe radiation across a stochastically perturbed water surface with a narrow spectral energy distribution.

The complex reduced width of an active semiconductor waveguide is introduced as a parameter of waveguides with symmetric and asymmetric refractive index profiles in the p-n junction plane (Epstein layer model). The parameters of the angular distribution diagrams of the radiation emitted by such waveguides are plotted as a function of the real and imaginary parts of the complex reduced width. The coupling coefficients of the modes are obtained in a model describing a heterolaser, inhomogeneous along its length formed by two (or more) active waveguides in contact. A comparison is made with the output characteristics of planar stripe heterolasers without lateral optical confinement.

A description is given of the first mercury halide photodissociation laser pumped by wide-band thermal radiation from a plasma and emitting three-color visible radiation. Simultaneous lasing was observed for ionic-covalent electronic B–X transition in molecules of mercury monochloride λ_l≈558 and 559 nm, monobromide (λ_l≈502 and 504 nm), and monoiodide (λ_l≈443 and 444 nm). The laser radiation energy was ~0.3J emitted in the form of ~2.5μsec pulses and the lasing efficiency was ∼0.07%.

A distributed-feedback dye laser pumped by an excimer laser and by another dye laser was used to develop a frequency-tunable laser source with the following parameters of the output pulses: duration 70 psec, spectral width 0.02 nm, power up to 140 kW, and energy instability 20%. The apparatus was used to determine the kinetics of fluorescence emitted by chlorophyll-α under conditions of electron transfer from the chlorophyll molecule to a solvent.

A study was made of lasing in the active medium of 2-μ lasers utilizing Cd_2.813Tm₀₁₇Ho_0.017Sc_yCr_0.05Ga_4.95–yO₁₂ crystals. The absolute efficiency in the case of free lasing at the wavelength of 2.088μ at room temperature was 0.85%.

Complex color centers were generated in a KCl:Tl crystal by irradiation with 1.6–1.8 MeV electrons at liquid nitrogen temperature. Lasing was achieved with the aid of these centers.

A study was made of coherent propagation of small-area pulses across a resonant absorber. At least five-fold reduction in the duration of subnanosecond pulses with a steep leading edge (τ_e ≲ 20 psec) was observed as a result of passage through a ruby rod cooled to 100 K. This reduction in the duration was due to the finite time needed to establish absorption. The experimental results were in agreement with a numerical solution of a system of Maxwell-Bloch equations describing the interaction of a field of a pulse with a resonant medium.

A review is given of the papers presented at the Third All-Union Symposium on Optical Echo and Coherent Spectroscopy. The physics of optical transient and superradiant phenomena and the results of applications of these phenomena in spectroscopy were discussed at the Symposium. A new branch of optical spectroscopy is now in existence and it is called coherent spectroscopy. Methods used in this spectroscopy and possible technical applications of these phenomena were discussed in detail at the Symposium.