Investigation On Polarization And Coherence Characteristics Of Laser In Atmospheric Turbulence

In recent years,the properties of coherence and polarization of laser in atmospheric turbulence is one of the frontier topics in the area of optics and laser industry at home and abroad. The research work can provide theoretical model and experimental basis for the application of free space optical communications. Taking the random electromagnetic sinh- Gaussian(Sh G) beam as example, the properties of coherence and polarization of laser propagating through atmospheric turbulence are studied in this thesis. The main results obtained are as follows:We emphasize the motivation and significance of this dissertation and introduce the theoretical basis and the fundamental method used in our work. Then, the hot domains in this field are summarized and analyzed. Finally, we introduce the basic theory of the basic theory of partially coherent light, the properties of the atmospheric turbulence: the structure constant of the turbulent atmosphere and the refractive index spectrums model in the basic theory of beam propagating through the atmospheric turbulence.Based on the extend Huygens-Fresnel principle, taking the random electromagnetic Sh G beam as a typical example of random electromagnetic beams, the analytical expressions of the cross-spectral density matrix elements for random electromagnetic Sh G beam propagating through atmospheric turbulence are derived. In this article, we analyze in detail the properties of coherence and polarization of laser beams propagating through atmospheric turbulence.There exist the changes in the states of polarization when random electromagnetic Sh G beams propagating through atmospheric turbulence. The states of polarization depends on the general structure constant, correlations length, Sh-part paramter, and the propagation distance z. With the decrement of structure constant C_n~2, as well as the increment of the Sh-part parameter W(15), the transition position of orientation angle will increase, and the distance for minimum degree of polarization and maximum ellipticity will increase. However, after a long distance transmission, the influence of Sh-part parameter W(15) on the degree of polarization P, orientation angle q and ellipticity e can be ignored.The degree of coherence of random electromagnetic Sh G beams are depend on the structure constant, correlations length, Sh-part paramter, inner scale of turbulence and the propagation distance. The degree of coherence of stochastic electromagnetic Sh G beams in atmospheric turbulence is different from those in free space. The larger structure coonstant C_n~2, the smaller Sh-part paramter W(15), the smaller the inner scale of turbulence, the longer the propagation distance of the distribution of the degree of coherence into Gaussian profile is.