A panoramic electronic speckle pattern interferometer

Electronic Speckle Pattern Interferometry (ESPI) measurements are typically restricted to specimens that are flat or have some minimal curvature associated with them due to errors introduced by the geometry of the object and the shape of the wave front used for illumination and viewing. The objective of this research was to develop an ESPI system capable of obtaining full field, out-of-plane displacement measurements on the interior walls of a cylindrically shaped tube. It was accomplished in a relatively simple and accurate manner, when compared to conventional systems that attempt to make out-of-plane measurements on the walls of a pipe, by designing a unique electronic speckle pattern interferometer.; The Panoramic ESPI system developed relies on two collinear panoramic annular lenses, one to illuminate and the other to image the entire circumference of a section of pipe. Phase stepping is performed to remove the sign ambiguity of the displacement vector using a piezotranslator. Images obtained with a CCD Camera are acquired and stored using a frame grabber. Customized software is employed to map the PAL image into a conventional format. Finally, the intensity distribution is analyzed with customized fringe analysis routines: filtering is performed with the addition of a digital carrier fringe to remove noise and phase unwrapping is used to obtain the phase map associated with the displacements.; The governing equation relating the change in phase, obtained with the dual PAL interferometry system, to the displacements has been derived. Development of the equation is based on a detailed optical analysis performed in this study to determine the sensitivity vector associated with the system over its field of view. The results of the sensitivity analysis were used in processing the experimental fringe data. Experimental results obtained for out-of-plane displacements agree with those found analytically using a known solution and demonstrate the accuracy in making full field measurements using panoramic ESPI.