Electronic Speckle Pattern Interferometry (ESPI)

Abstract

Speckle metrology includes techniques such as speckle photography, photography-based speckle interferometry, electronic speckle pattern interferometry (ESPI) and speckle shearography. ESPI, developed from speckle pattern interferometry (SPI), is a whole field deformation measurement technique that uses laser speckles as the carrier of deformation. The temporal phase-shift method extracts phase from multiple images recorded at different times with a known phase shift, while the spatial phase-shift method extracts phase from a single image. The main applications of ESPI are for deformation measurements, including out-of-plane, in-plane and three-dimensional deformation measurements, for vibration measurement, and for non-destructive testing. The time-Averaged and stroboscopic-illumination methods are usually utilized for harmonic vibration measurement, while double-pulse spatial phase-shift ESPI is used for deformation measurement under a transient loading or an impact loading. The time-averaged technique can be used to monitor the spatial distribution of the vibration mode and can also be used to detect subsurface defects and structural properties of the object.