Differential wavefront sensing-based high-precision dual closed-loop control of point-ahead angle mechanism in space gravitational wave detection

Laser pointing jitter noise can significantly impact heterodyne interferometric ranging in space gravitational wave detection. Existing differential wavefront sensing (DWS)-based laser pointing control systems fail to achieve the required accuracy due to inadequate disturbance suppression resulting from sensor performance degradation and actuator nonlinearity. In this study, a DWS-based high-precision dual closed-loop control for the point-ahead angle mechanism (PAAM) is proposed. A laser heterodyne interferometry experimental platform is constructed, and a high-precision DWS phase-to-angle conversion coefficient calibration method is presented. Experimental verification of both single closed-loop and dual closed-loop architectures is conducted. Experimental measurements demonstrate that the dual closed-loop control system achieves a pointing jitter noise of less than 5nrad/Hz^1/2 within the 1 mHz to 1 Hz frequency band, an 87.18% reduction compared to the single closed-loop system, representing a breakthrough at low frequencies. This system verifies the necessity of the PAAM dual closed-loop pointing control strategy based on differential wavefront sensing in a heterodyne interferometer optical system. It overcomes the ultra-low-frequency pointing control bottleneck and provides a feasible technical path that meets the noise budget for space gravitational wave detection missions.