Generation of carrier fringes in holography and shearography

Double-exposure holography and double-exposure shearography are often used together with the carrier fringe technique, which requires additional shift ing of the light source in a prescribed manner between exposures. In the ho lographic carrier fringe technique, difficulty in prescribing a suitable mo vement of the light source may be alleviated through visualization of the m oire fringes that are reconstructed by slight displacement of two overlaid families of ellipsoids in a holodiagram. Because shearography is the first differential of holography, it is often impractical to perform two successi ve optical differentiations on the ellipsoids to visualize the shearographi c carrier fringes. A simple method of discerning holographic and shearograp hic carrier fringes is described. The method is based on the hyperboloids i n a holodiagram that represent Young's (interference) fringes produced by t he interference of two point sources. The hyperboloids are analogous to hol ographic carrier fringes, whereas the moire patterns reconstructed from two overlaid hyperboloids are analogous to shearographic carrier fringes. Use of this method for explaining the formation of deformation hinges in plate bending, as well as the effect of light-source movement on the deformation fringes, is also illustrated. (C) 2000 Optical Society of America OCIS code : 090.2880.