Distance measurements using two 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) used as a source for two-wavelength interferometry. The synthetic wavelength is highly stable and accurate, owing to the frequency stability of the locked lasers and the precise determination of the frequency difference between Cs-2 and I-2 transitions. The dense spectra of the two molecular absorbers allows selection of synthetic wavelength Lambda over a wide range, between 8.5 mm and more than 1 m, thus enabling distance measurements with a large nonambiguity range. Fringe contrast and phase-shifting methods are used to measure the synthetic phase. An accuracy of 70 mu m is achieved for synthetic wavelength Lambda similar to 19 mm, corresponding to a phase interpolation accuracy of Lambda/260. (C) 1996 Optical Society of America