Table of contents

25%Eu : KGd(WO₄)₂ crystal is grown by a modified Czochralski method and its spectral and lasing properties are studied. Generation of stimulated emission in this crystal on the ⁵D₀→⁷F₄ transition of the Eu³⁺ ion is obtained, as far as we know, for the first time. The laser operates at room temperature at a wavelength of ∼703 nm under pumping into the ⁷F₀→⁵D₁ absorption band of the europium ion by the second harmonic of a Q-switched Nd : KGW laser (λ_pump= 533.6 nm). With a 9.4-mm-long active element, the output energy in the free-running regime reached 244 μJ, while the optical efficiency was 1.5%.

Tm : CaF₂ (4 mol % TmF₃) single crystals and ceramic samples have been prepared, the microstructure of the ceramic has been examined by SEM and AFM, and the luminescent properties of the crystals and ceramic have been analysed.

The effect of quenching additives on the luminescence properties of helium — neon mixtures under pumping by α particles emitted from ²¹⁰Po atoms is considered. It is concluded that, under excitation by a heavy charged particle, the population of the 3p'[1/2]₀ level of neon is not related to the dissociative recombination of molecular ions. It is suggested that the most likely channels for populating the 3p level are the excitation transfer from metastable helium atoms to neon atoms and direct excitation of neon by nuclear particles and secondary electrons.

We studied the possibility of controlling phase-locked lasing of a set of lasers with self-pumped phase-conjugate gain-grating mirrors by using a passive Q-switch and selecting the gain of one of the lasers. The ranges of stable operation are calculated by mathematical simulation and well agree with the experimental results. Single-mode radiation in the form of trains of phase-locked laser pulses are experimentally obtained for the first time in a three-channel diffraction-coupled gain-grating Nd : YAG laser system with a LiF :F ⁻₂ passive Q-switch. The space-time pattern of the trains of 1.064-μm nanosecond pulses is the same in the channels with and without Q-switch and their interference pattern contrast reaches 0.81.

It is proved that lasers with different loop cavities with self-pumped phase-conjugate mirrors in low-gain active media can operate under injection of external laser radiation and can be used for the development of diode-pumped phase-locked multichannel neodymium laser systems operating both on the fundamental laser transition with the wavelength λ = 1.06 μm and on the transition with λ = 1.34 μm. The phase-conjugate oscillation thresholds in the case of injection of an external signal are determined for a multiloop cavity configuration and an increased number of active elements in the cavity. It is shown that phase-conjugate oscillation can occur even if the single-pass gain of the active element is as low as only ∼2. Under high-power side diode pumping of a multiloop Nd:YAG laser, single-mode output radiation was achieved at λ = 1.064 μm with a pulse energy up to 0.75 J, a pulse repetition rate up to 25 Hz, an average power up to 18.3 W, and an efficiency up to 20%. In a multiloop Nd:YAG laser with three active elements in the cavity, single-mode radiation at λ = 1.34 μm was obtained with a pulse energy up to 0.96 J, a pulse repetition rate up to 10 Hz, and an average power up to 8.5 W.

We study the nature of transition from stationary lasing to pulse-periodic oscillations when the phase of the delayed feedback and the diode laser pump current change. The appearance of oscillations can take place under the scenarios of soft or hard excitation of oscillations. We propose a semi-analytical approach to identify the nature of the transition and to determine the dynamic characteristics and stability of the arising spike regime with a change in the external parameters. Direct integration of the Lang — Kobayashi equations showed an acceptable accuracy of this approach.

We recorded the spectrum of delayed secondary electrons ejected from the target, which was coated with a layer of iron enriched with the ⁵⁷Fe isotope to 98%, under its irradiation by fluxes of broadband X-ray radiation and fast electrons from the plasma produced by a femtosecond laser pulse at an intensity of 10¹⁷ W cm^-2. Maxima were identified at energies of 5.6, 7.2, and 13.6 keV in the spectrum obtained for a delay of 90 — 120 ns. The two last-listed maxima owe their origin to the internal electron conversion of the isomeric level with an energy of 14.4 keV and a lifetime of 98 ns to the K and L shells of atomic iron, respectively; the first-named level arises from a cascade K — L₂L₃ Auger process. Photoexcitaion by the X-ray plasma radiation is shown to be the principal channel of the isomeric level excitation.

Experiments in the commutation of extended (∼1-m long) high-voltage (up to 390 kV) electric discharges were carried out with the aid of 100-ns long UV pulses of the GARPUN KrF laser, in which we demonstrated a one-and-a-half-fold lengthening of the discharge gap broken down in the presence of laser illumination. Total control of discharge trajectory along the direction of the laser beam was observed for a radiation energy of ∼300 mJ (the corresponding intensity I = 5×10⁸ W cm^-2 and its attendant initial electron density Ne ∼ 10¹¹ cm^-3) and partial control for an energy of 40 mJ (I = 7×10⁷ W cm^-2, Ne ∼ 8×10⁹ cm^-3) with a 100% probability of breakdown. We discuss the advantages of employing a UV laser for active lightning protection in comparison with IR lasers and ultrashort-pulse laser systems.

The design, assembly, and alignment of a Kirkpatrick – Baez X-ray microscope are described. A technique for the experimental evaluation of the resolving power of the microscope is outlined. This microscope permits obtaining simultaneous images of laser target plasmas in narrow energy regions belonging to the 0.3 – 1.5-keV X-ray range with a resolution of ∼2 μm.

We present the operator model of the laser resonator with an active output mirror based on the Fabry – Perot interferometer with nonflat (spherical and aspherical) mirrors and an adjustable gap. The results of numerical simulation of a microchip laser with a thermal lens and an active output interferometer-based mirror are given. It is shown that the use of an active interferometer as the output cavity mirror allows one to control the number of transverse modes of laser radiation and its power; in this case, the beam divergence can be reduced by a factor of 1.5 – 2.5.

A novel birefringent microstructured fibre (BMF) design is proposed, and its birefringence and dispersion characteristics are analysed using the finite element method. The results indicate that the proposed BMF design ensures high birefringence (∼5×10^-3) at a low mode asymmetry. At a certain core ellipticity, the BMF configurations considered may have equal mode field sizes along two orthogonal axes.

We report a theoretical analysis and experimental study of the possibility of producing a novel type of interferometric near-field aperture probe for near-field optical microscopy systems using a fibre Fabry – Perot microcavity with a nanometre-scale aperture made in one of its output mirrors. The probe ensures a spatial resolution no worse than λ/14.

A new method for fabricating large-area thin films of uniform thickness on a rotating substrate is proposed. Its distinctive features are (i) the presence of a diaphragm, partially transmitting the evaporated material, between the target and substrate and (ii) the translatory motion of the rotating substrate with respect to the target at a certain velocity. The method proposed makes it possible to obtain thin films of uniform thickness on substrates with sizes limited by only the deposition chamber size. The method is experimentally verified by depositing thin CuO films on silicon substrates placed over the radius of a disk 300 mm in diameter. The deviation of the film thickness from the average value does not exceed ±3% throughout the entire radius, which confirms good prospects of this method for microelectronics, optical industry, and other modern technologies.

The self-action of light in birefringent mesoporous silicon films is studied using picosecond laser pulses. Two mechanisms of self-action of light in mesoporous silicon are found. One of them manifests itself at laser intensities below 3 MW cm^-2 and tends to saturation. The other dominates at intensities above 10 MW cm^-2. The former is related to the resonant excitation of electronic states on the surface of silicon nanocrystals, whereas the latter is due to the local fields in the nanocomposite. For the aforementioned ranges of the laser intensity, the cubic nonlinear susceptibility of the films exceeds that of single-crystal silicon by six and four orders of magnitude, respectively, and the figure of merit for the films exceeds that for single-crystal silicon by an order of magnitude.

Special features of light-induced scattering of radiation (λ = 0.44 μm) with extraordinary polarisation in the SBN-75 photorefractive crystal are studied in detail and an efficient technique is proposed for exciting surface waves in this crystal. In the experiment carried out the efficiency of the surface wave excitation was ∼30%, which is 50 times greater than that achieved earlier in exciting nonlinear surface waves in the optical region. The patterns of the near and far fields of the surface wave are presented. It is found that at small excitation angles (0 – 1.5°) the presence of a metal changes the character of arising surface waves.

Spectra of Raman scattering of light by aqueous ethanol solutions in the range of concentrations from pure water to 96% alcohol are studied. For water, 25%, and 40% solutions of ethanol in water, as well as for 96% alcohol the Raman spectra are measured at temperatures from the freezing point to nearly the boiling point. The changes in the shape of the stretching OH band are interpreted in terms of strengthening or weakening of hydrogen bonds between the molecules in the solution. The strongest hydrogen bonding of hydroxyl groups is observed at the ethanol content from 20 to 25 volume percent, which is explained by formation of ethanol hydrates of a definite type at the mentioned concentrations of alcohol. This is confirmed by means of the method of multivariate curve resolution, used to analyse the Raman spectra of aqueous ethanol solutions. With growing temperature the weakening of hydrogen bonding occurs in all studied systems, which consists in reducing the number of OH groups, linked by strong hydrogen bonds.

We study the efficiency of Müller matrix diagnostics of birefringence in biological tissue layers with different optical thickness by measuring a set of third- and fourth-order statistical moments, characterising the coordinate distributions of the matrix element Z₄₄ at different points of the histological section.

We discuss the basic scheme of laser Doppler optical mixing spectroscopy for the analysis of media with multiparticle scattering. It is shown that the Rayleigh scheme, in contrast to the heterodyne and differential schemes, is insensitive to the effects of multiparticle scattering.