Table of contents

An investigation was made of the characteristics of the radiation emitted by a ruby laser with an active positive or negative feedback. Under negative feedback conditions the emission was in the form of smooth pulses modulated by not more than 10% (rms deviation not exceeding 5%) and with an instantaneous width of the spectrum of ≲0.0008 nm. Under positive feedback conditions the laser emitted one or several high-power pulses.

A CO laser, capable of operating for a long time without a change of the active gas, was constructed. The maximum output power of the laser was 17 W and the efficiency was 12%; these values were considerably better than those given in the published literature. An investigation was made of the emission spectrum and of the dependence of the output power on the transmission coefficient of the exit mirror under cw and Q-switched conditions.

An acousto-optic modulator of infrared radiation was built using a germanium crystal operating under acoustic resonance conditions. Optimal dimensions of the modulator were calculated. The parameters of the acoustic grating established in the crystal were stabilized using a lithium niobate transducer supplied from a self-excited oscillator. The dependences of the intensity of the diffracted light on the electrical power were investigated under standing and traveling acoustic wave conditions. The frequency characteristic of the modulator was determined in the range from 100 Hz to 100 kHz.

The equivalent layer method is used in the design of a dielectric mirror characterized by small residual reflection in one of the short-wavelength transmission bands. An analysis is made of the influence of the dispersion of the refractive indices on the spectral characteristics of such a mirror.

Cadmium sulfide optical resonators were pumped at atmospheric pressure by an electron flux generated in nanosecond gas discharges. The resonators were excited at –40°C, –50°C, and at room temperature. The emission maximum was located in the region of 521 nm and its halfwidth was 1.5 nm. This pumping method could be used in the end-resonator and radiating-mirror configurations. The method could be used in nonevacuated electron-impact excited semiconductor lasers of size approaching injection lasers but capable of emitting considerably higher powers than injection lasers.

Neodymium-doped phosphate glasses and selectors of different thickness were used in the generation of mode-locked laser radiation. This made it possible to study the emission of two bands with a variable frequency interval between them and the emission of one band of variable width. When the widest band was emitted, the duration of ultrashort pulses was measured by the two-photon luminescence and found to be 15–20 psec. This duration agreed with the reciprocal of the width of the spectrum. The output radiation parameters were highly reproducible irrespective of the nature of the selective resonator employed.

Stimulated emission due to the ⁴I_11/2–⁴I_13/2 transition (λ = 2.936 μ) in yttrium aluminum garnet (Y₃Al₅O₁₂) doped with Er³⁺ ions (30 wt%) was observed for the first time at 300°K. The output energy from crystals of 50×3 mm dimensions was 0.3 J under free-oscillation conditions and 0.05 J in the case of Q switching. The lifetime of the ⁴I_11/2 level was determined for crystals with 3–30 wt% Er³⁺. The energy from the higher Er³⁺ levels relaxed in a cascade manner through ⁴I_11/2 to ⁴I_13/2.

An investigation was made of the coupling of radiation into a thin-film waveguide by a diffraction grating with a period exceeding the wavelength of light. The efficiency of the coupling into the film was ~60%. The radiation emerging from the waveguide had a diffraction-limit divergence of ~3'.

An experimental investigation was made of the coupling of radiation into a thin-film waveguide through its tapered edge. The coupling efficiency was ~88%.

Coherent radiation of λ = 0.97 wavelength was obtained from diffused p-n junctions in InP_0.92As_0.08 solid solutions. The threshold current density was (5–7)×10³ A/cm² at 77°K. The output power reached 2 W for a quantum efficiency of 4%.

New applications of the nonlinear total internal reflection in the Q switching of a ruby laser are reported. A continuous transition is possible from the mode-locked case to the generation of smooth giant pulses: This can be achieved by varying the angle of incidence of radiation on an interface between a solution of a phototropic dye and glass.

An investigation was made of a method for effective coupling of laser radiation (λ = 1.15 μ) by a prism into thin (5–15 μ) GaAs films grown epitaxially on Al_xGa_1–xAs substrates. Waveguide modes were excited selectively. The optical parameters of the waveguides were deduced from the measured phase-matching angles of the excited modes.

The optical frequency of the 3s₂→2p₄ transition in a He-Ne laser was determined by comparison with a secondary radiofrequency standard operating at ν_st = 1999.3865 MHz. The measurement method was analyzed and the frequency deduced from a series of such measurements was found to be 473, 612, 162±23.8 MHz.

A calculation was made of the illumination-induced redistribution of the voltage in the structure between the dielectric (combined nitride and oxide layers) and a surface depletion layer in the semiconductor (silicon). The relaxation time of the space charge in the semiconductor was determined experimentally during illumination of the structure.

Self-interaction of a light beam in compressed hydrogen was investigated experimentally by the schlieren method. The self-interaction was deduced from the change in the angular spectrum of the pump beam. The effect was found to be related to the change in the refractive index of H₂ resulting from the excitation of the molecular vibrations in the stimulated Raman effect.

Modes with axisymmetric polarization and azimuthal indices m = 1 and m = 2 were generated for the first time in the optical range.

A brief review is given of the most interesting papers, from the quantum electronics point of view, presented at the All-Union Conference on Plasma Physics held in Zvenigorod, Moscow Province, in February 1974.

A theoretical analysis is made of the condition for the appearance of the negative photoconductivity, and its spectral characteristics are considered. An expression is obtained for the dependence of the photoelectron density on the frequency of the exciting light. It is shown that the photoconductivity spectra can be used to determine the dopant concentration. The negative photoconductivity may find applications in optoelectronics and other branches of semiconductor laser technology. Moreover, experimental studies of the negative photoconductivity spectra may give information on the validity of various models used in calculations of the laser gain in heavily doped semiconductors.

A report is given of the characteristics of liquid crystals used in recording the spatial distribution of the intensity of thermal radiation. It is shown that such crystals can be used to obtain half-tone records of the thermal radiation field, in the same way as the photographic films are employed in the visible range.

A carbon dioxide gas-dynamic laser was operated using CO₂ + N₂ + CO + H₂O mixtures with high concentrations of carbon monoxide and with N₂ replaced completely by CO. A three-mode model was used to calculate the vibrational relaxation and the gain in a mixture of gases flowing out of a Laval nozzle.

An investigation was made of the spectral-time characteristics of the laser emission from rhodamine 6G solutions pumped with pulses up to 340 J-energy. The leading edges of the pump pulses were 1, 6, and 17 μsec. The concentrations of the solutions were 0.01–1 g/liter. An analysis of the time dependences made it possible to determine the influence of the induced losses which were due to the triplet-triplet absorption and which shifted the emission spectrum in the direction of shorter wavelengths. This analysis also yielded the losses due to the absorption in the photoreaction products, which shifted the spectrum in the direction of longer wavelengths. The competition between these losses resulted in complex changes of the spectrum with time. The conditions for the emission of a stable laser band were determined. A method was developed for the determination of the intercombination conversion constant k_ST and of the triplet lifetime τ_T from the time dependence of the emission wavelength.

Design calculations are given for image contrast amplifiers in which the saturation of an absorption line of a substance is used. Expressions are obtained for the optimal parameters of such amplifiers.

A large number of the spectral lines of lithiumlike ions of Ti, V, and Cr emitted by laser plasmas were identified. The occurence of transitions from high (n = 4–9) levels made it possible to determine experimentally the ionization potentials of TiXX, VXXI, and CrXXII. A comparison of the experimental and theoretical wavelengths indicated that the calculated results could be used in predicting the properties of ions with higher values of Z (in particular, FeXXIV). The results obtained should be useful in astrophysical and spectroscopic applications and in obtaining information on the physical conditions in hot laser plasmas.

An experimental investigation was made of the angular and power characteristics of the conversion of the CO₂ laser radiation into visible light in a nonlinear proustite crystal. The pump radiation was provided by a low-power cw krypton ion laser (λ = 676.4 nm). The spectral width of the conversion band was 11.7 cm^–1. The measured quantum conversion efficiency (6.6×10^–9) was assumed to apply also to high-power pulsed pump radiation. An estimate of the maximum threshold sensitivity attainable in a real crystal was estimated allowing for the thermal background noise in the conversion band. The estimated sensitivity was 4×10^–13 W·Hz^–1/2.

An experimental study was made of the influence of metallic and dielectric coatings on the propagation of selectively excited TE and TM modes in thin-film dielectric waveguides. The theoretical and experimental results were obtained for different metals and different waveguide thicknesses.

An analytic quasisteady function is obtained for the distributions of multiply charged ions in accordance with their degree of ionization. This function depends on the electron temperature T_e, electron density N_e, and a parameter κ. The dependence of κ on time is determined and the relationship of this parameter to the initial conditions is found. This makes it possible to describe the dynamics of formation of multiply charged ions. A specific example of the ionization and recombination of multiply charged aluminum plasma is considered and the relevant distribution functions are calculated.

A method was developed for the determination of the rate constant k_t(1) of the transfer of the vibrational energy in collisions between the DF (v = 1) and CO₂ (00⁰0) molecules. This method was based on an analysis of the delay time of the stimulated emission signal of λ = 10.6 μ wavelength. It was supplemented by allowance for the losses due to the finite value of the Q factor of the resonator and by a careful selection of the function describing the shape of the initiating light pulses. This made it possible to determine the T= 300°K value of k_t(1) which was (4.9±0.3) × 10¹² cm³·mole^–1·sec^–1 or (8.2±0.5) × 10^–12 cm³/sec. This value agreed satisfactorily with the values obtained by other methods.

An analysis is made of the possibility of using nonlinear optics methods in the visualization of infrared radiation in nonlinear spectroscopy. Various nonlinear infrared spectrometers based on this approach are classified. A detailed theoretical study is made of an "integrating" nonlinear spectrometer in which the integrated intensity of the converted visible radiation is measured. This intensity is proportional to the spectral density of the infrared radiation intensity averaged within the limits of the phase-matching band. An investigation is made of the spectral resolution, light transmission, and other characteristics of a nonlinear spectrometer. The influence of the nonmonochromaticity of the pump radiation and of the spatial divergence of the interacting waves is considered. A similar analysis is also made of the "local" nonlinear spectrometer in which the converted radiation is analyzed by a visible-light spectrometer. The results of the general theory are illustrated by calculations performed for specific nonlinear crystals.

Calculations are reported of the parameters of a rectangular-core fiber waveguide needed to achieve an efficient matching to an injection laser which is in direct optical contact with the waveguide. Simple expressions are obtained for the relationships between the permittivity discontinuity at the core-cladding interface and the optimal thickness of the core on the one hand, and the laser parameters on the other. The requirements which the passband of the waveguide must satisfy impose restrictions on the laser-waveguide coupling coefficient. If the permissible distortion of a laser pulse is 30 nsec/km, about 65% of the injection laser radiation can be coupled into the waveguide.

An analysis is made of the feasibility of "picture" informs tion processing with the aid of the electro-optic effects in liquid crystals. The dynamic scattering and the twist effect, which are not greatly affected by external perturbations, can be used in building logic devices which can deal with 10 Boolean algebraic functions at processing rates up to 10⁶ bit/sec. Such devices require no more than 50 W for the optical input, processing, and output of information. The most promising applications of such devices are matrix transformations, filtering of images, etc.

The results are given of an experimental study of changes in the shape of the surface and value of the refractive index of glass as a result of action of continuous CO₂ laser radiation. The nature of these changes is such that a plane-parallel plate acquires the properties of a lens. The optical characteristics of lenses induced in this way are considered.

A theory of the hyper-Raman scattering in gases is considered. Allowance for the polarization features of the scattering process shows that it is preferable to use circularly polarized radiation as the pump wave. It is shown that the nuclear contribution to the nonlinear polarizability of molecules may increase considerably the efficiency of the hyper-Raman scattering when an infrared laser is used as a pump source.

Microscopic amounts of HF, NO, and CO₂ molecules were detected in air and in nitrogen by the optoacoustic method using radiation of a pulsed HF laser. The minimum detectable concentration was one part impurity in 10⁶ parts of air. The absolute calibration of the recording system was performed using the absorption of pulsed CO₂ radiation in a standard mixture of CO₂ and N₂.

An investigation was made of the volume damage of sapphire and quartz crystals and of optical glasses of various kinds by laser pulses of 1–7 nsec duration. The roles of microscopic absorbing defects and of the self-focusing effect in the damage process were analyzed. It was found that they dominated the damage which occurred in real transparent media. This led to the proposal and study of a criterion of the optical purity of transparent dielectrics based on a comparison of the intensities of the Rayleigh and Brillouin scattering of light.

A quasisteady-state approximation is used in the derivation of the equations for estimating the lower limit of the maximum duration of stimulated emission from a CF₃I photodissociation laser. If the parameters of the pump source, active medium, and resonator are known, these equations can be used to determine which of the two principal quenching mechanisms of the stimulated emission—accumulation of iodine molecules or pyrolysis—limits the duration of the output pulses. This information makes it easier to optimize the parameters of this laser.

The relative quantum efficiency of solutions of 9,10–diphenylanthracene, N–phenylacridone, POPOP, and anthracene was determined as a function of the intensity of pumping with the third (353 nm) and fourth (265 nm) neodymium laser harmonics. The fall of the quantum efficiency with rising pumping intensity was attributed to the appearance of an induced absorption at the pump wavelength.

A theoretical investigation is made of photochemical polymerization waves in a gas. The wave velocity is found as a function of the external parameters such as the intensity of the exciting radiation, density of the original monomer, and constants of elementary stages in the chain polymerization reaction. The dependence of the quantum efficiency on the wave velocity is established. An analysis is made of the influence of the termination of the chain reaction on the propagation of a steady-state wave.

An investigation was made of the technology of deposition of chemical coatings on transparent substrates. A suitable selection of the coating material and an improvement in the quality of the substrate surfaces made it possible to prepare dielectric mirrors with a reflection coefficient up to 60% and an optical strength of the same order as that of the K-8 glass substrates. A nondestructive method for measuring the optical strength of coatings was developed. The problem of increasing the productivity in the manufacture of chemical coatings was considered.