Table of contents

A method was developed for the generation of short (down to 0.6 ns) light pulses in a dye laser pumped by a Cu laser at a high repetition frequency. When rhodamine 6G was used as the dye, the energy of a subnanosecond pulse was ~ 3 μJ for a pump energy of 250 μJ. The results demonstrated that short light pulses could be generated if the dye lasing was suppressed by the yellow line of the Cu laser.

An investigation was made of the linear and nonlinear optical properties of LiNbO₃:Zn crystals grown from congruent melts characterized by a wide range of dopant impurity concentrations. The composition dependences of the optical properties were found to be nonmonotonic and a strong suppression of photorefraction was observed at a molar zinc concentration in excess of 6%. Crystals containing more than 6% Zn were characterized by a 47% efficiency of generation of the second harmonic of YAG:Nd³⁺ radiation.

It is shown that a super-Rayleigh spatial resolution can be realized in a phase image of an object. Measurements carried out using a computer-controlled phase microscope confirm the feasibility of determination of the coordinate of an abrupt change in the height of a semiconductor structure profile with an accuracy better than 10 nm.

A single-mode fiber waveguide with zero chromatic dispersion at the wavelength of 1.55 μm was made. This fiber had a refractive index profile which was nearly triangular. The optical losses at 1.55 μm were below 0.3 dB/km.

The general principles and the state of the art of picosecond optoelectronics are reviewed. The physical phenomena underlying this field are discussed, including picosecond photoconductivity of semiconductors, electrooptic effect in crystals, and propagation of ultrashort electrical pulses in microwave transmission lines. A description is provided of the components used in picosecond optoelectronics. Characteristics of the materials employed, which influence the response time and sensitivity of specific devices, are considered. Much attention is given to the methods of generation of ultrashort optical pulses by injection lasers. The results are reported of experiments on picosecond photoconductors used as electromagnetic energy sources (Hertz dipoles) and of studies of the electrooptic Vavilov–Cherenkov effect. Descriptions are given of some applications of picosecond optoelectronic devices in physics research, metrology, and ultrafast data processing systems.

An investigation was made of the characteristics of a laser with a new active medium in the form of neodymium-activated gadolinium scandium gallium garnet (GSGG:Nd³⁺), containing chromium and emitting ultrashort pulses in the case of passive mode locking. Statistical dependences of the duration, energy, and reproducibility of the output pulses on the position of a cell with a saturable absorber (dye 3274 in ethanol) in an interferometer and on the initial transmission of the cell were determined. A new resonator configuration with an asymmetric position of the active element inside an interferometer ring was used: it ensured simple emission of the lowest transverse mode without additional spatial selection. A comparison of the main parameters of the ultrashort pulses emitted by YAG and GSGG lasers demonstrated characteristic advantages of the new active medium in generation of picosecond pulses.

A study was made of the influence of smoothing of the edge of an exit mirror in an unstable resonator on the dynamics of the spatial structure of the radiation emitted by an electron-beam-controlled CO₂ laser. Numerical methods and experiments demonstrated that the self-interaction effects in the active medium of this laser were reduced by "amplitude smoothing" of the unstable resonator mirrors. Even when traditional working mixtures were used, the level of light-induced inhomogeneities in the active medium (and the divergence of the output radiation governed by these inhomogeneities) decreased strongly when "teeth" were formed along the perimeter of a metal exit window in the unstable resonator.

A pulse-periodic garnet laser system with phase conjugation and a 0.8 J output energy was constructed using passive polarization decoupling. High energy characteristics were obtained employing a decoupled ring laser as the master oscillator, so that there was no need for a Faraday rotator normally used in such systems.

The first pulsed dye laser with an intracavity self-induced nonlinear mirror formed in a photorefractive crystal. This nonlinear mirror could be employed as a spectral selector. Equalization of the intensities of the spectral components was observed in the case of multifrequency lasing in a system comprising a pulsed dye laser and a photorefractive crystal.

Experimental and theoretical investigations were made of the influence of the HCl and Xe concentrations in a mixture on the delay time and duration of 150-J output pulses from an XeCl laser. A method for numerical calculations of the spatial distribution of the pump power in the active medium was developed and applied. A mathematical modeling of the physical processes in the active medium was carried out. It was found that the delay and the duration of the output pulses depended strongly on the Xe and HCl concentrations in the mixture. The main process governing the dependences of these parameters on the mixture composition was the absorption of laser radiation by rare-gas molecular ions, by Cl ⁻ ions, and by Xe₂Cl molecules.

Theoretical and experimental investigations were made of the interaction between two modes of one component of a Zeeman doublet in the case when the Landé factors were different for the upper and lower active levels of a laser transition.

A spectroscopic investigation was made of Nd³⁺-activated crystals of calcium niobium gallium (CNGG) and calcium lithium niobium gallium (CLNGG) garnets. The energy parameters of active elements made of these crystals were determined for the first time. The absolute efficiency of a CNGG:Nd³⁺ crystal was 3.5%, higher than the efficiency (2.7%) of a YAG:Nd³⁺ crystal of high optical quality. The average output power obtained at a pulse repetition frequency of 50 Hz for a CLNGG crystal was 40 W and the efficiency was 2.7% for an active element 6 mm in diameter and 80 mm long. A comparison of the lasing characteristics of CNGG:Nd³⁺ and CLNGG:Nd³⁺ crystals revealed a considerable superiority of the latter in respect of several parameters: the damage threshold (which was twice as high), the divergence, and the influence of a thermal lens at high pump powers. Room-temperature lasing of CNGG:Nd³⁺ and CLNGG:Nd³⁺ crystals was observed as a result of the ⁴F_3/2 ← ⁴I_11/2 transition at three wavelengths: 1059.3, 1061.5, and 1066 nm.

A description is given of a new method for design calculations of multipass systems. This method is based on some properties of the Frantz–Nodvik equation. The condition for optimal, from the point of view of the efficiency, operation of an amplifier is found. An analysis is made of the dependences of the efficiency, backward-wave gain, and degree of distortion of the pulse profile on certain parameters (small-signal gain, reflection coefficient of the mirrors, and number of passes) of an amplifier operating under such optimal conditions. A comparison is made with traditional single-pass systems.

A description is given of a method of two-dimensional diffraction calculations of the characteristics of a cw CO amplifier. The results are reported of the application of this method to a study of the brightness, spectral, and energy characteristics of a CO amplifier with a subsonic velocity of circulation of the active medium. A study is reported also of the influence of the intensity of the input radiation on the spectrum and transverse distribution of the intensity of the output radiation. A reduction in the divergence and deflection of the output radiation obtained from a CO amplifier on increase in the input signal is investigated. It is shown that variation of the divergence of the radiation along the length of the amplifier may be different for different transitions.

Stimulated Brillouin scattering and phase conjugation of HF laser radiation in compressed SF₆ (22 atm) was investigated under single-frequency (λ ~ 2.91 μm) and multifrequency (λ ~ 2.6–3.3 μm) conditions. The scattering was observed simultaneously at wavelengths of nine lines, which carried ~ 80% of the laser radiation energy. The overall efficiency of conversion of the pump energy to the reflected radiation was ~ 30%.

Second harmonic generation in nonlinear gyrotropic media in the form of epitaxial films of rare-earth iron garnets was investigated for the first time both experimentally and theoretically. The anisotropy of the process in a magnetic field, as well as the Faraday and Kerr effects were studied. In the nonlinear interaction case the Faraday effect was half that in the linear case. An expression was obtained for describing the Faraday and Kerr effects for the case of a nonlinear interaction involving a semiinfinite nonlinear gyrotropic medium and a nonlinear gyrotropic layer: a characteristic feature of these effects was a nonlinear coordinate dependence. The experimentally observed characteristics of the two effects were explained by a model allowing solely for the linear magnetooptic parameters of the medium. Possible mechanisms of the appearance of the nonlinearity in iron garnets in a magnetic field were analyzed.

A nonlinear change in the spectral characteristics of quartz glass under the influence of excimer laser radiation was discovered and investigated for the first time. The change was attributed to two-stage absorption of λ = 248 nm laser radiation by defect complexes of the oxygen vacancy type. A study was made of the kinetics of thermal recovery of the initial spectral properties of laser-irradiated quartz glasses as a result of recombination of the products of laser ultraviolet photolysis.

A method is proposed for the determination of the nature of the scattering process and of the energy contribution of each type of scattering to a phase-conjugate wave by means of an interferometer with mirrors capable of phase conjugation of the wavefront. Phase conjugation of free-running laser pulses is shown to occur as a result of two competing processes of stimulated Brillouin and stimulated thermal scattering. The results are reported of an experimental determination of the fractions of the energy contributed by each type of scattering to a phase-conjugate wave.

A numerical experiment was carried out on resonant interaction of ultrashort light pulses with a radially symmetric power distribution. It is shown that in the case of an exact resonance the result of diffraction by a light-induced "bleached stop" in a beam gives rise to ring-shaped power distribution zones. An increase in the area under the profile of an ultrashort pulse results in a redistribution of the beam power out of its core to the peripheral ring zones. Detuning of the field frequency from the exact resonance blurs the ring structure of the beam.

The fraction of the energy propagating within an angle close to the diffraction limit was measured by a double-pass laser system with phase conjugation. The measurements were carried out at the fundamental frequency and at harmonics of this frequency. The brightness of the harmonics was considerably higher than that of the fundamental-frequency radiation. An analysis was made of the factors preventing the attainment of the theoretical brightness maximum. The results obtained were interpreted by assuming a combined influence of wave aberrations and a partial spatial coherence of the original fundamental-frequency radiation.

Theoretical and experimental investigations were made of the compensation of distortions experienced by laser radiation in a turbulent medium. Use was made of a phase-conjugating stimulated Brillouin scattering mirror. An increase in the structure characteristic of the fluctuations of the permittivity of the medium reduced the parameter representing the precision of the correction of the laser beam distortions.

Phase conjugation of XeCl excimer laser radiation (λ = 308 nm) as a result of stimulated Brillouin scattering in a multimode quartz fiber was observed for the first time. The scattering threshold and the frequency shift were determined and an approximately threefold reduction in the duration of the scattered radiation pulses was achieved.

The rate equations representing the populations of the states of an H-like ion characterized by m ≤ 10 are solved numerically allowing for reabsorption of the radiation emitted in the form of m = 2, 3, 4 → m' = 1 lines broadened by the thermal and dynamic Doppler effects in a planar plasma layer. An allowance is made for the effects responsible for the partial redistribution of the frequencies in the course of reemission in a collisionless plasma. Calculations are reported of the gain for the 4–3 transitions in the Al XIII ion, and of the emission and absorption spectra of the Ne X and P XV ions.

Experimental and theoretical investigations were made of the photoluminescence, scattering, and infrared absorption in quartz optical fibers. The temperature dependences of the intensities of the Raman and Brillouin scattering, and of the photoluminescence excited by light of diiferent wavelengths were determined. The transmission spectra of the fibers were recorded in the infrared part of the spectrum at various temperatures. The frequency shift of the Brillouin scattering lines increased as a result of longitudinal elongation of the fibers. The results obtained were used to consider the prospects for constructing distributed fiber-optic sensors of various physical parameters.

A two-dimensional theoretical model is developed for the description of the transfer of energy from a surface-breakdown plasma, maintained by CO₂ laser radiation, to a target. An investigation is reported of the efficiency of the interaction of laser radiation with a target as a function of the radiation intensity and spot size. A strong localization of the laser interaction is shown to be due to a heat-conduction energy flux, whereas the energy deposited outside the irradiation spot is due to radiative energy transfer at ultraviolet frequencies.

An investigation was made of the feasibility of reaching the quantum limit of the sensitivity of a projection system with a brightness amplifier, including a laser amplifier and a phase-conjugating mirror. A sensitivity of about 5 photons per resolution element was achieved in the near infrared (λ = 1.06 μm) when the number of elements in the field of view was ~ 350 × 350.

An experimental investigation was made of the refraction of microsecond CO₂ laser pulses in a surface-breakdown plasma. The existence of the focusing and defocusing stages depended on the interaction parameters such as the pulse energy, focusing angle, and density of the surrounding air. A correlation was found between the space–time distribution of the radiation reaching a target and the stages of development of the surface breakdown. A qualitative theoretical explanation of the results was also provided.

An investigation was made of a double radio–optical resonance (DROR) in a multilevel system of the alkali metal type. Equations for the density matrix were solved to obtain expressions for the signal, DROR line width, and shift of the maximum of DROR line peak. A study was made of the principal characteristics of a DROR in an optically dense medium in the form of a rubidium vapor. The ultimate short-term frequency instability of a rubidium discriminator was estimated to be 2 × 10 ^{− 14}t^{− 1/2}. Several experiments were carried out using an injection laser as an optical pump source. The results of the measurements yielded a short-term instability of 3 × 10 ^{− 12}t^{− 1/2}. An investigation was made of the optical frequency shift and an anomalous dependence of the shift on the intensity was observed. The results of the experimental and theoretical investigations were compared. The requirements for stabilization of the DROR parameters needed to reduce the frequency instability of a rubidium discriminator to the 10 ^{− 14} level were identified.

A new aperture-tagging algorithm for adaptive optical systems with multichannel phase modulation is proposed and investigated. It has a number of advantages over the familiar gradient methods. The use of this algorithm makes it possible to eliminate the dependence of the controlling signals in control channels on one another and to reduce the response time of the system.

A nonreciprocal phase shift experienced by both the pump and output waves, which appeared in the presence of linear aberrations in a photorefractive-crystal loop resonator, was compensated by a frequency shift or by generation of other longitudinal and/or transverse modes. A theoretical model describing the experimental results was developed.

An investigation was made of the influence of heating in the temperature range 20–900 °C on the losses and backscattering signal observed in quartz fiber waveguides with SiO₂–GeO₂–P₂O₅ and SiO₂–GeO₂ cores. The temperature sensitivity of the backscattering signal was 0.33 × 10 ^{− 3} dB/°C in the range 20–750 °C and 0.5 × 10 ^{− 3} dB/°C in the range 20–850 °C, respectively. In the case of the fibers with the SiO₂–GeO₂–P₂O₅ core the backscattering signal increased irreversibly because of heating by an amount which depended on the maximum temperature reached in the experiments.

A theoretical investigation is made of an optical absorption bistability in a Fabry–Perot interferometer filled with a nonlinear medium exhibiting reversible optical bleaching due to interaction with radiations with two different wavelengths. It is shown that the optical feedback efficiency can be enhanced, which makes it possible to reduce significantly the requirements in respect of the level of the residual absorption by the nonlinear medium.