Imaging System Design Scheme for the Point-Ahead Angle Mechanism in Space-Based Gravitational Wave Observation

In space-based gravitational wave detection, the Point-Ahead Angle Mechanism (PAAM) is crucial for high-precision pointing of intersatellite laser links, but its rotation introduces tilt-to-length (TTL) noise that severely limits interferometric accuracy. To suppress local TTL noise caused by PAAM angular jitter, this paper proposes an imaging system that optically images the detector onto the equivalent rotation center of the PAAM, actively mitigating geometric TTL noise. A highly symmetric equal-arm heterodyne interferometer test platform was constructed, and IFOCAD simulations were performed to evaluate suppression performance under non-ideal conditions (angular jitter, rotation center offset, installation errors, thermal deformation). Results show that under ideal alignment, the imaging system suppresses 98.9% of lever-effect optical path changes and 98.2% of piston-effect changes. With installation errors, TTL noise is suppressed within $ 1\;\text{pm/}\sqrt{\text{Hz}} $, and remains below $ 10\;\text{pm/}\sqrt{\text{Hz}} $ when thermal noise is introduced. Simulations confirm that lever noise has a second-order correlation with angular jitter, while piston noise has a first-order correlation, consistent with theoretical analysis. This study provides theoretical and simulation support for designing high-stability beam pointing control systems and assessing noise in future missions.