Laser diode interferometer used for measuring displacements in large rangewith a nanometer accuracy

In this paper, the displacement of an object is measured with a phototherma l phase-modulating laser diode interferometer. A feedback control system is designed to reduce the measurement errors caused by the fluctuations in th e optical wavelength of the laser diode and the vibrations of the optical c omponents in the interferometer. A new method is proposed to enlarge the me asuring range of displacement. Using this method, the measuring range is en larged from half wavelength to nearly 125 mum and the measurement accuracy is about 1 nm. The simulation and experimental results have shown the usefu lness of the method and the feedback control system. (C) 2001 Elsevier Scie nce Ltd. All rights reserved.