Application Cases

Experiment Name: Performance Evaluation and Experiment of Phase-Modulated Homodyne Interferometer

Experiment Purpose: To test the phase difference in the interference signals between the measurement interferometer and the reference interferometer caused by environmental parameter changes when the measurement mirror is stationary, i.e., the drift error of the measured displacement relative to the zero point.

Testing Equipment: ATA-2088 high-voltage amplifier, nanopositioning stage, single-frequency laser interferometer, photodetector, Redpitaya signal processing board, etc.

Experiment Process:

Figure 1: Photograph of the Phase-Modulated Homodyne Interferometer

The assembly and debugging of the phase-modulated homodyne interferometer mainly consist of three parts: mechanical structure assembly of the interferometer optical components, preliminary debugging according to the optical structure design, and final debugging combined with hardware circuits and upper-computer software. The assembled and debugged phase-modulated homodyne interferometer is shown in Figure 1.

After the initial adjustment of the optical path structure, power on the photodetector, high-voltage amplifier, Redpitaya signal processing board, and operational amplifier. Observe the output voltage amplitude of the photodetector through an oscilloscope and adjust the photodetector's voltage divider potentiometer to set the interference signal amplitude to around ±1V.

Open the upper-computer software based on LabVIEW for elliptical fitting effect display. Determine whether the input signal amplitude of the Redpitaya signal processing board exceeds the voltage limit by observing whether there is any distortion in the graph before elliptical fitting. Assess the elliptical fitting effect under the current optical path condition by observing the fitted ellipse and the quality indicator light of the elliptical fitting.

If the elliptical fitting effect is optimal under the current condition, proceed with the installation of the interferometer cover and other components to enable the normal use of the interferometer. Otherwise, continue adjusting the optical path until the best elliptical fitting effect is achieved.

Before the experiment, turn on the constant-temperature air conditioner and set the environmental parameters to a temperature of 21.5°C and relative humidity of 50% to ensure a stable experimental environment. Activate the air-floating vibration isolation optical experimental platform to eliminate vibration effects. Simultaneously power on the phase-modulated homodyne interferometer and the Renishaw laser interferometer, with their measurement mirrors installed back-to-back to ensure they are equally affected by the environment. Adjust the measurement mirrors of both interferometers to achieve the best elliptical fitting effect for the phase-modulated homodyne interferometer and full brightness of the interference signal quality indicator light for the Renishaw interferometer. After two hours of interferometer operation, when the environment has stabilized, begin the measurement, counting every 500 ms for a total measurement time of 2 hours.

Experimental Results:

As shown in Figures 2 and 3, the static stability comparison experiment results between the phase-modulated homodyne interferometer and the Renishaw interferometer reveal that over the 2-hour experiment, the total displacement drift values of the phase-modulated homodyne interferometer and the Renishaw interferometer were approximately 65 nm and 165 nm, respectively. This demonstrates that the static stability of the phase-modulated homodyne interferometer is superior to that of the Renishaw interferometer under the same measurement conditions. The drift direction of the Renishaw interferometer is consistent with that of the measurement interferometer in the phase-modulated homodyne interferometer, with a drift displacement difference of only about 20 nm. This fully proves that incorporating a reference interferometer measurement path in the phase-modulated homodyne interferometer can effectively reduce measurement errors caused by base deformation, etc. Observing the displacement drift curve of the phase-modulated homodyne interferometer over 10 minutes shows a drift of only about 5.5 nm.

Figure 2: Static Stability Comparison Experiment Measurement Results

Figure 3: Drift Range of the Phase-Modulated Homodyne Interferometer within 10 Minutes

Voltage Amplifier Recommendation: ATA-2088

Figure: Specification Parameters of the ATA-2088 High-Voltage Amplifier

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