采用移相式干涉成像光谱技术研究天文光梳输出光谱的非线性漂移

Served as a standard “spectral scale” in spectroscopy technology and optical testing, the spectral accuracy of an Astronomical Optical Comb (AOC) not only determines the manufacture level of astronomical spectrometers, but also has a close relation to the high resolution of radial velocity and acceleration measurement of a series of extrasolar planets. However, due to its unique special properties of output spectrum such as wide wavelength coverage, uniform intensity and frequency interval of each wavelength as well as ultra-high spectral resolution and ultra-short pulse of each spectral line, the non-linear spectral drifting error of an AOC can be barely observed and measured using a traditional dispersion grating spectrometer. As a consequence, a testing method for AOC output with high dynamic range, ultra-high spectral resolution as well as ultra-fast and real time response is in urge. To solve this problem, a novel dynamic calibration and testing technology for AOC output spectrum is proposed in this research, which is based on Fourier imaging interference spectrum as well as dynamic phase-shifting interference technology. This research will mainly focus on realizing ultra-high spectral resolution, an active compensation of field-of-view (FOV) technology and design of a globally optimized dynamic phase-shifting interference algorithm. Overall, these theories and techniques will be studied and demonstrated in this research and moreover, will offer fast and accurate calibration and testing method applied in other major and key astronomical spectral instruments.

作为光学检测中的标准“光尺”，天文光梳的光谱精细度不仅直接决定天文光谱仪的制造加工能力，同时也和光谱法测量系外行星的视向速度和加速度的精度息息相关。然而，由于天文光梳输出光谱具有谱线族覆盖波长范围较宽、谱线光强和间隔均匀分布、谱线频率间隔十分密集和超短脉冲等特性,针对该特性传统的实验室型色散型光栅式光谱仪的分辨率已经无法区分天文光梳谱线族的非线性漂移，因此急需一种大动态范围、超高分辨率、超快时间响应的检测手段。本项目申请以傅里叶变换成像干涉光谱技术为基础，结合实时动态移相干涉仪概念，提出一种可应用于天文光梳的动态标定和测试技术。项目围绕实现超高光谱分辨率、主动的视场增强补偿技术、全局优化的动态干涉算法设计在内的关键问题展开研究，以实现快速而精确的天文光梳以及其他大型天文光谱仪器的标定与测试。

由于天文光梳输出光谱具有谱线族覆盖波长范围较宽、谱线光强和间隔均匀分布、谱线频率间隔十分密集和超短脉冲等特性,急需一种大动态范围、超高分辨率、超快时间响应的检测手段的现状。许多前人研究工作中仍然存在两个尚未妥善解决的问题：1、视场受限。普通型偏振干涉成像光谱仪存在远场条纹的弯曲而使系统视场角限制在±2°以内，严重影响傅里叶变换后的光谱重构精度；2、相位热漂移。晶体的热胀冷缩和双折射率之差随温度变化的特性导致像面干涉条纹发生随机抖动误差，将严重影响以多普勒频移为原理的视向速度等测量精度。因此，本项目以偏振干涉成像光谱仪为研究对象，搭建了相关的实验装置，研究了结构参数的定标算法，并且对一系列光谱定标源进行了测试和重构。其中在以下关键技术中取得了具有一定学术和应用价值的原创成果，其中包括：1、设计了视场补偿性的Savart剪切分束器，使系统视场角从±2.9°扩展到±10.4°，校正了视场边缘干涉条纹的非线性弯曲，有效提高了光谱重构的精度；2、通过采用长度分别为160mm的BBO晶体和20.80mm的LiNboO3的晶体组合作为相位延时模块，消除了系统的相位热漂移误差，通过实验表明在18℃~40℃之间的环境温度波动下，相位热漂移不超过0.002rad且不存在明显趋势项；3、 引入了独特的电光晶体部件并且设计了三步移相的算法，将条纹采样时间缩短了25%。通过这些方案改善偏振干涉成像光谱仪的测试精度，拟实现对天文光梳以及其他大型天文光谱仪器快速而精确的标定与测试。