宽带高灵敏双电光频率梳光谱技术研究

Development of miniaturized and high-sensitive technique for detection of multiple gas molecules based on laser spectroscopy is the prerequisite of many advanced fields, including industry, national defense, medical science, fundamental research and so on. Along with prompt development of optical fiber device, laser spectroscopy with electro-optic comb as light source has become a spotlight in international research, due to its advantages of all fiber structure and compact design. Moreover, the combination of electro-optic comb and dual frequency comb, i.e. dual electro-optic frequency comb (EO-DCS), can realize the detection of multiple trace gas with high resolution, high selectivity and rapid response. However, the bandwidth of the developed electro-optic comb is relatively narrow, as a result, it is unable to measure multiple gas spectra separated with certain wavelength distant. And the sensitivity of the developed EO-DCS is inferior, which is not enough for some specific applications. In this project, we will develop a novel cavity-enhanced EO-DCS, which extend the bandwidth from 25 GHz to 1 THz and improve the sensitivity by 3 orders. Finally, this novel system will be used to simultaneously detect H2O, CO2, NH3 and H2S with high sensitivity and high resolution. The technique studied in this project for trace gas detection will have wide application in many fields and improve the technological and equipment level of our country.

发展小型化、高灵敏多组分激光痕量气体检测技术是我国工业、国防、医学以及基础研究等领域的重大需求。随着光纤器件的快速发展，以电光频率梳为光源的激光光谱技术成为了国际上研究的热点，其具有全光纤和结构紧凑的优点。同时结合双光梳光谱技术可以实现多组分、高分辨率、高选择性、快速响应的痕量气体实时检测。然而目前的电光频率梳光谱覆盖范围相对较窄，对于波长相差较大的不同气体谱线很难同时测量；同时已发展的双电光频率梳光谱系统的探测灵敏度较低，无法满足特定领域的使用需求。为此，本项目拟研制一种新型的腔增强宽带双电光频率梳光谱系统，将可测量的光谱覆盖范围由现有的25GHz拓展到1THz，将气体检测灵敏度提高3个数量级。最后使用该系统对H2O、CO2、NH3和H2S四种集成电路制造中主要的微量杂质气体实现高灵敏、实时检测。本光谱装置的研制成功将会在多个气体测量领域有着广泛的应用，大大提升我国的装备技术水平。

发展高灵敏痕量气体检测技术在环境监测、工业生产、国防安全、精细农业等领域都有重要的应用。双光梳光谱技术具有分辨率高、频谱范围宽、选择性好、探测方式简单等优势，可以实现对多组分气体的同时监测。特别的，基于外部调制器的双光梳系统还具有相位噪声小，信噪比高的特点，因此成为研究热点。然而，该类光梳受限于调制系数有限，其频谱覆盖范围较小，很难实现多气体光谱的同时测量。为了解决这个问题，我们发展了基于光纤放大环路的双光梳光谱系统，采用的光纤放大环路是由外部电光调制器、光纤功率放大器、光纤分束器等组成，环路内的激光会多次通过电光调制器，从而实现光梳的扩展，最终将梳齿数目从10个扩大为200个，同时将光梳的频谱覆盖范围从5 GHz扩大到200 GHz。同时利用一个电子反馈回路实时动态控制两个光纤环路的长度，稳定两个光梳之间的相位差，从而获得了稳定时长大于12小时的双光梳光谱输出。为了提升探测灵敏度，我们进而发展了光学反馈线性腔增强光谱技术。腔增强光谱技术利用光学腔延长激光与腔内气体介质的作用次数，可以将探测灵敏度提升4个数量级。然而激光到腔耦合效率低且起伏大严重影响其信号稳定性。为了解决这个问题，我们引入了光学反馈技术，可以将激光的频率短暂锁定到光学腔上，抑制了激光频率噪声，有效地提升了耦合效率，将腔透射光谱信号幅度放大了5倍，实现了对大气中CH4气体得高精度测量，探测灵敏度达到了7.8×10-10 cm-1，最小可探测CH4浓度为1 ppb。我们的研究为发展高灵敏、高精度多气体检测仪的提供了技术支撑。