Coherent and incoherent synthetic-aperture imaging ladars and laboratory-space experimental demonstrations [Invited]

This paper reviews our studies on coherent and incoherent synthetic-aperture imaging ladars (SAILs). Using optical diffraction, a systematic theory of side-looking SAIL was mathematically formulated and the necessary conditions for assuring a correct phase history are established. Based on optical transformation and regulation of wavefront, a down-looking SAIL of two distinctive architectures was invented and the basic principle, systematic theory, design equations, and necessary conditions are presented. An incoherent spotlight-mode SAIL was proposed, and detailed mathematically. To validate the concepts, laboratory experiments were conducted. The spatially and temporally dependent laser speckles are analyzed by applying the partial coherence theorem, and proposals to reduce their effect are given. Optical antennas and their components are discussed. It is shown that for down-looking SAIL the width of the scanning strip may be greatly increased without loss of high resolution, and the influences from atmospheric turbulence and unmodeled line-of-sight motion can be automatically compensated.