Two-frequency interferometer for a displacement measurement
Heterodyne-detection apparatus for displacement measurements. OSC: oscillator, MOD: special modulator, BS: non-polarizing beam splitter, LP: linear polarizer, PD: photodetector, CH: oscilloscope channel, : polarizing beam splitter for the Michelson interferometer, M: mirror, and PZT: piezoelectric transducer.
Acousto-optic modulator (AOM) and polarizing optics used to produce a sideband with a polarization perpendicular to that of the carrier. HWP: half-wave plate. This assembly plays the role of the special modulator (MOD) in Fig. 1 .
Beating signals from the photodetector before the interferometer (squares) and after the interferometer (circles).
Measured displacements of mirror when the PZT voltage is ramped up (squares) and down (circles). The error bars are smaller than the size of the squares and circles.
Drift of the measured displacements of mirror at a fixed PZT voltage. The displacements are measured at 20-s intervals.
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