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The two-point generalized Mueller matrix method and phase screen approximation are applied to determine features of light scattering on mosaic birefringent layers composed of structurally similar d...

We investigate the optimal subharmonics selection for atmospheric turbulence phase screen simulation with a given precision using the fast Fourier transform-based subharmonic method. A criterion ap...

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.

Here, we theoretically demonstrate that if a Gaussian optical vortex is distorted by a random phase screen (diffuser) then the average intensity distribution in the focus of a spherical lens has a form of a ring with a nonzero value on the optical axis. The radius of the average-intensity ring depends on both the topological charge of an optical vortex and on the diffusing power of the diffuser. Therefore, the value of the topological charge cannot be unambiguously determined from the radius of the average intensity ring. However, the value of the topological charge of the optical vortex can be obtained from the number of points of phase singularity that can be determined using a Shack-Hartmann wavefront sensor. It is also shown that if we use a linear combination of two optical vortices, then the average intensity distribution has local maxima, the number of which is equal to the difference of the topological charges of the two original vortices. The number of these maxima no longer depends on the scattering force of the diffuser and can serve as an indicator for optical vortex identification. Modeling and experiments confirm the theoretical conclusions.

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

The mean irradiance profile has been widely applied in performance analysis and atmospheric channel research for free space optical communication; however, the modeling method and a closed-form expression of the mean irradiance profile under random jitter have rarely been discussed. To the best of our knowledge, this work presents a modeling method and a closed-form expression for a mean irradiance profile under random jitter through the ensemble average principle for the first time. We find that, with an increase in random jitter variance, the mean irradiance profile varied from an approximately Gaussian profile to a flat-topped profile to a hollow profile. These findings were verified using multilayer random phase screen simulations. The model of the mean irradiance profile under random jitter developed in this study will improve the accuracy of performance analysis and atmospheric channel research.

During the last decade, optical memory effects have been explored extensively for various applications. In this letter we propose phase screen models to facilitate the analysis and the simulation of wave propagation through optical media that exhibits memory effects. We show that the classical optical memory effect, which implies tilt wave correlations of the input and the scattered fields, can be readily modeled by a single random phase screen. For the recently discovered generalized optical memory effect, which implies the existence of shift wave correlations in addition to the tilt correlation, we propose an appropriate generalized random phase screen model.

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.

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.

It is shown that the validity of the random phase screen approximation in coherent wave scattering from random media can be determined from the correlation between symmetric sidebands in the scattered field. Analysis of doublet correlations in microwave reflectometer data taken on the Tokamak Fusion Test Reactor confirms the validity of the model and allows for the numerical back propagation of measurements without the use of imaging optics.

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.

A significant improvement to the recently introduced complex screen (CS) method for generating partially coherent Schell-model sources is presented. The method, called the modified phase screen (MPS) technique, applies a deterministic amplitude and the phase portion of a CS to an initially coherent light source using a single phase-only spatial light modulator. The MPS technique, unlike the CS approach from which it is derived, does not produce a fully developed speckle pattern in the source plane, and therefore converges faster and more uniformly to the desired partially coherent source. The analytical development of the MPS method is presented. Experimental results of a Bessel-Gaussian-correlated Schell-model source, generated using the CS and MPS approaches, are compared to demonstrate the validity and utility of the MPS technique.

We present a new approach for simulating time-evolving speckle patterns, by combining the shift of a rigid phase screen with its evolution. Thus, the two time-scales associated with speckle boiling and speckle motion can be adjusted independently. The statistical properties of the phase perturbation and the speckle pattern are investigated by using the temporal phase structure function and the temporal intensity correlation. We found a very good agreement with experimental results.

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.

The enhanced-backscattering (EBS) phenomenon is investigated for the case in which a phase screen is placed close to a multiple-scattering medium. This situation results in a narrowing of the EBS peak that depends on the strength and the position of the phase screen. The resulting enhancement peak is essentially the sum of two contributions: the EBS produced by the multiple-scattering medium in the absence of the phase screen and the enhancement obtained when the multiple-scattering medium is replaced by a plane mirror.

The propagation effects of spatially pseudo-partially coherent Gaussian Schell-model beams in atmosphere are investigated numerically. The characteristics of beam spreading, beam wandering and intensity scintillation are analyzed respectively. It is found that the degradation of degree of source coherence may cause reductions of relative beam spreading and scintillation index, which indicates that partially coherent beams are more resistant to atmospheric turbulence than fully coherent beams. And beam wandering is not much sensitive to the change of source coherence. However, a partially coherent beam have a larger spreading than the fully coherent beam both in free space and in atmospheric turbulence. The influences of changing frequency of random phase screen which models the source coherence on the final intensity pattern are also discussed.

The effect of a random phase screen on the performance of an imaging system is described. Analytical expressions of the average image spectrum are developed for both coherent and incoherent radiation. It is shown that the random-phase-induced ansioplanatism can give rise to the characteristics of superresolution. The conditions of superresolution are derived, and the relationship among various parameters for the occurrence of superresolution is discussed.

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.

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.