Stray light analysis of the K-DRIFT G1 enabling low surface brightness astronomical observations (Invited Paper)

To enable accurate observations of low surface brightness (LSB) astronomical structures, the K-DRIFT (KASI Deep Rolling Imaging Fast Telescope) G1 system has been developed at the Korea Astronomy and Space Science Institute (KASI). The telescope employs a Linear-Astigmatism-Free Three-Mirror System (LAF-TMS) optimized for wide-field imaging with minimal aberrations and high optical throughput. Since LSB observations are highly sensitive to unwanted illumination, a detailed stray light analysis is essential to ensure sufficient system contrast and uniform background levels. In this work, we performed a model-based stray light analysis using scattering and coating models. The scattered light was evaluated using the Bidirectional Scattering Distribution Function (BSDF) model to represent microscale surface structure and coating effects, while ghost images were modeled based on optical coating properties to account for multiple internal reflections. To quantitatively assess stray light performance, the Point Source Transmittance (PST) was computed to trace stray light propagation from both on-axis and off-axis sources. The PST-based analysis identified dominant stray light paths and guided the design optimization of baffles and vanes, effectively reducing unwanted light and improving system contrast. The results demonstrate that combining scattering and coating models with PST-based evaluation provides a practical and accurate approach to predicting and mitigating stray light in asymmetric wide-field telescopes such as the K-DRIFT G1. Future work will extend the analysis by incorporating experimentally measured BSDF and coating properties, thereby enabling more realistic and accurate predictions of stray light performance within the K-DRIFT G1 telescope.