Vol 29, No 5 (2016)

A model of single filamentation of a high-power ultrashort light pulse has been developed on the basis of evolutionary dependencies of phase and amplitude parameters of the light field found from the numerical solution of a nonlinear Schrödinger equation for air. A key role of aberration and diffraction effects during the formation of localized stable dynamic light structures near the propagation axis is shown. It is found that the angular divergence of the postfilamentation light channel decreases with an increase in the laser beam radius at a fixed peak pulse power and is saturated when the radius is greater than 1 mm.

Transformation of C₂H₄, CO₂ and C₂H₆ absorption spectra confined in nanopores of SiO₂/Al₂O₃ aerogel is studied for the first time in comparison with the spectra of these molecules in the free state. It is shown that the integral intensities of confined C₂H₄ within 5700–6250 cm^–1, CO₂ within 4760–5160 cm^–1, and C₂H₆ within 2830–3030 cm^–1 are higher by 13.3, 15, and 18 times, respectively, than those of free gases.

Airborne lidar sounding of aerosol clusters by a laser beam sent forward in the aircraft flight direction is considered. Observability of the temporal evolution of short-lived (from a few to tens of seconds) aerosol clusters with horizontal scales from a few hundreds to a few thousands of meters are shown by numerical simulation. It is shown that, unlike stationary lidar observations, airborne lidars allow the evolution of aerosol clusters to be analyzed without involving additional hypotheses about their spatial and temporal structure.

The average crosswind and intensity of atmospheric turbulence are simultaneously estimated by the classical laser scintillation method and by the passive optical method from the analysis of the light scattered by natural or man-made topographic objects in the natural daylight illumination conditions. The passive sensing method does not require artificial light sources, and consists in the formation of incoherent images of sunlit topographic objects and in the analysis of images’ distortions induced by the turbulence between the object and the image plane. Estimates of the integral average crosswind and the structural constant of the air refractive index are compared in atmospheric experiments on the same optical measurement path by both methods. Comparison with lidar data is made. The optical measurements of integral characteristics were accompanied by independent local acoustic measurements using an ultrasonic anemometer.

Based on the numerical solution of the parabolic wave equation for the complex spectral amplitude of the wave field, the propagation of short-pulse vortex optical beams in a homogenous medium is studied by an example of a Laguerre–Gaussian femtosecond beam. It has been shown that the diffraction spreading of the Laguerre–Gaussian beam decreases with decreasing pulse duration as compared to continuous wave beams.

The threshold characteristics of lasing in a 20-μm layer of colloidal solution of Rhodamine 6G dye with plasmon-resonance Au nanoparticles and non-plasmon-resonance Pt nanoparticles excited by 532-nm radiation are experimentally studied. The spectral dependence of the scattering and absorption cross sections of gold and platinum nanoparticles are calculated within the Mie theory. It is found experimentally that the addition of nanoparticles to the active medium decreases the lasing thresholds by two orders of magnitude. It is shown that the lasing thresholds are 1.5–2 times lower when adding gold nanoparticles than when adding platinum nanoparticles of the same concentration.

A model based on neural networks with a teacher is suggested to reconstruct the data of observations of hydrophysical parameters. The indices of global climate oscillations in the ocean–atmosphere system were used as input signals for the model. The processes of model training and adaptation, permitting the most accurate solution of the modeling problem, is described. A comparison of model-predicted monthly mean of the Danube runoff volumes with observational data showed their good agreement. Gaps in data of observations of the water transparency (visibility depth of a white disk) in different years are filled by reconstructed data. A close correspondence in absolute value between reconstructed and measured visibility depths of the white disk is reported. Some features of interannual variations in reconstructed data on water transparency, caused by both climatic factors during 1950–1962 and changes in the chlorophyll а concentration during 1998–2010, were revealed.

Methodological problems and theoretical results on determining boundaries of laser-dangerous zones (LDZs) during the action of direct and scattered radiation created by the laser landing system (LLS) on human eyes are discussed. Algorithms for calculating LDZs when observing the LLS in real operational conditions are considered. Dimensions of laser-dangerous zones are calculated for a single laser source and a group of sources for different meteorological conditions. A computer program for carrying out calculations on laser radiation dosimetry when the landing system operates in real conditions is presented.

Particular properties of formation of optical fields in composite spherical microcapsules of different size consisting of a polymer absorbing shell and a nonabsorbing liquid core are considered. The numerical simulation shows that changes in the thickness of the shell grown on the fixed-radius core and in the coefficient of proper radiation of the shell determine the nature of spatial distribution and amplitude characteristics of the absorbed power. Variations in these parameters allow changing the position and peak values of the regions of the effective spatial absorption of the particles and, consequently, create conditions favorable for opening the shells in the appropriate spatial zones. This is important for the solution of practical tasks associated with the problem of release of the encapsulated material.