Table of contents

Continuous tuning of the emission wavelength of a neodymium-glass pulse laser was achieved by using a dispersive prism in combination with an electrooptic deflector inside the resonator. Variation of the control electric field within the range ±50 kV/cm provided a frequency tuning range of 12 nm. Possible methods for increasing the rate of tuning and the spectral brightness of the laser were considered.

Achromatization experiments were performed on real images of transparencies reconstructed from a hologram memory array using quasimonochromatic radiation sources.

An investigation was made of the spectral characteristics of an LiNbO₃ crystal which converted infrared radiation to the visible range by summing the infrared and ruby (pump) Irser frequf icies. The dependences of the spectral width of the conversion band on the pump line width and on the angle of divergence of the infrared radiation in the crystal were determined experimentally. The results were compared with theoretical estimates.

The results are given of polarization-optical investigations of the stressed state of condensed matter subjected to laser radiation. Shock waves, resulting from the fracture and decaying smoothly into longitudinal acoustic vibrations, are reported. It is shown that the dynamics of the process of optical damage is related to the development of the wave pattern of the stressed state in the irradiated matter.

An analysis is made of the physical processes in laser targets subjected to different heating and compression regimes. The results are given of numerical calculations for CD₂ targets of different types carried out using a program allowing for the main physical processes. It is shown that calculations predict simultaneous heating and compression of a part of a specially selected hollow spherical target. An analysis of diagnostic possibilities shows that this situation can be identified using currently available diagnostic apparatus and laser systems.

A description is given of a laser system emitting up to 40 mW at λ = 84 μ. The results are reported of an investigation of the power characteristics and of beat signals between a D₂O laser, on the one hand, and HCN and H₂O lasers, on the other.

An investigation was made of the distribution of the gas density in a discharge gap of a continuous-flow CO₂ laser with a heated cathode. The influence of the cathode heating on the laser threshold was determined. It was established that the use of a heated cathode made it possible to increase the molecular gas content in the working mixture by improving the homogeneity of the discharge.

An investigation was made of a YAG:Nd³⁺ laser with means for longitudinal and transverse mode selection and with frequency stabilization by an external standard. The longitudinal modes were selected by a T-shaped resonator and an inclined Fabry-Perot interferometer. The external standard was the resonator of an He–Ne laser stabilized at λ = 1.15 μ using the Lamb dip. The frequency stability achieved in this way was 10⁸ for an output power of 300 mW.

An experimental investigation was made of the two-photon absorption in GaAs using laser radiation of 2ω= 1.50, 1.75, 1.89, and 2.34 eV energies at room temperature (the for jidden band width of the semiconductor was Δ = 1.43 eV). An anomalous rise in the absorption was observed at the band edge and this was interpreted theoretically as the influence of a deep impurity level in the middle of the forbidden band.

An experimental and theoretical study was made of the maximum efficiency of second harmonic generation in the presence of diffraction effects and stimulated Brillouin scattering.

Stimulated emission at a high pulse repetition frequency was obtained as a result of self-terminating transitions in the copper atom in CuCl and CuBr vapors. The repetition frequency was equal to the excitation pulse frequency (16.5 kHz). The efficiency of the CuBr laser was ~1%. The average output power in the form of the λ = 510.5 and 578.2 nm lines was 12 W. The stimulated emission was observed in 12, 18, and 30 mm diameter quartz discharge tubes.

An investigation was made of the optimal conditions for the operation of a copper vapor laser emitting at 510.6 and 578.2 nm. Stimulated emission was obtained as a result of a discharge in an Ne–CuI mixture. A simple power supply system ensured a stimulated emission pulse repetition frequency of 30 kHz.

An investigation was made of the fine structure of the intensity and spectrum of giant pulses emitted by a YAG:Nd laser. These ultrashort pulses were recorded using an image-converter streak camera with a resolution of at least 25 psec. In general, a "domain" spatial-temporal structure was observed in the radiation and it corresponded to a partial locking of the longitudinal and transverse modes. Special cases of the transverse or longitudinal mode selection were investigated. A fine structure of this kind should be allowed for in estimating the optical strength of the resonator elements and in nonlinear conversion processes.

An experimental study was made of the action of cw CO₂ laser radiation in acute experiments on the mucous lining of the stomach of rabbits. It was found that laser radiation with certain parameters caused necrosis of the mucosa without disturbing the other layers of the stomach wall.

A possible photochemical self-interaction between light beams is demonstrated theoretically. It is shown that, in contrast to other self-interaction mechanisms, the important parameter is the critical absorbed energy and not the beam power.

Measurements were made of the ultraviolet and vacuum ultraviolet radiation emitted as a result of 3-μsec pulse discharges in IFP-800 lamps. The discharge energy was 48 and 188 J and the lamps were filled with xenon, krypton, and their mixtures with other inert gases. About 36% of the discharge energy was emitted in the wavelength range 165–250 nm and 26% in the range 250–1100 nm. An investigation was made of the influence of the xenon pressure, discharge energy, and composition of the gas mixture on the emission of ultraviolet radiation.

A Johann-type focusing x-ray spectrograph with a concave mica crystal was constructed. When a laser plasma was used as an x-ray source, this spectrograph was found to be characterized by a high luminosity, good spectral resolution, and minimum influence on the source size on the resolution. When the radiation flux density generated by a neodymium laser was (5–7)×10¹² W/cm² on the target surface, a single laser flash was sufficient to record the hydrogen- and helium-like spectra of the Na, Mg, and Al ions. The high luminosity of the instrument made it possible to record the Mg XI and XII spectra with a spatial resolution of 120 μ, and to determine the dependences of the electron temperatures T_e and electron density N_e on the distance from the target.

Thin-film waveguides were prepared by polymerization of aromatic organic compounds in a high-frequency discharge. The refractive indices and the losses in the films were determined. Heat treatment of orthoxylene films reduced the refractive index and the film thickness; heating to 160°C increased the losses in the films.

Waveguide layers were formed in fused quartz by irradiation with 6.5 MeV protons. The possibility of excitation of both TE and TM waves was demonstrated. An investigation was made of the waveguide layers in polarized light and by the phase contrast method. The measured values of the thickness and depth of these layers were in good agreement with calculations. Heating to 360°C reduced the losses because of the annealing of color centers.

Separation of the H, C, and O isotopes was achieved by the excitation of glyoxal (H₂C₂O₂) vapor with the radiation emitted from a pulse laser whose resonator contained an absorption cell filled with an H₂C₂O₂ dye.

The use of thick layers for recording purposes in holographic memory devices makes it possible to increase the diffraction efficiency and the memory capacity. A simple approximation is used to analyze the recording and reading of individual volume holograms with the aid of a diffraction-limited aperture. Some features not found in thin-film holograms are revealed by this analysis. For example, the average diffraction efficiency of thin-film holograms is inversely proportional to the size w_k of the spot formed by the reconstructing (read) beam. The corresponding dependence for thick-film (volume) holograms has a maximum but in the range of small values of w_k a direct proportionality is observed. In the plane of incidence the dimensions of spots formed by the signal and reconstructing beams are equal. At right-angles to this plane the spot size is less for the reconstructing beam, i.e., the distribution is asymmetric.

A theoretical study is made of the influence of the rotational relaxation on the laser stimulation of chemical reactions. Two rotational relaxation models (weak and strong collisions) are considered analytically. It is shown that according to these models, rotational relaxation does not affect significantly the possibility of selective excitation of molecular vibrations by infrared radiation.

The rate of a laser-stimulated chemical reaction and the distribution function of molecules over vibrational levels are calculated for the case when the probability of the reaction involving levels of energies exceeding the activation energy can have an arbitrary value.

An analysis is made of kinetics of a multilevel laser utilizing vibration-rotational transitions in molecules. A solution is obtained of the rate equations for quasisteady emission. This solution is used in the derivation of an analytic expression describing the dependence of the output power of a laser on its principal parameters.

A thin-film semiconductor laser is analyzed theoretically. The gain is calculated for transitions between magnetic-film levels. The threshold conditions are deduced.

It is shown that, in general, the interaction between relaxing quantum systems and radiation is described by non-Markov transport equations for the density matrix ρ^p and the relaxation matrix depends on the properties of the radiation. The usual Markov-type equations for ρ^p are obtained from these equations if γτ_c≪1 and (∊²+4V²)^1/2τ_c≪1 (γ is the width of the investigated transition in a quantum system, rc is the correlation time of the perturbations causing relaxation, e is the frequency detuning, and V is the energy of the interaction between the system and the radiation field). When the second inequality is disobeyed, the relaxation process deviates strongly from the Markov type. In the case of small values of V, this results in a non-Lorentzian profile of the absorption lines characterized by a steep descent in the wings. In the range of high values of V, when 2Vτ_c 1, the whole relaxation process becomes greatly modified: the dependence of the relaxation coefficients on V becomes strong and a coupling appears between the relaxations of the diagonal and the nondiagonal elements of the density matrix. This is manifested, in particular, in the saturation effect: the term describing saturation in the expression for the polarizability changes considerably and the expression for the line width loses the component due to the adiabatic (elastic) perturbation.

Measurements were made of the Einstein coefficients of the spontaneous transitions from the ⁴F_3/2 metastable level of Nd³⁺to all the levels of the ⁴I ground-state multiple! occurring in several silicate and phosphate glasses. The cross sections of the ⁴F_3/2→⁴I_11/2 laser transition were determined. It was demonstrated that the spectroscopic methods suggested in the literature for the determination of these quantities could give rise to basic and uncontrollable errors.

An investigation was made of the luminescence of iodine vapor excited by λ = 530 nm laser radiation of up to 10 MW/cm² intensity. The usual "fast" luminescence was accompanied by a weak and slowly decaying luminescence of recombination origin. The latter luminescence was evidence of the efficiency of the twostage excitation of the molecules. The effective photon-absorption cross sections were estimated within the framework of a proposed model. These estimates made it possible to determine the best performance characteristics of a molecular iodine laser and the optimal pumping conditions.

The results are given of an investigation of the kinetics of the luminescence spectra of rhodamine dyes carried out using a fast shutter based on the optical Kerr effect. The measurements were carried out during a period of 2–100 psec from the beginning of an exciting pulse and they demonstrated that during this period the luminescence spectra did not change but were identical with the time-integrated spectra determined under the same excitation conditions. However, the shape and position of the spectra changed considerably when excitation with continuous low-power radiation was replaced with high-power ultrashort laser pulses. This was due to the possibility of formation of excited stereoisomers of the dyes.

An analysis is made of the efficiency of recognition of objects viewed through a turbulent atmosphere in the two cases when objects are recognized on the basis on their optical images and on the basis of reconstructed intensity holograms. The conditions for optimal selection of one of these two informationprocessing methods are formulated.

A theoretical analysis is made of the interaction between fields whose frequencies satisfy the relationship ω_p–ω_s=ω_g±ω_a≈ω₂₁ , where ω_p, ω_s, ω_g and ω_a are the frequencies of the pump, Stokes, generated, and auxiliary fields; ω₂₁ tne frequency of a transition between two levels in the investigated susbstance. The conditions are established for the maximum efficiency of the conversion of the fields ω_p and ω_a into the field ω_g. It is shown that the optimal conversion conditions are obtained for a certain ratio of the pump and auxiliary field powers when the phases of the interacting waves are locked. Numerical estimates are obtained of the conversion efficiency and interaction length when the active substance is potassium vapor or compressed hydrogen.

An investigation was made of the emission of stimulated radiation from CO⁺ molecules formed as a result of the flash-photoinitiated reaction C₃O₂+O→3CO⁺ in the presence of SF₆. A study was made of the dependences of the stimulated emission characteristics on the composition of the mixture and its pressure. The kinetics of the photoinitiated CO-forming reaction was investigated. The probable elementary processes occurring in parallel and in series with the main reaction were analyzed and their role in the kinetics of formation of excited CO⁺ molecules was determined. The relationship between the stimulated emission and the kinetics of the chemical and relaxation processes was established.

Experimental investigations were made of the mechanisms of the population inversion and depletion of an infrared transition in N₂, of the role of field effects in the formation of infrared stimulated emission pulses, and of the dependence of spectral-time characteristics of infrared emission on the gas pressure. Stimulated infrared emission was observed at a pressure of 0.5 atm in pure nitrogen and at 1.5 atm on a N₂ + He mixture. A comparison was made with the results obtained for a laser excited by a longitudinal discharge. An analysis was made of the possibility of constructing of a continuously tunable infrared-emitting molecular nitrogen laser.

An investigation was made of the action of continuous CO₂ laser radiation of 1 kW power on metals in air and oxygen at pressures of 10^–3 –1 atm. The results obtained indicated a considerable (severalfold) increase in the absorptivity of metals in an oxidizing medium. It was established that the surface oxidation initiated optical discharges in air near the target, which were maintained by combustion of the target material.

An investigation was made of the visible luminescence emitted by SF₆ and BCl₃ gases as result of excitation with CO₂ laser radiation. The influence of the gas pressure, duration of irradiation, and some diluents on the luminescence threshold was studied. Two luminescence stages were observed in the threshold region. Kinetics of the luminescence emitted from BCl₃ agreed with the bleaching kinetics. The luminescence and bleaching of BCl₃ were not related to the heating or dissociation of the gas. The absence of dissociation was confirmed by infrared and mass-spectroscopic analyses of the gas after illumination with laser radiation. The nature of the luminescence threshold was considered.

A magnetically tunable laser, emitting in the range 9.6–12.2 μ, was constructed. It was pumped with various CO₂ laser lines hi the range 10.2–10.9 μ. Stimulated emission from this laser was obtained at the Stokes and anti-Stokes frequencies. A system composed of a gate amplifier and a signal store was used to record the absorption spectrum of ammonia in the 11 μ range. The measured width of the stimulated emission line, which governed the resolution of the laser spectrometer, was 0.2 cm^–1. Factors responsible for the broadening of this line were considered.

The approximate method of smooth perturbations is used to obtain an integral representation of the frequency spectrum of fluctuations of the difference between amplitudes of optical beams traveling at different angles in the atmosphere. A numerical analysis of the expression obtained is made for a "longitudinal" wind and this is done as a function of the diffraction size of the beams and angles between the beam axes. It is shown that low frequencies make the dominant contribution to fluctuations of narrow (in the diffraction sense) beams. Asymptotic expressions are obtained for the low- and high-frequency spectral densities.

A theoretical analysis is made of the polarization characteristics of the Raman and hyper-Raman scattering in gases under resonance excitation conditions. It is shown that these characteristics may differ very considerably in the resonance and nonresonance cases. It is also shown that polarization measurements can be used to separate the laser effect (or resonance luminescence) from the Raman scattering. A new system for generating far infrared radiation is suggested.

A theoretical analysis is made of the main forms of vibrational energy losses in heterogeneous media used in gasdynamic lasers. Calculations show that the most important losses in a CO₂ gasdynamic laser are optical (absorption of light by particles); these losses increase with the gas pressure in the resonator and with the weight concentration of the particles. The most important losses in a CO gasdynamic laser are those associated with the deactivation of the excited molecules on the surfaces of condensated particles.

Two-dimensionsal radiative transfer equations and population inversion rate equations are used to calculate various parameters of an electron-beam-pumped laser. Dependences of the threshold current density and output power on the transverse dimensions of the laser are obtained. The influence of amplified spontaneous radiation on the laser parameters is considered.

A theoretical analysis is made of the excitation of sound in a liquid as a result of absorption of timemodulated optical radiation. Attention is concentrated on steady-state generation of monochromatic sound resulting from quasicontinuous irradiation of the liquid. The patterns established in the far and near acoustic wave zones are considered; definite advantages of the far-zone generation are pointed out. The optimal modulation frequency ensuring the maximum amplitude of the acoustic wave in the far zone (for given laser radiation power) is considered. A statistical analysis is made of the influence of random inhomogeneities in the transverse distribution of the intensity of a laser beam. Numerical estimates are obtained for the generation of sound in water by CO₂ and YAG laser radiations.

An ultraviolet nitrogen laser with a double transverse discharge was provided with an efficient cooling of the gas by heat transfer to the walls. This made it possible to dispense with a rapid flow of the gas. The same cooling method should be suitable for laser systems with an average output power of ~1–10 W. An output exceeding 0.5 W was obtained experimentally at gas flow rates of <0.3 liter/sec.

An analysis is made of the influence of the magnetic hyperfine splitting of the methane line at λ = 3.39 μ on the profile of a nonlinear power resonance in the field of a standing frequency-modulated wave. Resonance of this type has been used to stabilize the emission frequency of an He–Ne laser with a methane absorption cell: the frequency reproducibility achieved in this way is ~3×10⁻¹⁴. The shift of the resonance under investigation is found for different modulation frequencies as a function of the homogeneous width of the transition line and of the standing-wave field intensity.

A study was made of the optical control of the birefringence induced in zinc selenide crystals. The photoinduced birefringence was investigated under pulse excitation conditions. A prototype spatial light modulator based on a ZnSe crystal was constructed. The time, contrast, and spectral characteristics of this modulator were studied and the requirements to be satisfied by the control radiation were formulated.

Theoretical calculations are made of the dynamic range of a holographic phase transparency (a planeparallel transparent plate with a one-dimensional sinusoidal signal recorded on one of its faces) made of a thermoplastic storage material. A random modulation of reading signal is assumed in the derivation of explicit expressions for the dynamic range at different spatial frequencies. These expressions are obtained as functions of the spatial frequency number, modulation index of the reading signal, aperture of the lens used for the spectral analysis, and corresponding correlation characteristics of noise. Noise sources of various kinds, causing random amplitude phase modulation of the recorded signal, are considered: they include sources with short-range correlation and long-range correlation, those which are spatially homogeneous or periodically inhomogeneous. An analysis is made of the characteristic features of the dependences of the dynamic range on the parameters of the problem.

A description is given of a new type of the Raman scattering of light by thermal oscillations of the shape of a spherical liquid particle. This type of scattering results in a frequency shift of the scattered radiation. The single-valued relationship between this shift and the size of an aerosol particle should make it possible to use the scattering effect in the determination of the size distribution of aerosol particles.