Phase-stepped television holographic technique for measuring phase and amplitude maps of small vibrations

Phase stepping between frames in TV holography is combined with sinusoidal phase modulation to determine phase and amplitude distributions of objects vibrating with small amplitudes (<λ/20, where λis the wavelength of the laser light used). This technique has applications in, for example, optical modal analysis and the determination of harmonic sound fields in air and water. The noise reduction that is obtained with the phase-stepping technique reduces the number of interferograms needed by one-half, which can shorten experimental time. The technique is robust, easy to use, and illustrated by modes of vibration in a simple plate and in a more complicated structure (a violin).