Distance measurements using two frequency-stabilized Nd:YAG lasers

Two diode-pumped tunable Nd:YAG lasers locked to sub-Doppler transitions of (127)I(2) and (133)Cs(2) are 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 A 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 µm is achieved for synthetic wavelength Λ ~ 19 mm, corresponding to a phase interpolation accuracy ofΛ/260.