Table of contents

A brief historical review is followed by an account of the main results of many years of experimental and theoretical investigations of the problem of direct conversion of the nuclear energy into coherent radiation (nuclear-pumped lasers) and of constructing a reactor-laser. The main difficulties encountered in solving this problem and ways of overcoming them are discussed.

An investigation was made of an eight-pass amplifier based on titanium-doped sapphire, pumped by the second harmonic of a YAG laser and intended for terawatt femtosecond laser systems. The gain reached 2×10⁷ for a pump energy density of 3.2 J cm^-2.

A transient self-consistent kinetic model is developed of an Xe — Sr — H₂ laser emitting as a result of the 6s²S→5p²P_3/2 (λ = 430.5 nm) transition in the strontium ion when pumped by hard ionising radiation. The optimal lasing conditions are found under which the efficiency of the active medium, in terms of the deposited energy, may exceed 3%. It is shown that efficient lasing is possible when the laser is pumped by electrons from a RADAN-type accelerator.

An experimental investigation was made of the optical gain saturation in a supersonic oxygen — iodine laser with a stable cavity. The measured saturation intensity, 15 kW cm^-2, was close to that calculated for homogeneous saturation of the gain line and for a finite rate of mixing of the hyperfine-structure levels of the iodine atom. The reported calculations and experiments showed that the transfer of energy from oxygen to iodine and mixing of the hyperfine I(²P_1/2) sublevels set limits on the conversion of the stored energy into radiation in a laser with a finite length of the mirrors along the gas-flow direction.

A powerful supersonic cw chemical HF laser was subjected to a bench investigation with the aid of a semiconductor ionisation-type chamber. This investigation yielded information on the distribution of the laser radiation field and of its power density, on the beam profile, on the geometric dimensions of the cross section and 'jitter' of the beam, on the energy divergence of the radiation, and on the evolution of these characteristics during the laser start process.

Numerical simulation is used to investigate the influence of spatially inhomogeneous steady-state pumping on the dynamics of operation of a laser with fast crossflow of the active medium through an unstable cavity. It is shown that, depending on the distribution of the pumping rate inside the cavity, the pumping may stabilise cw lasing or may lead to its instability. The appearance of an instability is associated with the formation, under the action of inhomogeneous pumping, of considerable transverse gradients of the steady-state gain and field intensity distributions. If the spatial pumping profile is characterised by a steep fall of the excitation rate near the optic axis of the cavity, the calculations predict — depending on the system parameters — not only cw lasing, but also various self-pulsing regimes and chaotic lasing.

The self-consistent field theory and the method of local mapping are used in an investigation of mode locking in a solid-state laser. An analysis is made of the structure of the ultrashort pulse generation zone of a laser with an antiresonant ring.

An investigation was made of the characteristics of the competition between concurrent and counterpropagating stimulated Raman scattering of 120 ps pulses of the 1.064 μm wavelength in high-pressure methane. The conversion efficiencies calculated for various regimes agreed well with the results of measurements.

The effective nonlinear coefficient for sum-frequency generation with collinear phase matching is calculated taking account of the birefringence (anisotropy or drift) in biaxial crystals. It is shown that the components of the unit vectors along the directions of oscillations of the electric vector of the 'fast' and 'slow' wave can be found without resorting to direct solution of equations derived directly from the wave equations. These components are expressed in terms of the birefringence angles which, in turn, are calculated in terms of the components of the ray vectors and the refractive indices of the waves. A method for calculating the effective nonlinear coefficient is given. All the calculations are made for collinear phase matching.

Second-harmonic generation was used in an investigation of the quadratic optical susceptibilities and of the structure of Langmuir — Blodgett films of a number of azobenzene derivatives. The angular distribution of second-harmonic radiation could differ significantly for films containing domains with the average size r considerably less than the second-harmonic wavelength λ and films consisting of relatively large domains (r ≫ λ). The orientation of the molecules relative to the substrate was determined in both cases.

A spatiotemporal instability of a high-intensity (10¹⁵ — 10¹⁶ W cm^-2) laser pulse in a defocusing medium (plasma) is demonstrated and investigated. The plasma is assumed to form in the course of passage of the pulse through an atmospheric-density gas. The reason for the appearance of this instability is the time dependence of the nonlinear response of the medium (nonlinear dispersion).

The method is described and the results are given of a calculation of the diffraction of a finite Gaussian light beam by a finite grating. It is shown that a waveguide grating can be used as a mirror in a plane — plane cavity. An experimental demonstration is reported of the operation of a waveguide mirror in a dye microlaser.

A study is reported of the characteristics of the principal wave in an optical coaxial metal waveguide. The real properties of metals at optical frequencies are taken into account. An approximate formula is derived for the dependences of the eigenvalues of the transverse wave vectors on the geometric parameters of a coaxial line and on its permittivity. The exact eigenvalues are determined for several values of the parameters of practical interest. It is shown that such a coaxial line can concentrate radiation with domains much smaller than the radiation wavelength.

An investigation is reported of the task of tomographic reconstruction of vector physical fields from sets of contour integrals of the projection of a vector and of the projection of the derivative of a vector along a given direction. It is shown that such reconstruction is possible with the aid of fibre-optic measuring lines. In those cases when the output signal is proportional to the integral of the projection of a given vector, use is made of measuring lines in the form of a narrow loop. The solution of the problem then reduces to the application of integral theorems. However, if the output signal is proportional to the integral of the projection of the derivative of a vector along a direction (representing the problem of a deformable two-dimensional object), it is essential to use measuring lines of stepped form; the potential component of the field is then reconstructed.

New types of acousto-optical 2×2 switches of optical beams with different wavelengths, intended for fibre-optic gyroscopes, are analysed and proposed. These switches make it possible to transmit two different radiations through the same fibre coil and thus obtain two independent Sagnac signals related to coil rotation. A method for calculating the angular and frequency characteristics of the switches is described. Experiments on volume acousto-optical diffraction in a TeO₂ single crystal confirm, on the whole, the theoretical conclusions.

The probability W of the forbidden magnetic-dipole 2¹S₀ — 2³S₁ transition in the helium atom is calculated to be 6.11×10^-8 s^-1. An estimate is obtained of the number of atoms excited to the 2¹S₀ state by a travelling wave which is in resonance with the frequency of this transition.

A theoretical simulation is reported of a pulsed chemical H₂ — F₂ laser. The possibility of simultaneous generation of the fundamental tone and of the first overtone is considered. Superluminescence at the fundamental harmonic is included specifically in the adopted model. It is shown that efficient overtone generation in a mixture of high energy capacity at a pressure of 1.1 bar is possible at initiation levels of 10¹⁶ and 10¹⁷ cm^-3 when the length of the active medium does not exceed 50 and 10 cm, respectively. The corresponding calculated specific output energy of the first-overtone H₂ — F₂ laser can reach 11 and 75 J litre^-1, respectively, which represents 20% and 40% of the specific output energy at the fundamental tone.

In memory of G.A.Askar'yan — outstanding Russian physicist, who made a great contribution into many fields of quanum electronics.