Electronic speckle pattern interferometry

Abstract

This chapter describes the theory of electronic speckle pattern interferometry (ESPI); the technique can be considered the video equivalent of holographic interferometry (Leendertz, 1970; Butters and Leendertz, 1971; Ennos, 1975; Jones and Wykes, 1989). It generates fringe patterns where the fringe spacing is a function of laser wavelength and, since this wavelength is defined and stable, it therefore provides data which is absolute and does not require any form of calibration. Optical configurations can provide the three Cartesian displacements — out-of-plane (z), vertical and horizontal in-plane (x, y) — to be uniquely and independently acquired (Jones, 1976). These three individual maps of surface displacement can be combined to yield complete surface motion analysis without the need for any presurface treatment or contact (Moore and Tyrer, 1990; Shellabear and Tyrer, 1991). New techniques allowing automatic analysis without any operator involvement have overcome some of the problems associated with the large volumes of data acquired using interferometric techniques (Nakadate and Saito, 1985; Mendoza, Shellabear and Tyrer, 1991;Robinson and Reid, 1993).