Table of contents

Studies of the photophysical and photochemical processes accompanying the photolysis of UF₆ molecules in the field of UV and IR laser radiation are analysed. The characteristic features of the electronic and vibrational absorption spectra are discussed. The excited states and transitions as well as the molecular deactivation and dissociation channels are identified. The influence of secondary processes on the quantum yield and the photolysis yield is determined. The photolysis of UF₆ molecules in the presence of chemically active reagents and buffer gases is considered. The isotopically selective laser photolysis of UF₆ molecules as a method for the separation of uranium isotopes, as well as other prospects for the application of the laser photolysis of UF₆ molecules in nuclear power engineering, are discussed.

The propagation of a probe field in a medium consisting of two-level atoms, degenerate in relation to the J_g = 1/2 → J_e = 1/2 transition, is examined. The atoms are pumped by a circularly polarised resonant field in the presence of a static magnetic field. It is shown that under these conditions one of the normal waves may be amplified in the absence of inversion in the medium. In strong optical and magnetic fields, inversion-free amplification is possible for a pump with a finite spectral width, which may be much greater than the natural width of the excited level.

An investigation was made of the propagation of partially coherent radiation in refractive media with strong absorption when account must be taken of the ray trajectory curvature owing to the inhomogeneity of the imaginary component of the relative permittivity of the medium. This investigation was carried out on the basis of the equation for the coherence function. It is shown that the equation can be reduced to a system of ray equations permitting construction of effective numerical algorithms for its solution. A self-similar solution was obtained for the coherence function in the case of a parabolic distribution of the relative permittivity of the medium and an initially Gaussian distribution of the average radiation intensity. In the geometrical-optics approximation, an equation was derived for the ray trajectorys of partially coherent radiation. The distinctive features of the propagation of coherent and partly coherent Gaussian beams, with the same Fresnel numbers, in an inhomogeneous medium were discovered.

A description is given of a detailed nonsteady-state multiwave kinetic model of a laser, based on xenon atom transitions with λ = 1.73, 7.03, 2.65, 2.63, 3.37, and 3.51 μm in an He — Ar — Xe mixture pumped by a hard ioniser. The proposed kinetic model is tested against the results of experiments on electron-beam pumping of an Xe laser containing pure xenon, as well as binary and ternary mixtures. Numerical modelling is used to identify the main mechanisms pumping the upper active levels: three-particle recombination of atomic Xe⁺ ions (He — Xe mixture), dissociative recombination of molecular Xe₂⁺ ions (pure Xe), dissociative recombination of molecular ArXe⁺ ions and electron excitation from the 6s' xenon atom states in an (He) — Ar — Xe mixture. It is shown that the contribution of each of the mechanisms to pumping of the upper active level is determined by the composition and pressure of the mixture.

The results of calculations based on a new detailed nonsteady-state multiwave kinetic model of a laser based on xenon atom transitions with λ = 1.73, 2.03, 2.65, 2.63, 3.37, and 3.51 μm in an He — Ar — Xe mixture were compared with the results of experimental studies of a nuclear-pumped xenon laser carried out making use of several experimental setups. A satisfactory agreement between the calculations and experiments was achieved. The causes of the impairment of the nuclear-pumped xenon laser characteristics with increase in the temperature of the medium were discovered. It was found that nuclear pumping of a Ar — Xe mixture can result in attaining a lasing efficiency up to 3.5%. A laser nuclear-pumped by the VIR-2M reactor was fully optimised.

The design of the 'Foton' electric-discharge laser, optimised for operation on the basis of KrCl* molecules, and its energy parameters were investigated. At λ = 222 nm the radiation energy was up to 250 mJ per pulse. The specific output radiation energy was 2.5 J litre^-1 and the laser efficiency was in excess of 0.8%. The possibility of further improvement of the characteristics of electric-discharge KrCl lasers are discussed.

The fundamental principles of the operation of a solid-state laser are presented for the case when the active element is a thin disk. An analytical model of this laser is developed. The model is used to calculate the influence of the various parameters on the operational efficiency of the laser. A detailed model is also developed for calculations relating to a specific laser design and this model takes account of the geometry of the active medium, of the diode pump configuration, and of the operating conditions. Experiments yielded a cw output power up to 350 W and an optical pumping efficiency of ~ 50% (the corresponding values obtained in this single-mode regime were approximately 100 W and 440%). These results were obtained below 0 °C for eight passes of the pump radiation through the active medium. At room temperature and for 16 passes the same parameters were several tens of watts and an efficiency up to 58%. These experimental results were in good agreement with the predictions of the theoretical model.

A multifunctional single-frequency submillimetre (sub-mm) optically pumped laser with rapid replacement of the active medium was investigated experimentally. The output characteristics of the laser were obtained for different parameters of the medium and the cavity. The lasing frequency shift of the sub-mm laser was studied as a function of the pump frequency (~39 Hz kHz^-1). A method of stabilising the frequency of the sub-mm laser by phase locking to a microwave frequency synthesiser is briefly described.

Saturated-absorption resonances were investigated experimentally in He — Ne/¹²⁷I₂ lasers pumped by a transverse rf discharge. The much lower amplitude noise reduced sixfold the laser frequency instability, compared with the frequency instability of a laser pumped by a dc discharge, down to 5 × 10^-13 for an integration time of 100 s. The modulation shifts of the radiation frequency of stabilised He — Ne/¹²⁷I₂ lasers were investigated with a high accuracy and over a wide range of frequency deviations (1.5 — 20 MHz). The nature of the asymmetry of the saturated-absorption resonances, resulting from the joint effect of the lens-like properties of the nonlinearly absorbing medium and of the elastic velocity-changing collisions of absorbing medium molecules was clarified.

The divergence of the radiation from a repetitively pulsed electric-discharge transversely excited XeCl laser with an unstable cavity and asymmetric coupling-out of the radiation was studied experimentally. A cavity with convex mirrors made it possible to generate radiation with a near-diffraction divergence and to retain the energy at the level of 40% — 50% of the energy of a laser with a plane — plane cavity. The generation of a circular spot with a uniform intensity distribution by focusing a rectangular beam is described. Calculations and experiments are used to show that this phenomenon does not arise from diffraction and is not a result of the interaction of the laser radiation with the medium or with the target material.

The influence of an additional perturbation (the ac Stark effect) of neutral barium atoms on the formation of doubly charged ions in the course of ionisation of these atoms by visible light (by the second harmonic radiation of an yttrium-aluminium garnet laser) was investigated experimentally. The frequency-tunable radiation of a colour-centre laser (ω = 8500 — 8950 cm^-1 ) was used in these investigations to effect the additional perturbation of barium atoms. It was found that this perturbation changed the mechanism of formation of the doubly charged Ba²⁺ ions from a stepwise to a two-electron mechanism. The yield of the Ba²⁺ ions increased sharply under these conditions.

A series of studies was carried out on the ablation of steel, Si₃N₄ ceramic, and diamond in air by femtosecond (200 and 900 fs) pulses of different wavelengths (532 and 266 nm) and in a wide energy density range (1 — 10³ J cm^-2 ). The ablation rates were measured for different geometries of the irradiation surface [a shallow crater and a channel with a high (up to 10) aspect ratio]. The ablation rates (in a shallow crater) and the morphologies of the irradiated surface were compared for femtosecond and longer (220 ps, 7 ns) pulses. The role of the laser-generated plasma in the ablation of materials by subpicosecond pulses as well as the prospects for the practical application of ultrashort laser pulses in the processing of materials are analysed.

The characteristic features of stimulated light scattering and optical parametric oscillation in noncollinear wave interactions, excited by radiation with the wavelength λ_p = 532.1nm in the xy plane of a KTP crystal, were studied experimentally. Stimulated scattering on polaritons was observed on excitation of the KTP crystal, by an ordinary (o) beam. Radiation in the far IR was generated within the crystal at the wavelength λ_r ≈ 52 μm and the frequency ν_r = 192.3 cm^-1. The generation and amplification of Stokes radiation with λ_s1 = 537.6 nm were achieved (frequency shift~192.3 cm^-1 ) with an efficiency of ~18% at 22 °C. It was established from the threshold oscillation characteristics that the stimulated scattering gain was ~30 cm GW^-1 . Simultaneous parametric generation of two collinear signal waves with λ_so = 1054.5 nm and λ_se = 1069.2 nm and two noncollinear idler waves with λ_ie = 1074.1 nm and λ_io = 1059.3 nm was observed on excitation by the extraordinary (e) beam. Addition of the frequencies of two collinear signal waves in the KTP crystal led to the appearance of anti-Stokes radiation with λ_as = 530.9 nm.

It is shown that the currently available traps for cooled atomic beams, which are analogues of optical wave-guides for the de Broglie waves, are capable of transmitting quantum images. This process consists of expansion of the input image as a series in terms of the eigenfunctions of a two-dimensional potential well (waveguide) and the transmission of information about the terms of this series by travelling de Broglie waves to a section of the waveguide (remote from the input) where the initial image is synthesised as a result of the cophasal superposition of the terms of the series.

Temporal separation of photons in an ultrashort laser pulse transmitted through a strongly scattering medium was reliably observed in experiments. The selected combination of the initial pulse parameters and of the characteristics of the scattering medium made it possible to ensure conditions necessary for the generation of a bimodal temporal profile of the transmitted radiation.

Measurements were made of the Kerr constants of several mineral and silicone oils. The results indicate that these oils can be used to improve the sensitivity of measurements of the quadratic electro-optical effect in crystals. The possibility of using the electro-optical Kerr response of oils to determine experimentally the distribution of the electric field in high-voltage devices is discussed.

The intracavity absorption spectra of CO₂ and H₂O in the range 2.03 — 2.05 μm, as well as NH₃ and CH₄ in the range 2.23 — 2.26 μm, were obtained with the aid of a Co:MgF₂ laser. It was found that an intracavity laser spectrometer based on a Co:MgF₂ laser emitting for 1 ms can be used to detect many impurity gases in the atmosphere at a concentration level of (1 — 40) × 10^-9.