Cheslav E. Pogutsa

The influence of the vortex phase on the random wandering of a Laguerre?Gaussian beam propagating in a turbulent atmosphere: a numerical experiment

A numerical experiment is used to study the variance of the wandering of a Laguerre–Gaussian laser beam propagating in a turbulent atmosphere. It is shown that a laser beam with an initial intensity distribution coinciding with that of the Laguerre–Gaussian beam but not having a vortex phase distribution is less resistant to the action of atmospheric turbulence than the Laguerre–Gaussian beam except in the near diffraction zone. The regularities of the beam wandering associated with the values of the azimuth and radial indices of the beam as well as with the intensity and the outer scale of the turbulence are determined.

Increase in laser beam resistance to random inhomogeneities of atmospheric permittivity with an optical vortex included in the beam structure

The role of the vortical phase in the initial structure of the wave field of a laser beam propagating in the turbulent atmosphere in statistical regularities of beam wandering is studied. It is found that in the near diffraction zone the variances of wandering of the vortical beam and the fundamental Gaussian beam turns out to be identical, if the initial radius of the Gaussian beam is equal to the radius of the ring intensity distribution of the vortical beam. In the far diffraction zone, the vortical beam wanders more slightly than the Gaussian beam with the same effective radius of the initial intensity distribution does. It is also shown that laser beams with the initial ring intensity distribution similar to the intensity distribution of a vortical beam, but not having the vortical phase distribution, are less resistant to the atmospheric turbulence than the vortical beam.

Random wandering of laser beams with orbital angular momentum during propagation through atmospheric turbulence

The propagation of laser beams having orbital angular momenta (OAM) in the turbulent atmosphere is studied numerically. The variance of random wandering of these beams is investigated with the use of the Monte Carlo technique. It is found that, among various types of vortex laser beams, such as the Laguerre-Gaussian (LG) beam, modified Bessel-Gaussian beam, and hypergeometric Gaussian beam, having identical initial effective radii and OAM, the LG beam occupying the largest effective volume in space is the most stable one.

Orbital angular momentum of a laser beam in a turbulent medium: preservation of the average value and variance of fluctuations

The process of the propagation of vortex laser beams in a turbulent atmosphere with recording of the total orbital angular momentum (OAM) and determination of the beams statistical characteristics, such as the average over realizations of the turbulent medium and the variance of fluctuations, has been simulated numerically. The dependences of OAM fluctuations on the turbulence intensity and the initial topological charge of the beam have been obtained. Numerical results are compared with the earlier asymptotic estimates.

Mean energy distribution and averaged pattern of optical vortices of a partially coherent light beam propagating in a randomly inhomogeneous atmosphere

Spatial evolution was studied of energy and phase distribution of a fluctuating laser beam carrying an optical vortex. Fluctuations of the optical field were induced by fluctuations of the generator parameters or by random variations of the index of refraction in a thin layer of the atmosphere represented by a phase screen. It was shown that vortex-like flow of energy typical for a coherent beam manifests itself in averaged characteristics of a partially coherent beam. Particularly, the mean tilt of the wavefront can be represented as a sum of the vortex and potential components, while the circular flow of energy is influenced mainly by the rotor of the vector field of wavefront tilts. As it turned out, after the phase screen having a quadratic structure function of fluctuations the vector filed of energy flow is formed with the vortex component corresponding to the model of fluid current known as Scullys vortex. The potential component of the filed induces focusing of the beam. This results in the gradual annihilation of the vortex in the far filed.

Optical Scully vortex and its spatial evolution

The structure of an optical vortex formed in a partially coherent Laguerre-Gauss laser beam was considered. The main object of study was the recorded vector field of wavefront tilts that consisted of the vortical and potential components. It was found that the vortical motion weakened as the coherence decreased. Main regularities in the behavior of the vortical component can be described by the Scully vortex model of vortical liquid flow. In the spatial evolution, the potential component of tilts may alternate the sign, thus determining the direction of energy flow to the center or to the periphery of the vortex. Energy flow lines in the beam demonstrate the pattern of decay of an optical vortex similar to the pattern of decaying vortical motion in viscous liquid.

Orbital angular momentum of the vortex laser beams in a turbulent atmosphere: Numerical modeling and asymptotic theory

The total orbital angular momentum (OAM) of laser beams propagating through the turbulent atmosphere has been studied numerically and analytically. The variance of OAM fluctuations calculated from the numerical simulation is in a good agreement with the asymptotic estimates of the OAM variance in the domain of their applicability.

Fluctuations of the orbital angular momentum of vortex laser beam in turbulent atmosphere: dependence on turbulence strength and beam parameters

The dependences of the orbital angular momentum of a Laguerre–Gaussian beam propagating through a turbulent atmosphere on its azimuthal index and atmospheric turbulence strength are analyzed in the numerical simulation. The effect of errors in alignment of the beam and receiver axes on the average value and variance of orbital angular momentum fluctuations is studied. The statistics of the orbital angular momentum distribution at the end of the atmospheric propagation path is analyzed.

Vortex stabilization of the direction of laser beam propagation in randomly inhomogeneous medium

It is found that if a laser beam has vortex properties, then its random wandering in a turbulent medium decreases. The higher the orbital angular momentum (topological charge) carried by the beam, the higher the beam stability. The most stable vortex beam occupies the largest volume in space.