Table of contents

A method of phase locking of optically coupled lasers by gain gratings in an active medium is proposed. The criterion for phase locking is determined and optimal relations between the energy parameters of waves upon four-wave mixing are found. Two-channel parallel laser systems based on self-phase-conjugation loop oscillators are studied and the possibility of their phase locking with the phasing degree up to 0.9 is shown.

The characteristics of turbulent pulsations of the gas density and velocity and the structural characteristic of fluctuations of the refractive index in the gaseous-mixture flow of a fast-axial-flow CO₂ laser are determined using optical diagnostic methods: the luminescence, interferometry, and degenerate four-wave mixing techniques. The influence of a gas discharge and lasing on turbulent small-scale optical inhomogeneities of the active medium is investigated. It is shown that, in the presence of a gas discharge and laser oscillation, the inhomogeneities appreciably increase due to nonlinear effects of a local heat release in the thermodynamically nonequilibrium turbulent gaseous medium.

An F₂ laser operating at a pressure of an F₂ — He — Ne gas mixture of up to 3300 mbar is investigated. The conditions for obtaining a maximum lasing efficiency are determined as a function of the parameters of the excitation system. It is found that small amounts of neon (~100 mbar) added to the working mixture insignificantly (by ~15%) reduce the output energy, but substantially improve the discharge homogeneity. A 157-nm F₂ laser operating at a comparatively low pressure in the active medium is developed. Its pulse energy is 28 mJ and the efficiency is 0.14%.

The polarised two-photon (IR) and one-photon (visible) luminescence excitation spectra of Nd³⁺ nanoclusters in CaF₂ and SrF₂ crystals are measured at 10 K using a :LiF colour centre laser tunable in spectral ranges 1090 — 1230 nm and 545 — 615 nm with an emission linewidth of ~0.02 — 0.03 cm^-1, an average output power of ~55 mW, and a pulse repetition rate of 10 Hz. The two-photon excitation spectra at the ⁴I_9/2 → ⁴G_5/2 transition reveal the structure, which is absent upon one-photon excitation, which can be explained by different selection rules for some Stark — Stark transitions upon one- and two-photon absorption.

Experimental studies aimed at the optimisation of an unstable resonator of an ArF electric-discharge laser are performed. Several optical schemes of an unstable resonator of a single-module laser are proposed and investigated. It is shown that the laser developed on the basis of these schemes is characterised by a high coherence (the spatial coherence length is 1 — 10 mm and the temporal coherence length is 0.5 — 30 mm at a pulse energy of 40 — 290 mJ).

A multilayer planar structure containing a corrugated waveguide and a highly reflecting mirror is described. The structure is used as a narrow-band optical filter operating in two different regimes. The efficiency of the proposed filters is demonstrated experimentally in the lasing regime.

A brief review is presented of the development of silicon-based optical integrated circuits used as components in modern all-optical communication networks with the terabit-per-second transmission capacity. The designs and technologies for manufacturing these circuits are described and the problems related to their development and application in WDM communication systems are considered.

The method of optical space-domain reflectometry for measuring local spatial characteristics of fibre Bragg gratings (FBGs) is described in detail. It is demonstrated experimentally that, by using IR and UV radiation sources, this method provides good sensitivity (~10^-4) of measuring the modulation amplitude of the induced refractive index in the core of an optical fibre and a high spatial resolution (~100 μm and better). The factors affecting the accuracy of measurements as well as technical and methodological limitations of the method are considered. A comparative analysis of modern methods for studying the spatial properties of FBGs is performed and applications of these methods are considered.

A change in the excitation angle of surface plasmons is found in a three-layer thin-film Ag — Al₂O₃ — AgI structure upon its optical sensitisation with the Arsenazo III dye [2,7-Bis(2-arsonophenylazo)chromotropic acid Disodium salt].

The production of noble metal (Ag and Au) nanoparticles upon the ablation of metal targets in liquids (H₂O, C₂H₅OH, etc.) caused by irradiation by a copper vapour laser is studied. The nanoparticles emerging in a liquid are investigated using X-ray diffractometry, optical absorption spectroscopy, and high-resolution transmission electron microscopy. The colloidal nanoparticle solutions exhibits a distinct plasmon resonance at 520 and 400 nm for Au and Ag, respectively. It is shown that the proximity of laser wavelength to the resonance makes it possible to decrease the dimension of nanoparticles by irradiating the colloidal solution. The size distribution function of nanoparticles is simulated taking into account the production, coagulation, and splitting of nanopartiles in the laser beam.

A highly sensitive automated car-borne detector for measuring methane concentration in real time is designed, developed and tested under laboratory and field conditions. Measurements were made with the help of an uncooled tunable near-IR 1.65-μm laser diode. The detector consists of a multipass optical cell with a 45-m long optical path and a base length of 0.5 m. The car-borne detector is intended for monitoring the methane concentration in air from the moving car to reveal the leakage of domestic gas. The sensitivity limit (standard deviation) under field conditions is 1 ppm (20 ppb under laboratory conditions) for a measuring time of 0.4 s. The measuring technique based on the detection of a single methane line ensured a high selectivity of methane detector relative to other gases. The methane detector can be easily modified for measuring other simple-molecule gases (e.g., CO, CO₂, HF, NO₂, H₂O) by replacing the diode laser and varying the parameters of the control program.

Fibre-Bragg-grating writing in single-mode optical fibres by the phase-mask method using 220-fs, 264-nm UV pulses of intensity 31 — 77 GW cm^-2 is reported for the first time. The achieved degree of modulation of the photoinduced refractive index was 1.9 × 10^-3 in an H₂-loaded SMF-28 telecommunication fibre and 1.1 × 10^-3 in a H₂-free Nufern GF1 fibre. The dependence of the induced refractive index on the intensity for the same irradiation fluences in the case of the H₂-loaded SMF-28 fibre shows that the refractive index is induced due to nonlinear absorption.

The dynamics of a two-mode laser is studied in the presence of a selective saturable absorber interacting only with one of the modes. The specific nature of the system is determined by the presence of the out-of-phase relaxation oscillation, which becomes undamped when a sufficiently dense saturable absorber interacts with the weaker mode. If the absorber interacts with the stronger mode, the in-phase relaxation oscillation is excited, and the situation becomes similar to that observed in a single-mode laser. In the case of a slowly relaxing absorber, the difference of populations of its working levels can be adiabatically excluded. This procedure substantially simplifies the model and does not change its dynamic characteristics.

The results of calculation of group-velocity matching for the generation of second harmonic of femtosecond laser pulses in 62 nonlinear-optical crystals are presented. The angular, spectral, and temperature widths of matching as well as the effective nonlinearity are calculated. The crystals providing the efficient generation of second, third, fourth, and fifth harmonics of the femtosecond Cr:forsterite laser radiation are found.

Analytic expressions describing the interference field of two laser beams in a medium with an acoustic wave are derived. The quantitative parameters characterising a degree of manifestation of the acoustooptic effect (AOE) in the interference region are introduced. These parameters are analysed for the model of a plane acoustic wave taking into account the refraction of laser beams and for the model of an acoustic wave with a spherical phase front for different radiation patterns. Based on the differential scheme of a laser Doppler anemometer (LDA), an experimental setup is built for the detection and study of the AOE characteristics. The values of one of the AOE parameters are measured and good agreement with calculations is obtained. Recommendations are given for performing LDA measurements in the presence of AOE.

Measurements of the high-temperature dependences of the heat capacity of solids heated by high-power laser radiation and the model of formation of structural point defects (vacancies) are used to estimate the heats of sublimation, evaporation and melting, as well as enthalpy of phase transformations for modern processing of steels and ceramics.