Forward looking innovations in electronic speckle pattern interferometry (ESPI)

Electronic Speckle Pattern Interferometry (ESPI) dates from 1971. Attempts at commercial exploitation were unsuccessful; at the beginning of this decade it remained essentially a laboratory technique. Problems arose from the practical operation of the instrument and the nature of the output. Correlation fringes are intrinsically noisy and their quality depends on many interrelated factors. It is shown that by simplifying the optical design and improving the quality of the optical components, the fringe contrast is greatly improved and the instrument is made easier to use. Extensions and improvements to the system are discussed: analogue image processing techniques as a low cost means of improving the appearance of the output; time invariant noise subtraction in time averaged fringes gives similar quality results as that of the subtraction mode; ensemble averaging of time variant noise is a new technique for producing holographic quality results. Electronic speckle contouring (ESC) gives a selection of methods for producing programmable contour spacings and orientations for shape measurement. ESPI is compared with other optical measurement techniques and is shown to have fundamental advantages.