Alexander V. Koryabin

Method of estimation of turbulence characteristic scales

We propose an optical method that uses phase data of a laser beam obtained from a Shack-Hartmann sensor to estimate both the inner and outer scales of turbulence. The method is based on the sequential analysis of normalized correlation functions of Zernike coefficients. It allows the exclusion C(n)(2) from the analysis and reduces the solution of a two-parameter problem to a sequential solution of two single-parameter problems. The method has been applied to estimate the outer and inner scales of turbulence induced in the water cell.

Laboratory simulation of large-scale wave front distortions in a turbulent atmosphere

Hybrid optical/digital laboratory setup that simulates large-scale phase distortions corresponding to various models of atmospheric turbulence is presented. Setup consists of flexible controllable mirror, computer, electronical interface, TV camera and framegrabber. Software for control signals generation is also developed.

Diagnostics of the scale of turbulence using a divergent laser beam

A method for estimating the parameters of turbulence that was originally developed for collimated laser beams is applied to the case of a divergent beam. The estimate is based on an analysis of the correlation functions of the Zernike expansion coefficients of the phase. The results suggest that the method can be used for the estimation of the inner scale of turbulence in an experiment with a divergent laser beam. In the case of isotropic turbulence, it is also possible to estimate the outer scale of turbulence from the correlation functions of lower-order modes.

Estimation of atmospheric turbulence parameters with wave front sensor data

Estimates of atmospheric turbulence parameters can be calculated on the basis of data, obtained with wave front sensor. The method described is based on decomposition of phase fluctuations into Zernike series and analysis of statistics of this decomposition coefficients. Estimates of turbulence outer scale L0 and refractive index structure constant C2/n obtained in experiments with turbulence in water cell showed good agreement with previous results.

Influence of large-scale wavefront aberrations on performance of adaptive systems with optical feedback

Influence of tip-tilts and general defocus aberrations on performance of adaptive systems with liquid-crystal phase modulator is analyzed. Main results concern the system with lateral shearing interferometer as phase visualization element. Some general estimation for performance degradation is obtained for this system.

Influence of phase distortion correlation on imaging of extended objects

We describe the uniform error algorithm of adaptive phase correction. This algorithm can be used for imaging of extended objects through turbulence. The description involves the fundamental statistical properties of the Zernike expansion of phase distortions on receiving aperture, while no other limitations (sensor noise, spatial resolution of phase corrector, etc.) are taken into account. An approach is also presented to the problem of approximation of the mutual structure function of phase of received light coming through turbulence. This approach enables us to substitute distributed turbulent layer by a small number of phase screens, statistically equivalent to the layer.

Adaptive methods for laser beam control

Some recent works on the problem of the adaptive laser beam control carried out at the Department of Physics of MSU are reviewed. The main directions of this research are outlined and some experimental results on adaptive compensation of adaptive control of low order thermo-aberrations in pulsed solid state laser are discussed.

Adaptive intracavity correction of the pulsed YAG laser radiation

This paper presents the experimental results on the intracavity adaptive correction of the thermooptical phase distortions in the pulsed YAG-laser. Average 3-times increase in the beam axes intensity has been achieved with only 10 loss in the total output laser pulse energy. The system stability to variations of the thermooptical distortions has been demonstrated. 1 .