Measurement of Small Amplitudes of Vibration with Doppler Shift of Laser Beam

Abstract

This paper gives experimental and theoretical studies of the measurement of small vibrational-displacement-amplitudes such as ultrasonic vibrators. The measurement is based on the Doppler shift of a laser beam from the vibrating surface. A measurement method which employs a laser beam with multiple axial-modes and a Michelson-interferometer-type optical system, is presented. It determines the displacement amplitude through the ratio of the harmonics of the frequency spectrum of detected signal, for example, the fundamental to the third-harmonics. An experiment was performed to verify this method. The resultant sensitivity was about 200i at the vibrational frequency 39 kHz.