Chih-Kung Lee, G. Y. Wu, T. D. Perng
Aug 16, 1996
Journal name not available for this finding
A dual-beam differential laser Doppler interferometer system was developed. This newly developed differential laser Doppler interferometer uses either a He-Ne laser or a wavefront corrected diode laser as the light source. The circular polarization interferometer configuration adopted provides us with an opportunity to remove the acoustic optical modulator (AOM) typically used in the Doppler system for directional ambiguity removal. The removal of the AOM significantly reduces the size of the interferometer and avoids the EMI effect induced by the high frequency driving signal of the AOM. A new signal decoding algorithm was also developed to compensate for the imperfect quadrature signals. That is, even when the two signals obtained from the circular polarization interferometer are not exactly 90 degrees out of phase and are not equal in amplitude, the signal decoding can still progress as if the two signals form perfect quadratures. Also, our newly developed signal decoding algorithm can remove noise efficiently and can provide us with a displacement resolution as high as a few nanometers. The 20 MHz bandwidth achieved in this system is approximately 50 times wider than the best commercially available Doppler interferometer. In addition, both velocity and displacement can be measured by this newly developed differential laser Doppler interferometer.