Sergei S. Chesnokov

Doughnut-like laser beam output formation by intracavity flexible controlled mirror

The formation of the given low loss and large beamwidth doughnut-like fundamental mode of stable resonator by an intracavity flexible mirror is discussed. The mirror is a bimorph one with one round and two ring controlling electrodes. An inverse propagation method is used to determine the appropriate shape of the controlled mirror. The mirror reproduces the shape with minimal RMS error by combining weights of experimentally measured response functions of the mirror sample. The voltages applied to each mirror electrode are calculated. The calculations are carried out for industrial CW CO2 laser.

Super-Gaussian laser intensity output formation by means of adaptive optics

An optical resonator using an intracavity adaptive mirror with three concentric rings of controlling electrodes, which produc low loss and large beamwidth super-Gaussian output of order 4, 6, 8, is analyzed. An inverse propagation method is used to determine the appropriate shape of the adaptive mirror. The mirror reproduces the shape with minimal RMS error by combining weights of experimentally measured response functions of the mirror sample. The voltages applied to each mirror electrode are calculated. Practical design parameters such as construction of an adaptive mirror, Fresnel numbers, and geometric factor are discussed.

Ponderomotive action of light in the problem of multiple scattering of light in a randomly inhomogeneous medium

The time correlation function of light reflected diffusely from a semi-infinite randomly inhomogeneous medium is calculated with allowance for the acceleration of the scatterers in the field of the laser beam incident on the medium. An analytical expression is found for the characteristic coherence time due to the ponderomotive action of light. It is shown that even with laser radiation power densities of the order of 1–10 W laser-acceleration effects substantially alter the character of the time autocorrelation function of the scattered light and must be taken into account in theoretical calculations.

Time-delayed nonlinear optical systems: temporal instability and cooperative chaotic dynamics

We present the results of numerical simulation of a nonlinear optical system with a time-delayed feedback which exhibits spatio-temporal chaotic states. The model incldues three main phenomena governing the system: temporal delay, diffusion and diffraction. We focused our attention on the statistical properties of this system and analyzed the join action of mentioned phenomena, features of spatial spectra in wide range of parameters, scaling relations. We found that under certain conditions powers spectrum of phase fluctuations in chaotic states monotonically decreases as a function of spatial frequency. This causes us to anticipate that such class of optical system can be used for an artificial optical turbulence simulation.

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.

Numerical analysis of the propagation of high-intensity laser radiation in the atmosphere

ConclusionThe application of numerical methods makes it possible to carry out comprehensive investigations of the process of propagation of laser radiation in the atmosphere and to assess the influence of various factors on the efficiency of transmission of light energy over a distance, an objective that is often difficult to achieve in natural experiments. The successes of numerical experiments in nonlinear optics have opened the way for the first time to attack the problem of optimizing the interaction of radiation with matter and, in particular, to develop optimal methods for the phase correction of thermal blooming. Mathematical modeling methods play an important part in the design of adaptive optical systems for the focusing of radiation in a nonlinear medium, providing the means for assessing a priori their ultimate capabilities. The range of application of numerical methods in nonlinear optics is steadily expanding. Their future development will clearly entail the formulation of standard procedures and algorithms as well as collections of standard programs for a broad class of problems.

Intracavity laser beam shaping by means of flexible corrector

The intracavity way of intensity distribution formation is discussed. The examples of a such formation by means of bimorph flexible corrector are shown. The whole structure of adaptive system for the intracavity given intensity formation is considered.

Given laser output formation: adaptive optics approach--theory and experiment

Diffraction analysis of the formation of low losses, large beam width and high far-field intensity peak value of the given super-gaussian fundamental modes by means of intracavity controlled mirror is presented. Such mirror is a water-cooled bimorph flexible one having four controlling electrodes. Analysis has confirmed the possibility to form various intensity distribution inside laser cavity and at the output of the stable resonators of industrial CW CO2 and YAG:Nd3+ lasers. Distortions of the given intensity distributions caused by thermal deformations of the resonator mirrors is taken into account. It is shown the possibility to compensate partially for such distortions with the help of the intracavity controlled mirror. Experimental formation of the super-gaussian fundamental modes of the 4th and 6th orders of the industrial CW CO2-laser with stable resonator by means of the intracavity flexible mirror is shown. The increase of power of the formed fundamental modes up to 10% and the enlarging of the peak intensity in the far-field zone in 1.6 times in the comparison with the traditional gaussian TEM00 mode of the same resonator are observed.

Diffusing-wave spectroscopy of flows

The technique of diffusing-wave spectroscopy (DWS) consists in deriving properties of random multiple-scattering media from measurements of the temporal autocorrelation function of scattered intensity. Both the characteristics of light- scattering particles (size, absorption and scattering coefficients, etc.) and the macroscopic dynamic structure of the sample may be studied by means of DWS. The technique has a considerable potential for application in medical diagnostics. We report theoretical and experimental results that allow the method of DWS to be extended to random media with hidden, spatially localized flows of scatterers. Our model experiments were performed with a flow of an aqueous suspension of polystyrene beads confined within a rigid sample made of titanium dioxide particles suspended in resin. We show that the method of DWS allows the noninvasive diagnostics of the flow. As a possible application of the method, we discuss the use of DWS for noninvasive in vivo optical monitoring of blood flow in humans and animals.

Three-dimensional model of optical atmospheric turbulence

The 3D model of continuous random medium as a chain of phase screens, describing both transverse and longitudinal correlation of wave phase in a wide range of spatial scales have offered. The constructed model essentially removes the lower restriction on thickness of random medium, replaceable by the phase screen. Analysis of phase screens, received through a modified subharmonic method, has been concluded. The statistical research of random walk of a beam in turbulent atmosphere have carried out.