Table of contents

An experimental investigation was made of the feasibility of achieving mode self-locking in a neodymiumglass laser with combined. Q switching by optomechanical and phototropic modulators. A study was made of the characteristics of the output radiation and it was found that mode self-locking was achieved on introduction of an additional semitransparent mirror into the resonator. The attainment of self-locking under combined Q-switching conditions reduced the number of ultrashort pulses in the output and stabilized the beginning of stimulated emission.

A study was made of a stabilized laser source based on a two-mode helium-neon ring laser with a circularly anisotropic resonator. This laser emitted at 0.63 μ. The frequency was stabilized by comparing the frequencies of the Zeeman beats between the orthogonal modes of the opposite waves. The relative frequency stability achieved in this way was 8.8×10^–12 in an averaging time of 1 min.

A theoretical analysis is made of the propagation of a monochromatic beam of arbitrary form through an amplifying medium with a coordinate-dependent gain. The Fourier transformation is used to obtain a system of integrodifferential equations for the Fourier components of the field. The results of numerical calculations are given for one specific case.

A modulation method for the determination of the relative excitation of a single-mode gas laser was developed and tested experimentally. The method has the advantage that no independent measurements of the temperature of the active substance are required.

An experimental investigation was made of the resolution of a neodymium-activated glass fiber laser image amplifier and of the dependence of the signal/noise ratio at the amplifier output on the signal power at the input. The resolution in the active regime (in the presence of pumping) was not inferior to that in the passive regime (without pumping) and the signal/noise ratio (and, consequently, the contrast of the amplified image) improved, compared with the passive regime.

The main primary processes in the photolysis of C₃F₇I (λ =254 nm) were found to be photodissociation into C₃F₇ and two iodine atoms in the states ²P_1/2 (absolute quantum yield Φ_I* = 0.95^+0.05_–0.08) and ²P_3/2 (Φ_I≈0.05). The photodissociation of CF₃I, C₃F₇I, and CF₃CFICF₃ in the vacuum ultraviolet (λ=155–175 nm) gave the following results: Φ_I*=0.0±0.1 for the ²P_1/2 state in all three cases; Φ_I=0.6±0.1 (CF₃I) and 0.4±0.1 (C₃F₇I and CF₃CFICF₃) for the ²P_3/2 state. The photodissociation of perfluoropropyl iodides produced also CF₃I or CF₃ (Φ=0.15) and C₃F₆ (Φ=0.03). The results obtained were analyzed.

A theoretical analysis is made of the frequency dependence of the scattering of atoms and molecules by a standing electromagnetic wave.

A description is given of a laser amplifier with a disk active element made of GLS2 (40×40×220 mm dimensions). This amplifier is filled with thionyl chloride (n=1.53, absorption coefficient k<10^–3 cm^–1 at λ=1.06 μ). The single-pass inactive losses, per 1 cm length of the active medium, are 4.3×10^–3 cm^–1. The results are reported of measurements of the small-signal gain and of the gain obtained at pump energy densities up to 25 J/cm³.

A report is given of the parameters of a pulse-periodic CO₂ laser with an active volume of 0.8 liter and a non-self-sustaining discharge. A description is given of a gas-pumping system, a power supply of the main discharge gap, and an electron accelerator producing a ribbon-like (40×500 mm) electron beam of 4 A/cm² current density and 36 nsec pulse duration. The specific output power of this laser was up to 150 W/liter, the pulse repetition frequency up to 16 Hz, and the pulse energy up to 10 J.

An investigation was made of the 4.2°K stimulated emission spectrum of a naphthalene crystal with a high concentration of ββ'-dinaphthylethylene when this crystal was illuminated with off-resonance radiation. The crystal was excited by the third harmonic of a neodymium laser (λ=0.35 μ) and the offresonance radiation was the second harmonic of the same laser (λ=0.53 μ). Simultaneous illumination with the λ=0.35 μ and λ=0.53 μ radiation resulted in a strong reduction in the intensity of stimulated radiation emitted at a frequency in the phonon wing. This effect was attributed to the Raman scattering of the λ=0.53 μ radiation by nonequilibrium phonons.

A method was developed for recording a one-dimensional optical field pattern using a photoelectric detector with a large sensitive area. A transient reference wave was formed as a result of approximately linear and uniform motion of an aperture in the front focal plane of a lens. Model one-dimensional transparencies were recorded in this way. It was found that amplitude and phase information, carried by the optical field, could be stored in this way.

An analysis is made of the possibility of using multicomponent solutions of IV-VI compounds in laser heterostructures free of lattice mismatch and associated defects and stresses. Characteristics of a PbSe–PbSnTeSe at λ=10 μ, are estimated. The relative jump in the refractive index needed for optical confinement is estimated to be 8%.

A study was made of the time dependence of the diameter of a neodymium laser beam in its focal plane and of the intensity distribution when it was focused in laboratory air. Self-focusing of the laser beam as a whole was observed. The collapse of the beam occurred in 3–8 nsec and it resulted in breakdown of air. Estimates deduced from the experimental results indicated that the critical self-focusing power was ∼10⁴ W and the nonlinear coefficient was n₂∼4×10^–12 (in absolute units).

Stimulated emission as a result of self-terminating transitions in the copper atom was observed in discharges in copper chloride and iodide. Pairs of discharge pulses were applied to a quartz tube with a heated zone 400 mm long and 20 pairs of electrodes. Neon was used as the buffer gas. The dependence of the peak output power on the separation in each pair of pulses was determined. The specific energy output per pulse was 50 μ/cm³ for CuCl and 40 μJ/cm³ for CuI; these values were higher than those obtained by other authors in transverse discharges.

A description is given of a CO₂ laser detector of petroleum oil pollution at sea. The results of field tests are reported. It is demonstrated that it should be possible to construct a lidar unit with a scanning beam for detection of oil pollution. Lasers of other types can also be used for this purpose.

A description is given of an infrared laser defectograph (flaw detector) based on the use of improved temperature sensitive luminescent screens which make visible the CO₂ infrared laser radiation transmitted by an investigated object. This defectograph can be used to study the internal structure and microdefects in semiconducting materials which are opaque to visible light.

A derivation is given of an approximate expression for the density distribution of the radiation power passing through a specified aperture which is illuminated by a laser beam subject to random displacements. The expression provides a good approximation to the exact distribution plotted graphically by means of a table of Q functions if the dimensions of the receiving aperture are such that up to ∼50% of the incident beam power passes through it.

The construction of a resonator for the λ≈300–700 Å range is discussed. A description is given of two normal-incidence resonators in which radiation is coupled out either through a slit in a mirror or by a diffraction grating (in a nonzero diffraction order). It is shown that the use of laser plasma as the active medium imposes stringent requirements on the optical strength of the resonator mirrors.

An experimental investigation was made of the amplification of λ = 1.06 μ radiation in a 2500-mm long Nd³⁺-activated quartz fiber. Stimulated emission was observed when the pump energy was 180–200 J and it was accompanied by a weak spontaneous noise. When the threshold was exceeded by a factor of 2, the gain rose to 7×10⁴.

A theoretical analysis is made of the efficiency of a system for the compensation of phase fluctuations of an optical wave traveling in a turbulent atmosphere. In this system the distortions are compensated on the basis of measurements of phase fluctuations in the reflected wave. A correlation function for the uncompensated error and the compensation parameter a are introduced. Calculations carried out in the approximation of smooth perturbations indicate that the compensation on the basis of reflected waves is effective only up to distances at which the Fresnel zone does not exceed the external scale of turbulence.

Certain experimentally recorded features of the stimulated scattering of light are interpreted in terms of the phenomenon of wavefront reproduction. Stimulated scattering is often accompanied by laser action in which the transverse structure (mode) of the scattered light is governed by coincidence with the pump maxima and the longitudinal structure by the length of the effective resonator. This mechanism explains the periodic temperature dependence of stimulated Raman scattering.

An analysis is made of the influence of the parameters of the pump radiation (power density, divergence, statistical properties of the pump regarded as a random field) and of the scattering medium (specific gain, interaction length) on the complex conjugacy between the Stokes and pump wavefronts in stimulated Brillouin backscattering.

It is shown theoretically that selective properties of a stimulated Brillouin scattering mirror improve considerably if use is made of wide-band pumping whose coherence length exceeds the interaction length in the active medium.

An investigation was made of a controlled phototropic switch which was initially bleached by flashlamps. Characteristics were determined of switches employing phthalocyanines Pc'GaCl (in ethanol) and Pc'H₂ (in polymethylmethacrylate). The ranges of switch control were studied and the parameters of a ruby laser with a switch of this kind were determined. An investigation was made of the influence of a flashlamp pulse on the time of appearance of a giant stimulated emission pulse.

A study was made of the optical losses in several batches of glass-fiber waveguides. These waveguides had a core of pure quartz glass and borosilicate cladding; the refractive index profile had a step of Δn≈0.01. The spectra of the total losses α(λ), radiation losses ρ(λ), and absorption losses κ(λ) were investigated in the wavelength range 0.45–1.1 μ. The effects of technological factors were investigated by determining the absorption losses in the blanks and the distribution of radiation losses along the finished waveguides. It was found that most of the waveguides were characterized by the following losses in the maximum transparency (λ=0.7–0.85 μ) range: α≈7–10 dB/km, ρ≈6–8.5 dB/km, κ≈1.0–1.5 dB/km. These results were evidence of a high degree of purity and homogeneity of the core material and they demonstrated that the process of drawing of the fibers did not give rise to any significant absorption losses and that the total losses in the λ=0.7–0.85 μ range were dominated by the escape of radiation because of geometric imperfections.

A theoretical analysis is made of a laser beam with monochromatically modulated intensity gliding along the surface of an opaque liquid. The region in which the laser radiation is absorbed can be regarded as an extended moving source of sound. An analytic expression for the pressure in the far wave zone is derived and analyzed (the far zone is defined in a coordinate system of a source moving at a supersonic velocity). The directions of propagation of strongest acoustic perturbations are determined (in a coordinate system at rest) for various relationships between the characteristic dimensions of a source, the Mach number, and the wave vector.

Nonlinear optical phenomena in anthracene single crystals were investigated by focusing exciting radiation into a stripe of dimensions and direction corresponding to the dimensions and direction of the optically most homogeneous channels in a crystal. The intensity of stimulated emission in the 23 692 cm^–1 band in such a channel exceeded 2×10⁸ W/cm². Two Stokes components of stimulated Raman scattering wereobserved under these conditions: they were due to the scattering of the stimulated radiation excited in a crystal by an intramolecular vibration of 1403 cm^–1 frequency.

A spectral-correlation experimental study was made of the fluctuations of the intensity of emission from a helium-neon laser. This study included measurements of the spectral power density of fluctuations of the emission intensity and discharge current, as well as measurements of the transfer coefficient and coefficient of mutual correlation between the current and emitted light. The measurements were carried out in the frequency range of discharge current fluctuations. The spectral power density of fluctuations of the radiation intensity was calculated. A qualitative analysis was made of the results obtained.

An investigation was made of the establishment of a spectral distribution of neodymium laser radiation in intracavity laser spectroscopy. The kinetics of the spectral distribution was studied at the moments of switching on and off frequency-dependent losses in the resonator. The transient losses inside the resonator were due to the absorption from excited electronic levels of the nitrogen molecule in an electric discharge. Lines representing excited nitrogen and acetylene dissociation products were amplified. A "memory" of the spectral distribution of the laser radiation was predicted theoretically and confirmed experimentally. The results demonstrated that intracavity laser spectroscopy was a suitable method for investigating transient absorption processes if allowance was made for the special features of the establishment of a spectral distribution. The lifetime of excited nitrogen atoms was estimated.

An experimental investigation was made of the dissociation of ethylene resulting from interaction of highintensity infrared CO₂ laser pulses with the ν₇ vibration; the resonance and threshold properties of the process were determined. This dissociation produced acetylene and ethane. A study was made of the manyphoton absorption of CO₂ laser radiation by ethylene and of the influence of the laser radiation intensity on the many-photon absorption spectrum. A fine structure was observed in this spectrum and it was attributed to a multiple vibrational-rotational resonance of symmetric-top molecules. The influence of the laser radiation frequency on the resonance characteristics of the luminescence resulting from such dissociation was investigated. The influence of the presence of buffer gases (H₂, D₂, He, Ar, Xe) on the intensity of the luminescence was also studied. It was found that the infrared excitation spectra of the luminescence and dissociation and the many-photon absorption spectrum of ethylene, which were of basically similar form, exhibited a short-wavelength shift by 4 cm^–1 relative to the linear absorption maximum due to the 0→1 transition in the ν₇ vibration.

An experimental comparison was made of a plane-parallel resonator containing a telescopic angular selector with an unstable telescopic resonator. The resonator with a telescopic angular selector made it possible to achieve for the first time a considerable reduction in the angular divergence of the radiation emitted from a moving stimulated emission zone.

A study was made of the interaction of laser radiation with Chlorella microalgae cells. The cell damage was found to be a function of the laser wavelength and power, and of the temperature of the cell suspension during irradiation. Possible damage mechanisms were considered, including local heating due to absorption of ruby laser radiation by intracell pigments when energy migration processes were saturated, heating-induced breaking of molecular bonds, and subsequent denaturation of biological membranes. These hypotheses were confirmed by spectrometric and pyrometric measurements.

It is shown that the feasibility of obtaining high-power short-wavelength radiation by reflection of electromagnetic waves from a bunch of relativistic electrons is limited by the high transparency of these bunches and the finite dimensions of the leading edge of the electron buildup in such bunches. A comparison is made of coherent (across an electron beam) and noncoherent scattering processes and it is shown that the latter predominate. Simple expressions are obtained for estimating the experimental feasibility of such frequency conversion.

An analytic investigation is made of the conditions for self-locking of laser modes. It is based on a system of reduced equations in terms of partial derivatives of the field amplitudes and polarizations and in terms of the difference between the populations of the active levels. The shape of the field pulses under modelocked conditions is calculated. The results of these calculations are applicable to ring gas lasers and to solid-state lasers with homogeneously broadened lines.

A study is made of the spectral, threshold, and energy characteristics of an electron-beam-controlled CO laser emitting long (10^–4–10^–3 sec) pulses. The study is based on a numerical solution of a system of rate equations which describe the populations of the vibrational levels of the CO molecule, stimulated emission as a result of transitions between these levels, and changes in the rotational-translational temperature of the gas.

The results are given of an experimental investigation of laser garnets with waveguide resonators. The use of such resonators made it possible to eliminate the influence of thermooptic distortions and to obtain highly coherent radiation.

Allowance is made for the two-dimensional nature of the flow in gasdynamic lasers. It is shown that inhomogeneities of the gas flow parameters deduced from the one-dimensional model may lead to a considerable (20–30%) inhomogeneity of the gain across the nozzle. The transverse distribution of the gain depends also on the kinetics of the vibrational processes in the gas and it is quite different for N₂O and CO₂ lasers.

An application is considered of the authors' algorithm for the solution of the Abel equation, stable on the right-hand side, in an analysis of the experimental data obtained as a result of contactless diagnostics of spherically symmetric plasma objects. Examples are given of calculations of laser plasma parameters whose distribution functions have different degrees of smoothness. A comparison is made of the proposed method with the techniques used currently in the solution of the Abel equation.

Fourteen lines were identified in the submillimeter emission spectrum of an HCOOH molecular laser pumped by CO₂ laser radiation. This was done by investigating experimentally the rotational spectrum of the ν₆ and ν₈ excited states in the 300–400 GHz range. The identified pump transitions and the known CO₂ laser frequencies made it possible to determine the central frequencies of the ν₆ (33 122 609 MHz) and ν₆ (31 982 778 MHz) bands to within ±50 MHz. It was found that the ν₆ and ν₈ vibrational states interacted. Identification was also performed by a double resonance method which did not require a study of the rotational spectra of excited vibrational states.

Measurements were made of the density of photoelectrons in He, N₂, and CO₂–N₂–He mixtures created by a planar ultraviolet radiation source ensuring a bulk discharge in a real CO₂ pulse laser. The experiments and calculations demonstrated that the photoelectron density in laser mixtures and its behavior as a function of the distance from the ultraviolet radiation source were governed by the ionization of impurities with low ionization potentials present in the gas and by the absorption of the radiation in the CO₂ molecules. Introduction of optimal numbers of such impurities (xylene and dimethyl aniline) made it possible to increase the photoplasma density by more than one order of magnitude; under these conditions the photoplasma decayed by recombination at a rate represented by the recombination coefficient 10^–5 cm³sec^–1.

A description is given of high-speed multiframe interferometry for investigating the spatial distribution of the electron density in plasmas. Special attention is paid to a method for synchronizing a laser source of probe radiation pulses of ≤1 nsec duration with the beginning of the process being investigated. It is shown that the proposed method can be used for effective monitoring of the degree of symmetry of a laser plasma during the initial stage of expansion after spherical irradiation of a target.

The quantum yields of the primary products of the photodissociation of CH₃I, C₂H₅I, C₄H₉I, CH₃CHIC₂H₅, and (CH₃)₂CHCH₂I were determined in the spectral range 254 nm. It was found that the main primary photolysis process was the splitting off of atomic iodine in the ²P_l/2 excited state and the quantum yield was 0.9, 0.79, 0.67, 0.80, and 0.75, respectively. The quantum yields of the formation of atomic iodine in the ²P_3/2 state were 0.1, 0.20, 0.32, 0.09, and 0.24, respectively. Regrouping photodissociation processes producing stable HI and C_nH_2n molecules (Φ=0.01–0.1) were observed. The quantum yields of other primary photodissociation products were of the order of 2×10^–2–10^–4.

The ranges of existence and stability of two-mode stimulated emission from a ring gas laser with a twoisotope active medium are investigated theoretically as a function of various laser parameters. The analysis is made using a complete system of amplitude and phase equations and the normal oscillation method. It is shown that a stable steady-state value of the difference between the phase shifts of the two modes in the opposite waves may lie in the interval (0, 2π) but need not be close to 0 or π. The actual value of this difference between the phase shifts is governed by the ratios of the backscattering coefficients and relative Q factors to the coefficients of the combination interaction of different modes of the opposite waves.

Measurements were made of the pressure on the surface of a target subjected to high-power CO₂ laser radiation under conditions ensuring one-dimensional motion of the resultant plasma. These measurements were carried out on lead, aluminum, and titanium targets using laser radiation of 10⁷–10⁹ W/cm² power density. The pressure in the air surrounding the target was varied from 0.07 to 760 Torr. It was found that the pressure on the target surface in vacuum was due to the evaporation of the target material but in air this pressure was governed by the gasdynamics of a laser-absorption wave traveling from the target to meet the incident radiation. The transition from one interaction regime to the other occurred when the air pressure was ∼80 Torr.

An analysis is made of the influence of different polarizations of the exciting and scattered radiations on the stimulated scattering efficiency. This difference may be due to a change in the polarization during the propagation of light under photoelastic birefringence and Faraday effect conditions. The intensity and degree of polarization of backscattered radiation are calculated allowing for spontaneous "seed" sources and an arbitrary relationship between gain and anisotropy. The results of an experimental investigation of stimulated Brillouin scattering of ruby laser radiation in polymethylmethacrylate confirm the theoretical prediction of an increase in the stimulated scattering threshold by a factor of about 2 on application of a mechanical stress to a sample.

Optical data storage in cadmium sulfide was investigated. The stored data could be read photoelectrically and optically. Experiments involving recording and reading "photoelectric images" were made on Cd- and Cu-doped CdS films. Moreover, volume holograms were recorded and reconstructed using single crystals of the same material. Some parameters of the photoelectric and optical memories were determined.

A study was made of the principal characteristics of holograms recorded in semiconductor-metal film systems. The holograms were found to be similar to thin phase gratings. The optimal thickness of each of the films was determined and factors limiting the diffracting efficiency of the holograms were identified.

Laser excitation methods were used in a study of the kinetics of conversion of infrared into visible radiation in Yb³⁺- and Er³⁺-activated La₂O₂S, The experimental time dependences of the intensity of the visible luminescence of the Er³⁺ ions were in good agreement with the calculated curves. The mechanisms of infrared excitation of the visible Er³⁺ luminescence were identified and a device was developed for visualization of the radiation of pulse and cw neodymium glass and garnet lasers emitting at ∼1.06μ.

The rate constants k_H2, k_CH4, k_HCl and k_Cl2 of the F+H₂→iHF+H, F+CH₄→HF+CH₃, F+HCl→tHF+Cl, and F+Cl₂→tFCl+Cl reactions were determined by two methods: 1) determination of the delay times of the stimulated emission signal relative to the beginning of the reaction-initiating pulse; 2) determination of the decay time of the stimulated radiation. The constants k_H2 and k_CH4 obtained in the present study were in good agreement with the published values. The constants k_CH4, k_HCl, and k_Cl2 determined by the two methods were in satisfactory agreement.