###### Abstract
In the actual production and processing process, the specific stray radiation suppression measures can be divided into three parts [14; 15]: one involves optimizing the macrostructure of the infrared detection system, such as the lens hood and light blocking ring; the second involves improving the microstructure of the infrared detection system, such as increasing the roughness of the reflection surface; the third involves changing the optical characteristics of each inner surface in the infrared opto-mechanical system, such as coating and blackening treatment. The first two methods have been widely used to suppress the stray radiation in infrared imaging and detection systems. However, it is rare to apply an effective anti-stray radiation coating inside the infrared opto-mechanical system. Blackening is a common method. However, it is difficult to achieve high-absorptivity stray radiation absorption in a wide band; thus, the actual effect of eliminating stray radiation is rather limited. In this paper, a novel broadband and high-absorption nano ceramic coating is proposed to be coated on the inner wall of the infrared opto-mechanical system. By using the absorption characteristics of ceramic coating materials, the infrared stray radiation can be effectively absorbed, which can overcome the shortcomings of conventional blackening treatment in the long-wave infrared absorption rate and the narrow absorption spectrum range. Ceramic materials have excellent oxidation resistance, corrosion resistance, high-temperature mechanical properties, and stability [16; 17; 18]. They allow for the creation of laser protective coatings with good comprehensive performance and excellent laser damage resistance. Generally, the preparation methods of ceramic coatings mainly include resin coating [19; 20; 21], air spraying [22; 23; 24], plasma spraying [25; 26; 27], and plasma electrolytic oxidation (PEO) [28; 29; 30]. Because the applied voltage in the PEO reaction breaks through the limitation of anodic oxidation in the Faraday region, under the action of high temperature and high pressure of micro plasma discharge, the surface of the substrate is melted and sintered, and then a typical porous ceramic oxide film is grown in situ. Research has shown that the bonding mode between the ceramic film and the substrate is typical metallurgical bonding, which can endow the matrix material with excellent mechanical and functional properties that cannot be achieved by other technologies. Therefore, compared with other conventional surface engineering technologies, PEO technology has many advantages, such as high hardness and electrical insulation, strong operability, close and firm combination with the substrate, relative simple preparation process, high processing speed,unlimited requirements on the shape and size of the substrate, high cost performance, and suitability for automatic manufacturing and production [31; 32; 33; 34]. However, the in situ growth process of a PEO ceramic coating is very complex, involving many aspects such as thermal diffusion, electrochemistry, and plasma technology. The laser damage resistance of the coating depends greatly on its chemical composition and structure size. Therefore, the preparation of ceramic coatings with high absorptivity, a wide spectral absorption range, and high adhesion requires several experiments and technical accumulation. In this paper, we first studied the preparation method and material properties of a novel broadband ceramic coating with high absorption. Then, we coated the high-absorption ceramic coating on the aluminum alloy metal substrate and developed a long-wave infrared imaging optical system with the high-absorption ceramic coating on the inner wall. According to the above research results, the suppression effect of the high-absorption ceramic coating on the stray radiation formed by multiple scattering inside the infrared opto-mechanical system was investigated under different incident angles and different incident laser energy outside the FOV.