Electronic Speckle Pattern Interferometry techniques for non-destructive evaluation: a review

Electronic Speckle Pattern Interferometry (ESPI) is a fast developing whole field optical technique widely used for measuring displacement components, their derivatives, surface roughness, shape and slope contours of surfaces etc. This non-contact and highly sensitive technique has developed into a powerful on line inspection tool for non-destructive evaluation. The salient feature of ESPI is its capability to display the correlation fringes in real time on a TV monitor without the need of photographic processing or optical filtering. From the very inception of its discovery in 1970s a number of optical configurations have been developed for accurate measurements and better optimisation of results in engineering and non-engineering metrology. This paper reviews the main developments in the field of Electronic Speckle Pattern Interferometry that have been published over the past 20-25 years. The paper is illustrated with different optical configurations and their applications such as displacement and slope measurements with extensive references. The ESPI experimental set-up and the results obtained by the authors for its engineering applications such as non-destructive evaluation of low modulus materials used for space vehicle components are presented.