Abstract
Heterodyne interferometry is a high-precision method applied in roll angle measurements. Phase metering is essential for high precision. During a high-precision measurement, a phase fluctuation appears even when the roll angle does not vary, which has never been analyzed before. Herein, the reason for the phase fluctuation is revealed, which results from the frequency-difference fluctuation and time difference between measurement and reference beams. A mathematical model of that phase-fluctuation mechanism is established, and that model provides a theoretical basis for analyzing and reducing the phase fluctuation. The impact that the main factors have on the phase metering is analyzed quantitatively, and experiments are carried out to validate the model. Finally, the phase fluctuation decreases to 0.02° by frequency reduction, which conversely verifies the theoretical model.
Highlights
The heterodyne interferometer has been a widely applied metrological instrument for displacement measurements for the past 40 years [1,2,3,4,5,6]
A high-sensitivity measurement scheme for a small roll angle is shown in Figure 1, in which a phase retarder such as a half-wave plate (HWP) is adopted as the sensor for the roll angle test and a phase shift of the measurement signal and the reference signal is detected by a phase meter to demodulate the roll angle [8,9,10,11,12]
The precision of the phase metering is required to be higher for high-precision roll required to be higher for high-precision roll angle measurements, and in many practical experiments, angle measurements, and in many practical experiments, we have found that the phase shift we have found that the phase shift fluctuates continuously even when the roll angle does not vary
Summary
The heterodyne interferometer has been a widely applied metrological instrument for displacement measurements for the past 40 years [1,2,3,4,5,6]. A subsecond precision angle measurement can be achieved by adopting a high-precision phase meter [8,9,11,12]. Various error sources causing phase errors have been investigated, such as the imperfection of polarizing beam splitters, misalignment of their optical setup, amplitude variation in coherent transmission, multiorder Doppler frequency shift, elliptical polarization, and nonorthogonality of light beams [13,14,15,16,17,18,19,20] These error sources cause a periodic nonlinear error. That small fluctuation may be ignored in the general phase metering, but it has a significant ignored in the general phase metering, but it has a significant impact in high-precision phase impact in high-precision phase metering. In high-precision phase metering, small phase fluctuation cannot be ignored. The organization of the paper measurements is described It is the theoretical basis for modeling the phase fluctuation.
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