Method for phase sensitive measurements of surface vibrations using homodyne interferometry without stabilization

A method for detecting phase and absolute amplitude of surface vibrations with homodyne laser interferometry is presented. An advantage of this detection scheme is that no stabilization of the optical path is required, hence allowing for a simple homodyne interferometer design. The principle of the detection concept is described and the method is implemented to an existing homodyne scanning laser interferometer, originally developed for measuring relative amplitude data of surface vibrations in microacoustic devices. Selected measurements from two different piezo-actuated micromechanical resonators are presented to demonstrate the detection method. With current electronics, the interferometer is capable of detecting out-of-plane vibrations up to 2.5 GHz with lateral resolution of < 1 ¿m and with minimum detectable amplitudes of ~ 1 pm.