Measurement and analysis of mechanical vibrations by means of optical heterodyning techniques

It is shown that a Michelson type interferometer, where one arm includes the vibrating surface, can be used for the analysis of the vibration. There are no requirements about the optical quality of the surface, as the principle of the operation requires only diffuse reflection and not a specular one. The system utilizes the Doppler shift due to surface motion, and the frequency structure of the reflected light is obtained from the spectrum of the photocurrent of the detector. This spectrum contains the information about the frequency and amplitude of the vibration.