Abstract

The design, operation, and characteristics of an optically phase-locked electronic speckle pattern interferometer (OPL-ESPI) are described. The OPL-ESPI sensor generates real-time equal Doppler speckle contours of vibrating objects from unstable sensor platforms with a Doppler resolution of 30 Hz and a maximum tracking range of ±5 MHz. Laboratory measurements of the sensor’s characteristics indicate a velocity tracking range of at least 8 μm/s to 8 cm/s, or a dynamic range of 40 dB. The optical phase-locked loop (OPLL) not only compensates for the deleterious effects of ambient background vibration, but also provides the basis for a new ESPI video signal processing technique which produces high contrast speckle contours. The ability to locate the OPLL lock point anywhere within the field of view of the sensor also allows examination of the spatial detail of low contrast speckle contours whose low visibility would otherwise make interpretation difficult. Since the OPL-ESPI system has local oscillator phase modulation capability, it offers the potential for detection of vibrations with amplitudes of less than a hundredth of a wavelength.

© 1986 Optical Society of America