Shape measurement using additive-subtractive phase shifting speckle interferometry

This paper describes an optical technique for shape measurement that works satisfactorily in relatively severe noisy conditions by using additive-subtractive phase-modulated electronic speckle pattern interferometry (AS-ESPI). Through repetitively altering the illumination angle of one interfering beam at a frequency much higher than the video frame rate, and by simultaneously locking the beam tilting via laser strobing, random noises that normally are of much lower frequency than that of the repetitive tilting can be removed by frame averaging of the AS-ESPI correlation fringe patterns. A procedure of phase shifting that is synchronized with the repetitive tilting is utilized to perform data reduction. Quantitative experimental results obtained under rather noisy conditions are presented to show the validity of the principle.