Light scattering is an important and classical method for optical surface testing. Typical scheme of light scattering measurement often uses a single laser beam incidence, and then evaluates the surface quality via detecting and analyzing the scattering signal. In this work, a developed method for optical surface testing is proposed and demonstrated, and whose measuring principle is based on the scattering interference effect. In this approach, a single longitudinal mode laser beam is divided into two beams, when these beams irradiate the optical surface, their respective scattering fields would interfere with each other. If the phase between these incidence lights is scanned periodically, their scattering light interference signal would fluctuate simultaneously. Through analyzing this kind of scattering signal, our method can not only determine the scattering loss of optical surface, but also scale its inhomogeneity performance. A simply set of experimental apparatus is built up and used to demonstrated this method, which uses a single mode laser as the light source. Furthermore, to modulate the phase difference between two incidence beams, a piezoelectric ceramic is used. Some typical cases are then experimented and discussed, the results show that this method can be used to calibrate the quality of optical surface.
Based on the vector scattering theory, we analyze and discuss the interference effect of the surface scattering lights on the folded mirror of V-shaped cavity. It is found that the interference effect can introduce the periodic fluctuation of scattering loss, and this phenomenon is similar with the spectral ripple effect existed in optical-feedback Cavity Ring-down Spectroscopy (CRDS). We believe that the interference effect of the scattering lights on folded mirror is an important source of spectral ripple effect, and it can be used to explain the mechanism of spectral ripple phenomenon.