Electronic Processing for Holographic Interferometry

Abstract

In many interferometric setups, heterodyne or quasi-heterodyne techniques have become a powerful tool for high accuracy interference fringe interpolation. In holographic interferometry, heterodyning has been applied to real time as well as to double-exposure holography. For double-exposure holography two reference beams are required. During reconstruction a change of the relative phase between the two references allows the shifting of the fringes in the interferogram at will.Heterodyne holographic interferometry offers high spatial resolution and interpolation up to 1/1000 of a fringe. However,it requires sophisticated electronic equipment and mechanical scanning of the image by photodetectors. Quasi-heterodyne techniques are more adequate for digitial processing and TV detection. Two-reference-beam holography with reference sources close together and video-electronic processing allows measurement of the interference phase with an accuracy of 1/100 fringe at any point in the TV image. This system combines effectively the simplicity of standard double-exposure holography, video-electronic processing, and the power of heterodyne holographic interferometry.