Table of contents

An experimental study was made of the kinetics of light scattering during exposure of films As₂S₃ to monochromatic and white light. It was established that the experimentally observed considerable enhancement of light scattering was due to the coherence of light. Hie maximum enhancement depended on the initial degree of scattering and on the film thickness. The surface layer of a film acted as the source of the strong initial scattering in the case of films whose thickness exceeded 7 μ.

Infrared helium-neon laser radiation (λ = 1.15 μ) was transformed to the ultraviolet range (λ = 377.6 nm) in thallium vapor by parametric mixing with radiation from a rhodamine 6G dye laser (λ = 568.6 nm). Use was made of a two-photon resonance of the pump (dye laser) radiation with the 6P_1/2–7P_3/2 forbidden transition and of the proximity of the frequency of the radiation being temsformed to the frequency of the 7P_3/2–7S_1/2 transition.

An experimental study was made of the integrated (average per pulse) absorptivity of craters on metal targets irradiated with giant ruby laser pulses. The targets were Cu, Al, Mg, Cd, and Sn. Abrupt changes in the absorptivity were due to optical breakdown on the target surface. Under advanced evaporation conditions the absorption by a crater was of the steady-state type: its value was 70% and practically the same for all the investigated materials. The conditions were such that the absorption of laser radiation in the crater, regarded as a geometric cavity, could be ignored. The heat transfer coefficient was also measured.

Optical fibers consisting of a glass and a polymer were fabricated. They had a numerical aperture of 0.37 when the core was made of quartz glass and 0.5–0.56 when it was made of multicomponent glasses. A study was made of the optical and physicomechanical properties of various polymer claddings. The results led to a recommendation for the use of a silicone composition characterized by a high transparency in the visible part of the spectrum. Fibers with losses of 20 dB/km and a breaking strength in excess of 400 kg/mm² were obtained.

It is proposed to use aerosols of dye solutions as active media. Methods of creating aerosols with particle densities of 10¹⁴–10¹⁵ cm⁻³ are considered. The results are given of experiments on condensation of solvent molecules at molecules of a complex organic compound (paraterphenyl) in a heated Wilson chamber. The limiting energy characteristics of aerosol active media are discussed.

It is shown that the diffraction losses and the distribution of the field amplitude in complex resonators with an internal diaphragm are governed only by three parameters. A relationship is found between these parameters and the elements of the transfer matrices describing optical components of a given resonator. The results obtained make it possible to simplify greatly an analysis of complex resonators with an internal diaphragm.

An investigation was made of the polarization modulation in a thin-film ridged waveguide based on a planar GaP–GaAsP heterostructure. A practically 100% modulation of the radiation was obtained under the action of a half-wave force of 0.05 kg.

An investigation was made of the efficiency of stimulated Raman scattering in sodium, barium, and lead nitrates, compared with that in calcite. Measurements were made of the energies of two Stokes components of stimulated Raman scattering. The suitability of nitrate crystals for Raman stimulated emission was demonstrated.

An investigation was made of conversion of neodymium laser radiation to the 2-μ wavelength range by means of a BaYb₂F₈:Ho³⁺ laser crystal. The most important spectroscopic and lasing characteristics of the crystal were determined.

An oscillator chain phase-locked to a primary frequency standard was developed: this chain included D₂O and HCN lasers, as well as klystrons emitting in the millimeter and centimeter ranges. Phase locking to a frequency standard of wavelength shorter than 100 μ was achieved for the first time. The error of tracking of the standard frequency by the frequency of the D₂O laser did not exceed 3 x 10⁻¹³ and the nominal frequency of this laser was 3557147500000 Hz. This laser was used to measure the frequency of a CO₂/OsO₄ laser with an error of ~3×10⁻¹¹ and this error was due to the frequency instability of the CO₂/OsO₄ laser. It should be possible to improve the precision of these measurements by two orders of magnitude.

A scalar wave equation is solved to find the distribution of an electromagnetic field in a telescopic resonator filled with an amplifying medium. It is shown that the normal oscillation modes can be described by Laguerre functions. The conditions for oscillation of various modes in this resonator are found.

A theoretical study is made of the stimulated scattering of radiation whose spectrum is much wider than the frequency of a vibrational transition in the scattering medium. It is shown that the efficiency of the scattering process then depends strongly on the statistical properties of the incident (pump) radiation.

A theoretical model is developed for the formation of a plasma due to the interaction of CO₂ laser pulses with an aluminum target in air. This model allows for the heating and evaporation of the target and for the absorption of the laser radiation in the moving vapor whose state is described in the two-temperature approximation. Use is made of the experimental shapes of the laser radiation pulses of 1–400 MW/cm² intensity and 0.01–10 μ sec duration. The calculated plasma-formation times are in agreement with the experimental data, especially when allowance is made for the possibility of existence of thermally insulated microregions on the irradiated target surface.

An experimental study was made of semiconductor lasers with periodic structures. The use of a special surface profile in which the mirror area exceeded the area of the transverse cross section of the resonator made it possible to improve considerably the angular distribution of the output radiation.

An experimental study was made of the dependences of the absorption coefficients on the chemical and phase composition of vacuum-condensed copper-tin alloys (with 17-60 wt.% Sn) and of the γ phases of copper-aluminum and copper-gallium systems in bulk and thin-film forms. The minimum absorption coefficient, amounting to 2.1%, was obtained for the compound Cu₃Sn with 38-40 wt.% Sn.

A study was made of the influence of microbending of fiber waveguides on their total losses, depending on the numerical aperture of the guide. Measurements were made also of the total losses in fiber waveguides before and after assembly of an optical cable. The total losses of guides with a numerical aperture of ∼0.30 were not affected significantly by cabling.

Passive locking of argon laser modes was used in generation of tunable picosecond pulses in a synchronously excited dye laser. An experimental study was made of the characteristics of the dye laser radiation as a function of the argon laser characteristics.

A review is given of theoretical and experimental investigations of the optical rectification effect (ORE) in nonlinear crystals. Attention is focused on aspects of using this effect for measurements of the nonlinear susceptibilities of crystals, measurements of the power, polarization, and profile of laser pulses, excitation of electromagnetic waves in waveguides and resonators, generation of infrared radiation, and nonlinear spectroscopy. Further potential uses of the ORE are discussed.

A quantitative two-phase model is developed to analyze the contribution made by the mechanism of displacement of the melt to the damage to thin absorbing films. This contribution is considered as a function of the main characteristics of the process which are the radiation parameters, properties of the film and substrate materials and their adhesion, surface tension and viscosity of the film, and also thermophysical and optical properties, thickness of the film, and size of the exposed area.

A theoretical analysis is made of the energy exchange between four counterpropagating plane waves during their interaction in a medium having an instantaneous cubic reactive nonlinearity. A solution of a complete system of equations in terms of Jacobi elliptic functions is obtained. The interaction pattern is constructed using concepts of dynamic holography. It is shown that the high energy exchange efficiency of a local nonlinear response of the medium is due to a shift of a hologram with respect to the interference pattern of the diffracted waves.

Investigations were made of the temperature dependences of the lifetimes of excited states of pigments in photosynthetic membranes and their fragments in the picosecond and subnanosecond ranges. Fluorescence was excited by a single second-harmonic pulse from a neodymium laser (λ = 530 nm, t_p ~ 10 psec) and was recorded using an image converter. An analysis was made of various processes for the transfer of the electron excitation energy and its photochemical conversion in reaction centers. The mechanisms of these processes were analyzed allowing for possible conformational states of pigment-protein complexes.

The results are given of an experimental investigation of fluctuations in the intensity of a laser beam passing through a turbulent absorbing liquid medium (ethyl alcohol). On increasing the beam power, the intensity fluctuations were found to weaken. A qualitative explanation of this phenomenon is given. Conclusions following from calculations of weak intensity fluctuations, in which the temperature variation of the medium was described by a semi-empirical turbulent heat-conduction equation, were experimentally verified.

An analysis is made of a theoretical model of a laser utilizing POPOP vapor with added pentane. The model presupposes instantaneous redistribution (thermalization) of the optically generated excess vibrational energy of the active molecules between all the molecules of the active volume. Calculations are made of the time dependences of the lasing power and of the temperature of the active medium for different pentane pressures. The feasibility of pyrolysis of the active molecules as a result of overheating is discussed by comparing the calculated temperatures of the active medium and the experimentally determined rate constant for thermal dissociation of pure vapor.

Nonreciprocal effects in a helium–neon ring laser, which arise when a transverse magnetic field is applied to the active medium, were discovered and investigated in detail. One of these effects appears because, due to a difference between the polarization characteristics of counterpropagating waves, the anisotropy of the saturation of the medium in a magnetic field is also different for the two directions. The effect is nonlinear. The second effect is produced by the action of a transverse magnetic field on the drift of the active atoms in a dc discharge. The effects discovered depend on the square of the magnetic field.

An analysis is made of the dependence of the efficiency of the Bragg acoustooptic interaction between TE modes in a diffused optical waveguide on the acoustic surface wave frequency. It is found that two waveguides having different optical parameters, but supporting the same number of modes, are described by almost the same frequency dependences. This conclusion is confirmed by calculations for two fourmode waveguides utilizing Y-cut lithium niobate. The frequency dependences of various processes were measured experimentally in the range 50–550 MHz.

A study was made of the characteristics of a pulsed CF₄ laser, optically pumped by a pulsed CO₂ laser whose frequency was stabilized by injecting a signal from a low-pressure cw CO₂ laser. The laser output energy was observed to saturate with increasing pump energy, the maximum value obtained being 0.1 J at an efficiency of up to 1%.

The characteristics of heterostructures and the main radiative properties of infrared (1.4–1.8 μ) heterojunction lasers using quaternary solid solutions of AlGaAsSb, grown by liquid-phase epitaxy of GaSb substrates, are presented. A threshold current density of 2–4 kA/cm² was obtained in heterojunction injection lasers at 300°K and estimates were made of the waveguide effect and the optimal thickness of the active layer. It was found that the relative discontinuity of the refractive index at the interfaces of the active layer was approximately 5% for a 25% reduction in the Al concentration from the wide- to narrow-gap layers of the heterostnicture. Continuous-wave laser action at 77°K was obtained in the 1.40-1.57 μ wavelength range.

An analysis is made of the feasibility of developing an atomic collisional gas-discharge laser utilizing a transition between levels one of which is unexcited. Several binary atomic gas mixtures suitable for such an investigation are proposed. Numerical estimates are made of the population inversion under conditions characteristic of a glow discharge.

The results of an experimental investigation of the nonlinear optical properties of thin absorbing films (solutions of cobalt chloride in ethanol) are presented. The dependence of the reflectivity of an absorbing plane-parallel film on the energy density of the incident radiation was obtained for different thicknesses of the film and different angles of incidence. It was found that near the critical angle of total reflection, the reflection coefficient of thin (of the order of a few microns) absorbing films varied fairly widely (approximately between 0 and 1). This was due to the establishment of a thermal mechanism of nonlinearity of the refractive index in the thin film, combined with interference. Q-switched laser action was achieved using a thin plane-parallel absorbing film as the Q switch. The pulse energy was 1–1.5 J with half-width durations of 140–30 nsec, respectively.

Investigations of phase-polarization and amplitude modulation of radiation are reported. Effective control voltages of ~10 V were obtained for a modulation depth of ~70%. A radiation deflector utilizing an array of channel waveguides was investigated.

A report is given of the generation of high-power laser pulses, having an energy of 1.5 J and an efficiency of 20%, by exciting ammonia with CO₂ laser radiation. The spectral and temporal characteristics of the NH₃ laser were investigated. Discrete tuning of the frequency was obtained over a range 770–890 cm ⁻¹. A study was made of the mechanism by which the ammonia absorbed the pump radiation and a procedure was found for increasng the NH₃ laser efficiency.

Excitation of the investigated lasers by pulses lasting a few microseconds produced light pulses whose shape differed from those of the current pulses. The top of a light pulse had a step (radiation power discontinuity) where the top of the current pulse was flat. A study was made of the emission spectrum and of the angular distribution in the case of such abrupt changes in the radiation power. Self-focusing was assumed to explain such behavior of stripe-contact lasers.

An investigation is made of the mechanism of spontaneous antiphase fluctuations of the intensity of the opposite waves in a solid-state ring laser. It is found that backscattering-induced coupling of the waves is only responsible for fluctuations at a frequency higher than that of the relaxation oscillations. A hypothesis is put forward that the lower-frequency fluctuations may be due to instability of the laser parameters. Computer calculations using a laser model with low-frequency antiphase modulation of the opposite wave losses confirm that this interpretation is feasible.

A simple method was developed for the fabrication of strip waveguides in glass with losses below 1 dB/cm. A technique for the determination of the parameters of these waveguides was also developed. An integrated-optics structure was constructed from strip waveguides, which could be used in multimodefiber communication lines.

The feasibility of reducing the angular divergence of the output radiation from a laser with an unstable resonator by conversion of the cross-sectional profile of the beam using conical optics is discussed. The results of experiments using a CO₂ laser are presented. These show that the use of a conical converter at the output of a laser with a low gain (having an unstable resonator with a magnification close to unity) should give an appreciable improvement in the directionality of the radiation.

An analysis is made of the characteristics of an active method for suppressing fluctuations of the output power of a cw laser, by an external control element, to the level of noise in the detection system. A description is given of two complementary experimental systems for the stabilization of the output power of a CO₂ laser, intended to suppress slow and fast fluctuations with fluctuation-suppression coefficients exceeding 10².

Methods are proposed for determining the thermal characteristics of injection lasers from the threshold currents under various operating conditions. A feature of these methods is the easy determination of the initial data required to calculate the thermal characteristics. It is found that some of the Joule heat released due to the resistance of a laser diode is efficiently removed by a heat sink and does not heat the active region. A method of determining the thermal power which results in heating of the active region is proposed. It is shown that neglect of this mechanism for removal of some of the heat can give rise to significant errors in the determination of the thermal characteristics.

A new mechanism is proposed for optical breakdown in gases, based on molecular ion reactions. It is shown that a molecular ion breakdown mechanism must play the dominant role at high gas pressures. A simplified model is used to obtain an expression for the threshold power density w_th. Experiments are discussed in which low-threshold gas breakdown was observed. Optical breakdown in heated air is considered; this is distinguished by anomalously low values of w_th ~ 100–1000 kW/cm² and is due to ionization-thermal explosion of the air in the laser radiation field.