The calibration and use of a laser heterodyne system for nonsinusoidal vibration measurements are described. A frequency-shifted beam is heterodyned in a photomultiplier with an unshifted central light beam that has been phase modulated by motion of a reflecting surface. The output of the phototube is passed through a limiter-discriminator receiver, and then through an integrator resulting in a linear reproduction of the surface vibration as long as the frequency-amplitude product is within limits. The linearity and calibration technique has been tested out to a product of 13 kHz × 4700 Å. A minimum amplitude measurement of 3.5 Å was obtained. Measurement of time delay or spatial cross-correlation functions is demonstrated, using two heterodyne detectors.
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Eberhardt et al. (1970) studied this question.