Three-dimensional whole field deformation measurement by the diffraction principle

A method for measuring deformation using diffraction of light from a grating attached to the surface of flat specimen is presented. By detecting the amplitude and the phase of the diffraction pattern of this grating, its transmission or reflection function can be calculated by the Kirchhoff-Integral. The comparison of these functions in different state of load, leads to the whole-field information of the inplane strain and the out-of-plane dispacement distribution for the illuminated area of the specimen.