Table of contents

The possibility of using relaxation oscillations in a semiconductor laser to obtain time marks is analysed.

The dynamics of free-running lasers and lasers operating in the amplification regime is considered. It is shown that the stability of a wave propagating in the amplifier depends on the wave velocity. A regular wave propagating at the superluminal velocity in class A amplifiers can lose its stability, and its propagation becomes random. The appearance of the periodic or random pulsations of the amplitude in the laser-generator with a saturable absorber operating in the hard excitation regime leads to the self-switching off (quenching) of lasing despite continuous pumping.

The theoretical model of a radiation-frequency-discharge-pumped CO laser is described. The model consists of a block for calculating the spatial characteristics of a capacitive radiation-frequency discharge along the interelectrode distance and the distribution of the translational temperature of the gas. Another block contains the equations of the vibrational kinetics and the condition for stationary lasing in the resonator. The model was used to calculate the energy and spectral parameters of the CO laser in the stationary regime for different temperatures of the walls and two different spatial intensity distributions. The results are compared with the experimental data reported in the literature.

Changes in the refractive index of a Nd:YAG laser crystal caused by intense pumping are measured using a polarisation interferometer. A significant electronic component in the refractive-index changes associated with the excitation of the ⁴F_3/2 electronic level of Nd³⁺ ions is revealed in the crystal pumped by 808-nm radiation of a pulsed diode array. An appreciable increase in the electronic component of the refractive index, which is caused by the population of the ²F(2)_5/2 high-energy level, is observed in a Nd:YAG crystal additionally pumped by a 266-nm laser beam. Analytic calculations show that the short-wavelength 4f—5d transitions provide a predominant contribution to the polarisability of excited Nd³⁺ ions at the 1064.2-nm lasing transition.

The anomalous dependence of the lasing parameters of ethanol solutions of coumarin, rhodamine, oxazine, and laser dyes of other classes on the spectrum of microsecond pump laser pulses is found. The dependence is determined by the shape of the induced singlet — singlet absorption spectra and absorption spectra of short-lived photoproducts. The elucidation of the influence of these factors makes it possible to choose optimal pump spectra and to enhance the efficiency and stability of microsecond dye lasers.

Polycrystalline ceramics differ significantly from single crystals in that the crystallographic axes (and hence of the axes of thermally induced birefringence) are oriented randomly in each granule of the ceramic. The quaternion formalism is employed to calculate the depolarisation in the ceramics and the efficiency of its compensation. The obtained analytic expressions are in good agreement with the numerical relations. It is shown that the larger the ratio of the sample length to the granule size, the closer the properties of the ceramics to those of a single crystal with the [111] orientation (in particular, the uncompensated depolarisation is inversely proportional to this ratio).

The method and results of precision measurements of the intermode frequency of a Ti:sapphire laser after the propagation of its radiation through a tapered optical fibre are described. It is shown that the stability of the intermode frequency is impaired by half at short averaging times (10 s) and by a factor of 1.1 at long averaging times (1000 s). The results of investigations of the spectrum of a femtosecond Ti:sapphire laser, which is broadened in a tapered optical fibre are presented. It is shown that, by varying the fibre parameters and the characteristics of input pulses, the envelope of the broadened spectrum can be profiled, which is important for practical applications.

A mathematical model for optimising the beam formation direction in an active medium with three-dimensional periodic perturbations is developed. This model is applicable to the refractive-index distributions that can be represented in a multiplicative form with separated variables. The analysis of the actual structure of perturbations that appear behind the original nozzle assembly of a cw chemical laser has shown that the optimal direction of the beam formation lies in the region of partial self-compensation for distortions, which ensures an acceptable wave-front quality of the formed radiation.

The IR multiphoton dissociation of trichlorosilane (SiHCl₃) molecules irradiated by pulses from CO₂ and NH₃ lasers is studied. The dependences of dissociation yield on the frequency and energy density of laser radiation, as well as on the parent pressure of SiHCl₃, are determined. It is found that HCl and a solid precipitate, probably with a common chemical formula (SiCl₂)_n, are the main products of dissociation of trichlorosilane.

Approximate scaling dependences of the generation efficiency of the first five harmonics of the exciting field on thier number are determined in the case of Coulomb degeneracy. Analytic dependences of the efficiency of harmonics of a given number on the principal quantum number of the atomic level from which ionisation of an electron occurs are derived. Approximate scaling dependences of the harmonic generation efficiency on the generated harmonic number and the principal quantum number of the ionised atomic level are obtained.

The atomic photoeffect is studied in the pulsed fields of two coherent waves: a high-order harmonic wave and the fundamental wave. Expressions are derived for the intensity of the main peak and satellites in the photoelectron energy spectrum for an arbitrary delay between the pulses. The role of inelastic Coulomb rescattering of photoelectrons from the residual ion in the fundamental wave field, in the production of satellites is analysed.

The properties of optical solitons in variable-dispersion fibreoptic communication lines in which distributed Raman amplification of optical signals is used are studied by numerical simulation. It is shown that solitons can serve as carriers of information in communication systems with a data transmission rate exceeding 10 Gbit s^-1.

The properties of solitons appearing during the propagation of whispering-gallery waves in a homogeneous glass cylinder are considered. It is shown that such solitons can be used for the light frequency conversion.

A method for studying the dynamics of transformation of defects in optical fibres, exposed to UV radiation, by the dose dependence of the induced refractive index is proposed. The processes of transformation of defects in a low-loss phosphosilicate fibre, loaded with molecular hydrogen, irradiated at the 193-nm wavelength are investigated using this method. It is assumed that such a fibre has at least two types of defects, responsible for the induction of the refractive index.

The results of 1.05-μm laser measurements of optical properties of the POCl₃ — SnCl₄ — UO₂²⁺ liquid containing vapour bubbles generated by the fission fragments of ²³⁵U nuclei formed upon irradiation of this liquid by neutrons in a BARS-6 pulsed reactor are presented. The average size of a bubble and its mean lifetime are obtained from experiments. The effect of pressure on the bubble size is studied. It is found that the lifetime of a bubble increases with increasing the concentration of molecular chlorine in the liquid due to its radiolysis induced by fission fragments.

The spatial structure of light waves of the electric type in a cone with perfectly reflecting metal walls is theoretically analysed. The exact formulas and asymptotic expressions are derived which describe the dependences of the energy density of different components of the field inside the cone on the radial coordinate. A special attention is paid to the study of the character of the field decrease near the cone apex depending on the cone angle and the wavelength. The effects of reflection of waves from the truncated cone-free space interface are studied. The obtained results are used for measuring the transmission coefficient of a truncated cone in the optical range for a broad range of parameters, including the diameter of the output aperture of the order of 0.05 — 0.1 of the wavelength. The possibility of obtaining a high transmission coefficient of light in a truncated metallised cone is theoretically substantiated.

The possibility of detecting birefringence induced by a magnetic field in vacuum is analysed. It is shown that the state of the art of the laser measuring technique allows one to hope for setting up successful experiments.