Distance measurements using frequency stabilized Nd:YAG lasers

Two diode-pumped tunable Nd:YAG lasers locked to sub-Doppler transitions of I-127(2) and Cs-133(2) are used as a source for two-wavelength interferometry. The synthetic wavelength, Lambda = c/Delta nu, is highly stable and accurate, owing to the frequency stability of the locked lasers and the precise determination of the frequency difference Delta nu between Cs-2 and I-2 transitions. The dense spectra of these molecules allows selection of Lambda over a wide range, between 8.5 mm and several meters, thus enabling distance measurements with a large non-ambiguity range. Fringe contrast and phase-shifting methods are used to measure the phase difference. An accuracy of 70 mu m is achieved for Lambda similar to 19 mm, i.e. Lambda/260.