Table of contents

The problem of stability of single-frequency lasing is considered using a model including one lasing mode and two nearest subthreshold modes. It is shown that, the parametric interaction of the laser and subthreshold modes, due to the electron concentration beats at the intermode frequency, can cause the self-stabilisation of the single-frequency lasing regime, in which the laser frequency detuning with respect to the spectral gain maximum can exceed the mode interval, and spectral hysteresis can be observed.

Theoretical and experimental studies of spectral and energy characteristics of radiation of a photoinitiated HF/DF laser working on the chain reaction in the F₂:(H₂+D₂):O₂:He=3:1:0.3:6.7 mixture are performed under atmospheric pressure as functions of the ratio of the initial concentrations of H₂ and D₂ and the resonator losses. Optimal conditions are determined for simultaneous lasing in HF and DF molecules in the spectral range 2.7 — 4.8 μm.

The absorption spectrum, refractive index, and relief of the surface of a germanosilicate glass film are studied upon the non-destructive action of the 216-nm (5.75-eV) fifth harmonic of a repetitively pulsed Nd:YAP laser. It is shown that laser irradiation of films induces a strong photorefractive effect despite the relatively low absorption coefficient. For the 100-mJ cm^-2 energy density and above, two-photon process make a noticeable contribution to the absorption of laser radiation at 216 nm. The diffraction efficiency of photoinduced phase gratings achieved ~7×10^-3 for the exposure dose ~6 kJ cm^-2, which corresponds to the induced refractive index 1.5×10^-3. At higher exposure doses, a relief appears on a film surface and the diffraction efficiency of a phase grating is reduced.

The properties and parameters of volume-structured metal media produced by exploding thin conductors in a high-power electric discharge are analysed. Such media are proposed for the production of nonequilibrium high-temperature laser plasma as a high-power X-ray and neutron radiation source. The physics of the interaction of a high-power laser pulse with a volume-structured metal medium and the properties of produced nonequilibrium plasma are considered.

Photophysical processes proceeding in polyatomic organic molecules (pyran derivatives and cyanines) excited by high-power laser radiation at 532 nm are studied. Some properties of their changes depending on the structure, solvent, and excitation conditions are determined. The effect of limitation of high-power exciting radiation by the organic molecules is found. The maximum limitation (K_max = 15.0 at the initial transmission equal to 70%) was observed for the cyanine derivative and is comparable to this effect for fullerenes C₆₀, which are widely used as radiation limiters.

Laser deposition of zinc oxide films is studied. An intermediate screen is used to prevent microparticles formed during laser ablation of the target from falling on the film. The effect of deposition conditions on the morphology of the film, its electrical properties and crystal structure is studied. It is shown that the laser deposition technique can be used to obtain films of both types. The resistivity of the films was 0.07 Ω cm for films with the n-type conduction and 0.08 Ω cm for films with the p-type conduction. The photoluminescence studies of the films have shown that stimulated radiation is generated in the films under pump intensity exceeding 6 MW cm^-2.

The effect of an impurity film lying on the surface of a target in a vacuum of up to 10^-5 Torr on the ion acceleration in a plasma, which is formed by a 2×10¹⁶-W cm^-2 femtosecond laser pulse is studied using the time-of-flight and mass spectrometry techniques. It is shown that, under such conditions, the maximum mean energy per unit charge (8 keV) is gained by protons, whereas the ions constituting the target substance (Si, Ti) acquire an energy per unit charge of <1 keV. The use of a <10 J cm^-2 nanosecond laser pulse applied 0.1–100 ms before a femtosecond laser pulse allows the target surface to be efficiently cleaned due to the removal of H-, C-, and O-containing molecules from it. Unlike a continuous thermal heating of a surface, the pulse laser cleaning ensures higher heating temperatures and can be efficiently applied to any solid targets in both the thermal and plasma cleaning modes.

Based on the analysis of frequency-nondegenerate four-photon parametric scattering, the spectral-angular dependences of the increments of perturbing modes are obtained in the field of an intense light wave propagating in a medium with cubic nonlinearity.

An efficient generation of 350–600-nm wavelength-tunable radiation is experimentally demonstrated through nonlinear-optical frequency conversion of femtosecond Cr:forsterite-laser pulses in an array of submicron fused silica threadlike waveguiding channels in a microstructure fibre. Nonlinear-optical spectral transformation of femtosecond pulses in such waveguide channels gives rise to new isolated spectral components with frequencies exceeding the frequency of the third harmonic of pump radiation. Some of these new spectral components are separated from the central pump frequency by a frequency gap exceeding 580 THz.

The quasi-resonance interaction of a laser pulse with an inhomogeneously broadened quantum transition is numerically simulated under conditions corresponding to the experiment on the study of self-induced transparency in rubidium vapours. It is shown that the experimental shift of the pulse spectrum is caused by the initial stage of the formation of a precursor pulse and the influence of irreversible relaxation. It is found that the precursor pulse is more stable to the destructive action of relaxation than the 2π pulse and appears even in the case when the input pulse area is insufficient for the formation of the 2π pulse.

It is shown that a specific dip in the spectral dependence of the nonlinear response of ultrathin metal films observed by the method of degenerate four-photon spectroscopy is caused by a change in the phases of interfering components of the electron nonlinear susceptibility. This allows one to measure the time scale of subpicosecond intraband processes using picosecond light pulses.

The propagation of light beams is studied in a planar photorefractive waveguide fabricated by high-temperature diffusion of metal ions in the Z-cut substrate of the 3m symmetry crystal. The wave equations are obtained for single-mode light beams with TE and TM polarisations in planar diffusion waveguides, which take into account the two-dimensional distribution of the optical field. Expressions are found for a nonlinear change in the refractive index when the photovoltaic mechanism makes a dominant contribution to the photorefractive effect. The propagation of single-mode light beams is analysed numerically for a Ti:Fe:LiNbO₃ waveguide fabricated by the successive diffusion of titanium and iron into lithium niobate. It is shown that single-mode light beams with a smooth amplitude envelope can propagate without significant changes in the region of a dip in the intensity modelling a dark soliton. The relations between the amplitude and width of a dark spatial soliton are obtained for the TM modes of a photorefractive planar waveguide.

An X-ray resonator design is proposed in which peculiar pear-shaped reflectors, which are grazing-incidence X-ray mirrors, serve as optical elements. Special features of this resonator are relatively high reflector efficiencies and the axial symmetry of the output radiation.

Time sweeps of the autocorrelation function and the emission spectrum of an actively mode-locked Nd:YAG laser are recorded during the development of quasi-continuous pre-lasing maintained by a negative feedback loop. It is found that higher Hermitian—Gaussian supermodes are present at the transient stage of radiation, and the ultrashort pulse shortening is accompanied by the shift of the lasing spectrum to the red wing of the gain band of the active medium.

A simple astigmatic scheme for obtaining focused Laguerre—Gaussian beams upon the π/2 conversion of Hermite—Gaussian radiation modes is described. A zone in the vicinity of the focal region of a lens is estimated where the beam satisfies the conditions for the capture and confinement of microparticles. It is shown that this optical scheme uses the fractional Fourier transform, whose application in the π/2 converter is demonstrated for the first time.

The propagation of phase-modulated optical pulses through thin-layer interference antireflection structures is studied. An analytic expression relating the parameters of the incident and reflected pulses is obtained. The time dependence of the phase modulation of the incident pulse was obtained using this expression together with experimental data. The splitting of the pulse after its reflection from the interference structure into two pulses with different spectra allows the use of these pulses in compressors to obtain ultrashort pulses with different carrier frequencies.

A modification of the quantum-mechanical theory of rotation of polyatomic molecules (binary rotation) is proposed, which is based on the algebra and representations of the SO(4) group and allows the introduction of the concept of parity, as in atomic spectroscopy. It is shown that, if an asymmetric top molecule performing binary rotation finds itself in a spatially inhomogeneous electric field, its rotational levels acquire the additional energy due to the quadrupole moment. The existence of the rotational states of polyatomic molecules that cannot transfer to the free rotation state is predicted. In particular, the spin isomers of a water molecule, which corresponds to such states, can have different absolute values of the adsorption energy due to the quadrupole interaction of the molecule with a surface. The difference in the adsorption energies allows one to explain qualitatively the behaviour of the ortho- and para-molecules of water upon their adsorption on the surface of solids in accordance with experimental data.

The propagation of a partially coherent (random) wave field in inhomogeneous media is considered. The equation for the second-order coherence function is solved by the ray diffraction method and an algorithm is obtained for taking into account the effect of refraction (linear and nonlinear) as well as the turbulence of refractive index fluctuations on the variation of beam radius and the coherence radius during propagation of radiation with an arbitrary initial coherence on atmospheric paths.