A High-Stability Off-Axis Four-Mirror Infrared Telescope System for Gravitational-Wave Detection

To address the stringent performance requirements of space-based gravitational-wave detection telescopes in terms of superior wavefront quality, a high beam–compression ratio, and exceptional thermal stability, this study proposes a 1064 nm off-axis four-mirror infrared telescope system. Ultra-low-expansion glass (ULE), 4J36 Invar, and T800-based carbon-fiber-reinforced polymer (T800 CFRP) are integrated to achieve optimal thermal-expansion compatibility among the principal structural components, while a three-point symmetric bipod flexure support is specifically developed for the primary mirror. A compliance model is formulated based on Castigliano’s second theorem, followed by systematic optimization of the key structural parameters. Furthermore, coupled analyses of gravitational loading and orbital thermal effects are conducted in conjunction with a staged assembly and alignment procedure. The results demonstrate that, under a 1 g gravitational load, the maximum displacement of the primary mirror is approximately 1.72 μm, while the surface-figure error over the effective reflective aperture is maintained below λ/100. Across an orbital temperature range of −18.16 to 63.45 °C, the maximum root-mean-square and peak-to-valley surface-figure errors of the primary mirror are limited to 3.61 nm and 14.97 nm, respectively. These numerical results indicate favorable static optomechanical and thermomechanical stability under the investigated gravitational and orbital thermal conditions, thereby providing a technical reference for the development of the TianQin space-based gravitational-wave telescope.