Vol 30, No 5 (2017)

A quasi-steady-state approximation for the problem of stimulated Mandelstam–Brillouin scattering (SMBS) in the air as in a multimode acoustic medium is formulated. In this approximation, a numerical solution of the equation for the envelope of the complex light field amplitude is implemented. Based on a series of performed numerical experiments, it is established that the SMBS effect can lead to a discernible increase in the angular divergence of laser beams during the propagation of a sufficiently powerful laser radiation with a wavelength λ = 1.315 μm in air.

Calculations of line broadening and shift of carbon monoxide (CO) molecules confined in nanoporous media are presented. A model is considered in which the line broadenings and shifts are caused by collisions of free CO molecules with walls and adsorbed CO molecules with and without rotational degrees of freedom.

Numerical simulation is carried out in order to estimate possibilities of crosswind velocity determination along an observation path between a distant object and observer. The estimation is based on the analysis of atmospheric distortions in the object images. The disturbing effect of limited atmospheric regions on the object image and possibilities of the drift velocity retrieval in these regions are analyzed. A new method for filtration of turbulent distortions by their characteristic sizes is suggested with the aim of estimating the wind velocity at different segments of the observation path. It is shown that the technique suggested allows one to determine crosswind velocity with high accuracy when it is applied to a thin layer of atmospheric inhomogeneities.

We analyzed how the asymmetry factor of the atmospheric aerosol phase function can be estimated from spectral measurements of light attenuation and scattering. An empirical formula is suggested to parameterize the asymmetry factor as a function of the Ångström exponent and complex refractive index. Several approaches to determining the asymmetry factor from data of integrating nephelometers are considered. An analytical formula, relating the asymmetry factor to the nephelometer-measured ratio of the radiative fluxes scattered into the forward and backward hemispheres, is derived. The asymmetry factor at three wavelengths is calculated according to data of field measurements in St. Petersburg suburbs in 2015.

The first estimates of a midge contribution to extinction of optical radiation for background summer conditions of Western Siberia are received. The radiation extinction coefficient due to midges (RECM), found from experimental data at a wavelength of 1.06 μm, changes from 0 to 0.14 km^–1. An estimate of the mean RECM value in visible and infrared regions is 0.07 km^–1. It is shown that the relative contribution of midges to the extinction coefficient of optical radiation in the 0.5–16 μm band is significant and varies on average from 26 to 63%.

The results are presented of the experimental study of spatial characteristics of postfilamentation light channels in air formed by femtosecond pulses of a Ti:Sapphire laser with different energy for focused and collimated beams. It is found that the angular divergence of channels is dozens of times lower than the angular divergence of a beam as a whole for focused beams in the far zone from the filamentation region. The angular divergence of the channels first significantly decreases with an increase in the pulse energy and then saturates. For collimated beams, at a fixed distance from the source, an increase in the pulse energy also leads to stabilization of the channel cross section.

A technique is developed for retrieving the vertical profile of the mass saltation flux from measurements of the saltating sand mass concentration and wind velocity in the surface air layer. The technique is based on the solution of direct and inverse problems of the saltation sand dynamics and aimed at determining the sliding coefficient of sand grains. The calculation results for the sliding coefficient of sand grains are compared with data of measurements in wind channels. The conditions under which saltating sand trajectories fall in the height ranges from 5 to 10 mm and from 10 to 20 mm are revealed. The effect of variations in the diameter, lift-off velocity and angle, and friction velocity on the sliding coefficient of sand grains is analyzed. The sliding coefficient for 100-μm diameter sand particles is estimated for the first time.

We analyze how remote sounding instruments can help to improve our understanding of the atmospheric boundary layer and how regional synoptic models can be used as a hindcasting tool in studying and perfecting boundary layer models. A method is suggested for estimating the quality of boundary layer reproduction in these models using remote sensing data.

Laser technologies that are used for the development of sensor elements for Remotely Operated Vehicles (ROVs) are presented, as well as the latest developments in underwater robotics where laser spectroscopy methods are applied to environmental monitoring. A submersible laser spectrometer unit intended for studying Raman scattering and laser-induced fluorescence (LIF) spectra is presented. The spectrometer was developed as an element of an ROV sensor system for remote detection and measurements of organic matter concentrations in sea water and underwater objects. The results of environmental tests of the submersible LIF spectrometer in various marine areas, including the Arctic, are described.

The improvement of the experimental setup based on a Fourier spectrometer Bruker IFS-125 and a 30-meter multipass optical cell is described. The improvement includes the cell equipment with a system of automated adjustment of the number of beam passes without cell depressurization and ensures the cell work at high temperatures.

The results of an experimental study of a gas-discharge Ne–Eu laser are presented. In this work, lasing lines, pulse shapes in the europium atom and ion are identified under the conditions of this experiment. The effects of the buffer gas pressure and pulse repetition rate on the energy characteristics of the laser are ascertained; their optimal values are found. It is shown that the output power is 1 W at the 1759 nm line and 70 mW at the 664.5 nm line for the corresponding transitions under optimal operating conditions.