Table of contents

The results of experimental studies of the parameters of a 223-nm electric-discharge KrCl excimer laser on a He—Kr—HCl mixture depending on the excitation conditions and the composition of the active gaseous medium are presented. To achieve the maximum values of the output energy and the efficiency of the KrCl laser on mixtures with buffer gaseous helium, an excitation system was used that included a circuit with an LC inverter with a high-voltage switch based on an RU-65 spark gap. An output energy of 320 mJ with an efficiency of 0.5% relative to the energy stored in the capacitors is obtained in a KrCl laser with an active medium based on the buffer He gas at a charging voltage of 30 kV. Radiation pulses with a duration of 22±1 ns and a pulse power of 15 MW are obtained.

A model of a pulsed liquid solar-pumped laser is constructed. A neodymium-containing phosphorus oxychloride (POCl₃—SnCl₄—Nd³⁺) liquid is proposed as an active medium. The lasing parameters of this medium are calculated for a spaceborne laser as functions of its size and the coefficient of solar energy concentration.

The specific energy yield is calculated as a function of the pressure of oxygen and SF₆ buffer gas taking into account the secondary processes with the participation of the HO₂ radical. The results of these calculations are compared with the experimental data. A significant role of reactions with the participation of the HO₂ radical is revealed. A numerical analysis of the experiments also makes it possible to appreciably refine the rate constant of a process of interrupting a chain reaction with the participation of H₂ and F₂ as third bodies.

An Er-doped fibre laser pumped at 1480 nm by a Raman converter of radiation from a diode-pumped ytterbium-doped fibre laser is built and investigated. The laser can operate in the soliton and stretched pulse regimes. The laser emits 1550-nm, <100-fs pulses with a pulse repetition rate of 25 MHz and has an average power of 10 mW.

The influence of UV illumination of a discharge gap on the stability and homogeneity of a volume self-sustained discharge (VSD) in working mixtures (SF₆ with hydrocarbons) of a non-chain HF laser is studied in broad ranges of the discharge-current duration and the energy deposition. It is shown that the UV illumination in lasers with the cathode area S≤300 cm² and in lasers with the current-pulse duration T≤150 ns stabilises the delay time and the voltage amplitude of the electric breakdown of the gap and leads to the levelling (due to photoeffect) of the VSD current density distribution over the cathode surface. The volume preionisation of the working mixture of a non-chain HF laser by UV radiation is impossible because of strong absorption of this radiation by SF₆. There is no need in UV illumination in wide-aperture, large-volume lasers when small-scale (∼50 μm) inhomogeneities are present on the cathode surface.

The lasing efficiency and the service life of pyrromethene and phenalemine dyes doped to nanoporous glass-polymer composites are studied upon monochromatic laser pump. The absorption and luminescence spectra of these dyes are investigated. The spectral parameters of the dyes determining their lasing efficiency are found from the analysis of their spectra and lasing characteristics, and the dyes are classified according to their lasing efficiency. A correlation between the lasing efficiency and the service life of laser elements is also established.

It is shown that, when a narrow-band signal with a non-Gaussian envelope propagates in a medium with a strong dispersion, the signal envelope being distorted due to the dispersion of the gain (or) absorption in the medium. Nevertheless, the amplitude-modulated signal having a symmetric (even) intensity envelope remains the same. The propagation velocity of the `middle point' (i.e., the symmetry centre) of the signal coincides with the real group velocity of the wave with a given carrier frequency in the medium and can be subluminal, superluminal or negative. Therefore, the concept of a real group velocity (including the superluminal or negative velocity) is also applicable in media with a strong dispersion of the gain (or absorption).

The lateral (in the substrate plane) interaction between dipoles induced in particles adsorbed on a solid surface is studied in a comparatively weak laser radiation field with a Gaussian transverse distribution. It is shown that the particles migrate over the surface in the radial direction either outside an illuminated spot with the formation of a 'crater' or inside the spot with the formation of a 'mound'.

A new mechanism of laser acceleration of charged particles is investigated in detail. Upon irradiation by tightly focused high-intensity ultrashort laser pulses, the acceleration of electrons travelling along the laser beam axis is determined by the longitudinal ponderomotive force and the longitudinal component of the electric field of the laser wave. It is found that the action of the longitudinal field on an electron may be unidirectional during many optical cycles, i.e., the phase slip effect is overcome. Lasers with currently highest possible parameters are shown to enable electron acceleration up to energies ε ∼ 1 GeV, which is comparable to the energies attainable on `large' accelerators of the SLAC type (ε ∼ 30 — 50 GeV). Unlike the schemes considered in the literature, the acceleration in this case is insensitive to the initial field phase (the effect of electron bunching is absent), it is possible to accelerate slow (nonrelativistic) electrons, and the problem of accelerated electron extraction from the field does not exist.

The plasma formed by femtosecond laser radiation with an intensity higher than 10¹⁶ W cm^-2 at the free surface of a liquid (VM-1 vacuum oil) in vacuum has parameters which are similar to the parameters of the high-temperature plasma produced at the surface of a solid target. The hot-electron temperature (derived from X-ray and ion time-of-flight measurements) is 6 ± 3 keV for the VM-1 oil target and 4 ± 1 keV for a crystal silicon target. The optical diagnostics of the relaxation of the liquid target surface revealed that the limiting laser pulse-repetition rate whereby the interaction takes place with the unperturbed liquid surface may be as high as 10 Hz.

The nonlinear transmission of high-power 532-nm and 308-nm laser pulses of duration 7–13 ns by solutions of porphyrins and phthalocyanines and their metal complexes (13 compounds) is studied. The limitation of optical radiation at wavelengths 532 and 308 nm is studied depending on the laser radiation intensity, the solvent type, and the concentration of solutions. The effective cross sections for absorption of radiation by excited molecules are estimated. The induced short-lived absorption in the visible spectral region is studied in the range of hundreds of nanoseconds. The mechanisms of limitation of laser radiation are discussed.

The coefficients of two-photon absorption of 30- and 70-ns ArF laser pulses in high-purity CaF₂, BaF₂, and Al₂O₃ crystals are measured by the method of nonlinear transmission to be 2.2 ± 0.8, 2.3 ± 0.8, and 5.6 ± 2.2 cm GW^-1, respectively. The thresholds of the laser breakdown of the surface of crystals are determined.

The role of diffraction in the propagation of few-cycle pulses is studied in hydrogen-containing ferroelectrics in the case of the active role of optical electronic and tunnelling transitions. It is shown that, unlike optical electronic transitions, tunnelling proton transitions can produce the defocusing effect if they are overlapped by the spectral components of the pulse. The parameters of a medium and the pulse are estimated at which the defocusing effect dominates over self-focusing. It is shown that nonresonance quasi-monochromatic pulses in the optical range are subjected to self-focusing in such media.

Nonlinear refraction, nonlinear absorption, and optical limitation are studied in Bi₁₂SiO₂₀ (BSO) and Bi₁₂GeO₂₀(BGO) crystals at the 532-nm emission wavelength of a picosecond Nd : YAG laser.

The influence of the third-order dispersion on the propagation of short pulses in optical fibres is considered. The appearance of coupled nonlinear structures consisting of dark and bright envelope solitons is described. The wavelength range is found in the vicinity of the zero-dispersion wavelength where the effect of the third-order dispersion on the pulse propagation proves to be dominant. It is shown that in this case a nonlinear structure in the form of an embedded soliton appears.

The possibility of using the fractional Fourier transform (FrFT) in optical schemes for astigmatic π/2 converters of Hermite—Gaussian modes to donut Laguerre—Gaussian modes is considered. Several schemes of converters based on the FrFT of the half-integer and irrational orders are presented. The lowest FrFT order than can be used in astigmatic mode converters is found. The properties of converters based on the fractional and ordinary Fourier transforms are compared.

The scheme of a tunable astigmatic π/2 mode converter is described. The converter provides the use of input beams with the twofold variable Rayleigh length, while variations in the optical length of the converter itself do not exceed 1/6.

Photosensitivities of hydrogen-loaded silica fibres doped with germanium, phosphorus, antimony, and aluminium are estimated and compared. It is shown that although all the fibres can be pre-exposed, the degree of this effect is noticeably different for different fibres because the induction of the refractive index is determined by a combined contribution from a one-step photochemical reaction and a two-step reaction responsible for pre-exposure. One-step reactions dominate in more photosensitive optical fibres, while two-step reactions dominate in less photosensitive fibres.

Periodic spatial structures formed by cooled beams of free ions of the same sign in traps of one or another type are considered. These structures can be treated as quasi-crystals. Coherent nuclear radiative processes proceeding in the beams depend on a regular arrangement of nuclei in the structure of such crystallised ion beams. These processes include the Dicke superradiance, directional emission of gamma quanta, the establishment of a distributed feedback, and the appearance of the hidden inversion of nuclear states. Conditions required for the emergence of these effects are quantitatively estimated.

A Cr²⁺ : ZnSe laser emitting 100-μs pulses tunable in the 2–3-μm region is used for the first time for the highly sensitive detection of absorption spectra by the method of intracavity laser spectroscopy. The intracavity absorption spectra of the atmospheric air were recorded at different instants of lasing in the spectral region from 2.41 to 2.46 μm. An increase in the sensitivity of the laser emission spectrum to intracavity absorption was observed over the entire range of lasing durations studied.