Study On Optical Heterodyne Detection Based On Synthetic Aperture Ladar

Heterodyne detection has many advantages over direct detection, and has been widely used in many technical areas such as optical communication, laser radar system. However, there are many difficulties to keep laser heterodyne detection from widely use because of its stringent requirements in terms of laser spectral linewidth, wave vector matching, and beam front matching etc. For example, coherent optical communication systems have not been commercially deployed till today; And Synthetic aperture ladar (SAL) can hardly put into practical use. Unstable and low efficient are the key problems. Besides, a rough surface will strongly distort the wave front and degrade the heterodyne efficiency. Heterodyne detection can be widely and well used only when these problems are conquered successfully.In this paper, effects of separate angle, spot size and rough surface to heterodyne detection are presented theoretically and experimentally. Some useful results are concluded: the efficiency of heterodyne detection will not increase due to the increasing of spotsize; Laser signal reflected from a rough surface will strongly degrade the detection performance, the phtotocurrent of a laser signal by a mirror reflection may be two or three orders greater than that of a laser echo reflected by rough surface.