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The contours of constant phases across sinusoidally vibrating objects have been mapped using reference wave phase modulation in time-average electronic speckle pattern interferometry.

The vibration patterns of the human eardrum in vivo have been recorded by time average electronic speckle pattern interferometry--ESPI. The necessary stability was achieved by shortening the exposure time of each TV frame. The amplitude--and phasedistribution was mapped across the drum by phase-modulation techniques which also could show the vibrations in slow motion. By photoelectric detection of the TV image intensity, amplitudes down to 2 nm could be measured. Preliminary results are presented.

We describe a new method for real-time detection and measurement of small vibrations, based on phase modulation in time-average electronic speckle pattern interferometry. The modulation frequency is shifted relative to the vibration frequency, which makes the intensity of the reconstructed image vary at the difference frequency. The amplitude detection limits are about 20 A by visual observation and 0.1 A by photoelectric measurement using a lockin technique. No auxiliary system for fringe stabilization is required. At higher amplitude levels we can study the deformation of the object in slow motion. Measurements on different objects, including human ear preparation, are presented.