Table of contents

A review of investigations of kinetic processes in active media oxygen — iodine lasers (OILs) performed in the last decade is presented. The mechanisms of pumping and quenching of electronically and vibrationally excited O₂ and I₂ molecules are considered, and dissociation mechanisms of I₂ in the active medium of the OIL are analysed. The values of kinetic constants of processes proceeding in the active media of OILs are recommended.

We consider the operation principles of noise-immune near-IR receiver — transmitters with the quantum sensitivity limit, in which active quantum filters based on iodine photodissociation quantum amplifiers and iodine lasers are used. The possible applications of these devices in laser location, laser space communication, for the search for signals from extraterrestrial civilisations and sending signals to extraterrestrial civilisations are discussed.

The system of balance equations is modified for quasi-three-level passively Q-switched lasers with a slow saturable absorber. Optimal parameters of a Yb³⁺:YAG microchip laser with a passive Cr⁴⁺:YAG Q switch are calculated at a pulse repetition rate of ∼100 kHz. The single-mode operation of the Yb:YAG—Cr:YAG laser with a pulse repetition rate above 100 kHz, the average output power 0.45 W and peak power 1.5 kW is experimentally demonstrated. In the multimode lasing regime, pulses with a peak power of 4.2 kW are obtained at an average output power of 0.8 W and a pulse repetition rate of 10 kHz.

The alternative method of atomic iodine generation for a chemical oxygen — iodine laser (COIL) in chemical reac-tions with gaseous reactants is investigated experimentally. The influence of the configuration of iodine atom injection into the laser cavity on the efficiency of the atomic iodine generation and small-signal gain is studied.

A three-dimensional numerical model of a vertical-cavity surface-emitting laser (VCSEL) containing a resonance grating of quantum wells (QWs) is developed. The Helmholtz equation for a field and the diffusion equation for a medium, in which an electron beam is the source of charge carriers, aresolved self-consistently, which allowed us to find the longitudinal and radial profiles of the generated field, its frequency, and the threshold pump current. The characteristics of the higher-order modes are calculated against the background of the frozen medium formed by the generated mode. The stability limit of the single-mode regime and the type of a mode at which lasing begins to develop with increasing pump power are found from calculations of the gain balance and losses for higher-order modes. An iteration algorithm is developed for calculating the parameters of a VCSEL with many QWs, the calculation time increasing linearly with the number of QWs. The profiles of the resonator modes and their frequency spectrum are calculated for a cylindrically symmetric VCSEL. The stability limits of single-mode lasing are determined. The results are compared qualitatively with experiments.

Analytic expressions are derived for one-dimensional distributions of temperature and thermoelastic stresses in an active element (AE) upon stationary multipass pumping equal to or exceeding the threshold. Three events caused by the AE heating are considered, each of the events damaging the laser: a decrease in the efficiency due to the change in the spectral and luminescent properties of the active media, violation of the normal regime of the AE cooling, and destruction of the AE due to the increase in the thermo-mechanical stresses. The domains of the parameters (such as the AE absorption coefficient, the AE thickness, etc.) are determined at which one of the above events first occurs as the pump intensity and correspondingly the AE temperature are increased. Expressions for estimating the limiting pump intensities for each set of the parameters are obtained.

The possibility of protecting a mirror of a laser on the 4d — 4p transitions of nickel-like tantalum ions against spontaneous X-rays by means of a carbon or potassium filter is considered. It is shown that such filters can transmit 75% — 80% of laser radiation at 44.83 Å, attenuating at least by half the intensity of radiation incident on the mirror in other spectral regions, which considerably suppresses the double-pass amplification.

The dependence of the radiation frequency of a solid-state laser on the laser radiation field amplitude is studied theoretically. It is shown the non-isochronism of the laser frequency appears only when the contribution of spontaneous emission to the generated resonator mode is taken into account and is manifested most strongly at small excesses of the pump over the threshold.

The beam spatial structure of a diode-side-pumped Nd:YVO₄ slab laser with grazing-incidence bounce geometry is studied. It is found how the mode structure changes with changing the cavity parameters in the cw and active Q-switching regimes. The parameters that allow one to improve the output beam quality retaining high output laser power are found.

A new method for generating periodic lattices in quadratically nonlinear media by the three-wave cascade interaction is proposed. This method allows one to obtain stable structures with changeable parameters. These structures make it possible to realise the all-optical control of the character of the laser beam propagation. The use of the discrete diffraction allows the signal multiplexing in optical processing and information transfer devices and the control of the number of channels at the crystal output. The effect of the discrete diffraction anisotropy in the system of induced waveguides makes it possible to redistribute in the specified way the energy in the channels at the output. It is shown that the optical switching efficiency is maximal in the regime of the transverse Bragg resonance. The signal switching rate in optical lattices induced in a quadratically nonlinear medium is limited by the time of light propagation though the crystal and can achieve several terahertz.

This work examines IR multiphoton excitation of SF₆ molecules subliming from the surface of (CO₂)_N van der Waals clusters (nanoparticles) in a cluster beam (the number of monomers per cluster, N≥10²). The SF₆ molecules are captured by clusters when a cluster beam intersects a molecular beam and sublime from the cluster surface after a certain time, carrying information about the velocity and temperature (internal energy) of the clusters. The multiphoton absorption spectra of the SF₆ molecules subliming from the cluster surface are markedly narrower than those of the SF₆ molecules in the parent, gas-dynamically cooled molecular beam, indicating that the vibrational temperature of the molecules subliming from the cluster surface is lower. Therefore, the proposed technique can be used to produce strongly vibrationally cooled molecules, which are of interest for a number of applications, in particular for achieving high-selectivity IR multiphoton excitation and isotopically selective dissociation of molecules.

The possibility of using temporal analysis to find the relation between chromatic properties of probe radiation and coherent properties of the optical images of rough non-planar objects is substantiated. The analysis is based on the use of the time correlation function and on the study of the speckle pattern contrast in the optical images. The conditions are determined under which the different parts of the optical image of an object are coherent, partially coherent and incoherent, while probe radiation is manifested as monochromatic, quasi-monochromatic, and polychromatic. It is shown that these conditions depend considerably on the object surface shape. The use of the temporal analysis for three-dimensional imaging of an object by its planar images and improving the optical image quality by removing its speckle pattern is illustrated by examples.

Anisotropic, polarisation-maintaining fibres have been studied using a reflectometer and integrated optic polariser. Linearly polarised pulses were launched into the fibre under test at different angles between their plane of polarisation and the main optical axis of the fibre. A special procedure for the correlation analysis of these reflectograms is developed to enhance the reliability of the information about the longitudinal optical uniformity ofanisotropic fibres.

A new process for bismuth doping of optical fibres is proposed in which the dopant is introduced into a thin layer surrounding the fibre core. This enables bismuth stabilisation in the silica glass, with no limitations on the core composition. In particular, the GeO₂ content of the fibre core in this study is 16 mol %. Spectroscopic characterisation of such fibres and optical gain measurements suggest that the proposed approach has considerable potential for laser applications.

We report a simple design of spun holey fibres and the first experimental study of the magneto-optical response of spun microstructured fibres with high built-in birefringence. Such fibres enable the Faraday-effect-induced phase shift to effectively accumulate in a magnetic field even at very small coiling diameters. For example, the magneto-optical sensitivity of a 5-mm-diameter fibre coil consisting of 100 turns is ∼70% that of an ideal fibre, in good agreement with theoretical predictions.

We demonstrate a Raman-based all-fibre temperature sensor utilising a pulsed erbium fibre laser. The sensor is made of a standard single-mode telecom fibre, SMF-28, and includes a number of directional couplers as band-pass filters. The temperature profile along a 7-km fibreoptic line is measured with an accuracy of 2^oC and a spatial resolution of 10 m. In data processing, we take into account the difference in attenuation between the spectral components of the backscatter signal.

The propagation of optical pulses through a fibreoptic communication line with a phase shift of odd bits is directly numerically simulated. It is shown that simple analytic expressions approximate well the error probability. The phase shift of odd bits in the initial sequence is statistically shown to decrease significantly the error probability in the communication line.

Polariton modes are studied in two-dimensional traps based on quantum-well heterostructures allowing the production of a Bose — Einstein condensate of indirect excitons. The characteristic equation for the modes is derived using the boundary conditions on the exciton layer located inside a resonator formed by such a trap. The spectrum and the structure of high-Q modes are found analytically and numerically. It is shown that some of these modes become unstable at the high exciton density and long polarisation relaxation time. According to the estimates, this instability can take place in experiments on the Bose condensation of dipolar excitons, thus explaining the origin of their coherent emission.

This work examines spatial separation of femtosecond electron bunches using the ponderomotive potential created by femtosecond laser pulses. It is shown that ponderomotive optical potentials are capable of effectively deflecting, focusing, and collimating narrow femtosecond electron bunches.