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In this paper, a novel evaluation algorithm of turbulent influence is presented for influence investigation of Gaussian beam and Airy beams in atmospheric turbulence, in which a parameter to quantify the influence of turbulence is proposed and named by Intensity Variation Index. The algorithm is beneficial to analyze the distortion caused by the atmosphere. The effects of wavelength, channel condition, and the type of beams are simulated. The results show that the Intensity Variation Index of Gaussian is dually affected by atmospheric coherence length and wavelength, furthermore, the change trend is similar to the scintillation index, which shows the correctness of proposed algorithm. Meanwhile, Airy beams also affected by two factors. After performance comparison, the turbulence effect of Airy beams is greater than that of the Gaussian beam and the reason is the loss of Airy beams’ side lobes during transmission in turbulent flow. The proposed evaluation algorithm can evaluate the effects of turbulence and can accurately represent the affected trends of the beam under different conditions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The resolution of a conventional optical imaging radar system is constrained by the diffraction limit of the telescope's aperture. The combination of lidar and synthetic aperture processing techniques can overcome the diffraction limit and provide a higher resolution air borne remote sensor. Atmospheric turbulence is an important factor affecting lidar imaging, and the phase screen simulation method is an effective method to simulate the degradation of laser signal propagating through turbulent atmosphere. By using Monte-Carlo random factor, the randomness of phase screens can be improved. The lidar imaging with different turbulence intensity is also calculated in this paper, then the improved rank one phase estimation autofocus method is used to compensate the imaging phase errors. The results show that the method of generating phase screen is consistent with the statistics of atmospheric turbulence, which can well simulate the effect of atmospheric turbulence on synthetic aperture lidar, and the influence on synthetic aperture lidar azimuth resolution is greater when atmospheric turbulence is stronger. Improved rank one phase estimation algorithm has good autofocus effect, which can effectively compensate the phase errors and enhance the image quality degraded by turbulence. [ABSTRACT FROM AUTHOR]

An arbitrary thickness phase screen model can describe scintillation index for Gaussian beam propagating through a phase screen more accurate than thin phase screen model. To describing actual scintillation index for Gaussian beam propagating through an extended medium using a phase screen in weak non-Kolmogorov turbulence, the scintillation index and Rytov variance for arbitrary thickness phase screen model are derived. Specially, the ratio of the Rytov variances for a phase screen and extended random media is found under the assumption of equivalence in scintillation index of the two cases. The theoretical results show that the normalized Rytov variance varies with the power law of the turbulence spectrum, the relative thickness of the phase screen, the position of the phase screen, the transmitter beam parameters and the radial position at output plane. The influences of these variables are also simulated. These results will be applied to simulation of adaptive optics and laser communication. [ABSTRACT FROM AUTHOR]

Abstract: Using the anisotropic phase-screen method, we derive the generalized Mueller matrix of an inhomogeneous, linear, birefringent medium in the single-scattering case. We show that the Mueller matrix include eight nonzero elements with relations among elements given by m 11=m 22, m 12=m 21, m 33=m 44, and m 34=m 43. Using the derived Mueller-matrix model, we simulate polarization optics for calcite, quartz, and sodium nitrate crystals. At λ=0.63μm and with small inhomogeneities, the matrix elements are a function of the standard deviation of the crystal thickness, while m 12 shows pronounced sensitivity to the difference of refractive indices. At an observation angle of 0°, inhomogeneous birefringent media behaves as if they are partial polarizers. Matrix elements most sensitive to the inhomogeneity in the UV to near IR wavelengths have been determined. [Copyright &y& Elsevier]

The atmospheric turbulence can severely affect the azimuth imaging of the Synthetic Aperture Ladar (SAL). Based on a neural network, this study generates atmospheric phase screens complied with marine atmosphere spectrum. The SAL imaging results with different turbulence intensities and laser wavelengths are calculated, and the changing law of the ratio of real aperture length to atmospheric coherence diameter with turbulence intensity under different slant ranges and laser wavelengths are analyzed in this paper. The results suggest that the SAL imaging becomes worse as the turbulence intensity is stronger, and even the target is not able to be distinguished. A longer laser wavelength can be used to alleviate the defocus effect, and the phase error compensation algorithm based on marine phase screens can effectively improve the SAL imaging quality to guarantee the real–time process of echo signals of SAL in the marine atmosphere. [ABSTRACT FROM AUTHOR]

Generating phase screens to replace phase fluctuation caused by atmospheric turbulence is essential for simulation of light propagation through the atmosphere. Error between power spectral density of actual turbulence and traditional Kolmogorov model illustrates the importance of generating non-Kolmogorov phase screen. Meanwhile, methods used to generate phase screen at present show different kinds of disadvantages respectively. In this paper, we adopt a new method named "intrinsic embedding fractional Brownian motion (IE-FBM)". First, relationship between phase screen and FBM is analyzed. Next, principle of IE-FBM is clarified. We expand the correlation matrix and generate a stationary Gaussian surface through two fast Fourier transforms, which is the principle of intrinsic embedding. After that, we adjust the Gaussian surface into an FBM surface. Finally, simulation results demonstrate that IE-FBM combines advantages of traditional methods. Phase structure function becomes closer to theoretical value no matter how we set parameters of phase screen. Besides, both low and high frequency components of phase screen are sufficient and creases don't exist. In addition, time consumption reduces apparently. In conclusion, our method is comprehensively optimal choice to generate phase screen. [ABSTRACT FROM AUTHOR]

Anisoplanatic effect caused by atmospheric turbulence is an important issue affecting the imaging resolution of ground-based telescopes when observing astronomical objects. Based on the optimized multilayer phase screens distribution model on inhomogeneous turbulent path, this paper establishes a theoretical model of telescope imaging related to optical system parameters. The effects of aperture, photon limited and optical aberration on anisoplanatic imaging are analyzed. The results show that aperture has obvious influence on diffraction effect of short-exposure point spread functions (PSFs), and the defocusing aberration only slightly affect the anisoplanatic imaging and do not influence on restoration methods of such images. [ABSTRACT FROM AUTHOR]