用于高精度天文光谱定标的固体光学参考腔色散及其补偿研究

High-precision velocity measurement is one of the most important tools for exoplanet exploration and basic cosmic physics research. Its rapid development has placed extremely high demands on the spectral calibration methods for high-resolution astronomical spectrograph systems. In recent years, a new calibration method that employs optical reference cavity to filter wide-spectrum white light and generate comb-like frequency standard has emerged and attracted great international attention in the field of astronomical instrumentation. However, to the best of our knowledge, there has been little domestic research in this specific area to this day. On top of that, the use of a solid reference cavity can be expected to further reduce the costs while improving structural compactness and mechanical reliability. However, current studies have not placed enough attention on the problem of material induced dispersion in solid cavities and its impact on calibration accuracy. Therefore, the goal of the proposed research is to design an economical, solid optical reference cavity suitable for high resolution spectral calibration. The main focus is to study the wide spectral filtering performance of the solid optical cavity, evaluate the subsequent material-dispersion-induced calibration errors, and explore novel dispersion compensation methods aimed at improving the calibration accuracy. By integrating material characterization with instrumental design, a low-cost system with the potential to meet the short-term high-precision requirements of high resolution astronomical spectrograph calibration could be achieved. On the technological aspect, some of the proposed compensation techniques are original and carry certain exploratory traits. Funding the project would also help to accumulate technical experience and cultivate relevant talents for future generation high-precision astronomical instrument development.

高精度视向速度测量这一重要的系外行星探测和基本宇宙物理研究工具对高分辨率天文光谱定标手段提出了极高的要求。近年来出现了一类使用光学参考腔对白光光源进行宽光谱滤过后产生类光梳型频标用于光谱定标的新方法，在国际天文仪器领域颇受关注。然而，目前国内尚未见有此方面的针对性研究。在此类方案基础上，采用固体参考腔结构有望进一步显著降低成本，提高仪器紧凑性和机械可靠性。但其腔体材料会引入一定色散问题，而目前国际上尚缺乏此类腔结构用于宽光谱定标及相关色散问题的深入研究探讨。本项目拟将材料特性与天文仪器设计相结合，研究固体光学腔的宽光谱滤光特性及由其色散所引入的定标误差，并探索相应的色散补偿方法，有望在大幅降低成本的同时满足下一代高分辨率天文光谱仪器的短期高精度定标要求。部分相关技术目前国际上尚未见有类似研究报道，有一定探索性和原创性，有助于为我国高精密天文仪器科研力量的发展累积技术经验、培养相关人才。

使用视向速度法对可能宜居的太阳系外行星进行探测，需要1 m/s以上精度的长期探测，必须通过高精度参考源和同步定标等技术手段实现。激光频率梳是目前精度最高的天文光谱定标参考源，可以在宽光谱范围内实现0.01 m/s量级精度的长期波长定标精度。然而，目前的激光频率梳技术存在故障率高、耗材寿命有限、点亮成本高、难以覆盖短波波段等尚待解决的问题，更适合用作间歇性的定期校对基准。对于日常对天观测曝光过程中的仪器漂移追踪来说，基于法布里-珀罗标准具的新型定标源具有高可靠、低使用成本等优点，是目前最佳的同步观测定标参考源，已在HARPS、ESPRESSO等专用视向速度探测仪器中实现成功应用。但目前国际上用于天文观测实践的法珀定标源，基本均采用气隙腔结构标准具，使用时必须通过真空系统进行严格的气压、温度控制，结构较为复杂，体积较为庞大，并不适合空间应用等对尺寸、重量有严格限制的场景。固体光学参考腔具有结构紧凑、气压不敏感等优点，但由于腔体材料特性，其温度敏感性远高于真空环境下的气隙腔，并且不同波长处的温度响应特性存在明显差异。本项目针对固体光学腔的宽光谱天文光谱定标应用及色散相关漂移差异问题，开展了一系列理论仿真分析、样机设计搭建、出射光谱特性测试及天文光谱仪现场实测研究，分别对光纤固体法珀腔和一般固体法珀腔实现了0.03 mK RMS和0.5 mK RMS的高精度温度控制，满足维持1 m/s定标参考光谱稳定性所需的理论温度控制要求。项目利用2.16米望远镜高分辨率光纤光谱仪和天文光梳仪器平台，首次实现固体法珀定标源与天文定标用激光频率梳的双通道直接对比测试，并对其温度响应和色散特性进行了详细分析。结果表明所设计的定标源样机稳定工作时的短期光谱稳定度≤1 m/s RMS，不同波长处的温度响应色散差异约为0.49 m/s/K/nm，均与理论预期相吻合。设计系统无需真空环境控制，不同级次处的光谱等效视向速度漂移差异在cm/s量级，可通过温度调节实现高精度的出射谱峰位置调控，具有优秀的天文光谱定标应用潜力。