基于2.16m天文望远镜光谱定标用光学频率梳梳齿偏移特性研究

High-precision radial velocity(RV) technique is a basic way in research of search of Earth-like extrasolar planets, the measurement of the expansion of the Universe, a new technique for precise wavelength calibration of high-resolution spectrographs using laser frequency combs (LFC)has recently been proposed to accomplish the long term accuracy at the cm/s level or even below. The laser optical frequency comb with the frequency spacing of 25GHz is installed on the high resolution astronomical spectrograph of 2.16-meter telescope in Xinglong observatory, the precision improvement of the RV is strongly limited by the transmittance noise, such as laser speckle, modal noise, which all decrease the signal-to-noise ratio(S/N) of the comb tooth. A set of coupling system via multimode fibers for connecting the LFC and the spectrograph is needed, the frequency-noise measurements of optical frequency combs by the heterodyne interference beat of laser is presented, explore the relationship between the S/N of the comb and the contrast of the laser, the modal noise, the slit width, the resolution of the spectrograph, the section shape of the fiber, provide the approximation between the tooth error and the transmittance parameters, the effectiveness of approximation is tested with the broader comb bandwidth achieved by the astronomical spectrograph. All works increase the stability of the optical frequency comb tooth and provide a theory insight to help the precision improvement of the RV.

通过视向速度测量技术进一步寻找系外类地行星，探索宇宙膨胀及其演化规律，需要使用天文光学频率梳作为定标光源，将探测精度提高到cm/s量级。我国25GHz天文光学频率梳在兴隆2.16m望远镜上安装调试后，由于光梳传输系统产生的噪声（如散斑噪声，模式噪声等）降低光梳梳齿信噪比，成为限制视向速度测量精度提高的主要因素。基于此，需要建立一套连接光学频率梳和天文光谱仪的传输系统，提出使用单频激光干涉测量技术测量光梳梳齿噪声，通过系统探索散斑对比度、模式噪声、狭缝尺寸、光谱仪分辨率及光纤截面面型对梳齿噪声的影响，给出梳齿偏移与传输参数的近似表达式，并与天文光谱仪测量的宽波段梳齿噪声相互验证，为进一步提高光梳梳齿稳定性，提高视向速度测量精度提供理论指导。

通过视向速度测量技术进一步寻找系外类地行星，探索宇宙膨胀及其演化规律，需要使用天文光学频率梳作为定标光源，将探测精度提高到cm/s量级。我国25GHz天文光学频率梳在兴隆2.16m望远镜上安装调试后，由于光梳传输系统产生的噪声（如散斑噪声，模式噪声等）降低光梳梳齿信噪比，成为限制视向速度测量精度提高的主要因素。. 基于此，本课题基于2.16m天文望远镜光谱定标用光学频率梳梳齿的偏移特性进行研究，其主要的工作成果包括：1）通过光线追迹方法对双光纤扰模器的扰模特性进行分析，表明八边形光纤相对于圆形光纤的扰模特性较好（近场径向和角向），双光纤扰模器有效提高光束稳定性。2）对天文光学频率梳的光谱展宽和平滑进行测试，光谱覆盖可见光范围270nm以上，光谱平滑度可长期保持1dB范围内，边摸抑制比达到42dB。3）;建立光谱展宽演化监测系统，观察光纤出射光的偏振消光比与光谱展宽的相关性。4）对中国2.16m望远镜的25GHz光梳梳齿进行了实测标定，获得光梳的短期定标精度为0.1m/s，相对于钍氩灯定标精度提高了2-8倍，后期对光谱重叠区域进行梳齿修正，会获得更高的梳齿稳定性。以上工作为进一步提高光梳梳齿稳定性，提高视向速度测量精度提供理论指导。