## 4 Experimental Verification  
To verify the accuracy of the simulation process above and the credibility of the simulation results, we designed the following experiment. The experimental platform is shown in Figure 9. A beam of parallel light is emitted by the collimator (Figure 9a), passes through the beam expanding system (Figure 9d), and then reaches the Shack-Hartmann wavefront sensor (Figure 9c). The gas being introduced into the beam expanding system is provided by the air supply system (Figure 9f), which is connected to gas cylinders (Figure 9e). For the distribution of the inlet holes, we adopted the optimal plan E introduced above; the corresponding layout is shown in Figure 9. The total number of inlet holes is 5760, divided into 16 rows with 360 holes in each row (Figure 10). During the intake process, the temperature and inlet pressure of gas for the beam expanding system are controlled by means of the intake control system to avoid large errors due to the changes in the refractive index that would be caused by changes in the temperature and pressure of the filling gas. During the experiment, we set the intake time to 50 s, and the wavefront aberration measurements were collected by the wavefront sensor (Figure 11). Figure 11a shows that before the start of gas intake, the peak-to-valley (PV) and RMS values of the wavefront aberration were small and flat. When we began injection at 18 s, the wavefront aberration increased rapidly; the RMS value approached 0.62 \(\upmu\)m before levelling off. Subsequently, when the gas flow was stopped at 68 s, the RMS wavefront aberration rose to nearly 1 \(\upmu\)m and then quickly dropped to the pre-flow level, levelling off in approximately 100 s.  
Figure 8: Zernike coefficients of the wavefront aberrations for plans D and E.  
Figure 10: Distribution of the intake holes. Figure 9: Experimental platform and equipment: (**a**) collimator; (**b**) wind speed sensor; (**c**) [PERSON]–Hartmann wavefront sensor; (**d**) beam expander; (**e**) cylinders; (**f**) flow rate control system; (**g**) screen. The results of another measurement performed after eliminating the tilt in the experimental set-up are shown in Figure 11b. Because of the processing errors and unevenness of inflation, a larger tilt is introduced into the wavefront aberration. Since the tilt can be eliminated by adjusting the mirror, we no longer consider the tilt in the calculation process. As seen from this figure, the results were consistent with the trend observed in Figure 11a. The wavefront aberration was stable at approximately 0.04 \(\upmu\)m before the gas flow was started. When gas intake started at 12 s, the wavefront aberration rose rapidly, and the RMS value finally stabilized at approximately 0.12 \(\upmu\)m. When the gas supply was stopped at 62 s, the wavefront aberration initially rose to 0.2 \(\upmu\)m and then quickly returned to the pre-flow level. From the experimental results, we found that the RMS of wavefront aberration caused by the introduced airflow was 0.08 \(\upmu\)m while the RMS value estimated from the simulation was only approximately 0.03 \(\upmu\)m. Through comparisons of the experimental and simulated scenarios, we found that one important reason for this discrepancy was that the length of ray tracing was insufficient. In our simulation, ray tracing was performed only up to the exit of the beam expanding system, corresponding to a tracing distance of 1151 mm. However, during the experiment, we placed the Shack-Hartmann wavefront sensor one metre from the beam expanding system to prevent the wavefront sensor from affecting the flow field at the outlet of the beam expanding system and to avoid gas expelled from the beam expanding system from blowing into the wavefront sensor. To account for this, we repeated the ray tracing process for plan E with a tracing length of 2151 mm. With this analysis, the RMS of wavefront aberration was found to be 0.077 \(\upmu\)m, which is close to the experimental result.