Measurement of changes in optical path length and reflectivity with phase-shifting laser feedback interferometry

The operating characteristics of a novel phase-shifting interferometer are presented. Interference arises by reflecting the light from a sample back i nto the cavity of a cw He-Ne laser. Changes in phase and fringe visibility are calculated from an overdetermined set of phase-shifted intensity measur ements with the phase shifts being introduced with an electro-optic modulat or. The interferometer is sensitive enough to measure displacements below 1 Hz with a rms error of approximately 1 nm from a sample that reflects only 3% of the 28 mu W that is incident on its surface. The interferometer is a pplied to the determination of cantilever bending of a piezoelectric bimorp h. (C) 1999 Optical Society of America.