Optical detection of ultrasound with a phase-modulated Michelson interferometer

摘要

A phase-modulated Michelson interferometer for optical detection for ultrasound is described. The operating point of the interferometer is kept to the minimum intensity of the interference pattern. This scheme allows the use of a high power laser to improve the sensitivity without a photodiode saturation. Ultrasonic displacement amplitudes as small as 10pm can be detected when the maximum intensity on the photodiode is 100mW.