Abstract
The stabilisation of a Michelson interferometer for studying high frequency small amplitude surface displacements is described. The stabilising element is a piezoelectric multimorph crystal supporting the reference mirror of the interferometer. The instrument is stable against low frequency, DC-200 Hz disturbances and has a sensitivity of 25*10-12 m over the range 1 kHz-10 MHz which is limited by shot noise in the detector. A theoretical and experimental study of the system parameters leads to optimisation of the instrument. The device has been used to capture small amplitude high frequency ultrasound displacements associated with acoustic emission transduction.

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