Interferometer for measuring displacement and distance.

A simple interferometer for measuring both relative displacement and absolute distance is fabricated that uses a laser diode. The sign of the displacement is detected by means of a lambda/8 plate, and the distance is measured by a FM radar technique of modulating the laser-diode frequency. Measurement accuracies of 0.02 microm for displacement and 100 microm for distance are obtained over a range of a few meters.