Electro-Optic Holography System For Vibration Analysis And Nondestructive Testing

A TV system has been developed for detecting and displaying a two-dimensional hologram image that permits concomitant (real-time) hologram interferometry. The optics employed are the same as for electronic speckle pattern interferometry (ESPI), wherein a uniform reference field interferes at zero offset angle with a speckled image of an object. Rather than detecting spatial modulation to indicate interference, as in ESPI, this system modulates the phase of the reference beam by 120° between picture frames to vary speckle irradiance. Each incoming frame is compared with the two previous frames, and only pixels that vary in brightness are passed as white pixels in the video output. The use of binary-valued pixels allows inexpensive data processing at standard video rates.