Polarization interferometer as a proximity sensor

A simple interferometric phasemeter which can be used as a proximity sensor is described. It is based on the measurement of the phase shift between the p- and s- components of a field caused by the processes of attenuation in total internal reflection. The role of the interferometer is to restore the p- and the s- components from the resultant totally reflected field, with minimum amplitude and phase distortions and to let them interfere. The phase shift as a function of the attenuation of the total internal reflection can be determined from the interference signal. The interferometer is of a common path polarization shearing type, consisting of Rochon beamsplitter and a linear polarizer. An experiment for measuring the distance between glass plane surface and a plane attenuater made of Si mono-crystal is described. A good agreement between theory and experiment for separations less than 300 nm is observed. This device can be applied in research and metrology. After further modifications, the optical system could be used for proximity sensing, surface geometry control, variable optical retarders, contamination monitoring, etc.