Stray light analysis for TianQin laser interferometry

Abstract Stray light is one of the critical noise components in space-based gravitational wave observatories, such as TianQin and LISA. The noise contribution of stray light effect depends on its phase difference and power ratio compared with the nominal light, which are determined by the overall optical system design rather than being solely dictated by the characteristics of the stray light source. To accurately characterize the propagation of interfering lights, this study establishes a comprehensive model including optical path, efficiency, drag-free performance and the mounting stability between the telescope and the optical bench. Furthermore, we examine noise transfer functions based on the time-delay interferometry Michelson combination and conduct simulations to quantify the stray light noise. Our findings identify the constraints imposed by mounting stability on the stray light from telescope and the impact of the distance between the test mass and the optical bench on the stray light from backlink. Finally, we propose two stray light noise budgets, encompassing requirements for stray light source characteristics, related noise sources, link efficiency, and balanced detection performance.