On-axis Scintillation Index Of Echo Waves In Slant Atmospheric Turbulence

Laser propagates in the slant atmospheric channel where contains atmospheric turbulence when used in active detection optical systems such as free space optical communication systems, lidar systems, target tracking systems etc. The development of applications of laser propagating from earth to space is restricted by the optical scintillation caused by fluctuations of turbulent refractive index. It is very necessary to model the scintillation index of echo waves, in order to accurately study the physical properties of intensity fluctuations and provide theory references for relevant laser transmission systems.Based on Rytov approximation and extended Rytov theory, the on-axis scintillation index of echo waves in slant atmospheric turbulence was studied in both biastatic systems and monostatic systems.First of all, the classical theories about atmospheric turbulence and related quantities with scintillation were introduced.Secondly, based on the theory of optical wave propagation in the slant path and the ITU-R turbulence structure constant model which is altitude dependent, the on-axis scintillation index of the optical waves from the transmitter to the corner reflector and from the corner reflector to the receiver is studied. Considering both inner scale and outer scale, the expression of the on-axis scintillation index of the echo wave is obtained. The relationship of the on-axis scintillation index and the Fresnel rate is calculated and analyzed with various parameters. The results shows that the on-axis scintillation index is influenced by inner scale, outer scale, beam wavelength and target altitude.Finally, based on the extended Rytov theory, a model of scintillation index of echo waves from the point target in double slant atmospheric turbulence is proposed. The model extends the scintillation index from weak fluctuation regimes to the moderate and strong fluctuation regimes in both monostatic system and biastatic system. Besides the inner scale, the model also contains the outer scale which changes with altitude. Numerical analysis shows that the outer scale affects the scintillation index little in the weak regime but plays an important role in the strong regime.