Optical setup for two-wavelength superheterodyne interferometer using frequency-doubled Nd:YAG lasers emitting at . AOM, acousto-optic modulator; BS, beam splitter; CC, corner cube; IR, infrared output; M, mirror; PD, photodetector; PZT, piezoelectric ceramic; SW, synthetic wavelength.
Superheterodyne detection system: AMPL, amplifier; PD, photodetector; RF, radio-frequency; LO, local oscillator; DAQ, data acquisition.
Standard deviation of the first estimation of (experimental values) vs the frequency variation . 25 measurements have been performed for each value of , with a distance . Integration time of the phase measurements is 1 s. Lasers are phase-locked around 12 GHz . Fitting the curve with Eq. (23) gives , consistent with values given in Sec. IV A.
Assessment of the system stability. The left (resp. right) vertical axis is the deviation from the mean measured phase (resp. distance) vs time. The phase was averaged over 1 s. The measurement was performed with a distance . Lasers were phase-locked at .
Allan deviation of distance vs averaging time.
Variation in the measured synthetic phase with synthetic frequency. Averaging time of the measured phase is 30 s. Uncertainties (phase deviation less than ) are not noticeable at this scale. The top graph represents the residuals of the measured phase from the linear fit.
Variation in the measured as a function of the displacement measured with the reference system.
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