具有kHz超高分辨率的中红外双光梳光谱学研究

Dual comb spectrometer(DCS) is a kind of Fourier transform spectrometer(FTS) with high resolutin and real sampling time based on the frequency comb technique.Comparing with the traditional FTS, which has resolution of MHz and sampling time of second , DCS can reach kHz spectral resolution, and us sampling time. 2-5um is the aera of absorb spectrum for most of molecular, also called "molecular finger". This project plans to develope an creative mid-infrared dual comb spectrograph system by use of our homemade 350MHz ,sub 10fs Ti:sapphire DFG combs. By optimizing the output power and the duration, shaping the spctrum, the mid-infrared spectral range generated from DFG in Ti:sapphire frequency comb will be extended to 2-5um, and in order to increase the sensitivity of molecular absorb spectrum, an enhanced cavity will be built. Based on above techniques, the dual comb with kHz resolution and us sample time will be realized, and will have wide applications on the fields of air，medicine,environment and biology.

双光梳光谱仪是近年来基于光梳技术发展起来的具有高分辨率、实时采样功能的傅立叶变换型光谱仪，相比传统傅立叶光谱仪最高MHz量级分辨率和几十秒采样时间，双光梳光谱仪的分辨率可以提高三个数量级，达到kHz量级，采样时间降低到微秒量级。2-5um波段是大多数分子的吸收光谱区，因此也被称为"分子指纹"，本项目拟采用自建的重复频率为350MHz、脉宽5fs的自差频钛宝石激光频率梳，通过优化其输出功率和脉宽，整形其光谱，使自差频产生的中红外飞秒激光脉冲能够覆盖"分子指纹"区，同时为了提高分子吸收光谱探测的灵敏度，建立分子吸收共振增强腔。在此基础上，建立由两套重复频率略有差异的自差频中红外光学频率梳结合共振增强腔，获得kHz分辨率、实时采样的增强型中红外双光梳光谱仪，为大气、医疗、环境、生物等等领域提供有力的诊断和测量工具。

利用双光梳光谱仪研究中红外分子吸收谱为大气环境检测、呼吸气体检测等提供了有效先进的工具。本项目采用自建的两套350MHz亚10fs钛宝石光梳组成了双光梳系统，首先对激光器外壳机械结构优化为一体化无缝切割设计，使底板和侧板不用螺钉连接，这样的结构大大提高了光梳的稳定工作时间；然后通过自差频技术得到了相位自稳定的中红外飞秒脉冲，光谱覆盖范围为2~5um；接着将两套光梳的重复频率和载波包络相移频率同时锁定到外部的微波参考上，并采用相干外差拍频技术测量了两套光梳的拍频信号，得到线宽约几十kHz，证明这套双光梳光谱仪的分辨率可达到十kHz量级。为了提高中红外飞秒激光的功率，我们又采用掺镱的光纤飞秒激光器搭建了放大功率的Yb光纤光梳，为下一步建成稳定可靠的光纤双光梳光谱仪设备打下坚实基础。