N. A. Suhareva

Turbulence-induced laser-beam distortions in phase space

A consecutive analysis of spatial-temporal disturbances of a laser beam propagating through a turbulent media was carried out. Evolutionary equations for the intensity distributions were obtained for a channel with different types of regular and stochastic spatial dispersion. The relative simplicity and physical validity of the integral relationships allows one to build them in the control algorithm for jam-protection of open-space operating channels.

Scintillation index of the Gaussian beams propagated through the paths with strong turbulence

Theoretical and experimental studies of the local statistical characteristics of Gaussian beams propagated through the paths with strong turbulence were carried out and their results are presented. It is ascertained that the applicability of the scintillation index meanings are substantially limited for the assessment of the performance quality of the optical data transmitting channels. On the basis of the experimental data got under different propagation conditions the peculiarities of the localized intensity distributions and those of the scintillation index are revealed.

Super narrow beam shaping system for remote power supply at long atmospheric path

Wireless power transmission technology based on high power diode and fiber lasers have a high potential for Earth and space applications. Narrow infrared laser beam can deliver up to 1 kW of electrical power to a photoelectric receiver with dimensions 10-20 cm at distance 1-10 km. To achieve high efficiency it is necessary to fit the beam to the dimension of receiver moving with angular velocity in range 0.5-3 /sec in all range of distance. Thus beam shaping system has to provide fast control of shape, dimensions and position of the beam with high accuracy in condition of atmosphere which distorts the beam. The description and results of the experimental testing of optical system corresponding to the declared characteristics is submitted.

Tensor analysis of the refraction distortions dynamics of a sounding optical beam

The capabilities of dynamics analysis of the sounding-beam intensity profile at the output of an atmospheric path on the basis of the chronogram structure tensor are considered. The spatio–temporal structure of the velocity field of refraction distortions is investigated. The characteristic dimensions of the regions of the translational and rotational types of flow motions are determined. The profiles of local velocity projections are obtained, as well as their statistical properties under the conditions of weak variations of meteoparameters in the output flow recording interval. Comparison of the characteristic values of wind velocity that is recorded with an array of anemometers and those calculated with the suggested method allowed us to elaborate an approach to the rough estimation of the translational and fluctuation components of aerodynamic flows at the path.

Modeling of laser beam propagation through turbulence

Our approach for modeling laser beam propagation through turbulence involves parabolic equation method and results of experimental investigation in laboratory. The analytic solution to the problem of the Gaussian beam propagation through non-uniform gas has been derived. The solution depends on the refracted index, i.e. on the gas density. The density distribution can be found from the Navier-Stokes system. The appropriate solution may be constructed by two ways : (i) as a series in powers of vorticity which is supposed to be small; (ii) with the aid of the parametrix method which includes an iterative procedure. It follows from the solution that acoustic radiation of vortex rings arises. Statistical properties of the propagating beam were found from the solution to the parabolic equation as average over time. In experiments the propagation path was equal to 7 m. The laser beam propagation was accompanied by convection and lateral wind. The frequency of turbulent fluctuations was equal to 2-10 Hz. Phase trajectories were found as well as statistical properties of the beam intensity in turbulent gas flow. The conclusion is as follows. Statistical characteristics traditionally used for the estimation of the laser beam special distortions in the open space transmission channels are to be complemented by the dynamic parameters such as the space of embeddings dimension, characteristic frequencies for the phase trajectories and so on.

Conversion characteristics of silicon photovoltaic cells for optical beaming

The photoconversions efficiency of powerful collimated coherent single-mode and multimode wave beams with λ= 808 nm and 1064 nm was studied and the experimental results are presented. A set photocells based on silicon with different topological structure is considered including monofacial and bifacial cells, as well as those that have a vertical orientation. Photocell characteristics (short-circuit current Isc, open-circuit voltage, Voc and fillfactor) obtained in the temperature range from 25°C to 50°C and also at a beam power, P, of up to 100 Suns are discussed.

Transfocal analysis of unsteady stochastic structures for a signal from a retro-reflector

The applicability of the returned spatial intensity distribution and its variation in time is discussed for the investigation of nonequilibrium and nonstationary properties of the optical path, in particular, for determining the degree of turbulent distortions, thermal nonequilibrium, transverse crosswind. The results of an experimental analysis of the spatial structures obtained in the focal plane of the registrator are considered for the case of collimated laser beams reflected from a retroreflector for the 1000 m inclined atmospheric path.

Propagation of the non-paraxial Gaussian beam through the inhomogeneous atmosphere

Turbulent fluctuations in the atmosphere distort a laser beam during its propagation. There exist two problems : (i) adequate description of the atmospheric turbulence and (ii) analysis of the propagation of the beam through turbulence, investigation of the beam spreading and distribution of its intensity. Unfortunately, only the scalar case of beam propagation has been considered often in the literature. Most part of authors studied only paraxial beams. Non-paraxial beams are considered in [1, 2]. Below we consider the propagation of a non-paraxial laser beam. The analysis has been made on the basis of the Maxwell equations. Two cases have been considered: (i) the permittivity and permeability are constant (the homogeneous atmosphere); (ii) the case when the permeability is equal to unity, the permittivity being dependent on coordinates. We assume that the permittivity is close to unity. Let us consider the first case. Some details of the solution were recently published in [3]. We have a linear system of ordinary differential equations with constant coefficients due to the Fourier transform. The unknown functions are determined from the condition at the plain x3 = 0 ( x3 being the coordinate along the axis of the beam). In the second case (the permittivity is the function of coordinates being close to unity) we have a system of linear ordinary differential equations after the Fourier transform, too. The right-hand terms depend on the previous solution which was obtained for the homogeneous atmosphere. The solution is the sum of that one for the homogeneous atmosphere and that one for the variable part of the permittivity. Thus we have the solution which describes the propagation of the non-paraxial beam through the inhomogeneous atmosphere on condition that the variation of the refractive index is small. Numerical calculations were fulfilled for the components of the electric field.

Positional characteristics of generalized decentered elliptical Gaussian beams propagating through extended atmospheric paths

The experimental and theoretical study of the topography of regular and random collimated Gaussian beam aberrations due to distortions over the paths with non-centric refractive inhomogeneities was carried out and the results are presented. Experimental samples were obtained using a lab path of 100 meters length for stationary modes and an extended atmospheric path of more than 1000 meters length for non-stationary ones. The collimated Gaussian beam under the conditions of dry turbulent atmosphere demonstrates the increasing of the contribution of high-frequency spatial components for weak and moderate turbulence. In the presence of hydrometeors, the spatial-frequency beam spectrum loses its high frequency range. Accordingly, the initial astigmatic characteristics appear to be feebly marked, the wave beam acquires the isotropic Gaussian profile.

Atmospheric turbulence effects on the performance of the laser wireless power transfer system

Application of adaptive correction is necessary to control wandering of the laser beam in wireless power transfer (WPT) system. In this paper we describe experimental results of using different adaptive correction techniques for both weak and strong turbulence conditions. All experiments were performed over a 1.5 km near-horizontal atmospheric path. Some criteria for choosing parameters of adaptive correction are given.