Scintillation Of Polarized Laser Beam In The Double-passage Atmospheric Turbulence

The study on transmission characteristics of laser propagating in atmospheric turbulence has important significance for laser radar, laser ranging, satellite remote sensing and laser weapon, and the refractive fluctuation in the turbulence makes the beam wander, spread and twinkle by which the photoelectric system is influenced deep. Compared with the general beam, the polarized beam has a bigger degree of freedom to be controlled, so it has a wider applied range and more advantage. The radar based on polarized beam has a longer detection distance and a stronger recognition capability for target than general beam. In the field of communication, the anti-interference ability of polarized beam is poorer and the system makes less mistakes. This article discusses the scintillation of polarized laser beam, which is influenced by the double-passage atmospheric turbulence, on the receiver of the active laser radar systems. The results of this study are shown as follows.At first, Intensity distributions and scintillations on two orthogonal directions and cross scintillation of two directions profiting from calculating the four-order polarized and coherent matrix express the scintillation of polarized and partially coherent laser beam, and tensor analysis is used to solve the problem of intensity distribution and the extended Rytov theory is used to achieve the three scintillations.Second, the combination of the extended Huygens-Fresnel principle and matrix methods in optics is used to study theoretical model that polarized and partially coherent laser beam is affected by scattering of target and double-passage turbulent path, then the scintillation on the receiver is obtained. The influences of the refractive-index structure constant, the wavelength, the spot radius, the spatial correlation length and the state of polarization of the beam on the scintillation index are discussed.The numerical results show that the scintillation index increases to peak at first and then decreases gradually with the increase of distance between target and transmitter, the beam whose wavelength is longer has smaller scintillation for close target and smaller peak scintillation. When the refractive-index structure constant is low, the peak scintillation is small and the beam properties are stable when propagating. The beam whose coherence property is poor or whose spot radius is little induces a small scintillation, but the influence will be weakened with the increase of the spot radius and the spatial correlation length. Scintillation presents periodic change with the change of the phase difference between the two orthogonal electric field components. The cycle is 2π and when the phase difference shows 2π, Scintillation is smallest, and biggest for π.