Detection of Small Amplitude Vibrations by Modulated Reference Wave Holography

Abstract

Modulated reference wave holography is applied to the detection of small amplitude vibrations which are hardly observable by the normal time average or stroboscopic method. Small amplitude vibrations are detected as a slight intensity variation against the dark background of stationary regions on the reconstructed image. The sinusoidal, sawtooth and triangular phase modulation methods are theoretically considered and the detection sensitivities are compared with each other. The sensitivity is maximum in the case of the sinusoidal phase modulation if the relative phase between vibration and modulation is zero. Vibration amplitude as small as 0.012 times the wavelength of light can be detected. An experiment using the sinusoidal phase modulation has been performed and satisfactory results are obtained.