## 3 Design, Simulation and Implementation for Scattering Measurement System
### Influence of Design Parameters on Measurement Results  
In order to quantitatively evaluate the influence of the design parameters on the simulated results, four influencing factors, namely, the radius of integrating sphere, the radius of the incident beam opening, the diameter of the incident beam and the coating reflectivity on the inner wall of the integrating sphere, were simulated and analyzed. The simulation results are shown in Figure 7.  
Figure 6: Influence of trace ray number on simulation results. Firstly, the variation of the luminous flux received by detector with the radius of the integrating sphere was simulated, as shown in Figure 7a. The radius of integrating sphere was set to 40-60 mm, the diameter of incident beam opening and measuring opening was equal to 20% of integrating sphere diameter, the diameter of sample opening was equal to 15% of integrating sphere diameter, the diameter of detector hole was 12% of integrating sphere diameter, the beam diameter was set to 2 mm and the luminous flux of laser source was 1 W.  
It can be seen from Figure 7a that the luminous flux received by detector hardly changed with the varied radius of the integrating sphere. The further calculation showed that the average received luminous flux was 0.0757 W, and the standard deviation was \(1.5\times 10^{-4}\) W. The coefficient of variation was only 0.2%. However, if the radius of integrating sphere was too small, the laser incident and sample opening would be too small, it is not easy to adjust the laser incident spot and the relative position of sample plate. Therefore, the larger integrating sphere should be selected appropriately. Since the diameter of integrating sphere had no obvious influence on the simulated results, the  
Figure 7: Influence of design parameters on the received luminous flux of the detector: (**a**) radius of the integrating sphere, (**b**) incident opening radius, (**c**) diameter of the incident beam and (**d**) reflectivity of the inner wall for the integrating sphere. following simulation process would select the integrating sphere with a radius of 50 mm as the general design parameter. Secondly, the variation of the luminous flux received by detector with the different opening radius of the incident beam was simulated. The simulation results are shown in Figure 7b. The opening radius of the incident beam was set to 5-15 mm, the beam diameter was 2 mm and the luminous flux of the output laser was 1 W. It can be seen that there was a negative correlation between the luminous flux of the incident light and the opening radius of the incident beam. Moreover, with the increasing of the diameter of incident beam opening, the more light escaped from the hole, the total luminous flux remained in the integrating sphere decreased. Therefore, the opening radius at the position of laser incidence should be as small as possible. However, the small opening radius would lead to increasing the difficulty for adjusting the spot position on the sample plate. The simulation results showed that, when the opening radius was set to 10 mm, the laser incident position could be adjusted in a large range, and the light flux escaping from the opening is relatively small. Therefore, the radius of 10 mm was selected as the parameter of incident beam opening. Thirdly, in order to investigate the influence of the incident beam diameter on the simulated results, the variation of the received luminous flux with the incident beam diameter was simulated. The results are shown in Figure 7c. The beam diameter was set to be 1-3 mm. The luminous flux was still 1 W. The radius of the integrating sphere was 50 mm, the opening diameter of the incident beam and the measuring opening was set to be 20% of the integrating sphere diameter, the diameter of the sample opening was 15% of the integrating sphere diameter and the measuring opening diameter of detector was set to be 12% of the integrating sphere diameter. As can be seen from Figure 7c, the influence of the beam diameter on the luminous flux was found to rather small.