This talk reviews high resolution phase shifting methods which have the capability of accommodating the requirements inherent in multiple beam holographic interferometry. These methods facilitate the use of multiple PZTs in an optical setup, offer the flexibility of using arbitrary phase steps and spherical beams, and provide the ability of making simultaneous multidimensional deformation measurements. The main sources of errors in implementing phase stepping are caused by the miscalibration of the piezo electric device (PZT) and by the presence of non-sinusoidal waveforms (consequence of CCD nonlinearity or multiple reflections inside the laser cavity). The proposed phase stepping methods render the holography related interferometry techniques insensitive to the error sources mentioned above. Experimental results show the feasibility of the proposed methods.
NDT Techniques: Laser-based P.M. Boone, in Encyclopedia of Materials: Science and Technology, 2001 2 Holographic Interferometry
Holographic interferometry (HI), which provides interferometric comparison of real objects or events separated in time and space, is a technique of unparalleled applications. Various kinds of HI have been developed, e.g., real-time, double-exposure, and time-averaged HI. Furthermore, HI can be performed with one, two, or more reference waves, which can be of the same or different wavelengths. The reference wave can come from the same side of the hologram as the object wave, or from the other side of the hologram. HI can be performed with a continuous wave laser, or a pulsed laser. The possibilities are endless, and so are the applications. The detection of an internal defect of polythene pipe.