GRATING HOLOGRAPHIC-INTERFEROMETRY

A holographic interferometric techniqne, combining an image hologram w ith a grating approach, is proposed for three-dimensional deformation measurements on opaque planar object surfaces. In this technique, the holographic plate is brought close to the object surface, onto which a high-frequency crossed-line diffraction grating has been replicated. The grating surface produces multiple object waves rather than the usu al diffusely reflected object waves. The double-exposed single hologra ms can be reconstructed at multiple off-axis angles. Four independent high-contrast fringe patterns are extracted simultaneously. Displaceme nt vectors over the entire measurement area are separated in three ort hogonal directions. The resultant displacements are presented as three -dimensional meshed plots and topographic contour maps. The optical sy stem for both recording and reconstruction of the holograms has been s implified compared to conventional holographic interferometry. Experim ental errors associated with fringe readout and system geometry are re duced because of the sharp images and the well-defined spatial orienta tion in the reconstruction system.