Abstract

The optical path difference (OPD) in a classical heterodyne interferometer is derived from the phase of a sinusoidally oscillating signal[l]. Thus surfaces with discontinuities > A cannot be measured due to ambiguities of 2% in phase. Similarly, target distances > A cannot be measured except by counting fringes under translation from a known reference point. If the optical beam is interrupted the reference point can be lost, making heterodyne interferometers difficult to use for robotic applications.

© 1987 Optical Society of America