Propagation Properties Of Polarized Laser Pulse Beams Through Turbulent Atmosphere

The issues of propagation properties of laser beams propagating in atmosphere has an important significance for the research projects of some practical applications, such as laser ranging, laser radar, laser weapon and satellite remote sensing, et al. Affected by turbulent atmosphere, the random fluctuation of the atmospheric refractive makes the wavefront of beams distortion, resulting in a series of turbulence effects such as the intensity fluctuations, beam spot wandering, beam spread etc., by which the normal operation of the photoelectric system in field is seriously influenced. Compared with the other beams, the polarized beams have higher degrees of freedom on the beam control, so they have advantages of wider range of applications, stronger abilities of target recognition and anti-interference and lower bit-error rates etc. In this paper, we take the polarized laser pulse beams as a typical example, and study the properties of pulse broadening, beam spread and depolarization of the beams when the laser beams propagate through the turbulent atmosphere. The results of this paper are listed as follows:(1) Taken the elliptically polarized Gaussian pulses beam as a typical example, we study the pulse broadening of the beam propagating through the turbulent atmosphere in the slant path. According to the extended Huygens-Fresnel principle, the two-frequency mutual coherence function and Rytov approximation method, the novel expressions for average intensity and pulse broadening of elliptically_polarized Gaussian pulse beam in receiver through turbulent atmosphere in a slant path are in turn derived. The results of numerical calculation show that the pulse broadening of the elliptically polarized Gaussian pulse beam on slant path turbulence atmospheric depends on the zenith angle η and receiver height H, and the inner scale factor appears to have an insignificant effect on the pulse broadening.(2) Taken the elliptically polarized Gaussian pulses beam as a typical example, we obtain the novel expression for the beam effective spread radius in receiver through turbulent atmosphere in a slant path. Then we study the properties of beam spread of the elliptically polarized Gaussian pulses beam. The results of numerical calculation show that the beam spread mainly depends on the initial waist radius w0, wavelength A, and polarization angle (?). With the increasing of propagation distance L, beam effective spread radius w(L) decreases as w0 increases, and it increases with λ, in addition, w(L) increases as (?) increases.(3) We take the elliptically polarized spatially and spectrally partially coherent EGSMP beams as a typical example. Based on the unified theory of coherence and polarization of stochastic electromagnetic beams and the extended Huygens-Fresnel principle, combined with the quadratic approximation of Rytov’s phase structure function and the generalized Stokes parameters, the analytic expressions for the electromagnetic cross-spectral density matrix (CSDM) elements and the degree of cross-polarization in the receiver plane of a class of polarized and spatially and spectrally partially coherent EGSMP beams propagating through atmospheric turbulence in the slant path are derived. Finally, we calculate and analyze the effects of interrelated factors on both elliptically polarized and partially polarized beams. The results show that the influences of the turbulent intensity, the initial pulse duration, waist width of the beam, the spatial coherence length and temporal coherence length et al. on the depolariz-ation properties of fully polarized beams are larger, while the effects of those parameters on the partially polarization beams are smaller.It is noted that the results of this paper have established sound theoretical basis on the topic of improving performance of the laser system propagating through the turbulent atmosphere.