Fringe visibility enhancement and phase calculation in double-pulsed addition ESPI

摘要

We report the calculation of the optical interference phase directly from double-pulsed electronic speckle pattern interferometry (ESPI) addition fringes using phase-stepping techniques, for an object undergoing harmonic vibration. The optical phase is used to calculate the harmonic-vibration amplitude and phase. This involves shifting the laser double pulses with respect to the object-vibration phase. Two techniques to improve the addition fringe visibility have been proposed in the literature: subtraction of a reference interferogram recorded when the object is stationary from an addition fringe pattern, and subtraction of addition patterns. We present a mathematical analysis of these two techniques and comment on some misconceptions that have arisen in the literature. These two techniques offer less immunity to environmental disturbances than addition ESPI, but improve fringe visibility. Phase calculation for the latter case (subtraction of addition fringes) is presented.