Study On Change Of The Degree Of Polarization Of Partially Coherent Light Propagating Through Turbulent Atmosphere

Along with Laser technology development, it has been found wide applications in atmosphere all over the world, such as lidar, atmosphere laser communication, laser energy transportation and laser ranging, etc. When light propagates in atmosphere, the degree of coherency and brightness will decrease, the beam will diverge and jitter, many physics properties will change, the advantages of laser will be reduced. The fluctuation of atmospheric refractive index resulting from atmospheric turbulence gives rise to random variation of the optical field. so it imposes restrictions on characteristics and governs technical feasibility in all the laser systems. In the recent several years, there have been subtantial interests studying the propagation of partially coherent light in the free space and turbulent atmosphere, and the polarization property of light has been paid more attention. It is important to study the changes of the degree of polarization of partially coherent beams propagating through turbulent atmosphere, and it has applications in free space optical communication and high power laser beam propagation in atmosphere.In the paper, we introduce the fundamental concept of degree of polarization and theory of atmospheric turbulence. Based on Gaussian Schell-model beam and the Huygens-Fresnel principle, the expression of the changes of degree of polarization are derived as the light propagates through turbulent atmosphere. In the far zone, approximate formula is obtained in different turbulent atmosphere models. Through theoretical analysis it is found that the degree of polarization in the far zone is related to all parameters in source plane when light propagates in free space. But in turbulent atmosphere the degree of polarization equals its initial value after light propagates through a sufficiently long distance, irrespective of atmospheric turbulence and spectral degree of correlation.We also numerically calculate polarization characteristics in far and near zone, and consider the influence of wavelengths, refractive index structure parameters as well as beam spot size on the changes of degree of polarization in near field. It is shown that the degree of polarization when light propagating through atmospheric turbulence tends to zero two times when its initial value is not too big. When initial degree of polarization increases, the distance between the two zero values of degree of polarization decreases. The initial value increases again, the degree of polarization no longer has zero value. In the far zone degree of polarization tend to its initial value. The wavelength can not change the range of the degree of polarization, the longer the wavelength is, the faster the degree of polarization changes, but the slower it tends to initial value. As refractive index structure constants increases, the change of degree of polarization become more and more slow, the distance between the two zero values of degree of polarization reduced, too. Regarding different beam spot sizes, the change of degree of polarization get slow with the spot size increases, the smaller the spot size, the more obvious the change of degree of polarization in the short distance.Approximation of degree of polarization in far zone is agreement with numerically computed results. All of the conclusions and results have guide significance to lidar, space optical communication as well as high power laser weapon.