Use of chopped laser light in electronic speckle pattern interferometry

Shortened exposure of each TV frame is used in conjunction with time-average ESPI to study the sinusoidal vibrations of extremely unstable objects. The effect of short exposures upon the fringe functions is calculated. It is shown how sinusoidal phase modulation techniques can be used at all realistic exposure values. We also discuss how double-exposure ESPI with a cw laser can be used to study more random movements, e.g. of biological objects. The lag characteristic of the TV target is used to extend the time separation. Fringe patterns illustrating applications of these techniques are presented.