F. Yu. Kanev

Wavefront reconstruction of an optical vortex by a Hartmann-Shack sensor

Reconstruction the phase front of a vortex laser beam is conducted by use of a Hartmann-Shack wavefront sensor. The vortex beam in the form of the Laguerre-Gaussian LG(0)(1) mode is generated with the help of a spiral phase plate. The new reconstruction technique based on measured wavefront gradients allows one to restore the singular phase surface with good accuracy, whereas the conventional least-squares approach fails.

Correction of vortex laser beam in a closed-loop adaptive system with bimorph mirror

The phase correction of a vortex laser beam is undertaken in the closed-loop adaptive system including a Hartmann-Shack wavefront sensor with singular reconstruction technique and a bimorph piezoceramic mirror. After correction the vortex doughnutlike beam is focused into a beam with bright axial spot that considerably increases the Strehl ratio and optical system resolution. Since the phase break cannot be exactly reproduced on the flexible mirror surface, off-axis vortices appear in the far field at the beam periphery.

Spatial coherence, mean wave tilt, and mean local wave-propagation vector of a Laguerre-Gaussian beam passing through a random phase screen

The spatial evolution of the energy distribution and local wave-propagation vector of a fluctuating laser vortex beam is studied. The beam’s fluctuations are induced by its propagation through a thin (in comparison with the total propagation path) layer of a turbulent medium (phase screen). It is shown that the vortex energy flow typical for a coherent beam is also manifested in the mean parameters of a partially coherent beam. In particular, the mean wave tilt is representable as a sum of the vortex and potential components. The rotor of the vector field of mean wave tilts plays the determining part in the circular energy motion. The vortex component for a screen with a quadratic structure function of phase fluctuations corresponds to one of the models of rotational fluid motion called the Scully vortex. The potential component of the mean energy direction field can result in beam focusing with an increase in the distance from the screen. The direction of the mean energy flow lines (mean diffraction rays) allows for an analogy between the evolution of an optical vortex carried by a Laguerre-Gaussian beam and the breakdown of the rotational fluid flow.

Potential capabilities of adaptive-optical systems in the atmosphere

Thermal-blooming correction can reduce high-power laser beam distortions in the atmosphere. We use computer simulations to estimate the efficiency of different phase and amplitude-phase correction algorithms over horizontal and vertical atmospheric paths.

Correction of phase distortions of laser beams by the backscattering signal in the atmosphere

The results of a numerical simulation of adaptive compensation for distortions of partially coherent laser radiation using the backscattering signal are presented. A combined optical scheme of a transceiver channel with annular transmitter and circular receiving apertures is considered. In this scheme, initial field fluctuations are caused by a phase screen with a Gaussian correlation function which is placed near the source aperture. The effect of the finite response rate and limitations caused by the wavefront corrector on the system control efficiency was determined.

Adaptive Correction of Thermal Distortions of Multichannel Laser Radiation

Results of the simulation of multichannel radiation propagation under conditions of thermal blooming are presented. The correction of nonlinear thermal distortion by means of the beam phase and amplitudephase control is considered. The results show the dependence of the correction effectiveness on the number of channels and on the precision of the reference beam phase retrieval. An additional increase in the effectiveness is possible by means of adjustment of amplification in the channels of the optical system, i.e., with the use of amplitude-phase control over the beam wavefront.

Dependence of the effectiveness of multichannel radiation turbulent distortion compensation on the method of phase control: Increase of efficiency with amplitude control

Numerical experimental results characterizing the propagation of multichannel laser radiation in the atmosphere are presented and the possibility of compensating turbulent distortions by use of phase control is considered. It is shown that the effectiveness of adaptive correction depends on the number of channels in the system and on the accuracy of the reference radiation phase reconstruction. The effectiveness can be additionally increased by gain control in each of the channels, i.e., by passing to amplitude-phase control.

Possibilities of joint application of adaptive optics technique and nonlinear optical phase conjugation to compensate for turbulent distortions

The efficiency of integrating the nonlinear optical technique based on forming a reverse wavefront and the conventional adaptive optics into a unified complex (for example, for adaptive focusing of quasi-cw laser radiation) is demonstrated. Nonlinear optical phase conjugation may provide more exact information about the phase fluctuations in the corrected wavefront in comparison with the adaptive optics methods. At the same time, the conventional methods of adaptive optics provide an efficient control of a laser beam projected onto a target for a rather long time.

Adaptive compensation of atmospheric distortions of multichannel laser radiation

This paper presents the results of modeling the propagation of multichannel radiation under free diffraction conditions and discusses features inherent in this type of beams under these conditions. In addition, the effect of distortions arising in a turbulent atmosphere on radiation quality is considered, and the efficiency of adaptive compensation of atmospheric turbulence is analyzed.

Adaptive correction of distortions in a multichannel optical system

Results of modern investigations of multichannel laser systems are analyzed; sources of aberrations in such systems and the methods of their active and passive compensation are described. Simulation results of combined beam propagation are also presented; a possibility of long-range energy transfer in systems of such a type is considered. Effects of random phase incursions and atmospheric turbulence on beam parameters in the plane of observations are studied. The use of the multidither algorithm for correction of random phase distortions in multichannel systems is considered.