# High-Precision Manufacture and Alignment of Image Slicer Based on Thin Glass Bonding
## 6 Measurement
### Test Result  
The distance between the two focuses in the X direction is 2 mm. The permissible eccentricity error is 20 \(\upmu\)m. The focus of the image slicer in the XY direction is shown in Figure 16a,b (light bars). The actual and ideal positions of the focal point are shown in Figure 16c. The \(XY\)-axis distances for the different channels are detailed in Table 8. The focus of bottom 3 exceeds the range allowed by the ideal focus position. It is found that the yaw error in the last stacking process is caused by the accumulation of the LOCTITE glue. It will be necessary to modify the fixture in future stacking processes to prevent the glue from accumulating. The \(Z\)-axis offset is obtained by detecting the exposure on a CCD mounted on a five-dimensional adjusting frame. The distance between the maximum exposure of the different channels and the first channel is measured by adjusting frame calibration. The  
Figure 14: Schematic of optical system detection. The parallel light incident into the image slicer is focused on the CCD side by means of a splitter prism.  
Figure 15: The detection optical system of image slicer focus.  
final location errors we measured are less than 0.01 mm compared with 0.02 mm of the initial design. To reduce the effect of the location error, pupil mirrors are appropriately adjusted, thereby allowing the reflected light to enter the slit.  
The surface accuracy RMS of each slice was evaluated using a 4D interferometer, and it was found to be better than \(1/60\lambda\) (\(\lambda=632.8\) nm). The surface accuracy RMS falls significantly below the specified tolerance of 40 nm. The roughness was measured using a Bruker white light interferometer, with a \(50\times\) objective lens and \(1\times\) eyepiece. The obtained roughness \(R_{a}\) is less than 1 nm. Detailed data for each slice are presented in Table 9. The excellent surface accuracy and roughness achieved demonstrate the inherent benefits of traditional polishing techniques. The lower surface shape accuracy simultaneously  
Figure 16: Test result diagram: (**a**) the focus test result of the top three channels and the fitting center spots are marked on the figure; (**b**) the focus test result of bottom three channels and the fitting center spots are marked on the figure; (**c**) the schematic of different channel focus.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Channel Number** & **Distance Error (mm)** & **Channel Number** & **Distance Error (mm)** \\ \hline \(\Delta W_{T1}\) & 0 & \(\Delta H_{T1}\) & 0.0000 \\ \(\Delta W_{T2}\) & 0.0144 & \(\Delta H_{T2}\) & 0.0096 \\ \(\Delta W_{T3}\) & 0.0072 & \(\Delta H_{T3}\) & 0.0024 \\ \(\Delta W_{B3}\) & 0.0312 & \(\Delta H_{B3}\) & 0.0048 \\ \(\Delta W_{B2}\) & 0.0192 & \(\Delta H_{B2}\) & 0.0072 \\ \(\Delta W_{B1}\) & 0.0048 & \(\Delta H_{B1}\) & 0.0168 \\ \hline \hline \end{tabular}
\end{table}
Table 8: The value of X-axis error and Y-axis error.  
demonstrates superior stress control during the glue bonding process, thereby preventing deformation in the working area of the image slicer.