Interferometric Measurements on Diffuse Surfaces by Holographic Techniques

This paper presents a technique for the measurement of small translations and rotations undergone by any general three-dimensional object. This technique applies to those cases in which different portions of the object suffer displacements and rotations which are independent of the other parts of the object. Such a situation might exist when a complex object is stressed. In essence, the technique is simply one of interfering the coherently illuminated object with a perfect three-dimensional image of itself. This image is formed by constructing a hologram of the object. The image from the reilluminated hologram is then made to exactly overlay the object. By observing the fringe structure, the translations and rotations which each section of the object has undergone may be determined. The analysis which provides the necessary equations relating fringe structure to the object translations and rotations is carried out in detail. In addition, experimental results which verify the analysis are included. Photographs show the complex nature of the fringe formation when a complicated object is subject to stress.