Sub-nanometer Displacement Measurement Using Heterodyne Interferometer and Down-Beat Frequency Technique

Abstract

AbstractThe paper presents mechanical displacement measurements with sub-nanometer order for a double-path heterodyne interferometer using a laboratory-made phase meter based on a single phase-locked loop. We use a Zeeman-stabilized He-Ne laser source in the interferometer, whose beat frequency is in the megahertz regime. It requires a high-cost, high-sampling rate analog-to-digital converter (ADC) for the megahertz-regime interference signals. A down-beat frequency technique is implemented to obtain these interference signals for a low-cost, low-sampling rate ADC. The result measured by the laboratory-made phase meter is compared with that of a reference one. The results of both phase meters show that a mechanical displacement of ~2.6 nm is confirmed. The noise reduction of the laboratory-made phase meter under 1 nm is more efficient than that of the reference one. It demonstrates that the interferometer combined with the down-beat technique is capable of achieving sub-nanometer mechanical displacement measurements.KeywordsDisplacement measurementHeterodyne interferometerDown-beat techniqueSingle phase-locked loop