Design of freeform off-axis telescope with low tilt-to-length noise based on construction method

Abstract

In this paper, we propose a design methodology for low tilt-to-length (TTL) noise freeform off-axis telescopes, aimed at enhancing performance in space-based gravitational wave (GW) detection. Our design integrates advanced freeform surfaces to reduce TTL noise and improve optical quality, which is crucial for the requirements of GW detection mission. The novelty of our approach lies in the construction method, which directly computes the optical parameters, enabling simultaneous consideration of wavefront error (WFE) and TTL noise. This contrasts traditional optimization methods, which often handle these aspects sequentially, leading to inefficiencies and potential increases in design time. By incorporating TTL noise considerations at the design stage, our method significantly enhances the predictability and efficiency of the telescope design process. Based on this method, we present an off-axis telescope design which demonstrates that the root-mean-square (RMS) wavefront error remains well within the requirements of GW detection missions across the scientific field of view (FOV), and the TTL noise is maintained below the threshold across a wide operational range. The RMS WFE of the designed system is lower than 0.0025λ within the scientific FOV of ±7μrad. The maximum TTL noise within FOV of ±300μrad is less than 0.025 nm/rad.