Table of contents

Temperature-independent birefringence in a biaxial crystal was predicted theoretically and observed experimentally for the first time. The width of the plot against temperature (the range corresponding to the temperature independence of the birefringence) at a fundamental radiation wavelength of 632.8 nm in a KTP crystal 5.9 mm long was more than 160°C.

An electric discharge laser with an electrode unit of novel design was developed. An electric discharge system was based on multisectional plate-like electrodes and an automatic UV preionisation that makes it possible to form a highly stable volume discharge. High-efficiency lasing in N₂ and XeF lasers was achieved. A pulse repetition rate up to 200 Hz was realised in the N₂ laser without recourse to gas circulation.

A chemical electric-discharge laser with a new design of the electrode unit was developed. Both electrodes consisted of a set of electrically insulated plates connected to a common bus of a pump source with separate stabilising inductances. It was found that a stable diffuse discharge occurred in such a device in a wide range of active-gas pressures 20 — 130 Torr for an electrode gap of 10 — 50 mm. A radiation energy of 1.2 J and a technical laser efficiency of 3.5% were achieved for an H₂ — SF₆ mixture.

An optical system is proposed in which a switch based on frustrated total internal reflection (FTIR) is used to vary actively the Q-factor of longitudinally pumped erbium glass microlasers. Continuous pumping (with a power of 320 mW) generated giant pulses, of 500 — 600 W peak power and of 10 — 12 ns duration, at a repetition rate of 1 kHz. An FTIR switch in a laser transversely pulse-pumped by a linear laser-diode array delivering 100 W produced pulses of up to 7.5 mJ energy and of 30 ns duration.

Conditions for lasing at λ = 914 nm in a diode-pumped Nd³⁺:YVO₄ crystal were determined. The possibility of intracavity frequency doubling of the microlaser emission with the aid of an LiIO₃ crystal was demonstrated.

A mathematical model describing the dissociation of carbon dioxide in sealed-off CO₂ waveguide and slit lasers with radio-frequency excitation is presented. The theoretically calculated degrees of dissociation of CO₂ were tested experimentally. It was demonstrated theoretically and experimentally that the degree of dissociation increases by 5% — 10% with increase in the specific pump power. It was established that the degree of dissociation of carbon dioxide in lasers with the slit design of the discharge channel was approximately 1.5 times higher than in the usual waveguide lasers.

Nonradiative excitation transfer (NET) was observed between trivalent Pr³⁺ and Nd³⁺ ions in silicate glass. Cooperative sensitisation of the luminescence of Nd³⁺ ions by Pr³⁺ ions in the ⁴F_3/2 → ⁴I_13/2 transition was observed as a result of NET. The luminescence was excited by the cw radiation of an Nd³⁺:YAG laser with a power of ~800 W (λ = 1.064 μm) operating on the basis of the ³H₄ → ¹G₄ transition at the wavelength corresponding to the Pr³⁺ absorption band. The NET mechanism, responsible for the luminescence of the Nd³⁺ ion at the wavelength corresponding to the band with a maximum at λ = 1.34 μm, is discussed.

The influence of an nonuniform distribution of the unsaturated gain along a cavity on a competitive interaction of longitudinal modes was investigated experimentally and theoretically. This nonuniformity is the result of a partial filling of the cavity by the active medium and of an exponential absorption of the pump radiation along the active element. An analysis is made of the evidence in support of this approach to the description of multimode operation of solid-state lasers with longitudinal inhomogeneous pumping.

The dependences of the energy and spectral characteristics of the radiation of a pulsed photoinitiated chemical chain-reaction HF (DF) laser, operating at atmospheric pressure, on the optical cavity parameters were investigated. The maximum specific output energies of the HF and DF chain lasers (53 and 43 J litre^-1) and their fullest spectra (47 and 83 lines, respectively) were similar when the unsaturated gain exceeded the threshold by a factor greater than 50. An analysis was made of how the energy and spectrum of the radiation of the HF (DF) laser were influenced by the spatiotemporal inhomogeneity of the initiation and of the course of the chemical chain reaction. There was a marked effect of the CO₂ molecules in the active medium and in the air filling part of the volume of the complex cavity of the DF laser on its efficiency and emission spectrum.

Passive Q switching of Nd³⁺:YAG (λ = 1060 nm) and YAlO₃:Nd³⁺ (1340 nm) lasers, as well as of an Er³⁺ (1540 nm) glass laser was realised by using glass doped with oxidised nanoparticles of copper selenide. Nonlinear optical properties of the nanoparticles (radius of 25 nm) in a glass matrix were studied by the picosecond absorption spectroscopy technique.

An investigation was made of the photoreduction kinetics of a dye in a solid polymer solution under the influence of laser radiation corresponding to the band of the first singlet — singlet transition. Participation of higher triplet states was considered in a model of the photoreduction of a dye characterised by a high intersystem crossing yield. An analytic solution was obtained for a system of kinetic equations. This solution takes into account the difference between the photoprocess rates. It is shown that a linear dependence of the effective dye-photoreduction rate on the laser radiation intensity can serve as a test of the participation of higher triplet states in the reaction. A comparison of the theoretical and experimental results obtained in the present study is used to determine the ratio of the photoreduction and deactivation rate constants of the higher triplet state of eosin K.

A model of the repetitively pulsed gas-jet laser cutting of thick metals in an oxidising gas is developed. It is shown that the optimal choice of the time-dependent (radiation) and beam-focusing parameters will make it possible to increase the average cutting rate by a factor of 1.5 — 1.8.

An investigation was made of the interaction of intense laser radiation (λ = 1.06 μm) with previously irradiated corundum. The studies were performed in the collecting mode by employing time-of-flight mass spectrometry. Electron and ion currents were considered simultaneously with charge-state and energy characteristics of multiply charged ions of the plasmas produced at the source and previously irradiated targets. The combined consideration allows the conclusion that the prior neutron irradiation of a sample by a fluence of 10¹⁵ — 10¹⁹ neutron cm^-2 makes for production of a higher-temperature plasma.

The scattering and absorption of a high-power picosecond laser pulse by a solid target were investigated experimentally making use of the 'Progress-P' Nd:glass laser facility (λ = 1053 nm, τ = 1.4 ps) at radiation intensities I = 10¹⁶ — 10¹⁹ W cm^-2 on the target surface. It was found that, for I ≤ 10¹⁷ W cm^-2, more than 30% of the intensity of the scattered light was contained in the specularly reflected component. The absorption coefficient of the laser radiation with intensities ranging from 10¹⁸ to 10¹⁹ W cm^-2 was higher for targets made of materials with higher atomic numbers.

Results on spontaneous Raman spectroscopy of alkaline-earth tungstate crystals are presented. The frequency of the modes active in stimulated Raman scattering (SRS) modes was found to increase and their width to decrease with increasing cation radius and mass in the series of alkaline-earth (Ca, Sr, Ba) tungstates. High peak values of the Raman scattering cross section for barium and strontium tungstate crystals — new media offering promise for SRS — were predicted and observed in the experiments. Laser experiments on the SRS threshold showed that the SRS gain for the barium tungstate crystal was close to the record value observed for the barium nitrate crystal, which is extensively used in SRS.

The problem of maximising the relative intensity of the signal optical wave in the course of two-wave mixing was solved taking into account the self-diffraction in a Bi₁₂SiO₂₀ piezoelectric crystal. The maximisation was carried out simultaneously with respect to four parameters: the polarisation (Ψ) and orientation (θ) angles, the crystal thickness d, and the Bragg angle ϕ. It was established that there are two sets of optimal parameters for a Bi₁₂SiO₂₀ crystal at the wavelength of 632.8 nm and for a typical acceptor concentration of 10²² m^-3: ϕ ≈ 11°, θ ≈ 39.1°, Ψ ≈ 98.85°, d ≈ 7.11 mm (for the first maximum) and ϕ ≈ 11°, θ ≈ 320.9°, Ψ ≈ 54.15°, d ≈ 7.11 mm (for the second maximum). The dependences of these optimal parameters on the acceptor concentration in the range 10²¹ — 4 × 10²² m^-3 were found. The model proposed for two-wave mixing in the special case of a fixed Bragg angle and the constant visibility approximation improved the agreement between the theoretical results and the known experimental data.

A theoretical investigation is reported of the regime of azimuthally matched interactions in the process of conversion of the frequency of Bessel light beams. It is shown that this nonlinear interaction regime is accompanied by the establishment of correlations of the mutual azimuthal orientations of plane-wave components of Bessel beams and by an increase in the overlap integral.

The diffraction of light on the corrugated surface of a layered structure was investigated. It was shown that the excitation of waveguide modes in the layered structure alters significantly the diffraction efficiency of the corrugated structure. It was found that in the autocollimation regime the diffraction efficiency of the grating can reach 100% for moderate depths of the grating grooves. The suitability of a waveguide-grating mirror in dye lasers was demonstrated experimentally.

A polarimetric method for the detection of surface plasmons, excited by linearly polarised light, was proposed and tested. It was established that this method is not only more sensitive to variations in the parameters of the waveguiding structure but also makes it possible to increase by one — two orders of magnitude the precision of determination of the excitation efficiency and of the phase velocity of the plasmons, compared with the amplitude method for plasmon detection. The possibility of applying the method in sensor devices, in polarimetry, and in the microscopy of conducting surfaces is discussed.

Photon-counting optical tomography was used in the visualisation and projective reconstruction of the image of a strongly absorbing inclusion (a 'phantom'), 6 mm in diameter, hidden by multiple scattering processes in a model object (diameter 140 mm, absorption and scattering coefficients 0.005 and 1.4 mm^-1, respectively). It was demonstrated experimentally that when the probe radiation power was 10 — 13 mW the minimal (corresponding to the poorest signal/noise ratio ~1) measurement time (photon-counting time) was 0.8 s per one measurement point and the total time needed to scan the whole object was less than 410 s.

A large volume (30 cm³) of dense (up to 10¹⁵ cm^-3) Rb vapour was pumped optically by a high-power laser diode array. The conditions for the propagation of high-power broad-band optical pump radiation through an optically dense medium were examined. A spectroscopic method was developed for determination of the polarisation of Rb. The dependence of the polarisation of Rb on its vapour pressure was investigated at buffer gas pressures of 1, 8, and 13 bar. Under optimal conditions a 15-W diode laser made it possible to polarise at least 10¹⁸ of ³He atoms per second during collisions between Rb and ³He atoms, sufficient for the creation of an efficient neutron polariser.

Questions concerning precise measurements of the spectral-line-profile parameters by diode-laser spectroscopic methods were examined. The instrumental function of a distributed-feedback diode laser (λ =1.53 μm), consisting of the additive contributions of the noise due to spontaneous emission, frequency fluctuations, and intensity fluctuations, was investigated. An analytical formula was obtained for the spectrum of the diode-laser field formed by frequency fluctuations. The spectral density g₀ of the frequency fluctuations, determining the width of the central part of the emission line profile of a diode laser, was found by two independent methods (by fitting to a Doppler-broadened absorption line profile and by finding the intensity of the residual radiation and the saturated-absorption line width). The parameters Ω and Γ of the spectral density of the frequency fluctuations, coupled to the relaxation oscillations and determining the wing of the diode-laser emission line profile, were determined experimentally. By taking into account the instrumental function of the diode laser, involving successive convolution with the recorded emission spectra, it was possible to reproduce correctly the spectral line profile and to solve accurately the problem of the 'optical zero'. The role of the correlation between the intensity noise and the diode-laser frequency was considered.