## 3 Experiment
### Waveplate Parameter Measurement in the Entire Aperture  
To further realize the parameter measurements in the entire aperture, the fast-axis azimuth of the waveplate is rotated to an initial angle, and the precise two-dimensional electric translation stage is initiated to scan the 26 \(\times\) 26 mm area at 2 mm intervals. The waveplate parameters in the entire clear aperture are shown in Figure 6. The entire measurement area requires 1 min. For the visual display, the retardance at each spatial position is represented by a color chart, and the fast-axis azimuth is directly drawn as a straight line at each image position over the scanning zone.  
The results in Figure 6 show that the retardance and fast-axis azimuth parameters of the 632.8 nm 1/4 waveplate are consistent for the entire clear aperture, and the retardance values are generally distributed around 160 nm. However, outlier data points are observed at the edges of the scanned area. In the lower right area of the waveplate, the retardance values are slightly smaller. The area is subsequently further enlarged, as shown in Figure 6. The measurements of the two parameters in the entire light-passing area of the waveplate are recorded, as shown in Table 1.  
It can be observed from the measurement data that the retardance of the entire clear aperture of the waveplate is mainly distributed in the range of (158.4 \(\pm\) 0.5) nm. There  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Retardance (nm)** & **Legend** & **Data Points** & **Fast-Axis Azimuth** \\ \hline
131.49 & & 1 & 33.6 \\
149.03 & & 1 & 27.85 \\
157.4 \(\pm\) 0.5 & & 5 & 27.99 \(\pm\) 0.07 \\
158.4 \(\pm\) 0.5 & & 94 & 28.03 \(\pm\) 0.02 \\
175.5 \(\pm\) 0.5 & & 1 & 26.75 \\ \hline \hline \end{tabular}
\end{table}
Table 1: The 1/4 waveplate parameter measurements for the entire aperture.  
Figure 6: The 1/4 waveplate parameters measurements results for the entire aperture.  
are 94 data points, accounting for 92% of the total 102 data points. Three data outliers are observed at the edge of the waveplate. In the lower right area, there is a small section where the waveplate retardance is 1 nm smaller than the average value; however, it still meets the manufacturing retardance accuracy of \(\uplambda\)/300 (approximately 2.1 nm@\(\uplambda\) = 632.8 nm). Except for the data outliers, the fast-axis azimuth of the waveplate is about 28\({}^{\circ}\). The 1/4 and 1/2 waveplates at the wavelength of 532 nm, namely GCL-060401 and GCL-060411 (Beijing Daheng New Era Technology Co., Ltd.), are also measured. The results for the full clear apertures of the two waveplates are shown in Figure 7.  
In Figure 7, it can be observed that the retardance values of the 1/4 and 1/2 waveplates are mainly distributed in two value ranges; however, the difference is small, and the fast-axis azimuth for the entire waveplate aperture is generally consistent; the retardance value of the 1/4 waveplate is approximately 130 nm, and that of the 1/2 waveplate is approximately 270 nm. The measurement results depicted in Figure 7 are outlined in Table 2.  
From the statistical results, except for the numerical anomalies, the retardance value of the 1/4 waveplate is almost completely distributed between 134.5 nm and 137 nm. The fast-axis azimuth is around 83.33\({}^{\circ}\). Furthermore, the 1/2 waveplate retardance is generally distributed between 265.1 nm and 269 nm. The fast-axis azimuth is around 109.40\({}^{\circ}\). In this study, the proposed system realizes the measurement of the retardance and the fast-axis azimuth in the whole aperture range of the waveplate.