Table of contents

A series of publications devoted to the study of collisional deactivation of Xe atoms in the 6s and 6s' states in high-pressure Ar — He and He — Xe mixtures with a low content of Xe is summarised. The processes of quenching of the *P₁, *P₀, *P₁, and *P₂ levels are studied in two-particle Xe*+Ar(He) → products+Ar(He), three-particle Xe*+ 2Ar(2He) → ArXe*(HeXe*+Ar(He), and three-particle Xe*+Xe+Ar(He) → Xe*₂+Ar(He) collisions. The gases were excited by a fast-electron beam. The measurements were performed by the method of absorption probing by analysing the time dependence of the concentration of the excited states in the afterglow of the electron beam. The rate constants of 24 plasma-chemical reactions were measured, 17 of which — for the first time.

A 308-nm XeCl laser with an active volume of 200 L is described and the results of its tests are presented. The output energy of 660 J is obtained by pumping the Ar : Xe : HCl = 1520 : 40 : 2-Torr mixture. The FWHM laser pulse duration is ∼350 ns. The nonuniformity of the laser-radiation density distribution over the cross section of the output beam in the near-field zone is within 10%. An accelerator that forms a radially converging electron beam with an electron energy of up to 550 keV, a vacuum-diode current of up to 320kA, a beam-current pulse duration of ∼1 μs, and a beam current of up to 250 kA is used to pump the system. Two linear transformers with a 98-kJ energy stored in the primary storage serve as high-voltage sources. To reduce the effect of the self-magnetic field on the beam formation, the vacuum diode is divided into six diodes magnetically insulated from each other.

An H₂ — F₂ amplifier initiated by a resonant vibrational excitation of HF molecules by a pulsed hydrogen fluorine laser is theoretically simulated. Numerical calculations are performed with allowance for an inhomogeneity of the initial HF concentration that appears due to specific features of preparing the experimental laser mixture. The estimated energy output for a mixture of H₂ : F₂ : O₂ : He = 100 : 600 : 30 : 100 Torr is 10 — 20 JL^-1 for an average initial HF pressure along the amplifier axis of 0.1 — 0.5 Torr. The laser-radiation energy gain on a length of 4 m is 5 — 10.

Superluminescent diodes (SLDs) based on a three-layer quantum-well (GaAl)As heterostructure with a bent active channel emitting in the spectral range from 820 to 840 nm are studied. The diodes can operate without thermal stabilisation in the temperature range between -55 and +93 °C emitting 0.1 mW of optical power at the output of a single-mode fibre. They offer a significant advantage in operating currents and power consumption over conventional SLDs based on a bulk separate-confinement double heterostructure.

Superluminescent diodes based on a separate-confinement (GaAl)As heterostructure are studied in the 850-nm spectral region. A contact p⁺-GaAs layer in the output sections of a narrow active channel of width 4 μm was removed and a metal contact was not deposited. These sections played the role of saturable absorbers. This design provided a significant increase in the catastrophic optical damage threshold and ensured 250 mW of output cw power at the diode facet. The power coupled out through a single-mode fibre in the case of a simplest coupling achieved 110 mW.

A new scheme of a fibre Raman laser emitting at two wavelengths is proposed. The scheme uses a one-stage Raman converter with the output Bragg grating with the reflectivity above 99%. Lasing at two wavelengths is achieved due to the overlap of the output emission spectrum with the reflection spectrum of the output Bragg grating.

The orientation anisotropy of a molecular gas induced by a high-power femtosecond pulse is studied by the method of direct numerical integration of the nonstationary Schrödinger equation. The contribution of the anisotropy to the nonlinear polarisation of the gas is calculated. It is shown that the orientation nonlinearity caused by the efficient alignment of molecules along the laser field is accompanied by a considerable repopulation of the rotational levels of a molecule and cannot be described by the perturbation theory. It is found that the inertia of this nonlinearity depends on the laser-field strength.

The third harmonic generation in plasma ionised by a high-power pump field is theoretically studied. The dependences of the harmonic generation efficiency on the electric pump-field strength and polarisation are found. It is assumed that the observation of the maximum of generation efficiency at the nonzero pump-field ellipticity is the universal property of the harmonic generation. This effect is nonlinear and has a threshold.

A theory of the interaction between light waves in polydomain crystals with a random variation in the domain thickness described by a random telegraph process is developed. The second harmonic generation and parametric amplification upon high-frequency pumping are considered. It is found that the maximum efficiency of nonlinear conversion is achieved when the phase mismatch between the interacting waves is equal to the doubled spatial frequency at which the nonlinearity sign is changed (the condition of stochastic quasi-phase matching).

Quasi-phase-matched second harmonic generation at 542 nm by self-frequency doubling laser radiation at 1084 nm and quasi-phase-matched sum-frequency generation at 464 nm by summing frequencies of laser radiation and of nonabsorbed fraction of diode laser pump radiation at 810 nm are experimentally achieved. These processes are realised in a Q-switched laser based on a periodically poled active nonlinear Nd : Mg : LiNbO₃ crystal.

Stimulated Raman scattering of femtosecond pulses in a photonic crystal consisting of alternating quarter-wave dielectric layers and layers of a nonlinear-scattering medium is calculated taking into account the quantum fluctuations of the medium polarisation. Analysis of the calculations showed that the Stokes pulse duration and intensity depend substantially on the statistic properties of polarisation. The efficient SRS conversion in a photonic crystal occurs under certain dispersion conditions providing the minimum difference between dispersions of the pump and Stokes frequencies, which are determined by the length and the number of periods of the photonic crystal.

Optical losses in single-mode and multimode optical fibres heavily doped with germanium oxide and phosphorus oxide are studied. Optical losses in multimode fibres in a broad spectral range are found to be much lower than in single-mode fibres with the same concentration of dopants. The study of few-mode fibres showed that the core — cladding interface is the region of excess optical losses. The reasons for the observed relation between optical losses in single-mode and multimode fibres are discussed.

A broadband radiation source emitting in the 1.03 — 1.1-μm spectral region is built. The −3-dB level width of the emission spectrum of the source is 47 nm at the maximum output power of 22 mW. An Yb-doped fibre twisted with a passive fibre is used as the active medium in the source. The source is pumped through the passive fibre.

The operation principle of a quantum computer is proposed based on a system of dielectric nanoparticles activated with two-level atoms — cubits, in which electric dipole transitions are excited by short intense optical pulses. It is proved that the logical operation (logical operator) CNOT (controlled NOT) is performed by means of time-dependent transfer of quantum information over `long' (of the order of 10⁴ nm) distances between spherical nanoparticles owing to the delayed interaction between them in the optical radiation field. It is shown that one-cubit and two-cubit logical operators required for quantum calculations can be realised by selectively exciting dielectric particles with short optical pulses.

A method is analysed for obtaining laser beams with a phase singularity with the help of phase screens described by the function of the type exp(ilϕ). It is shown that this method is used to obtain laser beams in the form of single rings with a smooth intensity distribution in the far-field radiation zone (at the lens focus) representing the superposition of Laguerre — Gaussian modes. In the near-field zone and, in the presence of aperture clipping, also in the focal region, the beams with a more complicated structure can be observed. The scaling of the radius corresponding to the maximum intensity of the beam both in the absence and presence of aperture clipping occurs linearly with the singularity charge l. The influence of the beam decentration and of the phase screen on the structure of phase-singularity beams is estimated.

The frequency shift of a short electromagnetic pulse interaction with a plasma-like medium is discovered and studied. The shift is caused by elastic collisions of free electrons with ions or neutral particles.

The possibility of exciting convective motions with a toroidal symmetry in a disordered liquid-crystal cell with an open surface, which is locally heated by a Gaussian laser beam, is demonstrated experimentally. A perturbation of the free surface of the liquid crystal and a convective hydrodynamic motion are determined by temperature gradients. It is shown that a radial distribution of the director of a nematic liquid crystal appears in the convection region. Under certain experimental conditions, soliton-type hydrodynamic orientation waves are observed at the free surface of a nematic liquid crystal. It is found experimentally that the velocity of these waves is determined solely by the liquid-crystal parameters and is independent of the incident laser-radiation power.

A new optical device — an objective with deformable mirrors and parameters controlled in the dynamic regime is proposed. The computer simulation of the objective is performed. The dependences of some parameters of the objective on the control voltage are determined. The simulation showed that the ranges of control of the rear focal segment and the focal distance for the objective with the focal distance 602 mm were 1057 and 340 mm, respectively, which is substantially greater than in the control of an equivalent deformable mirror.

An acoustooptic generator in which the feedback signal is produced using optical heterodyning is studied theoretically and experimentally. The development of oscillations in this system is analysed by computer simulations. It is shown that the competition of modes caused by nonlinearity of the acoustooptic interaction can result in the degeneration of the generation spectrum and the establishment of a single-mode regime. The dependence of the generator linewidth on the parameters of the system is studied.

Based on the Talbot effect, a method is developed for measuring the phase-to-amplitude ratio for gain gratings in saturated laser media. Experiments performed by this method showed that the gain grating induced in a Nd : YAG crystal is predominantly the amplitude one, with the phase-to-amplitude ratio of no more than 0.3 under our experimental conditions.

A pulse generator is developed for pumping electric-discharge excimer lasers in which the capacitive energy storage is connected with the gas-discharge chamber of the laser with the help of a multichannel spark switch via a low-inductive strip line. This scheme of the generator reduces energy losses in the switch and the inductance of the discharge circuit of the capacitive storage. For the pump power equal to 800 MW, the efficiency of the stored energy transfer to a load achieves 85%. To ignite a homogeneous volume discharge, the generator produces a prepulse, which initiates a low-current volume discharge in the gas-discharge chamber. Upon excitation of an electric-discharge XeCl laser with the 3 × 5.4 × 80-cm active region and the Ne : Xe : HCl= 2000 : 2.5 : 1 mixture at a pressure of 4 atm, radiation pulses with energies up to 3.4 J and the FWHM duration up to 260 ns were obtained with a homogeneous energy distribution over the laser aperture.

Experimental studies are performed which demonstrate the use of dynamic gratings in a thin surface layer for investigations of the properties of solids strongly absorbing light. Methods are proposed for measuring the temperature conductivity χ of a gas adjacent to a surface and of a thin transparent film on the absorbing surface. The optical measurements of χ for porous silicon films on a substrate are performed.