## 6 Conclusions  
In conclusion, in order address the vulnerability of the infrared imaging system to stray radiation caused by an external laser, a novel infrared imaging system with a broadband and high-absorptivity ceramic coating was proposed and developed to suppress the internal stray radiation of the system, which is helpful for enhancing the imaging quality of the detection image in an external laser radiation environment. Firstly, the preparation method and properties of the ceramic coating based on LPPEO technology were studied. Then, a long-wave infrared imaging system with a high-absorption ceramic coating was designed and developed. According to the above results, the suppression ability of the high absorption ceramic coating on the stray radiation in the system was verified for the first time. Lastly, the effects of laser incident power and laser incident angle on the stray radiation were studied. The results are summarized as follows:  
1. The surface of the high-absorption ceramic coating was characterized by a dense porous structure. It was able to achieve absorption in a wide range of infrared wave band (the average absorptivity of ceramic coating is 95.4% in the range of 0.2-16 um) due to the absorption of a large number of micro-pores on the surface of the coating for the radiation from different wave bands. The experimental results showed that there was a saturation upper limit for the absorption capacity of the coating to stray radiation. Under the condition of a laser incident angle of 50\({}^{\circ}\), the saturation absorption laser power threshold of ceramic coating was 0.4 W.
2. A novel ceramic coating with a broad absorption band and high absorption was developed, which could obviously suppress the stray radiation in the opto-mechanical system of infrared imaging caused by laser. When the incident laser angle was 50\({}^{\circ}\) and the incident laser power was no more than 0.4 W, the ceramic coating could obviously suppress the stray radiation. Then, the stray radiation intensity in the system showed an obvious upward trend with the increase in laser power. At this stage, the ceramic coating mainly played the role of enhancing the stray radiation. The calculation of the average suppression ratio for stray radiation showed that adding a ceramic coating would decrease the stray radiation intensity in the system by 70% compared with that without coating, under the condition of a laser power of 0.2 W. When the laser power was 0.8 W, the average stray radiation ratio of the ceramic coating was lowest at \(-\)214.3%. 3. When the incident laser power was unchanged, the stray radiation intensity in the infrared opto-mechanical system strongly depended on the change in incident laser  
Figure 13: Variation of stray radiation suppression ratio with laser incident angle (laser incident power = 0.4 W). angle. The average stray radiation suppression ratio increased first and then decreased rapidly with the increase in laser incidence angle, under the condition of a laser power of 0.4 W. When the laser incident angle reached 50\({}^{\circ}\), the average stray radiation suppression ratio reached the maximum of 64.7%; when the laser incident angle dropped to 80\({}^{\circ}\), the average stray radiation ratio reached the minimum of 15.8%. Conceptualization, [PERSON] and [PERSON]; methodology, [PERSON], [PERSON], and S.L. ; software, [PERSON] and H.H. ; validation, [PERSON] and K.L. ; formal analysis, [PERSON] and [PERSON]; investigation, [PERSON], [PERSON], and K.L. ; data curation, [PERSON]; writing--original draft preparation, [PERSON]; writing--review and editing, [PERSON] and Z.Y. supervision, [PERSON] and K.L. ; project administration, [PERSON] and [PERSON]. All authors have read and agreed to the published version of the manuscript. This research was funded by the National Key Research and Development Program of China (No. 2017 YFB1105000), the National Natural Science Foundation of China (No. 61905053) and a Postdoctoral Fellowship in Heilongjiang Province (No. LBH-Z17092).