Table of contents

A new laser with frequency self-doubling in an orthorhombic Nd³⁺: β'-Gd₂(MoO₄)₃ crystal was constructed.

The Coulomb broadening of a magneto-optical resonance of degenerate two-level ions in the field of a standing wave is calculated. Under the conditions of linear polarisation of this wave, of the normal Zeeman effect, and of weak saturation, the broadening is described by familiar expressions for multistage and two-photon resonances in separate three-level subsystems and the coefficients in these expressions depend on the angular momenta. The profile of a nonlinear resonance in the dependence of the output power of a single-frequency Zeeman ionic laser on the applied magnetic field consists of a narrow central interference peak, a wide diffusion part, and Lorentzian wings. It is shown that, in the case of a broad lower active level, the J → J+1 transitions are more favourable for the observation of a two-photon resonance and the relative amplitude of the resonance is not less than 2/7.

An experimental investigation was made of the energy and temporal characteristics of a gas-discharge excimer ArF laser (λ =193 nm) with gaseous mixtures containing He as the buffer gas. An RU-65 spark gap was used. The parameters of a high-voltage excitation circuit, of the LC inverter type with automatic UV preionisation, were optimised. A gaseous active mixture had the He : Ar : F₂ = 79.7 : 20 : 0.3 composition and the total pressure was 2.5 bar. An efficiency of 1.5%, relative to the stored energy, was obtained for the first time for an output radiation energy of 360 mJ. The maximum output energy of the ArF laser was 550 mJ; the corresponding efficiency was 1.36% and the pulse duration at half-amplitude was 12ns.

The parameters of an XeCl laser with a 25 cm × 25 cm aperture, excited by two oppositely directed electron beams, were calculated and determined experimentally. The energy of the output pulses of 250 ns duration at half-amplitude exceeded 200 J, the small-signal gain was g₀ = 0.065 cm^-1, and the unsaturated absorption coefficient was α₀=0.015 cm^-1 for the optimal composition (Ar : Xe : HCl = 700 : 10: 1) of the mixture at a total pressure of 2.5 bar. The laser efficiency, calculated relative to all the energy deposited in the active volume, was 3.0%.

A numerical and theoretical investigation was made of amplified spontaneous emission (ASE) from an x-ray laser in which a gain zone appears in a plasma on irradiation of a thick target and is characterised by an asymmetric concave profile of the electron density. An analysis is made of the power, angular divergence, and spatial coherence of the ASE from flat and bent targets. In the case of a flat target a confirmation is obtained of the experimental observation that the ASE coherence length has a strongly nonuniform distribution across the beam in the far-field zone. The optimal bending of the target makes it possible not only to reduce the divergence of the ASE and to increase considerably its power, but also to enhance coherence and ensure a uniform distribution of the coherence length across a beam. In the case of a bent target, the coherence can be improved additionally by creating a convex electron density profile in the gain zone.

An experimental investigation was made of the influence of rare-gas impurities on the emission of the third continua. A kinetic model developed on the assumption that these continua result from transitions in molecular ions from R₂⁺* states [corresponding asymptotically to the ground state of an R⁺ ion and an excited state of an R*(³P_1,2) atom] to R₂⁺ states (corresponding asymptotically to the ground states of an R⁺ ion and an R atom). This model made it possible to predict the rates of quenching of the R⁺* and R₂⁺*(1, 2) states. According to this interpretation, it is doubtful whether lasing is possible in Xe and Kr.

An experimental investigation was made of the formation of a channel in the process of hole punching in glass by pulse-periodic radiation from a cw CO₂ laser in the presence of a concurrent stream of air reaching the target. The dependence of the punching velocity on the air pressure in the laser-radiation intensity range 40–270 kW cm^-2 and the rate of change of the hole radius were determined. The frequency of oscillations of the channel walls in the course of punching was measured. Formation of quasiperiodic structures on the channel walls was observed.

The first precision (with an error of 0.4–1.6 mÅ) measurements were made of the wavelengths of x-ray spectral lines emitted as a result of n=4 — n'=2 transitions in the Ne- and Na-like Kr XXVII and Kr XXVI ions. The spectra were recorded by means of a spectrograph with a spherically bent mica crystal, characterised by a spectral resolution λ/Δλ ≈ 5 × 10³. The dispersion characteristic of this crystal was determined with the aid of reference lines, which were emitted by the He-like Ar XVII ion. The wavelengths of a series of dielectronic satellites of the resonance line of the Ar XVII ion were identified and measured. The results obtained were compared with calculated data.

A theory of the interaction of a powerful laser radiation pulse with a low-density porous material is proposed. This theory describes satisfactorily the experimental results. It is shown that internal evaporation of the solid components of such a material into the surrounding cavities of the medium leads to interesting features of the interaction of a laser pulse with the medium: formation of a region of radiation absorption under conditions of increasing geometric opacity of the material, volume absorption of laser radiation in the material of density higher than the critical plasma density, and formation of a nonequilibrium plasma with a preferentially heated ionic component. A hypothesis is put forward and justified that it should be possible to construct a powerful neutron source operating on the basis of laser excitation of hydrothermal dissipation in a spatially structured medium.

Two-dimensional numerical calculations were made in a study of the symmetrising effect of an x-ray prepulse on the inhomogeneity of laser target compression. It is suggested that a two-stage target, with its outer stage formed by a thin metal layer, can be used to generate such a prepulse. Correct selection of the parameters of this layer and of a laser prepulse can ensure symmetrisation of the inner working target with minimal undesirable preheating of the fuel. Such a target is accelerated and compressed at the expense of the energy of the main laser pulse. The influence of a large-scale asymmetry of irradiation, associated with a specific geometry of the radiation reaching the target, may be reduced by a suitable variation of the shell thickness.

Anomalous self-reversal of the aluminium emission lines 396.1 and 394.4 nm was detected experimentally. The lines emitted by the hotter regions of a laser plasma on the surface of an aluminium target did not coincide with the absorption lines of the same atoms in colder regions of the plasma plume. Consequently, the centre of a dip in the emission lines, resulting from self-absorption, was not at the line centre. A qualitative explanation of the effect was based on a shock-wave-induced Stark shift of an emission line of a hot plasma region.

Series of liquids are proposed for use as optical components, and as laser cavities and waveguides. Pulsed pumping of such cavities at λ = 532 nm resulted in lasing in the range 630–640 nm, which was investigated. Special features of liquid optical components used as sensors and employed in investigations of a variety of nonlinear processes were considered. The use of volatile fluoro-organic compounds, which reduce the surface tension when in contact with liquids, induced a self-organising capillary instability of optical and laser components with constant wave-like or chaotic motion of their surface layers.

Multilayer cobalt—carbon mirrors on Si(111) substrates were made by electron-beam deposition and polishing of the metal layers by Kr⁺ ion bombardment. A new spectroscopic method was developed for estimating the parameters of plane multilayer x-ray mirrors by illuminating a sample with broad-band radiation from a laser-plasma source and by subsequent dispersion of this radiation with a diffraction grating operating in the transmission mode.

It is shown that among degenerate modes of a confocal cavity there are field distributions which can be described as Gaussian beams of the elliptical type. These modes can be excited in cavities with elliptical or rectangular apertures, and they can be used to increase the efficiency and beam quality of the lasers with rectangular active elements. A numerical simulation is carried out for the Fresnel number N=1, stability in respect of possible cavity misalignments is demonstrated, and the losses per round trip are calculated for some of the lowest-order modes.

Nonlinear optical properties of CuS and oxidised CuS (R=5 nm) nanocrystals were investigated by the method of picosecond absorption spectroscopy. Oxidation of nanocrystals gave rise to an absorption band in the region of 1.09 μm. This band was bleached by excitation with laser pulses of 15 ps duration. An energy level diagram was proposed for oxidised CuS nanocrystals.

The structure and spatial positions of dynamic gratings responsible of steady-state four-wave mixing are determined for nonlinear media with a nonlocal response. It is shown that an analytic solution found for a double phase-conjugate mirror is fundamental and that it can be used to obtain solutions for such a mirror when two pump beams are present.

It is shown that the efficiency of a cubic nonlinear optical response of matter, defined as the ratio of the cubic nonlinear susceptibility to its relaxation time, may reach ∼ 10⁸ cm² J^-1 for electronic mechanisms of this response. This is 10³—10⁴ times higher than the value achieved so far. The conditions for attaining the maximum efficiency are found.

A laser phase microscope with a conventional optical system was used to obtain images of latex spheres 100 nm in diameter, of various viruses, and of other microscopic objects. Satisfactory images were obtained when the focusing was exact ( ∼30 nm) and the numerical aperture of the objective was large. Specific properties of subwavelength phase images and typical artefacts in the images of submicron structures were analysed.

It is proposed to use a multipass cavity to increase the efficiency of multistage selective photoionisation of atomic vapours. A simple analytic model is used to describe the efficiency of utilisation of radiation in a zero-dimensional cavity filled with a two-level absorbing medium. A numerical calculation is made of the kinetics of multistage selective ionisation of ¹⁶⁸Yb in a zero-dimensional cavity, taking account of 10 energy levels of different isotopes. It is shown that the use of a cavity can increase the yield of the selectively ionised isotope by an order of magnitude.

An experimental investigation was made of the interaction of radiation from a frequency-selective pulsed electron-beam-controlled discharge CO laser on polymer materials (nylon and polyethylene terephthalate) with intense absorption bands near the wavelength ∼ 6 μm. The parameters of the interaction (geometry and method of irradiation of a material; temporal, spectral, and energy characteristics of the laser radiation) corresponding to the appearance of microstructures of different types on the surface of the processed material were determined. An analysis was made of the relationship between the structural changes in the materials at the microscopic level and visual macroscopic changes in the physical properties of the samples processed by laser radiation.