Abstract

The field inside a Fabry-Perot cavity made of a conventional mirror and a phase conjugate mirror (PCM) is the sum of two terms, one proportional to the input wavefront, the other to its complex conjugate. Near threshold, the amplitudes of the two waves are nearly equal, while their relative phase depends on the phase of the pumps. In steady state, the interference of the input wavefront and its conjugate forms a selfreferencing interferogram having double the resolution of a conventional interferogram and little sensitivity to variations of wavefront amplitude. To a good approximation, the device displays the real part of the input. When an abrupt change affects the input wavefront, the moire between the new and the old interferograms is momentarily displayed during the finite response time of the PCM. This moire can be used to measure wavefront perturbations or shifts in beam alignments. To measure the motion of an object against a stationary background, a transducer (LCTV, for example) captures the scene at time intervals larger than the PCM response time and inputs it to the interferometer as phase information. The device then acts as a real time speckle interferometer, showing object translations as Young fringes superposed to the scene spectrum.

© 1989 Optical Society of America