Spread And Drift Characteristics Of Polarized Laser Propagated In Atmospheric Turbulence

Laser propagation properties in turbulent atmosphere have been extensively investigated both in the theory and through practical applications. Currently, majority of studies are paid attention to spread and wander characteristics of laser propagation in horizontal and oblique turbulence. At present, most studies investigate spread and wander of Gaussian-shell model beam GSM beam propagated in turbulent atmosphere. However, there are few theories on how polarized laser beams are affected as they propagate in a turbulent medium. In terms of polarization, only coherence and polarization of electromagnetic Gaussian-shell model (EGSM) beam have been investigated. Atmospheric turbulence affects polarized laser beams by causing beams to spread and wander. This phenomenon must be considered to improve the efficiency of a free space optical communication system, a laser radar system, and a laser ranging technique, to name a few, or the accuracy of laser alignment and laser positioning.Cross-spectral density function of polarized and partially coherent laser propagated in turbulent atmosphere was determined based the extended Huygens-Fresnel principle and Collins Formula through investigating a partially coherent source, GSM with a Gaussian intensity distribution and the coherence distribution. Analytical expressions for spectral intensity, expansion radius, barycentric position wander and polarization degree of polarized Gaussian-shell model beam (GSM) under horizontal transmission at different distances of external fields were obtained. Changes in spread, wander and depolarization of polarized laser propagated in turbulent atmosphere were simulated under the same propagation distance with different polarization angles and different initial waist widths. Similar simulation was also carried out with the different wavelengths and the same polarization angle under different propagation distances.Through analyzing the spread and wander phenomena of the polarized and partially coherent laser beams in turbulent atmosphere, conclusions can be drawn as follows:changes in characteristics of the polarization of partially coherent laser as beams propagate in the turbulent atmosphere do not affect spread and wander of a beam at w0<5mm; for polarized GSM at different wavelengths, spread and wander of beams are lower; the depolarization of polarized and partially coherent laser beam is more regularity, stability and persistent than partially coherent laser beam propagated in turbulent atmosphere; polarization of partially coherent laser polarization is affected by the changes of initial waist width which hardly affect polarization of partially coherent beam, compared with general Gauss beams, this type of laser beams has a strong advantage in terms of the quality of spread and wander of beams during propagation. The conclusions could provide theoretical basis to improve propagation quality of polarized laser in an external field of turbulent atmosphere. The conclusions also play an important role in optical communication and in target recognition.