Two diode-pumped tunable Nd:YAG lasers locked to sub-Doppler transitions of 127I2 and 133C2 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 C2 and I2 transitions. The dense spectra of the two molecular absorbers allows selection of synthetic wavelength L 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 im is achieved for synthetic wavelength L - 19 mm, corresponding to a phase interpolation accuracy of L/260.
- Distance measurement
- Frequency-stabilized laser
- Phase-shifting interferometry
- Two-wavelength interferometry