Optical heterodyne measurement of vibration phase

An optical heterodyne system for measuring a vibration phase, which uses a frequency-shifted and phase-modulated reference beam, is proposed. This system is applicable to a rough surface. By using the light scattered by a standard vibrating point on the object surface as the reference beam (local reference beam technique), effects of the uniform displacement of the object can be eliminated, i.e. only the vibration component is detected with no sensitivity to the uniform displacement. Preliminary experiments demonstrate the validity of the theory.