Table of contents

A new fibre laser based on a bismuth-doped aluminosilicate glass fibre is proposed and fabricated. CW lasing is obtained in the spectral region between 1150 and 1300 nm. The fibres are fabricated by the method of modified chemical vapour deposition.

A brief review is given of the state of the art in the research on the photosensitivity of fibres and photoinduced fibre gratings. The most important properties of fibre gratings are considered and the main methods of their production and their applications are discussed. The photosensitive compositions of silica glasses are presented and methods for increasing their photosensitivity are indicated.

The rate constants of N₂⁺(B) quenching by nitrogen and helium and of two- and three-body charge exchange of He₂⁺ on H₂, D₂, and Kr are measured from luminescence at the 0–0 transition of the first negative system of nitrogen in mixtures of helium and nitrogen with hydrogen, krypton or deuterium excited by alpha particles emitted by ²¹⁰Po .

The small-signal gain (SSG) dynamics is studied experimentally and theoretically in the active medium of a pulsed e-beam sustained discharge CO laser in a broad range of vibrational transitions, various compositions and densities of the active medium, as well as various positions of a small-aperture probe laser beam in the gas-discharge region. The results of measurements are compared with theoretical calculations based on a spatially homogeneous CO laser model taking into account the multiquantum VV exchange processes. The sensitivity of the SSG dynamics to variations in the active medium and pump parameters is studied. Good agreement is demonstrated between theoretical and experimental data on the SSG dynamics obtained by using corrected values of local energy input in the calculations.

A quasi-continuous output power of 1.1 W is generated at 1.56 μm in a longitudinally pumped Yb³⁺, Er³⁺:LaSc₃(BO₃)₄ (Yb,Er:LSB) crystal. The lasing efficiencies of the Yb, Er:LSB laser and Er:phosphate glass laser are compared under the same pump conditions.

General approach is described to the rates, fluxes and current densities associated with spontaneous radiative and nonradiative Auger recombinations in heterostructure lasers with different types of a quantum-confined active region (quantum wells, quantum wires, and quantum dots). The proper way of defining the spontaneous radiative and Auger recombination coefficients and their dimensionality are discussed. It is shown that only in a quantum dot, true time constants can be introduced for spontaneous radiative and nonradiative Auger recombinations, which are independent of the injection level. Closed-form elegant expressions are presented for the radiative recombination coefficient as an explicit function of temperature and parameters in bulk and quantum-confined structures. These expressions clearly demonstrate inappropriateness of the common practice of deriving the recombination coefficients in low-dimensional heterostructures from the bulk values.

The radiation intensity distribution of linear diode arrays used for longitudinal pumping fibre-coupled solid-state lasers is studied experimentally and theoretically. A simple model describing the propagation of radiation is proposed which allows the calculation of the inversion population distribution in an active element. The radiation intensity distributions are calculated in cross sections for different angular distributions at the fibre output.

Lasing parameters of a rf discharge-pumped CO laser in a subsonic gas flow with subsequent cooling of the laser medium in a supersonic flow are studied. The output power of the laser achieved 2.1 kW for the efficiency up to 21% in the spectral range 4.9–5.7 μm corresponding to the V+1→V fundamental vibrational transitions in the CO molecule. The laser output power at the V+2→V first vibrational overtone transitions (2.6–2.7 μm) was 50 W. Possible ways of improving the laser design for generating radiation at higher overtone transitions of the CO molecule are discussed.

It is shown experimentally that a transverse rf discharge in tubes has a higher plasmachemical activity than a dc discharge, which deteriorates the parameters of rf discharge-pumped CO₂ lasers. The output power and efficiency of a sealed off CO₂ laser were substantially increased by using a distributed gold catalyst facilitating CO₂ regeneration. The output power of 0.77 W cm^-1 per unit length of an active medium with efficiency of 18.5% was obtained in an experimental CO₂ laser with tubes with a distributed gold catalyst pumped by a 27.1 MHz rf discharge.

A new type of modulation of the photoluminescence intensity of atoms excited by a bichromatic laser radiation with the frequency ratio 1:2 is proposed and analysed. The modulation is produced by alternating electric field acting on atoms and occurs due to the quantum interference of the amplitudes of two excitation channels of an atom, which proves to be possible because the applied electric field removes the parity selection rule for one of the excitation channels. An important feature of this process is the dependence of photoluminescence on the phase difference of monochromatic components of exciting radiation. The calculation was performed for an alkali metal atom excited at the s—s transition taking the saturation effect into account.

The theory of Coulomb explosion of a plasma is used to estimate the maximum energy of ions produced upon irradiation of an ultrathin foil by a relativistically strong ultrashort laser pulse.

A ring optical resonator with the simplest type of an inhomogeneity causing backscattering of waves is considered. A boundary problem of the periodic type is formulated in terms of the reflection and transmission coefficients. In the case of a small reflection coefficient, analytic expressions for eigenfrequencies are found in the limiting cases of their degeneracy and maximum splitting.

The scattering characteristics of a spherical particle placed into a regularly inhomogeneous medium are studied. It is shown that the inhomogeneity of the medium surrounding the particle substantially changes the scattering pattern of a light wave compared to scattering of light by a particle in a homogeneous medium considered in the classical theory. The expressions for the scattering amplitude are obtained for the conditions when an inhomogeneous medium can be represented as a defocusing or focusing channel. It is shown that the defocusing action of the medium is manifested in a significant broadening of the scattering amplitude and its shift compared to the classical case. The focusing of scattered radiation by the medium can cause both broadening and narrowing of the scattering amplitude, as well as periodic variations in its position. The influence of regular refraction on the propagation of a radiation beam in the scattering medium is estimated.

An analytic hybrid method is considered for solving the stationary radiation transfer equation in the problem on reflection of a narrow laser beam from biological media such as the 2% aqueous solution of intralipid and erythrocyte suspension with the volume concentration (hematocrit) H=0.41. The method is based on the reciprocity of the Green function in the radiation transfer theory and on the iteration solution of the integral equation for this function. As a result, the ray intensity is represented as a sum of two terms. The first of them describes the contribution of finite-order scattering to the intensity of a beam diffusely reflected from the medium. The second term contains the explicit analytic expression for a spatially distributed effective source of diffuse radiation emerging from the deep layers of the medium to the surface. This approach substantially improves the diffusion approximation for the problem under study and allows one to obtain the uniform asymptotics of the reflection coefficient at the specified interval of distances between the radiation source and detector on the medium surface with the relative error within ±6% for the 2% intralipid emulsion and erythrocyte suspension (H=0.41).

An integrated optical demultiplexer based on the SiO₂—SiON waveguide structure and operating in the wavelength range of 1.5 μm is fabricated. The demultiplexer chip has a size 10×10 mm. The parameters of the optical scheme of the device are presented, the technology of its fabrication is described, and the results of measurement of working parameters are given. It is shown that the crosstalk between communication channels (K = 8) does not exceed -25 dB. The operation of the demultiplexer as a selective reflecting mirror is demonstrated. It is shown that it can be used for constructing multifrequency lasers for fibreoptic communication systems.

Multiwave mobile lidar complexes (MLCs) are designed and developed. A number of vehicle-based MLCs are built. The set of complex lidar probing data obtained with the help of MLCs is synchronised in space and time, covers a large area (the operation range of an MLC is 15 km), and is based on a unified methodological approach. The results of probing contain information on the concentration and physical nature of atmospheric aerosol, chemical composition of the gaseous phase of the atmosphere, wind and turbulence. The obtained data form the basis for a complex analysis of the ecological situation and prognosis of its development.