Multi-channel Thermal Deformation Interference Measurement of the Telescope Supporting Frame in Spaceborne Gravitational Wave Detection

The Taiji program and the LISA (Laser Interferometer Space Antenna) program are proposed to realize the gravitational wave detection within the frequency band of 0.1 mHz-1 Hz through space laser interferometry. As a key optical component of the interferometric system, the telescope are required the dimensional stability better than 1 pm/√(Hz) and its deformation between the primary and the secondary mirrors needs to be small enough to reduce wavefront distortion. Therefore, in the case of satisfying the structural strength, the telescope supporting structural material also needs to meet the performance of the low coefficient of thermal expansion (CTE) and high thermal conductivity. In this paper, we fabricate a telescope supporting frame using the carbon/silicon carbide (C/SiC) composite, and build a high-precision and multi-channel thermal deformation interferometry system. Using this system, the uniform thermal expansion experiment and the temperature gradient thermal expansion experiment are carried out on the telescope supporting frame. The results show that the axial CTE and the transverse CTE of the C/SiC composite is about -8.3 × 10^-7 /K and 3.3 × 10^-5 /K, respectively, which indicate that the design and process of the C/SiC composite used may not be mature and need to be further studied. The high-precision multi-channel thermal deformation measurement interferometry system designed in this paper can be used for the subsequent thermal performance measurement of the telescope prototype.