Table of contents

A technique of vacuum-free deposition of thin films from laser-induced plasma arising upon the ablation of a target by intense laser radiation is proposed and experimentally realised. Experimental results on the deposition of hard carbon coatings onto stainless steel substrates upon evaporation of a graphite target in air by picosecond pulses from a Nd:YAP laser are presented. According to the data of X-ray electron spectroscopy and X-ray diffraction analysis, the films obtained in our experiments consist of sp²- and sp³-bound amorphous carbon with a small admixture of oxygen. The coating was tested for mechanical properties to exhibit excellent results, including nanohardness (12 — 14 GPa on the average, up to 40 GPa locally) and adhesion to the substrate (>60 MPa), undeniably testifying to the promise of this technique.

The polarisation absorption spectra of forsterite single crystals grown from a melt containing from 0.015 to 0.97 wt% of chromium are studied. Most of the crystals were grown by the Czochralski method under standard oxidation conditions (1.4–2.4 vol % of oxygen). Some crystals were grown in the atmosphere with a higher content of oxygen (~12 vol %) or in the neutral atmosphere (100% of Ar). Crystals grown from a melt containing more than 0.6 wt % of chromium exhibited the saturation of absorption of Cr⁴⁺ ions. The maximum absorption coefficient of Cr⁴⁺ ions at 1064 nm was ~3.2 cm^-1. The relative content of Cr³⁺ ions also increased (approximately by 70% in the range studied) with increasing the doping level. The relative content of Cr³⁺ ions in a crystal grown in the atmosphere with a high content of oxygen (~12 vol %) was approximately lower by a factor of 1.5 than that in a crystal grown in the standard oxidation atmosphere.

The polarised luminescence spectra of forsterite single crystals grown from a melt containing from 0.015 to 0.97 wt% of chromium are studied. Most of the crystals were grown by the Czochralski method under standard oxidation conditions (1.4–2.4 vol% of oxygen). Some crystals were grown in the atmosphere with a higher content of oxygen (~12 vol%) or in the neutral atmosphere (100% of Ar). The luminescence of Cr⁴⁺ ions excited to the ³T₂ level at 980 nm and to the ³T₁ level at 632.8 nm exhibited no quenching over the entire range of crystal doping. In crystals absorbing above 70% of laser energy, the self-absorption of luminescence of Cr⁴⁺ ions was observed. The reabsorption of luminescence of Cr³⁺(2) ions located in sites of the forsterite crystal with the mirror symmetry occurs stronger because of a greater overlap of the luminescence band of Cr³⁺(2) ions with the absorption bands of Cr⁴⁺ ions. The luminescence of Cr⁴⁺ ions is found to be polarised predominantly along the b axis for any polarisation of exciting radiation. The broadband luminescence of Cr³⁺(2) ions is polarised predominantly along the c axis for all the crystals studied, irrespective of the polarisation of exciting radiation and the oxygen concentration in the crystal-growth atmosphere. The luminescence of Cr³⁺(2) ions polarised along the c, b, and a axes has maxima at ~900, 860, and 850 nm, respectively.

A mathematical model of an HCl gas laser optically pumped into the third vibrational overtone is developed. The results of numerical calculations are in good agreement with experimental data. The characteristics of the laser are studied and its parameters are optimised using numerical simulations.

The parameters of an HCl gas laser optically excited into the third vibrational overtone are studied. The laser was excited by a single-frequency tunable :LiF colour centre laser. Upon pumping the HCl gas into the (3–0) R(3) transition at 1.189 μm, lasing was observed at the (3–2) P(5) (1.189 μm) and (2–1) P(6) (3.769 μm) transitions, respectively. The experimental slope efficiency of the molecular laser achieved 2%.

A new technique is proposed for the production of atomic iodine for a cw oxygen—iodine laser with the use of reactions between iodine donor molecules and oxygen atoms. The CH₃I, CF₃I, or I₂ molecules can be used as donors. Oxygen atoms are injected into the reaction region by admixing the flow of partially dissociated oxygen produced in an electric discharge. The use of atomic iodine instead of molecular iodine excludes the consumption of singlet oxygen O₂(¹Δ) for the dissociation of I₂ and quenching of I* by the I₂ molecules. The latter will supposedly allow raising the optimal density of I and accordingly the gain coefficient. Estimates were made of the required degree of dissociation of oxygen employed to obtain iodine atoms at which the above advantages can be realised.

Assuming the possibility of 'detachment' of the excited vibrational level from the level specified by temperature, the experimental data on Raman scattering of light in conjugated polymers are interpreted. It is shown that upon optical pumping, vibrational excitations in a chain of alternating C—C and C=C bonds are combined to form a vibrational 'condensate' and a 'quantum gas', which are localised at one of the bond types due to the spontaneous violation of symmetry. Scattering by the condensate and a part of the quantum gas captured by the condensate explains the appearance of the low-frequency wing of the anti-Stokes line in the Raman spectrum of conjugated polymers and the anomalous relation between the intensities of the Stokes and anti-Stokes components at temperatures up to room temperature.

It is shown that the interaction of counterpropagating coherent light beams at a wavelength of 633 nm in a Bi₁₂TiO₂₀:Ca:Ga crystal leads to the formation of a holographic reflection grating, which is a combination of phase and amplitude components related to photoinduced perturbations of the refractive index and absorption coefficient of the crystal. The formation of the grating is accompanied by a photoinduced decrease in the absorption coefficient of light Δα by -0.07 cm^-1. Photoinduced bleaching of the crystal occurs when the crystal is exposed to incoherent radiation at 600 nm (Δα= -0.12 cm^-1), while an increase in absorption is observed upon irradiation at 570 nm.

Coherent effects in the interference of overlapping laser-induced resonances in helium atoms are considered. The simultaneous action of single-mode radiation of the 294-nm second harmonic of a cw dye laser and a 1064-nm Nd:YAG laser on helium atoms provides the overlap of two resonances induced by transitions from the 1s2s¹S and 1s4s¹S helium levels. The shape of the overlapping laser-induced resonances in the rotating-wave approximation is described by analytic expressions, which depend on the laser radiation intensities and the ratio of laser frequencies.

The properties of the astigmatic π/2 converter are analysed upon the transformation of eigen- and non-eigenmodes, and beams of arbitrary type. It is shown that the action of the converter can be reduced to even and odd numbers of Fourier transforms performed independently in two orthogonal planes containing the optical axis of the converter. The operation of two arbitrary oriented π/2 converters in tandem is described. This scheme permits obtaining at the same plane alternatively either the object image or its Fourier transform. Examples of the numerical simulation of the radiation propagation through the examined optical schemes are presented.

Two types of rotators of arbitrary beams based on astigmatic π/2 and π converters of laser modes are described. Unlike traditional rotators of Dove prism type, proposed schemes use exclusively refracting optical components. Numerical simulations of the beam rotators are performed based both on Fresnel theory and ray-tracing method.

A theory of the transport and localisation of spherical dielectric particles in a liquid under the action of a gradient force in a laser-radiation field with a periodically modulated intensity is developed. An expression for the gradient force is derived in the Rayleigh — Hans approximation. The Langevin equation of motion is numerically solved using this expression. The transport and localisation of particles are investigated depending on their properties, the viscosity of the liquid, and the parameters of laser radiation.

The destruction of the spatial coherence of multimode laser radiation in a delay-line-based system is analysed theoretically and experimentally. A scheme of a coherence-transforming device operating in a broad wavelength range and various lasing regimes is proposed. This scheme is shown to be efficient for rapid speckle-noise suppression in optical recording and lithography.

A schematic solution is proposed for creating a highly efficient switching network with fully connected switching topology for use in supercomputers and telecommunication systems. An important characteristic of this solution is the use of vertical-cavity surface-emitting semiconductor laser arrays and polarising beamsplitters. Estimates show that the commercially available elemental base can be used for a practical realisation of an optoelectronic switching network with basic parameters and functional properties that are superior to those in known electronic analogues.

Single-mode fibres of a new type are manufactured. The fibres are made of high-purity silica and have a flat spectral dependence of chromatic dispersion in the region of 1550 nm varying over the fibre length. The new method and technology are proposed for manufacturing single-mode fibres with dispersion characteristics varying in a specified way along the fibre length.

The conditions for the appearance of the modulation instability of a wave packet in a medium with the imaginary components of the propagation constant and dispersion parameters are studied. The possibility of existence of modulation instability in the region of normal material dispersion, the bistable nature and the dependence of the dynamics of its development on the ratio of the imaginary and real components of dispersion parameters are revealed.

Glass fibres with a hollow core and a two-dimensionally periodic cladding are studied experimentally and theoretically. The spectrum of modes guided in the hollow core of these fibres displays isolated maxima, indicating that waveguiding is supported due to the high reflectivity of the fibre cladding within photonic band gaps. The main properties of the spectrum of modes guided in a hollow core of a photonic-crystal fibre and radiation intensity distribution in these modes are qualitatively explained in terms of the model of a periodic coaxial waveguide.

The effect of the inhomogeneous distribution of nitrogen impurity on the photosensitivity of germanosilicate fibres is studied. For this purpose, single-mode fibres with different alternations of the core layers sintered in nitrogen and oxygen atmospheres were specially prepared by the MCVD technique. Photoinduced variations in the quadratic nonlinear susceptibility and refractive index of these fibres were recorded. It is shown that the recording efficiency depends on the radial distribution of germanium oxygen-deficient centres, which can be controlled at the stage of sintering through a nonuniform doping by nitrogen over the cross-section.