High-accuracy surface profile measuring system using a BSO phase conjugating mirror

A highly accurate real-time surface profile measuring system has been constructed by combining a Bi(12)SiO(20) (BSO) phase conjugating mirror (PCM) with a Twyman-Green interferometer. In this new interferometer the convex lens collects and focuses the scattering object waves in the BSO crystal, and the PCM reconstructs the object field through the same lens. The method of deriving surface profile is similar to conventional ones but differs in that it does not require exact phase modulation of the interferograms. This system features a quite high measurement accuracy free of aberrations of the lens and of hysteresis or aging of the piston actuator used to change the phase of the reference field. The principle and basic experimental results are presented.