Quantitative analysis of backscattering contamination sources in the TianQin telescope

The utilization of smooth optical surfaces represents a critical approach for suppressing backscattering in spaceborne gravitational wave telescopes, such as those employed in the TianQin project. The bidirectional reflectance distribution function (BRDF) serves as an effective physical parameter for characterizing light scattering properties and has been extensively applied in stray light suppression research. This study employs surface scattering theory to quantitatively analyze the impact of three major stray light sources - surface roughness, defects, and contamination-on telescope system backscattering. Based on this analysis, we establish specific performance requirements for single mirror surface roughness, defect tolerance, and cleanliness levels.