Simulated alignment method for suppressing tilt-to-length coupling noise in space gravitational wave telescopes

Abstract

Space gravitational wave telescopes are critical in achieving precise interstellar laser interferometry. The coupling coefficient is a key metric for evaluating the ultimate performance of a telescope. However, alignment errors during the assembly phase can degrade the wavefront quality of the telescope, intensify coupling noise, and impair overall performance. Currently, no alignment scheme specifically targets the coupling-noise coefficient of telescopes. To address this, this study proposes a sensitivity matrix model that relates misalignment to the coupling coefficient and establishes clear sampling criteria for coupling noise at the exit pupil of the telescope. The model incorporates second-order correction terms, enabling a more accurate characterisation of the relationship between misalignment and tilt-to-length coupling-noise coefficients. Based on this model, an alignment scheme was developed using the coupling coefficient as the evaluation metric. Owing to the significant differences in the magnitudes of sensitivity among different misalignments and their mutual coupling effects, the predicted alignment parameters often differ substantially from the actual values. To resolve this issue, a misalignment grouping strategy was proposed to reduce prediction errors. Additionally, an iterative algorithm and a sequential adjustment strategy for components were provided to ensure alignment effectiveness. Finally, the feasibility of the proposed method was verified using a typical space gravitational wave telescope model. Experimental results show that the method successfully aligned 500 randomly misaligned samples, with all samples satisfying the requirement of a coupling noise of less than 25 pm μrad−1 after alignment. This method provides new guidance for the alignment of space gravitational wave telescope systems.