Table of contents

The generation and discharge are studied in a nonchain HF laser operating on mixtures of SF₆ with hydrogen and hydrocarbons. The specific output energy of the laser is 8.8 J L^-1 (73 J L^-1 atm^-1) and the total lasing efficiency is 5.5%. It is shown that the formation and maintaining of a volume discharge in self-sustained-discharge-pumped HF lasers with a large content of electronegative gases is caused by the accumulation of the volume discharge of negative ions in conducting regions.

The dynamic analogy between the Bose condensate of photons (laser), Bose condensate of atoms, and Bose condensate of Cooper pairs in a superconductor is discussed. It is pointed out that the coherent state of Bose condensates of different types can appear only due to stimulated transitions.The equations are discussed that combine into a unified dynamic system the order parameter of the Bose condensate and the concentration of atoms beyond the condensate for an ensemble of atoms captured by a trap, as well as the order parameter of Cooper pairs, the concentration of free quasi-particles, and the densities of phonons and photons in a semiconductor.

A semiclassical phenomenological model is developed which takes into account basic processes proceeding in experiments on picosecond nonlinear spectroscopy of thin ferromagnetic films. The results of numerical simulations of the evolution of the domain structure of Ni films upon spatially uniform biharmonic pumping (BP) and upon spatially nonuniform excitation in the case of degenerate four-photon spectroscopy (DFPS) are presented. It is shown that the destruction kinetics of the film magnetisation is much slower in the case of DFPS than upon BP. This is explained by the efficient suppression of 'optical spin mixing' (the domain-structure destruction due to the spatial migration of s electrons) by potential barriers formed upon spatially nonuniform excitation of stable domain walls.

Nanometre films of pseudoisocyanine N-alkyl-substituted J-aggregates are obtained on glass substrates by spin-coating from organic dye solutions. The optical and non-linear optical properties of these films are investigated. These films are shown to possess a high optical quality over the area of size more than 30 × 30 mm and a high photochemical stability. These films feature strong absorption saturation at the maximum of excitonic absorption of the aggregates. The radiative damage threshold of the films at the maximum of the excitonic absorption was measured to be 5 MW cm^-2. The dispersion of optical nonlinearity of the films within the J-band is measured by the Z-scan and probe field methods. The films can be used as two-dimensional optical light-controlled switches.

Based on degenerate four-photon spectroscopy of ultrathin (10 — 20-nm thick) Ni, Au, and Pt films, a conclusion is made about a dominating role of interband electronic transitions in the formation of a nonlinear response of the metals in the visible spectral range. It is shown that an excited electron subsystem in films of thickness less than the mean free path is thermalized and cooled due to rapid inelastic scattering of excess free carriers on the film surface. The estimates performed for the Ni film showed that up to 10% of 20-ps pump-pulse energy could be scattered in this way producing the surface deformation. Upon spatially nonuniform excitation, the efficient 'direct' generation of surface acoustic waves is possible.

The X-ray spectra of multiply charged ions were recorded from planar agar (C₁₂H₁₈O₉)_n based targets with an average density of 2 mg cm^-3 irradiated by high-power laser pulses (λ=1.054 μm, τ=2.5 ns, I ≈ 5 ×10¹³ W cm^-2). The spectra were recorded with a high spectral and spatial resolution employing spherically bent (focusing) crystals of mica and quartz. An analysis of the experimental data obtained by the irradiation of Al₂O₃-doped agar samples allowed us to determine the main parameters of the plasma produced inside the targets. The ion temperature of plasma in low-density porous targets was estimated for the first time to be 1.5 — 2 times higher than the electron temperature.

The results of radiation resistance measurements for twelve nonlinear crystals are presented. The crystals include the well-known nonlinear CdGeAs₂, ZnGeP₂, AgGaSe₂, GaSe, AgGaS₂, and Ag₃AsS₃ crystals operating in the middle IR range, new mixed AgGaGeS₄ and Cd_0.35Hg_0.65Ga₂S₄ crystals, two-phase (orange and yellow) HgGa₂S₄ crystal, and the doped GaSe:In crystal. The mixed crystals and the two-phase HgGa₂S₄ crystal are transparent in the range from 0.4 — 0.5 to 11.5 — 14.5 μm. The measurements were performed using a pulsed single-mode highly stability TEA CO₂ laser with an output pulse duration of ~30 ns. The damage thresholds of new nonlinear AgGaGeS₄ and Cd _0.35Hg_0.65Ga₂S₄ crystals and of the HgGa₂S₄ crystal (the orange and yellow phases) were found to be 1.5 — 2.2 times higher than for the crystals operating in the middle IR range.

The production of doubly charged ions is studied upon multiphoton ionisation of Ba atoms exposed simultaneously to two radiation fields: the fundamental radiation of a colour centre laser (ω = 8800 — 8880 cm^-1) and its second harmonic. A two-electron mechanism was shown to be responsible for the production of these ions.

The variations in the population densities of Rydberg states (with principal quantum number n ~ 50 — 100) in an expanding ultracold laser plasma (N_e ~ 10⁹ — 10⁴ cm^-3, T_e ~ 10 — 0.5 K) are calculated. The electron temperature measurement from the population densities of Rydberg states (T C Killian et al., Phys. Rev. Lett., vol. 86, p. 3759, 2001) is shown to be described by the conventional three-body recombination theory with the inclusion of recombination heating of free electrons.

The propagation of whispering-gallery waves in a dynamic cavity formed by a tapered quartz rod and the plane interface between two regions of the rod with different refractive indices moving along the axis of the rod is analysed. It is shown that the limiting frequency shift of light in such a cavity is determined by its Q factor and the attainable refractive index discontinuity. The possibility of using acoustic waves for obtaining a dynamic cavity is considered.

Fast approximate statistical nonlinear algorithms (capable of real-time operation) for solving direct and inverse problems in the diffusion optical tomography are described. These algorithms were tested by reconstructing a rather complicated internal structure (containing up to three strongly absorbing inclusions no smaller than 5 mm in size) of strongly scattering and weakly absorbing large (up to 140 mm) model objects (with scattering and absorption coefficients equal to 1.4 and 0.005 — 0.015 mm^-1, respectively). Experiments were performed using cw radiation of low-power diode lasers (with input power below 20 mW) in the near IR range (between 770 and 820 nm).

The reflection spectra of a multilayer random medium — the human skin — strongly scattering and absorbing light are numerically simulated. The propagation of light in the medium and the absorption spectra are simulated by the stochastic Monte Carlo method, which combines schemes for calculations of real photon trajectories and the statistical weight method. The model takes into account the inhomogeneous spatial distribution of blood vessels, water, and melanin, the degree of blood oxygenation, and the hematocrit index. The attenuation of the incident radiation caused by reflection and refraction at Fresnel boundaries of layers inside the medium is also considered. The simulated reflection spectra are compared with the experimental reflection spectra of the human skin. It is shown that a set of parameters that was used to describe the optical properties of skin layers and their possible variations, despite being far from complete, is nevertheless sufficient for the simulation of the reflection spectra of the human skin and their quantitative analysis.

The influence of speckles on the performance of a Shark—Hartmann wavefront sensor is investigated in the eye aberration studies. The dependence of the phase distortion measurement error on the characteristic speckle size is determined experimentally. Scanning of the reference source was used to suppress the speckle structure of the laser beam scattered by the retina. The technique developed by us made it possible to study the time dependence of the human eye aberrations with a resolution of 30 ms.

A new recirculating fibre ring interferometer with an intracavity fibre amplifier and a broadband light source is developed. A substantial increase in the threshold sensitivity of the interferometer to rotation and an increase in the scale factor are experimentally demonstrated in the near-threshold regime.

The photosensitivity of detectors of laser radiation based on the natural type IIa diamond (Alameda Applied Sciences Corporation, USA) are studied at the wavelengths 222, 308, 337, and 353 nm. The limiting intensities (0.5 — 4 MW cm^-2) of UV laser radiation are determined at which the detectors operate in a linear regime.