Characteristics Of Partially Coherent Beam Propagation In Slant Atmosphric Turbulence

Laser propagation in the atmospheric turbulence will produce the turbulence effects of radius expansion, angle spread, angle-of-arrival fluctuation variance, beam wander and scintillation. Study of beam propagation in slant atmospheric turbulence is supported by applications in areas such as laser satellite communication, laser ranging, guiding, laser radar and remote sensing, which is one of important research topics. The topic on characteristics of propagation, polarization of the partially coherent beam and the property of the wave returned by targets in the slant atmospheric turbulence have important value. The main results obtained are as follows:First, the expression for cross spectral density function(CSDF) of the partially coherent Gaussian-Schell model(GSM) beam propagation in the slant atmospheric turbulence under the Kolmogorov spectrum of refractive index, and expressions of the effective beam radii, phase front radii of curvature and effective beam parameters at the receiver are derived. The effects of the waist radius, wavelength, propagation height and atmospheric structure constant on the propagation characteristics of the partially coherent beams are discussed. Comparison between the propagation characteristics of GSM beams and that of the fully coherent Gaussian beams is made. The effects of inner- and outer- scale of turbulence on radius and average intensity are proposed under the Von karman spectrum.Second, based on the modified Rytov theory and the International Telecommunication Union-Radio(ITU-R) slant atmospheric structure constant model, the large- and small-scale log irradiance fluctuation variances, uniform scintillation index of partially coherent GSM beam propagation in the slant path is derived from weak- to strong-turbulence regions considering inner- and outer-scale effects under the modified Hill and von Karman spectra. Comparison between the scintillation of GSM beams under the von Karman spectrum and that of beams under the modified Hill spectrum is made.Third, on the basis of the extended Huygens-Fresnel principle, the scattering of partially GSM beams from a diffuse target in slant double-passage atmospheric turbulence is studied and compared with that of fully coherent Gaussian beams. We derive the expressions of the mutual coherence function, angle-of-arrival fluctuation, and covariance and variance of the intensity of the scattered field, taking into account both of the log-amplitude fluctuation and phase fluctuation. The influences of the wavelength, propagation distance, and waist radius on scattering properties are discussed. The effects of inner- and outer- scale of turbulence on average intensity and the log-amplitude variance are proposed under the Von karman spectrum.Fourth, on the basis of the extended Huygens–Fresnel principle, the cross spectral density matrix(CSDM) of partially coherent elliptically polarized GSM beams in the slant atmospheric turbulence is derived. The degree of Polarization(Do P) of the partially coherent GSM beams is represented by Stokes parameters. The expressions of the orientation angle, degree of ellipticity and polarized light intensity are derived. discussing the effects of polarized light intensity ratio, spot sizes, wavelength and receiving height on the Do P. Various parameters in Mueller matrix are derived by a Mueller matrix M that relates the incident Stokes vector incidentS with the exiting Stokes vector ExitingS. The depolarization index(DI) is obtained to describe the depolarized state. Results obtained are degraded to the condition of the horizontal path, which makes a comparision with the polarization of beams in slant path.Finally, the two-frequency, two-point CSDF of partially coherent Gaussian-Schell model pulse(GSMP) beam propagation in slant atmospheric turbulence under the von Karman spectrum is derived based on the extended Huygens–Fresnel principle. Using the Markov approximation method, expression of structure constant 12 D in isotropic turbulence is obtained. under the assumption that()()1 2 1 2ω-ω ω +ω ≤1, the theory obtained is valid for turbulence of any strength and can be applied to narrow-band signals. The expressions for average beam intensity, the beam size, and the two-frequency complex degree of coherence of a GSMP beam are obtained. The effects of the frequency, initial pulse width, initial beam radius, zenith angle and outer scales on the complex degree of coherence are discussed.