Coherent imaging via temporal heterodyne and spatial shearing methods

Abstract

Atmospheric turbulence rapidly decreases image quality at long ranges. Here multiple coherent imaging methods are discussed that lead to a new type of active imaging system, which may help mitigate the effects of atmospheric turbulence. This is accomplished via a self-referencing, linear frequency modulated laser signal, where the signal is both offset in transmitter location (spatial shearing), and is demultiplexed in the temporal frequency domain using unique time delays for each transmitter (temporal heterodyne). Spatial shearing allows one to capture a spatial derivative of the object's spatial frequency content, which if properly 'integrated' can be used to reconstruct an atmospheric phase-aberration-corrected image of the object. The system is illustrated from the starting point of temporal digital holography methods, and builds up to the self-referencing scheme. Various coherent imaging methods and situational parameters are compared.