Radiophysics and Quantum Electronics

The effectiveness of a multicycle wavefront-inversion (WFI) algorithm in the problem of laser-radiation focusing in a randomly inhomogeneous medium is evaluated. Both “local” (for a single cycle) and “integral” (for the entire observation period) effectiveness criteria are examined. The dependence of these criteria on the main parameters of an adaptive system with WFI are determined. It is shown, in particular, that the WFI system must be adjusted for local conditions to increase the effectiveness of WFI of a “noisy” signal.

A formulation and solution of the recurrent filtering problem are proposed for correlated nonstationary optical radiation intensity fluctuations with single-electron discrete-time registration. The Bayes theory is used to find a quasi-optimal algorithm for filtering of a Markov sequence with a gamma distribution in the class of Y2-minimax rules based on non-Gaussian approximations for a posteriori distributions.

We present a technique for narrow-sector finding of VLF-noise radiation sources. Hardware for the implementation of this technique is briefly described. Examples of the azimuthal arrival angles of VLF noise measured near Yakutsk in different day times in March 2000 are given. The noise radiation was mainly received from two world thunderstorm centers. These examples illustrate the possibility of resolving local sources in the global near-equatorial thunderstorm centers (at distances about 11,000 km from the African thunderstorm center).

We analyze the behavior of the ocean–atmosphere system characteristics based on direct (contact) and satellite microwave radiometric measurements. Some common and distinctive features of their dynamics in the mid-latitudes of the North Atlantic (in its Norwegian, Newfoundland, and Gulf Stream energy-active zones), which significanty affect the weather conditions in Europe, and in the tropical latitudes of the Atlantic (the Gulf of Mexico and the Bahamas area), which are the sources of tropical cyclogenesis, are considered.

The Institute of Applied Physics of the Russian Academy of Sciences has for many years been developing sub-terahertz and terahertz large-orbit gyrotrons that permit selective oscillation at higher cyclotron harmonics than is possible in the conventional gyrotrons. Currently, experimental studies are conducted at two specialized facilities. A prototype universal sub-terahertz source for magnetic resonance spectroscopy is studied using a facility that generates long-pulse and continuous electron beams with particle energies of up to 30 KeV. Continuous selective oscillation at the second and third cyclotron harmonics with frequencies of 0.267 and 0.394 THz was obtained for a radiation power of 900 and 370 W, respectively. New resonators with periodic phase correctors have been developed to increase the efficiency of third-harmonic oscillation and obtain fourth-harmonic oscillation with frequencies of up to 0.65 THz. Using a facility with an electron energy of up to 80 KeV, we study the possibilities of increasing the pulse generation power at the third harmonic at frequencies close to 1 THz to employ in experiments on obtaining a gas discharge in a focused terahertz wave beam and generating high-power extreme ultraviolet radiation.

We obtain the equations for determining the spatial moments of the radial distribution of brightness in the pulsed radiation field of a point isotropic source and similar characteristics of the distribution of irradiance from a point unidirectional source on the assumption of strong anisotropy of the scattering indicatrix of a medium and the studied light field. The procedure of analytical solution of these equations is shown. Formulas for calculating the spatial parameters of the light pulse at a given time instant, i.e., the distance between the front edge and the barycenter of the pulse, as well as its characteristic length, are derived. It is shown how and under which conditions the time parameters of the pulse can be determined from its spatial parameters.