Table of contents

An efficient cw single-mode double-clad Nd³⁺-doped fibre laser is developed which operates at room temperature in a quasi-three level scheme on the 925-nm ⁴F_3/2 — ⁴I_9/2 transition upon diode pump at 805 nm. The gain in the laser resonator at 1.06 μm is strongly suppressed due to a proper choice of the refractive index profile in the fibre core. The laser output power above 0.5 W is obtained with the slope efficiency exceeding 35 %.

The consequences of replacing the primary fuel, hydrogen, as a part of the conventional F₂ — H₂ — He DF-laser fuel composition by ethylene are studied experimentally. During comparative tests of the laser with different primary fuels, the completeness of combustion of the fuel mixtures is assessed and their optimal chemical compositions, at which the energy and spectral characteristics of laser radiation are measured, are determined. It is shown that, when C₂H₄ is used instead of H₂, an increase in the specific laser energy yield of 37 % without a change in the active-medium length is ensured and radiation within the range of 3.75 — 4.18 μm is generated.

An X-ray preioniser with an electron beam energy density of 0.1 J cm^-2 based on a high-voltage (20 — 40 kV) low-pressure glow discharge is developed for repetitively pulsed gas lasers. The electron concentration in the CO₂ — N₂ — He mixture as a function of the voltage across the preioniser is calculated for titanium and other foils. The preioniser can be operated both in a single-pulse regime and at pulse repetition rates ranging up to hundreds of Hertz. A specific energy yield of 51 J L^-1 is achieved in the X-ray preionised pulsed CO₂ atmospheric-pressure laser. This preioniser was shown to be efficient for other active media (CO and excimer lasers), which opens up new opportunities for the development of repetitively pulsed gas lasers.

A kinetic model of the active medium of a copper vapour laser with hydrogen additions is proposed. The model is tested using the available experimental data. Various points of view concerning the improvement of the emission parameters of the laser by adding hydrogen are analysed in detail. It is shown that the improvement of lasing parameters caused by the hydrogen addition is explained by different mechanisms. In the case of low pump-pulse repetition rates, the improvement is caused by an increase in the initial ground-state density of copper atoms and by quenching of the metastable states of copper atoms. When the pump-pulse repetition rate is high, the improvement is achieved due to a decrease in the prepulse electron concentration and temperature.

An atmospheric-pressure CO₂ laser with an electron-beam-initiated discharge produced in a working mixture is developed. The laser output energy of 18 mJ from a ~6-cm³ active volume is achieved. The laser operation with a pulse repetition rate of up to 5 Hz is demonstrated. The specific energy deposit of ~0.1 J cm^-3 is obtained in the CO₂:N₂:He = 1:1:4 gas mixture at the atmospheric pressure during a pulsed nonself-sustained discharge with ionisation amplification.

Continuous wave lasing is obtained for the first time in a flashlamp-pumped ytterbium — erbium-doped glass.

The near-surface plasma produced upon irradiation of an aluminium target by two successive laser pulses with nonresonance and resonance wavelengths is studied by the spectroscopic and probe-assisted methods. The feasibility of increasing the ion fraction in the laser-produced plasma in double-pulse ablation modes is demonstrated. The conditions are determined under which processes on the surface as well as selective excitation and ionisation in the plasma have a determining effect on the formation of its ionisation state.

The polarisation of radiation of high-power industrial multitubular, diffusion-cooled CO₂ lasers is studied. The conditions of the appearance of linear and elliptic polarisation and of polarisation instability are determined. The relation between the laser parameters and its polarisation characteristics is established.

The loss permutations of Fabry — Perot resonator modes caused by the harmonic spatial perturbation of the radiation phase on one of the mirrors are studied numerically. The periods and amplitudes of perturbations are found at which the second or third mode in the eigenvalue modulus becomes the first mode. It is shown that in the case of perturbations with the period l₀, at which the Talbot length is equal to the double resonator length, the permutations are caused by an increase in the losses of the fundamental mode. It is also shown that the perturbation amplitudes with the period l₀, which equalise losses of the modes, depend linearly on the inverse Fresnel number F_-1.

The nonlinear absorption of light by silicate glasses doped with copper nanoparticles is studied. Two-photon and saturated absorptions were observed simultaneously and interpreted. The measured two-photon absorption coefficient was 6 × 10^-6 cm W^-1 and the saturation intensity was 4.3 × 10⁸ W cm^-2.

A supercontinuum is generated for the first time and studied in twin tapered fibres with a micron waist upon pumping by femtosecond pulses. The supercontinuum is obtained in the range from 460 to 1070 nm at the −28 dB level with the degree of polarisation up to 97 %. The polarisation and coherent properties of the supercontinuum are studied experimentally.

The gain spectrum of optical modes is theoretically analysed in an antiwaveguide ribbon fibre in which the amplifying regions are made coincident with periodically arranged regions of a reduced refractive index. A class of resonance periodic structures is selected in which the gain of one mode with the field uniformly distributed over channels exceeds the gain of all other modes by the value independent of the number of channels up to their critical value, which was also found analytically.

Changes in the output power and emission spectrum of a two-stage Raman phosphosilicate fibre laser are measured during the temperature tuning of fibre Bragg gratings (FBGs) forming enclosed resonators (1.26/1.52 μm). The output emission spectrum of the dense resonator (1.26 μm) is split into two components, whose relative amplitudes change during the temperature tuning of FBGs. A simple analytic model is constructed which describes the broadening and splitting of the spectrum as well as the appearance of its asymmetry upon the relative detuning of FBGs. It is shown that these effects result in the increase in the effective transmission coefficient of the dense resonator at least by an order of magnitude, which affects the output power of the Raman laser.

Experiments are performed on the formation of coloured dots of a submillimetre size on the titanium foil surface irradiated by pulsed IR lasers. It is shown that the parameters of laser pulses can be selected so that the dots produced on the titanium foil surface will change their colour from yellow to blue with increasing exposure time. The threshold laser power densities required for the formation of contrast coloured dots on the titanium foil surface irradiated by laser pulses with low repetition rates are estimated as ~1.5 × 10³ J cm^-2 for a 1.73-μm Xe laser and ~2.3 × 10³ J cm^-2 for a 10.6-μm CO₂ laser.

The outlook for using narrow-band spontaneous emission sources for purification of smoke gases from sulphur and nitrogen oxides is demonstrated by calculations based on a nonstationary kinetic model of the N₂ — O₂ — H₂O — CO₂ — SO₂ mixture. The dependences of the mixture purification efficiency on the UV source power at different wavelengths, the exposure time, and the mixture temperature are calculated. It is shown that the radiation sources proposed in the paper will provide better purification of waste gases in the atmosphere. The most promising is a KrCl* lamp emitting an average power of no less than 100 W at 222 nm.

A substantial change in the spatial coherence of an optical field with a speckle pattern was experimentally observed during reflection of the field from a 'thick' Bragg grating. This effect is explained within the framework of the Gauss — Sheel model by the difference in the diffraction efficiencies of individual regions of the field represented by Gaussian beams with different angular divergences.

The specific features of contactless measurements of the body surface temperature by the method of repetitively pulsed laser photothermal radiometry are considered and the requirements to the parameters of the laser and measurement scheme are formulated. The sensitivity of the method is estimated. The advantages of laser photothermal radiometry over the conventional passive radiometric method are discussed.