Thickness contours of highly aberrant phase objects. I. Reduced sensitivity holographic interferometry for direct phase measurement

Abstract

A double-exposure holographic method is described that permits one to visualize thickness contours of highly aberrant thin phase samples. The hologram is recorded using a reference wave that bears a simple phase relationship with the subject wave while the reconstruction is made with a plane wave. The phase shaping of the reference wave is accomplished by making it traverse the test sample. If the test sample is thin and the hologram is recorded in the plane in contact with its rear surface, the phases of the hologram producing waves are correlated to each other at all points through a constant. Consequently, the reconstructed object wave contains direct phase variations of the object at reduced sensitivity, which can be varied by changing the hologram recording geometry. A double-exposure technique has been used for the vizualization of the phase variations of the object wave. Furthermore, a finite distance between the sample and the plane of the hologram produces a lateral shearing interferogram receiving variations of the phase gradients of the object. The method is applicable to thin samples that do not have high, rapidly varying surface deformations.