The combined use of adaptive optics and nonlinear optical wavefront reversal techniques to compensate for turbulent distortions when focusing laser radiation on distant objects

Abstract

Approaches to constructing a mock-up of a system for focusing laser radiation on distant objects using both adaptive optics elements and nonlinear-optical wavefront reversal methods providing compensation for turbulent distortions are considered. Numerical calculations were preliminarily performed, in which the split-step method was used as a numerical method for solving a second-order partial differential wave equation for the complex amplitude of the wave field of a laser beam. This method, combined with methods of spectral-phase Fourier transforms and statistical tests, is the most effective way to obtain reliable quantitative results for solving engineering problems of atmospheric wave optics. Quantitative data are obtained on the effect of turbulent atmospheric distortions along propagation paths on the main parameters of coherent laser beams – focusing, effective average radius, and the proportion of the beam energy in its diffraction spot. The preliminary results obtained of the system mock-up performance confirm the conclusions of the theory.

Experimental studies of phase adaptive correction of optical wave distortions

“…Note that the observed rings in Figure 2 are not diffractive, but are formed by the combined action of spherical aberration [2,4,5] and defocusing of the telescope's optical system. The value of the Strehl parameter obtained in the experiment is 0.2783 with adaptive correction when using a telescope with a Newtonian optical scheme.…”

“…Figure 1 shows a photo of the AO system model on the stand of the Institute of Atmospheric Optics of the Siberian Branch of the Russian Academy of Sciences, including the Newton telescope, WFS, shaping optics, and controlled optical elements [5]. The main laser radiation from a semiconductor laser was reflected from a deformable mirror and, using a Newton telescope, was focused into the plane of the screen, which was located in the receiving plane.…”

Features of Adaptive Phase Correction of Optical Wave Distortions under Conditions of Intensity Fluctuations

“…The question of the influence of amplitude (or intensity) fluctuations on phase measurements under conditions of propagation of optical waves in random media is extremely important and is associated with several features of the use of phase systems. It is known that phase distortions, primarily acquired when passing through an optically inhomogeneous medium, as the wave propagates, are transformed into a modulation of the spatial distribution of intensity [18,21,22]; with a sufficiently deep amplitude modulation of the field, points with zero intensity appear in it [18]. If we describe any optical wave in terms of the complex amplitude U, then such points are formed at the intersection (or touching) of the lines, where its real and imaginary parts are equal to zero.…”

“…To achieve this, let us analyze the results of numerical experiments performed in [19,22,25], which analyze the influence of intensity fluctuations and the wavefront dislocations generated by them on the efficiency of correction of turbulent distortions. At the same time, the following two aspects are of both practical and scientific interest.…”

“…The dependence of phase systems on the level of intensity fluctuations is manifested primarily in changes in the brightness (flickering) of images in each of the subapertures of the Hartmann matrix. In this case, phase measurements become incorrect [20][21][22][23].…”