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We proposed an accurate method for simulating turbulent phase screen. Different from the subharmonic method, the low-frequency grid is not equally spaced in our method, and the distribution of sampling points can be determined by only one parameter. It is found that the accuracy of simulation depends on the distribution of sampling points, and there is an optimal distribution that minimizes the relative error between expected structure function and theoretical structure function. In order to get the optimal distribution, a search algorithm is designed. Compared with existing subharmonic method, the maximum relative error can be reduced from 10% to 0.1%, and the computation costs reduced more than two times at the same time. And compared with other methods, this method still has the advantage of precision.

The phase screen method is a well-established approach to analyze the effects of atmospheric turbulence in free space optical (FSO) communication and astronomical imaging system. Owning to the variation of atmospheric turbulence, low complexity modeling is required. Meanwhile, low frequency power should be compensated to overcome shortcomings of classical methods. The method based on sub-bands division and multirate sampling is proposed to solve these problems, and analytic formulas of the model is derived correspondingly. Simulation results are provided to show that our method overperforms the existing methods when both computational complexity and power compensation are taken into account. Furthermore, the proposed method is flexibly in operating which could be used to simulate the base phase screen of time-varying atmospheric turbulence.

We measured the modulation transfer function (MTF) of a short multimode fiber (SMMF) probe and proposed the optical model including the thin random phase screen (TRPS) to explain degradations of imaging characteristics. SMMF is a graded index multimode fiber for optical communication. That length is 8.8 mm and the diameter of core is 50 µm. With the wavelength of 780 nm, for spatial frequencies from128 lp/mm to 228 lp/mm MTFs were measured at 0.179–0.062 in reflection images and these contrasts were 19% to contrasts without TRPS. With parameters of σ ϕ of 1.5 rad and W of 2–3.5 µm calculated results almost correspond to measured ones. Dependences of contrasts on wavelength were also measured. With the spatial frequency of 200 lp/mm, at the wavelength of 0.8 µm the contrast decreased to 17% due to TRPS and at that of 0.5 µm the contrast decreased to 6%. Measured dependences of contrasts on wavelength with the spatial frequency of 228 lp/mm approximately correspond to calculation results with 200 lp/mm. These basic characteristics are useful to design the imaging optics by means of SMMF.

We demonstrate analytically, numerically, and experimentally that the fractional topological charge shifting in perfect vortices having a ring-shaped distribution is precisely determined by the correlation coefficient of speckle distributions obtained by the scattering of these perfect vortices through a random phase screen. The scattering of elliptic perfect optical vortices is also analyzed and discussed. Fil: Bianchetti, Arturo Abel. Instituto Nacional de Tecnología Industrial; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Etchepareborda, Pablo Gonzalo. Instituto Nacional de Tecnología Industrial; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Federico, Roque Alejandro. Instituto Nacional de Tecnología Industrial; Argentina

By using the method of the power-spectrum inversion, the turbulence phase screen has been built up, and the propagation characteristics of high-frequency phase of laser beam in atmospheric turbulence have been analyzed; in addition, the phase correction effect of laser beams by using the adaptive deformable mirror has been simulated, and its affecting factors in turbulence have also been analyzed quantitatively. The results show that the phase correction effect of laser beams in turbulence is mostly determined by the percent of high-frequency phase in distorted wavefront. With the increase of the intensity of atmospheric turbulence and the propagation distance in turbulence, the percent of high-frequency phase in distorted wavefront increases, resulting in the degradation of the phase correction effect.

In order to restrain the scintillation effect in the course of laser transmitting through the atmosphere, the relation between the laser coherence and the scintillation index was researched. First, the mathematic model correlating with laser coherence was established based on the generation mechanism of scintillation effect. Then, the laser was divided into four beams, and the coherence was destroyed. On this basis, the atmosphere turbulence emulation experiment device was made using the random phase screen as core element, and the far field spot scintillation index with different laser coherence was evaluated. Experimental results indicate that the scintillation index with four beams reduce about 75% in comparison with single beam. So the availability of multiple partially coherent beams limiting laser intensity scintillation effect has been approved by the result of theory analyzing and experiment.

We analyze the radius of curvature of Bessel Gaussian (BG) and modified Bessel Gaussian (mBG) beams. The study is based on the results of analytic derivation as well as those of the random phase screen approach. Our results are displayed in graphs as variations of radius of curvature against propagation distance at various settings of beam order, width parameter, source focal length, wavelength, refractive index structure constant. Our findings indicate that mBG beams, in general will have larger radius of curvature values than BG beams. It is further observed that increases in beam order will lead to greater radius of curvatures. Rises in the width parameter will reveal more the differentiations between BG and mBG beams. At small focal lengths, the difference between BG and mBG beams is hardly noticeable. Higher wavelengths will initially cause a reduction in the radius of curvature, but at longer propagation distances, the reverse will happen. Increases in the refractive index structure constant will lead to smaller radius of curvature values. A general agreement is found in comparing the analytic results of BG beams with those of phase screen approach.

A statistical mechanical approach to random phase screens is adapted to describe telegraph-wave phase screens with a bias. The results agree with those found by Jakeman and Renshaw [ J. Opt. Soc. Am. A4, 1206 ( 1987)] for an asymmetrically correlated random-walk model for scattering.

We study theoretically the statistical properties of one-dimensional wave-field inversions. We show that the real and imaginary parts of the logarithm of the normalized coherence function are the invariants of the inverted field if the field is measured on the statistical symmetry axis. Using these invariants, one can easily reconstruct two-point statistical moments of the phase distribution on the screen. We derive equations for the reconstruction of phase-distribution moments in the general case. Numerical simulations show that these equations can be solved by an iterative technique. The convergence range of the iteration method with variation in the parameters is studied.

An efficient approximation method for simulating the dynamic effects of atmospheric turbulence on infrared digital imagery is presented. The method is based on the distant phase screen approximation for certain atmospheric turbulent conditions and is an application of the theoretical work published by M.I. Charnotskii et al. in 1990. The computational simplicity of the method allows realistic incorporation of the turbulence effects in high resolution interactive simulation environments for military and commercial applications. Simulations of turbulence effects on digital infrared images are presented together with actual images obtained from a commercial 8 to 12 μm infrared system imaging through thermally induced atmospheric turbulence.

On the basis of the analogy between the density evolution of a heated gas of noninteracting particles and the diffraction of monochromatic optical waves by a random phase screen, a formula is derived for the correlation function of intensity fluctuations behind the screen. A hypothesis on the statistical splitting of the geometric and diffraction means allows the multiplicity of the integral that determines this function to be reduced by half.

We consider the problem of multiple light scattering from a random surface set nearly perpendicular to a plane mirror. With an approach based on the thin phase screen model we show that this scattering system exhibits the phenomenon of enhanced backscattering. The predictions are supported by experimental results.

Back-reflection through a deep random phase screen is investigated for the case of an incoherently scattering reflector. General results are derived for simple imaging geometries which predict that, in scattering-limited situations, active object illumination can lead to a modest improvement in performance in comparison with passive imaging, but not to diffraction-limited operation. The predictions are explored with the help of an analytically tractable model.

An analysis of the speckle contrast in the diffraction field of a weak random phase screen when the illuminated region contains a few correlation areas is carried out. Curved illuminating wavefronts, and the Fresnel and off-axis terms are considered. The limitations of the method are pointed out. Comparison with a gaussian approximation is made. Some previous studies are examined to obtain a more comprehensive view of the problem. Some of the reasons proposed for observed departures of the theory from experimental results are discussed.

Observations are reported of enhanced backscattering in laser light reflected by a plane mirror placed close behind rigid diffusers. Measurements of both coherent and incoherent effects are achieved by a suitable choice of diffuser and scattering geometry, and comparisons are made with theoretical predictions.

Spatial and temporal parameters characterizing the dynamic behaviour of speckle patterns are compared using a random phase screen model. A method is suggested for the determination of correlation times in the range 10-22-102s, based on an analysis of the contrast of dynamic speckle patterns. The method has been verified experimentally using a model system of a random phase screen, and good agreement between theory and experiment is found.

Measurements are presented of scattering of CO2 laser radiation by a phase screen of rectangular grooves whose widths have a predetermined statistical distribution. The scattering statistics are interpreted using Huygens-Fresnel optics. The measurements provide a valuable model of scattering by naturally occurring phenomena.

A generalized Schell-model source generated by a random phase screen is considered. The coherence function, the intensity distribution, and the degree of coherence of the wavefield generated by such a source is obtained in the paraxial approximation. Various moments of beam radius are evaluated as a function of the distance propagated.

Let us consider intensity fluctuations of a wave that is passed through a random phase screen. For a Gaussian s t ructura l function of the phase fluctuations in the plane of the screen an increase in the dispers ion of the intensity fluctuations is noted in the focusing regions (i.e., at distances z ~ Rph, where Rph is the charac te r i s t ic radius of curvature of the phase front of the wave behind the screen). It is shown that the stat ist ical proper t ies of the field depend essential ly on the fo rm of the s t ructura l function of the phase fluctuations.

The authors interpret Takai’s [ N. Takai , J. Opt. Soc. Am. A3, 452 ( 1986)] Q(X) as the ordinary normalized convariance function.

It is shown that the speckle results presented by the author [ J. Opt. Soc. Am. A.2, 2318 ( 1985)] are correct, provided that the random phase introduced by the screen is complex so that the screen introduces both amplitude and phase fluctuations on the light.