S. Olyaee, Sh. Mohammad-Nejad,
Volume 3, Issue 3 (7-2007)
Abstract
A new heterodyne nano-displacement with error reduction is presented. The
main errors affecting the displacement accuracy of the nano-displacement measurement
system including intermodulation distortion error, cross-talk error, cross-polarization error
and phase detection error are calculated. In the designed system, a He-Ne laser having
three-longitudinal-mode is considered as the stabilized source. The free spectral range of
the 35cm laser cavity is about 435-MHz at 632.8-nm wavelength, which a secondary beat
frequency equal to 300-kHz is produced by combining the reference and measurement
beams. The resolution of the displacement measurement resulting from intermodulation
distortion, cross-talk and cross-polarization errors is limited to 18-pm. Also, the phase
detection uncertainty causes an error of only 5.9-pm in the displacement measurement.
Furthermore, frequency-path models of two- and three-longitudinal-mode laser
interferometers are modeled as the ac interference, ac reference, dc interference and optical
power terms. A comparison study between two- and three-longitudinal-mode laser
interferometers confirms that the performance of the designed system is considerably
improved.
