System and method for detecting ultrasound using time-delay interferometry

摘要

An ultrasound detection system that is relatively insensitive to rough workpiece surfaces, suppresses low frequency noise, and provides high sensitivity without the need for active stabilization. An optical probe beam is reflected and phase modulated by a workpiece surface that is being vibrated by ultrasound. A time-delay interferometer optically interferes the phase modulated probe beam with a time-delayed replica of itself. The optical interference generates optical interference fringes that move in accordance with the workpiece surface velocity. The interference fringes are detected by a non-steady-state photo- electromotive-force (NSS-photo-EMF) detector that generates an output signal when the frequency of fringe motion exceeds a predetermined threshold.