Photomixing with Diffusely Reflected Light

A method is presented for estimating the sensitivity of a coherent optical heterodyne receiver in detecting laser radiation reflected from a diffuse surface. A configuration typical of many optical radar applications is considered, and the effects of transmitter beam size, receiver aperture, and heterodyne field of view on the beat frequency signal are calculated. Two idealized surface models are used in the analysis. It is shown that the size of the scattering reflector elements in the surface can affect the optimum set of receiver parameters. The range of values of these parameters for most efficient detection is derived for both surface types and a given transmitter beam angle. The advantage of a receiver with large aperture and field of view equal to the transmitted beam width is demonstrated. The magnitudes of errors introduced by the simplifying approximations are discussed.