Improvement of speckle statistics in double-wavelength superheterodyne interferometry

In this paper we analyze the probability density function of the superheterodyne signal obtained in a two-wavelength interferometer from the beat of a local oscillator laser beam with a speckled return beam from a rough target. Theoretical investigation shows that, by using an increased number of spatially separated detectors, one can improve noticeably the detection probability of the superheterodyne signal. Experimental results obtained with a four-quadrant detector are in good agreement with theory.