Table of contents

Amplifiers based on neodymium phosphate glass rods 60 — 100 mm in diameter are experimentally studied. The amplifiers are pumped by INP-16/250 tubular flash lamps placed in a universal pump cavity with a two-section mirror reflector. A compact high-voltage capacitive energy storage with a preionisation circuit was developed to supply the lamps.

We report holmium-doped fibre lasers with a Ho³⁺ concentration of 1.6 × 10¹⁹ cm^-3 and lasing wavelengths of 2.02, 2.05, 2.07 and 2.1 μm at a pump wavelength of 1.15 μm. The slope efficiency of the lasers has been measured. The maximum efficiency, 0.455, has been obtained at a lasing wavelength of 2.05 μm. The laser efficiency is influenced by both the optical loss in the wing of a vibrational absorption band of silica and active-ion clustering.

We consider physical foundations of an eventual experiment aimed at observing stimulated gamma-photon emission of long-lived Mössbauer isomers through selective frequency modulation of gamma-resonances establishing hidden population inversion without exceeding the number of excited nuclei over unexcited ones and without additional pumping. The examples of suitable nuclei and numerical estimates of the parameters are presented.

We propose a new method of temporal shaping of picosecond laser pulses using interference of chirped beams reflected from chirped volume Bragg gratings. This method is numerically simulated and experimentally tested. Quasi-rectangular picosecond pulses are experimentally obtained.

The synchronisation of periodic self-modulation oscillations in a ring Nd:YAG chip laser under an external periodic signal modulating the pump power has been experimentally investigated. A new quasi-periodic regime of synchronisation of self-modulation oscillations is found. The characteristic features of the behaviour of spectral and temporal structures of synchronised quasi-periodic oscillations with a change in the external signal frequency are studied.

The dependence of the repetition frequency range that provides stable operation of a picosecond laser with longitudinal pulsed diode pumping on the parameters of the laser cavity and the thermal lens induced in the active element is analysed. The results of calculating the radius of the lower cavity mode as a function of pump beam average power and diameter are reported. Based on the measurements by the probe-beam method, the adequacy of the presented model of aberration thermal lens is demonstrated for the cases of uniformly doped Nd:YAG and composite YAG/Nd:YAG active elements upon tuning the pump pulse repetition frequency within the range of 0 — 1 kHz. The ways for implementing stable generation of millijoule pulses in a specified repetition frequency range are discussed.

The intensity of K_α radiation emanating from transversely limited thin laser targets with a periodic relief superposed onto its front side was calculated. The relief parameters and the geometrical target dimensions were optimised with the help of an analytic model. The optimal target was shown to possess a nearly 100% absorption coefficient for laser radiation and a high (up to 10^-3) coefficient of laser radiation conversion to the X-ray K_α radiation.

The spatial and amplitude characteristics of photonic nanojets from micrometre-sized composite particles consisting of a nucleus and several shells with different refractive indices were considered. We investigated the longitudinal and transverse dimensions of the photon jet as well as the dependence of its peak intensity on the optical contrast of the shells. It was shown that, by varying the refractive index of the neighbouring shells in composite spherical microparticles, it is possible to manipulate the photonic nanojet parameters, in particular, increase its length or raise the peak intensity of the photon flux.

Cross sections of scattering, absorption, and light pressure for a chiral spherical particle in a circularly polarised light field are studied for different values of the radius, dielectric constant, permeability, and parameter of the chiral particle. The conditions are found under which the cross sections of absorption and light pressure differ significantly when nanoparticles are exposed to light with different polarisations, which can be used to improve synthesis of chiral nanoparticles of complex structure.

We have proved for the first time and proposed an algorithm of unique spatial profile reconstruction of the components ⁽³⁾_yyyy of complex tensors ⁽³⁾(z, ω', ω', −ω, ω) and ⁽³⁾(z, 2ω±ω', ±ω', ω, ω), describing four-photon interaction of light waves in a one-dimensionally inhomogeneous plate, whose medium has a symmetry plane m_y that is perpendicular to its surface. For the media with an additional symmetry axis 2_z, 4_z, 6_z or ∞_z that is perpendicular to the plate surface, the proposed method can be used to reconstruct about one-fifth of all independent components of the above tensors.

Analytical formulas are derived to approximate the probability density functions of 'zero' and 'one' bits in a linear communication channel with a binary format of optical signal phase modulation. Direct numerical simulation of the propagation of optical pulses in a communication line with optical phase conjugation is performed. The results of the numerical simulation are in good agreement with the analytical approximation.

A nonlinear Schrödinger equation with varying dispersion, nonlinearity and gain (or absorption) is studied for ultrashort optical pulses propagating in inhomogeneous optical fibres in the case of normal dispersion. Using the modified Hirota method and symbolic computation, the bilinear form and analytic soliton solution are derived. Stable bright and dark solitons are observed in the normal dispersion regime. A periodically varying soliton and compressed soliton without any fluctuation are obtained. Combined and kink-shaped solitons are observed. Possibly applicable soliton control techniques, which are used to design dispersion-managed systems, are proposed. The proposed techniques may find applications in soliton management communication links, soliton compression and soliton control.

This paper examines the effects of surface roughness and absorption on laser light propagation in graded-profile waveguiding structures. We derive analytical expressions for the scattering and absorption coefficients of guided waves and analyse these coefficients in relation to parameters of the waveguiding structure and the roughness of its boundary. A new approach is proposed to measuring roughness parameters of precision dielectric surfaces. Experimental evidence is presented which supports the main conclusions of the theory.

Two-dimensional spatial intensity distributions of diffuse scattering of near-infrared laser radiation from a strongly scattering medium, whose optical properties are close to those of skin, are obtained using Monte Carlo simulation. The medium contains a cylindrical inhomogeneity with the optical properties, close to those of blood. It is shown that stronger absorption and scattering of light by blood compared to the surrounding medium leads to the fact that the intensity of radiation diffusely reflected from the surface of the medium under study and registered at its surface has a local minimum directly above the cylindrical inhomogeneity. This specific feature makes the method of spatially-resolved reflectometry potentially applicable for imaging blood vessels and determining their sizes. It is also shown that blurring of the vessel image increases almost linearly with increasing vessel embedment depth. This relation may be used to determine the depth of embedment provided that the optical properties of the scattering media are known. The optimal position of the sources and detectors of radiation, providing the best imaging of the vessel under study, is determined.

We study spectral composition, quantum yield and spatial intensity distribution of radiation of excited particles, escaping from the surface of some organic dyes and their mixtures with lipids under bombardment by Ar⁺ ions. Essential influence of the method of target preparation from organic compounds on the yield of the excited particles is demonstrated. The processes resulting in formation of excited particles under ion bombardment of complex organic systems are specified. The model of interaction of lipids with organic dyes is proposed.

Self-imaging of transparent objects and structures in focusing of a spatially phase-modulated laser beam into an extended weakly absorbing medium is described. The laser power level that is necessary for effective imaging corresponds to the illuminating beam power when thermal self-defocusing starts evolving in the medium. The effect can be described in terms of the ideology of Zernike's classical phase-contrast method. Edge enhancement in visualised images of transparent objects is experimentally demonstrated. Self-imaging of a microscopic object in the form of transparent letters and long-lived refractive-index fluctuations in liquid glycerol is shown. Due to the adaptivity of the process under consideration, unlike the classical case, self-imaging occurs also in the situations where a beam is displaced (undergoes random walk) as a whole in the Fourier plane, for example, in the presence of thermal flows.

The Jones matrix method is used to analyse the polarisation eigenmodes of a solid-state laser with an anisotropic Fabry — Perot cavity containing amplitude and phase anisotropic elements. The results demonstrate that, when the axes of these elements do not coincide, the eigenpolarisations become elliptical and nonorthogonal. The ellipticities and azimuths of the polarisation modes and the magnitude and phase of the nonorthogonality parameter are determined as functions of polariser angle at different relationships between the amplitude and phase anisotropies, and the effect is shown to be strongest at a polariser angle of 45°. There is critical phase anisotropy, dependent on amplitude anisotropy, at which the magnitude of the nonorthogonality parameter and ellipticity of the polarisation modes approach unity.

The information about the congresses held in Japan and devoted to fast imaging processes and photonics is presented. Reports devoted to the technique and the results of applications of superhigh-speed recording instrumentation in different fields of science and technology are considered.