Tatiana I. Arsenyan

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.

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.

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.

The mode conversion of structurally stable vector beams propagating through free space optical channels

The reconstruction of the spatial intensity distribution of structurally stable axially symmetrical beams in free space optical data transmitting channels has been studied experimentally. The structure transformation invariants of а beam as а space code bearer are discussed. The correlation and dispersion parameters of a random process of optical density modulation are estimated; a possibility of their multiple differences in different directions perpendicular to the beam axis is shown.

Superstatistics of optical beam scintillations over thermally nonequilibrium paths

Methods are presented for the analysis of sounding optical beam intensity variations at the exit of a nonstationary nonequilibrium path with the use of the superstatistics and nonextensive statistical mechanics. The connections of the first and the second moments of the experimentally recorded distribution functions of the intensity scintillations inside the subapertures of the output beam profile were applied to derive the models for nonequilibrium flows as well as the hypotheses about the distributions of the temperature and aerodynamic flow phase states over the path.

Dynamical anisotropy of the optical propagation paths

Dynamics of laser beam intensity profile spatial modulations over a model tropospheric path with the controlled meteorological parameters was studied. Influence of the underlying surface temperature as well as the side wind load were considered. The increase of dynamic anisotropic disturbances saturation with the path length was observed. Spatio-temporal correlation characteristics of the directivity pattern in the signal beam registration plane were obtained. Proposed method of the experimental samples analysis on the base of chronogram with the following definition of the dynamic structure tensors array allows to estimate local and averaged projections of the flow velocities over the chosen spatio-temporal region and to restore their geometry in the zone of intersection with the signal beam. Additional characteristics suggested for the diagonalized local structure tensors such as local energy capacity and local structuredness are informative for the estimation of the inhomogeneities spatial dimensions, time of access through the section considered, the dynamics of energetic jets. The concepts of rotational and translational dynamic anisotropy are introduced to discriminate the types of the changes of the local ellipsoids axes orientation as well as their values. Rotational anisotropy shows itself in the changes of the local ellipsoids orientation, thus characterizing the illumination variation over the beam cross-section. Translational anisotropy describes the difference between the axes values for local ellipsoids.

Nonequilibrium statistics of the laser beam intensity profile at the output of a model channel with strong turbulence

The experimentally obtained space-time distortions of the signal beam profile in the optical data transmitting channels are presented. Interpretation and prognostication of distortion structure was carried out using the non-equilibrium thermodynamics and statistics methods, particularly non-extensive Renyi entropy. The method of media state operational control using a single sampling frame is proposed.

Optimization of an optical system of lidar devices near the ground under conditions of turbulence intermittence

Physical factors affecting the signal to nose ratio in the optical location systems are considered under the conditions of turbulence intermittence. The experimental data on the effects of random wandering, turbulent broadening, changes of the coherence radius of the local intensity fluctuations are obtained for the narrow laser beams. Theoretical model accounting for the result of experiments by change of the ratio between the beam radius nd inner scale of the turbulence has been constructed. It enables to carry out optimization of the optical location paths.