## 5 Experimental Results and Discussion
### Effects of Incident Angle on Stray Radiation  
When the incident laser power was unchanged, the most obvious factor affecting the stray radiation intensity in the infrared opto-mechanical system was the laser incident angle. This is because different laser incident angles determine the radiation energy flux into the infrared imaging system, under the same laser power condition. Under the condition of an incident laser power of 0.4 W, the variation of stray radiation intensity in the infrared imaging opto-mechanical system with the laser incident angle was experimentally measured. The stray light distribution image obtained in the experiment is shown in Figure 11. It can be seen that the stray radiation in the infrared opto-mechanical system with ceramic coating was obviously weaker than that without ceramic coating. It is not difficult to conclude that the stray light distribution in the infrared imaging system showed a decreasing trend, indicating that, with the increase in laser incident angle, the laser radiation flux into the infrared imaging system was gradually reduced, and the stray radiation into the system after multiple scattering to the detector image plane was also reduced.  
This could also be seen from the variation of the relative intensity of stray radiation with the laser incident angle, as shown in Figure 12. It can be clearly seen that the relative intensity of stray radiation without ceramic coating was generally higher than that with ceramic coating. At the same time, the stray radiation intensity first decreased and then tended to be stable with the increase in laser incident angle. The results show that the stray radiation intensity entering into the infrared opto-mechanical system strongly depended on the change in laser incident angle. When the laser incident angle gradually increased from 0\({}^{\circ}\) to 50\({}^{\circ}\), the total stray radiation in the system decreased rapidly. Then, the stray radiation tended to be stable with the further increase in laser incidence angle. The experimental results show that, for the two cases with and without ceramic coating, the stray radiation  
Figure 10: Variation of stray radiation suppression ratio with laser incident power (\(\alpha=50^{\circ}\)).  
intensity formed at the laser incident angle of 50\({}^{\circ}\) was the smallest, which was 78.6% and 70.3% lower than that at the laser incident angle of 10\({}^{\circ}\).  
Similarly, by using the definition of average stray radiation suppression ratio \(R_{rel}\) in Equation (12), the variation of \(R_{rel}\) with laser incident angle was obtained under the condition of a laser incident power of 0.4 W, as shown in Figure 13. It can be seen that the average stray radiation suppression ratio \(R_{rel}\) increased first and then decreased rapidly with the increase in laser incident angle. When the laser incident angle reached 50\({}^{\circ}\), the average stray radiation suppression ratio reached the maximum, which was 64.7%. Then, when the laser incidence angle dropped to 80\({}^{\circ}\), the average stray radiation suppression ratio reached the minimum, which was 15.8%.  
Figure 11: Variation of stray light distribution with laser incident angle in optical mechanical system (laser incident power = 0.4 W).  
Figure 12: Variation of average stray radiation intensity with laser incident angle (laser incident power = 0.4 W).