## 5 Experimental Results and Discussion
### Effect of Incident Power on Stray Radiation
The specific statistical methods were as follows:  
\[I_{\text{total}}=\frac{1}{N}\underset{k}{\overset{l}{\sum}}\underset{i}{ \overset{m}{\sum}}\underset{j}{\overset{n}{\sum}}I^{k}(i,j)\ (k=1,\ \ldots\,\ l;\ i=1,\ \ldots\,\ m;\ j=1,\ \ldots\,\ n), \tag{11}\]  
where the \(I_{\text{total}}\) represents the overall average stray radiation relative intensity of 10 collected stray radiation images, \(m\) and \(n\) represent the number of image rows and columns respectively (\(m=480\) and \(n=640\)), \(N\) is the number of collected images (\(N=10\)), \(k\) is the serial number of collected images, \(i\) represents the \(i\)-th row of the \(k\)-th image, and \(j\)  
Figure 8: Variation of stray light distribution with laser incident power in optical mechanical system (\(\alpha=50^{\circ}\)). represents the \(j\)-th column of the \(k\)-th image. A higher value of \(I_{\text{total}}\) denotes stronger stray radiation. In this way, the overall average relative intensity of stray radiation could be used to quantitatively characterize the suppression degree of the stray radiation for the ceramic coating on the infrared opto-mechanical system and the variation with the incident laser power. The variation of relative intensity for stray radiation in the opto-mechanical system with and without ceramic coating with laser incident power is shown in Figure 9. It can be seen that, for the aluminum alloy substrate material, when the incident laser power was less than 0.4 W, the stray radiation intensity with ceramic coating was generally weaker than the case without ceramic coating. However, when the incident laser power increased to 0.5-0.8 W, the stray radiation intensity with ceramic coating was stronger than that without ceramic coating. Because the surface of the ceramic coating prepared in this paper was composed of many small holes and had a high-absorption characteristic in a wide range of wavelengths, the principle underlying its absorption light energy is the spread of photons in the holes and transfer of energy to the ceramic material upon their entry into these small holes, before completely releasing the light energy carried. The number of holes on the surface of the ceramic coating was constant; therefore, the ceramic coating had a certain saturation absorption threshold. When the external radiation energy exceeded this threshold, the ceramic coating could not further absorb the remaining photon energy. Therefore, when the laser power was greater than 0.4 W, the ceramic coating reached the absorption saturation state and a large amount of remaining stray radiation directly reached the image plane of the detector, resulting in a rapid increase in the stray radiation intensity. In order to further investigate the suppression degree of stray light after adding the ceramic coating, the average relative stray radiation suppression ratio \(R_{rel}\) was defined as  
\[R_{rel}=\frac{\sum\limits_{i}^{\text{m}}\sum\limits_{j}^{n}I_{0}(i,j)-\sum \limits_{i}^{\text{m}}\sum\limits_{j}^{n}I_{c}(i,j)}{\sum\limits_{i}^{\text{m }}\sum\limits_{j}^{n}I_{0}(i,j)} \tag{12}\]  
where \(I_{0}(i,j)\) represents the grayscale of the \(i\)-th row and \(j\)-th column in the stray radiation image without ceramic coating, while \(I_{c}(i,j)\) represents the grayscale of the \(i\)-th row and \(j\)-th column in the stray radiation image with ceramic coating. The average relative stray radiation suppression ratio \(R_{rel}\) reflects the stray radiation suppression ability of the ceramic coating. A higher \(R_{rel}\) denotes a higher stray radiation suppression ability of the ceramic coating. If \(R_{rel}\) is positive, it means that the ceramic coating has the ability to suppress stray radiation. If the value is negative, it means that adding the ceramic coating would increase  
Figure 9: Variation of average stray radiation intensity with laser incident power (\(\alpha=50^{\circ}\)). the stray radiation intensity.