Shape identification using phase shifting interferometry and liquid-crystal phase modulator

A phase shifting technique using a Michelson interferometry system is presented and applied to surface contour measurement. Hyperbolic fringes are produced by the interference of two spherical wavefronts expanded from a beam expander. The fringe pattern is projected on an object surface and the deformed grating image is captured by a CCD camera for subsequent analysis by a PC. Phase variation is achieved by a liquid-crystal device incorporated in the Michelson interferometry system. Results obtained using the proposed method for objects of various shapes and sizes compared well with those from a conventional profilometer.