Table of contents

An investigation was made of the dependence of the threshold current density and of the differential quantum efficiency of AlAs-GaAs heterojunction lasers on the width of the active region. It was found that the excitation of higher modes reduced the efficiency when the width of the active region was increased.

An analysis is made of the limitations of the depth of a scene which is reconstructed satisfactorily by focused-image holograms. The limitations are due to the dispersion of nonmonochromatic radiation and the finite size of the reference source. The depth of a scene reproduced by white light without visible blurring can be increased by viewing the image at angles corresponding to the extreme edges of the visible spectrum. A review is made of the factors limiting the depth of an image reconstructed with a hologram recorded using an extended reference source. The dependence of the depth of a satisfactorily reconstructed scene on the angular dimensions of the reference source is established. Attention is drawn to the special features observed in a reconstructed scene when a focused-image hologram is rotated.

A detailed description is given of a pulsed nitrogen laser emitting 2.1 MW or 0.011 J per pulse at λ = 337.1 nm. The use of a high-permittivity ceramic made it possible to construct a simple excitation system which could be used and tuned conveniently.

The relaxation characteristics of solutions of the Soviet-made polymethine dye No. 3955 in various solvents were determined. A suitable selection of the solvent made it possible to vary the temporal correlation interval from 45 to 11 psec and the reduction in the temporal interval increased the spectral correlation interval. Under certain conditions the width and structure of the emission spectrum in one axial period remained constant throughout a giant pulse.

A modified Michelson interferometer was used to investigate the temporal coherence of the radiation emitted from injection lasers with single- and double-sided heterojunctions. The lasers were operated in the pulsed regime at room and liquid-nitrogen temperatures. The coherence length for the single-mode emission was 8–30 mm at 300°K and below 30–45 mm at 77°K. The use of the apparatus as an intensity interferometer yielded the autocorrelation function of the field and the corresponding function of the intensity of the laser radiation. A comparison of these two autocorrelation functions indicated that the spectral broadening of a single mode was primarily due to phase fluctuations.

An investigation was made of the reflectivity of opaque metallic films during and after illumination with nanosecond laser pulses. The reduction in the reflectivity was interpreted on the basis of the Drude–Zener theory allowing for the temperature dependence of the electron-phonon scattering. The experimental and calculated results were compared.

An investigation was made of the stimulated Brillouin scattering through 180° in compressed gases when the width of the pumping line Δν_p was greater or smaller than the frequency shift δν_s of the Stokes component. There were no basically new processes in the stimulated scattering of focused beams in the range Δν_p ≲ 10δν_s.

A theoretical analysis is made of a new method for recording infrared Raman-scattering radiation. The essence of the method lies in the mixing of the scattered radiation and of the pumping radiation in a nonlinear crystal and detecting the resultant sum frequency with a photomultiplier. It is shown that this method should ensure reliable recording even of the radiation resulting from the Raman scattering in gases.

It was established that organic dye lasers could be used in very-high-sensitivity laser spectroscopy based on the selection of losses in the resonator. A smooth emission spectrum was obtained for rhodamine G and the abosrption spectrum of I₂ with an absorption coefficient of ~10^–3 cm^–1 was recorded in the 16450–17950-cm^–1 range.

A freely oscillating neodymium-glass laser is used as an example in an experimental demonstration that the angular divergence of the radiation emerging from a telescopic resonator is governed by the optical inhomogeneity of the active medium and not just by the resonator effects.

A holographic memory was constructed and used to store microprograms for tuning a homogeneous medium operating in conjunction with a digital computer. Holograms were recorded using a controlled transparency which made it possible to form optical tuning patterns and to project them directly onto a photodetector array of the homogeneous medium.

A discrete light-beam deflector was built using an electro-optic element in the form of a nematic liquid crystal with a positive permittivity anisotropy. The switching from one polarization of light to an orthogonal one resulted from an electric-field-induced reorientation of the molecules in the crystal, which altered its birefringence. The deflector was simple to build and it was characterized by an extremely low modulation voltage (10–60 V).

A CO₂ laser with an output energy of 15 J per pulse was built. The output energy and the efficiency were determiend as a function of the energy supplied to the gas and the influence of substances with a low ionization potential was studied. A homogeneous discharge was extremely stable in the pressure range 0.2–2 atm. The pressure corresponding to the output energy maximum could be shifted in the range 0.3–1.3 atm by altering the amount of He in the gas mixture.

A calculation is reported of the gain curve for a luminescence band associated with the process of inelastic collisions between two excitons, one of which is transferred to a higher excited state, and the other transformed into a light quantum. It is shown that in the case of II–VI compounds the luminescence band differs considerably in width and location from the usual P and M bands associated with the ionizing collisions between two excitons.

A study was made of the crystallization, morphology, and some defects of lithium formate. An interference method was employed in the determination of all the piezoelectric and linear electro-optic constants. The permittivities were also determined. The temperature of dehydration in a dry medium was found and the changes in the permittivity ε and loss-angle tangent tan δ during heating were measured. Lithium formate was found to be five times as effective as KDP crystals in simultaneous doubling of the emission frequency and Q switching of a laser emitting at λ=1.06 μ.

Longitudinal modes emitted by a GaAs laser pumped longitudinally with an electron beam were locked by a nonlinear KDP crystal inside the resonator. Ultrashort laser pulses of duration below 20 psec and with a depth of modulation of 100% were generated in this way.

The emission dynamics was determined for gallium arsenide and cadmium sulfide lasers pumped longitudinally with an electron beam of 10 μ diameter. Spikes were observed and they were attributed to the dependence of the refractive index of the active crystal on the density of the electromagnetic field in the resonator.

The results are given of calculations of the formation of an absorbing vapor layer during irradiation of an aluminum target in air with neodymium laser pulses of ~1 msec duration and maximum power of the order of 10 MW/cm². It is assumed that the illuminated spot is of ~1 cm radius. The role of various physical and gas-dynamic processes in the general interaction between the radiation and target is discussed. The main process which governs the most characteristic observable features is the screening of the laser radiation by an absorbing plasma layer. The calculated results are in satisfactory agreement with the experimental data.

A study was made of the degradation of injection lasers, some of which were subjected to bombardment with fast particles. It was found that the radiation defects did not accelerate the aging process during prolonged operation of the lasers. The fall of the output power after tests lasting 10⁴ h did not exceed 23%.

A theoretical analysis is made of the methods for achieving stimulated emission during the afterglow stage of a short pulse which ionizes a dense inert gas. The conditions favorable for stimulated emission are estimated.

Theoretical estimates are obtained of the possibility of using infrared laser radiation in the initiation of polymerization reactions in gases. A numerical solution of a system of vibrational and chemical kinetics equations shows that if the vibration-translational relaxation is sufficiently slow, it should be possible to polymerize such substances as acetylene, ethylene, etc.

The signal/noise ratio was improved in the measurement of the indicatrix of the light scattered by laser mirrors. The improvement was achieved by using the energy accumulated in a unidirectionally operated traveling-wave laser resonator. A description is given of the apparatus with which this method was put to test and the results of the measurements are given.

A description is given of a manometer-flowmeter based on the Michelson interferometer, one of whose arms contains an enclosure with the investigated substance and two diametrically opposed illuminators. The use of cat's-eye reflectors minimizes the influence of vibrations on the interferometer, which still retains a fairly high sensitivity of 0.0004 kgf/cm². The positioning of one of the reflectors behind the enclosure avoids the possibility of contact with the investigated substance and makes it possible to use the proposed instrument in the measurements of the pressure (flow) of transparent corrosive media.

The total evolution of heat in the bulb, electrodes, and leads was determined for pulse discharges in Xe, Kr, Ar, and Ne using a water calorimeter. The investigation was carried out in the specific power range 0.06–1.0 MW/cm² for discharges lasting from 70 to 2000 μsec. In all the gases there was a wide range of pulse durations (at least from 250 to 2000 μsec) in which the specific power input was a reliable characteristic of the energy balance.

A review is given of the applications of high-power cw and pulsed lasers in the technology of inorganic materials, including local hardening, welding, cutting of metals and dielectrics, film processing, drilling of holes, and so on. An analysis is made of the potential applications of high-power cw lasers in metallurgical processes, including preparation of refractory metals, remelting of high-temperature materials, growth of single crystals, processing of powder materials, etc.

A review is given of the scattering of coherent optical radiation in gaseous, liquid, and solid media. The spontaneous and stimulated scattering effects are considered. The direct methods for the measurement of the energy relaxation time and of the phase of the vibrations of the scattering particles are discussed. A review is also given of indirect methods based on the measurement of the frequencies, widths, and intensities of the scattering lines and of the corresponding quantities in the stimulated scattering. Practical aspects of the scattering investigations are considered, including the development of new tunable lasers.

The known mechanisms of the pumping of laser levels are used in calculations of the dependences of the gains of Cd-He, Se-He, and Sb-He cataphoretic lasers on the pressure of helium and on the discharge-tube diameter. The calculations are compared with the experimental results. It is found that when the helium pressure is increased, these dependences become strongly affected by a reduction in the optimal concentrations of the active substance in the discharge (Cd-He and Se-He lasers) and by a reduction in the electron temperature (Sb-He laser). The observed rise of the gain on reduction of the discharge-tube diameter is mainly due to an increase in the optimal concentration of the active substance.

It is shown theoretically that a power resonance peak of a ring laser reproduces exactly the central frequency of an absorbing gas when the centers of the gain and absorption profiles coincide. A method is suggested for ensuring the coincidence of these centers: It is based on the existence of laser power resonances associated with the competition between the effects of spectral saturation of a line, spatial de-excitation of the medium, and phase interaction between traveling waves.

A theoretical (analytic and numerical) study is made of a nonstationary (transient) plasma turbulence initiated by a parametric instability involving decay of a pump wave into two plasmons and saturated by the stimulated scattering of plasmons on ions. The main features of the relaxation of such a parametric turbulence are governed by the characteristics of the noise saturation mechanism and are in this sense typical of many other instabilities which can be stabilized by stimulated scattering. A solution of a nonlinear integro-differential equation for the spectral density of the noise energy reveals the complete evolution pattern of the appearance and growth of a turbulent noise, which oscillates in time, has a modulated spectrum, and finally attains a smooth stationary (steady-state) distribution. A nonstationary parametric turbulence can develop fully in a dense laser plasma during a nanosecond pulse emitted by a high-power neodymium laser.

An investigation was made of GaAs waveguide resonators up to 0.4 mm thick. These resonators were used in order to increase the working areas of the mirrors through which the laser radiation was extracted. The lasers were excited by bombardment with an electron beam of 75 keV energy and up to 20 A/cm² current density. The efficiency of lasers with such resonators rose to 6% and the service life of the lasers increased considerably.

A theoretical analysis is made of the vibrational kinetics of molecules under nonequilibrium conditions of the cascade excitation of molecules by resonant laser radiation. The exact solutions of the kinetic equation are obtained in the harmonic oscillator model. An expression is derived for the time dependence of the average vibrational energy accumulated in a specific vibrational mode. The analysis shows that the cascade mechanism has the following advantages: It provides means for an effective control of the rate of excitation of the molecular vibrations and it increases the average energy stored in the vibrational modes. Two methods for combined pumping of a specific vibrational mode are suggested: One is the combined action of a discharge and laser radiation and the other is a combined chemical and laser pumping.

A theoretical analysis is made of the possibility of the excitation of laser action in compressed xenon subjected to a static electric field causing ionization and irradiated with fast electrons from an external source. A solution of the kinetic equation gives the efficiency of this lasing method and it is found that under optimal conditions it should reach 70–80%. The concentration of excited molecules and the gain at λ≈173 nm are calculated for specific conditions.

An investigation was made of the spectral characteristics of the radiation emitted by a ruby laser with a pronounced transverse field structure when a narrow spectral line of a second laser was injected into the resonator of the first laser as a stimulus. The dynamics of the emission spectrum was found to be governed by the gap between the frequency of the stimulating radiation and the maximum of the gain profile.

The variance and average value of photocounts (counts of electrons emitted by the cathode of a photodetector) are calculated allowing for the existence of the following sources of noise in a frequency converter: fluctuations of the pump intensity, conversion of background radiation, thermal fluctuations of fields in the converter crystal, spontaneous generation of the difference frequency, and illumination of the photodetector with the pump radiation transmitted by filters. A function representing the distribution of photocounts is obtained for short time intervals allowing for fluctuations of the pumping intensity in the case of conversion of a random Gaussian signal.

The number of oscillation modes excited in all degrees of freedom in conventional and stripe GaAs and other lasers was determined for an excess over the threshold amounting to a factor of 3–5. The average output power per one excited mode was not more than 10 mW even when the total laser power reached tens of watts. The number of the longitudinal oscillation modes, governing the width of the spectrum, was in satisfactory agreement with calculations based on a spiking emission model. The influence of selective resonators, which could increase the single-mode output by a large factor, is discussed.

An investigation was made of the emission spectra of an injection laser with a selective feedback produced by a reflecting diffraction grating. The spectral characteristics of the laser were improved when the natural resonator was replaced with an antireflection coating and when a diode with a conventional resonator was used. A pulsed power in excess of 6 W was obtained at 300°K in a band not wider than 0.1 nm in the first case and 0.45 W in a band not wider than 0.01 nm in the second case.

A theoretical analysis is made of the generation of the second harmonic of optical radiation in an open resonator. A study is made of the conditions for the maximum transfer of power to the second harmonic in the presence of linear energy losses in the resonator and equivalent losses due to the conversion of energy into the second harmonic. It is shown that, depending on the linear losses and the power of incident radiation, one can find the optimal value of the reflection coefficient of the mirrors at the wavelength of the fundamental-frequency radiation.

An asymptotic theory is developed for fluctuations of the intensity of monochromatic radiation traveling in a turbulent medium with a power spectrum of fluctuations of the refractive index. The theory is based on an analysis of the solution of an equation for the fourth-order coherence function. The exact nature of the saturation of the relative fluctuations of the intensity of the radiation in the Fraunhofer zone of the transmitter is established. An estimate is obtained of the tendency of the correlation function of the intensity fluctuations to approach the asymptotic form. The results of the analysis are in good agreement with the experimental data.

A theoretical analysis is made of the vibrational kinetics in multicomponent gaseous media under nonequilibrium conditions of the cascade excitation by resonant laser radiation. The harmonic oscillator model is used to derive the exact solutions of the kinetic equations. It is shown that all the components of the distribution function retain their Boltzmann form if initially the system is in equilibrium. A system of equations for the vibrational energies is solved. The solutions are obtained for different rates of the vibration-translational relaxation in both modes of a two-component medium. A study is made of the steady-state conditions in a binary mixture. The analysis shows that the neglect of the vibration-vibrational exchange between different modes in polyatomic molecules may result in considerable deviations from the real kinetics in the whole system.

A theoretical investigation is made of the amplification in a transverse-flow CO₂ laser. It is shown that the energy efficiency of a laser system with a multipass amplifier may be higher than the efficiency under oscillation conditions.

An investigation was made of the characteristics of a POCl₃ + SnCl₄ + Nd³⁺ inorganic liquid laser. These characteristics were compared with those of a neodymium-glass laser. The specific output energy obtained was ~6 J/cm³. An investigation was made of the spectral composition of the radiation. The gain cross section at the frequency of the laser transition and the nonresonant losses were determined experimentally.

An investigation was made of the divergence of the radiation emitted by laser oscillators and amplifiers with a liquid active medium (POCl₃ + SnCl₄ + Nd³⁺) as a function of the change in the refractive index caused by the pumping radiation. It was found that the divergence of the output radiation was governed by the refractive-index inhomogeneities. In the case of strong inhomogeneities, the divergence was practically the same for oscillators and amplifiers.

An experimental investigation was made of the growth of the radiation intensity in the leading edge of a giant pulse generated in a ruby laser with passive and active modulation of the resonator losses. The experimental method employed made it possible to record the giant-pulse radiation beginning from the spontaneous noise level. The dynamics of the development of a giant pulse in the presence of the passive modulation was basically different from that in the presence of the active modulation of the losses. Direct measurements were made of the development time of a giant pulse produced using a bleachable filter, an electro-optic switch, and a rotating prism. In the first case the development time was several microseconds, whereas in the case of the electro-optic switch or rotating prism it was 200–300 nsec.

The results are given of an experimental investigation of the load characteristics of pulse-discharge xenon lamps with a luminous channel of 16-mm diameter. A description is given of the method of calculating the operating conditions of such lamps in a CLR series circuit.

Various aspects of the procedure for estimating the energy characteristics of lasers with unstable resonators are discussed. Some results of calculations are given for the general case of an inhomogeneously excited medium.

An analysis was made of the relationship between the duration of the stimulated emission τ_e from HF* and the "duration" of the reaction τ_r in F₂ + H₂, NF₃ + H₂, and N₂F₄ + H₂ mixtures. The values of τ_e and τ_r calculated from the kinetics of these reactions were of the same order of magnitude only for the F₂ + H₂ system but very different for the other two systems. These differences were attributed to the different roles of the secondary stages of these chain reactions in the course of formation of the vibrationally excited HF molecules in the inverted state. A comparison of the values of τ_e and τ_r could provide information on the degree of utilization of the reagents in the generation of coherent radiation.