Abstract

In an active laser interferometer, displacement measurement is achieved by compensating for any change in the interference signal by tuning the frequency of the laser. Measurement accuracy is theoretically limited only by the linewidth of the laser. Unfortunately, they are also extremely sensitive to environmental disturbances such as temperature variations. In this work we demonstrate an improved active interferometer which can automatically compensate external disturbances and is capable of subnanometer displacement measurement. Two Zeeman He-Ne lasers are employed. Laser I is used as the light source to stabilize the interferometer using a piezomirror in a feedback loop, while laser II is used for displacement measurement by tuning its wavelength. The variation in the interference signal due to the environment and displacement are differentiated using polarization optics. Because the heterodyne signal of the two lasers is used to directly calculate displacement, calibration of the absolute wavelength of the lasers is not necessary.

© 1989 Optical Society of America