Design of tilted-transmissive-plate-based point-ahead-angle unit with ultra-low tilt-to length coupling noise for spaceborne laser interferometry

A tilted-transmissive-plate-based point-ahead angle unit (PAAU) is proposed for spaceborne laser interferometry to achieve ultra-low tilt-to-length (TTL) coupling noise under TianQin mission requirements. An analytical model is developed incorporating angular jitter, parasitic motion, and geometric misalignment through lever-arm, piston, beam-offset, and transmissive-medium effects, enabling identification of key influencing factors. A sensitivity-guided tolerance-allocation method is applied to derive component-level requirements. Monte Carlo simulations demonstrate a total TTL coupling noise of 6.21×10 −14 m/Hz 1/2 in the 0.1 mHz–1 Hz band, meeting the allocated budget. Compared with representative existing designs, the proposed PAAU relaxes critical tolerances by mitigating first-order translational coupling, providing improved feasibility for high-precision intersatellite interferometry.