Digital recording and numerical reconstruction of holograms for nondestructive testing

Digital recording and numerical reconstruction of holograms is a new method of laser metrology: two or more Fresnel holograms, which represent different loading states of the object, are generated directly on a CCD-target and stored electronically. In contrast to speckle interferometry, no lens or other imaging device is used. The reconstruction is done from the digitally stored holograms with numerical methods. For both states, the intensity as well as the phase of the object wave can be calculated in the reconstruction process. This makes it possible to calculate the interference phase directly from the holograms, without generating an interference pattern. In this paper, applications of digital holography in the field of nondestructive testing are presented. A thin-walled pressure vessel (satellite tank) is loaded by changing the internal pressure and the resulting deformation field is measured quantitatively. Defects in the wall become visible as local peaks in the global deformation field.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.