Laser echo decoherence characteristics of rough plane in heterodyne detection with truncated GSM beam

Rough target can cause the wavefront distortion of laser return, which shows the decoherence phenomenon and reduces the detection performance of heterodyne lidar systems. In fact, the decoherece process includes both the laser source and the rough target. The actual laser beams are usually partially coherent, and the atmospheric turbulence aggravates the coherence of laser spots on the rough target and the backscattered laser return. The backscattered laser field of rough plane is derived based on the GSM beam and the generalized Huygens-Fresnel principle. And the beam truncation effect of actual optical transceiver is also analyzed by using the hard edge aperture function. The laser return intensity variations are obtained by considering the laser beam coherence, the rough surface height fluctuation and the atmospheric turbulence. Then decoherence effects are calculated via the complex coherence degree under typical roughness parameters and laser wavelengths. For practical target, the complex coherence degree can be approximated by the Dirac delta function, and then the system efficiency and the effective coherent solid angle can also be used for further analyses. The results show a positive correlation between the decoherence effect and the roughness. The research on the scattering characteristics of rough planes expands the scattering theory and provides a reference for the design and analysis of long-range and high-precision heterodyne lidar system.