Fig. 1. Schematic diagram of laser heterodyne interferometry optical path

Fig. 2. Physical system of laser heterodyne interferometry

Fig. 3. Preliminary test results of DBHI translational sensitivity. Pre-optimization: ordinary optical platform under atmospheric conditions; post-optimization: vibration-isolated optical platform under vacuum conditions

Fig. 4. Frequency spectrum of the frequency-shifted central frequency signal (200 MHz & 201 MHz)

Fig. 5. Interference signals generated by mixing frequency-shifted spurious sidebands with the main frequency signal^[14]

Fig. 6. Translational sensitivity results before and after frequency-shifted spurious noise optimization

Fig. 7. Translational zero drift and temporal drift of temperature measurements in the core optical path over 15 hours

Fig. 8. Sensitivity curves for the original translational data and the translational data after linear drift removal (including temperature noise-equivalent translational measurement sensitivity)

Fig. 9. Comparison of translational measurement sensitivity before and after frequency stabilization and laser frequency noise-equivalent translational sensitivity

Fig. 10. Comparison of DBHI translational measurement sensitivity before and after polarization optimization

Fig. 11. Sensitivity test results of the phase demodulation module

Fig. 12. Stray light generates interference beat signals. (a) Polarization leakage in PMHI interferometric path; (b) parasitic reflections in DBHI interferometric path

Fig. 13. Sensitivity of equivalent translational readout measurement to laser pointing drift noise

Fig. 14. Schematic diagram of laser intensity noise coupling. Interference signal (a) without disturbance, (b) with disturbance, and (c) with disturbance and changes in the amplitude and phase of the disturbance signal

Fig. 15. Estimation of equivalent translational sensitivity of partial noise in the DBHI interferometric system

Fig. 16. Sensitivity test results of the laser heterodyne interferometric translational measurement system. (a) DBHI; (b) PMHI