中远红外光频梳及分子指纹光梳光谱

Absorption spectroscopy of fundamental ro-vibrational transitions in the mid-infrared region provides a powerful tool for studying the structure and dynamics of molecules in the gas phase and for sensitive and quantitative gas sensing. Laser frequency combs permit novel approaches to perform broadband molecular spectroscopy. However, achieving high resolution within short measurement times in the mid-infrared still requires overcoming instrumental challenges. Here, we propose multiplex dual-comb spectroscopy based on mid- and far- infrared frequency combs. We harness nonlinear methods for effective noise suppression and use optical frequency down conversion techniques achieving highly stabilized laser combs in the 3-5 um and 8-14 um regions (atmospheric windows). Our scheme without moving mechanicals may achieve high-resolution (Doppler-limited), high-precision (atom clock level) and broadband molecular spectra within measurement times as short as microseconds. We will develop a new scheme based on constrained high-finesse optical cavity for boosting spectral sensitivity with remarkable signal-to-noise ratio limited by quantum noises. Our proposal is based on our previous results in the 3-μm region with Doppler-limited absorption spectra with resolved comb lines within milliseconds. Furthermore, the proposed technique, with its potential in recording speed, spectral resolution, accuracy and stability, will be applied to remote spectral sensing. We believe our technique holds much promise for fast and sensitive time-resolved studies of, for example, trace gases, or for other applications such as gas pollution detection and monitoring.

中远红外光学频率梳是精密分子光谱学、分子动力学、光谱诊断、精密光学测量的重要工具，对高分辨精密光谱技术的发展及应用起到了关键作用。但由于高性能红外器件的缺乏，中远红外飞秒光梳的实现困难重重。另一方面，由于受到红外光源技术的制约，红外分子光谱技术仍存在着耗时、精度低、分辨率有限、灵敏度不足、信息量有限等问题。因此，项目拟发展以中远红外光梳为光源的精密光梳分子指纹图谱技术。项目拟采用非线性噪声抑制与光学频率下转换技术，实现水窗波段（3-5 um与8-14 um）的光梳光源；发展原子钟精度的中远红外双光梳光谱技术，在微秒时间尺度上，实现对多种气体分子指纹峰的高分辨（多普勒极限）、精确识别；结合空间束缚的外腔共振增强技术，实现量子噪声极限的超灵敏中红外分子图谱识别；构建气体分子光梳光谱数据库，探索其在远距离光谱遥感中的应用潜能，为痕量气体的实时监测、追踪与精确测量提供新途径。

中远红外光学频率梳是精密分子光谱学、分子动力学、光谱诊断、精密光学测量的重要工具，对高分辨精密光谱技术的发展及应用起到了关键作用。项目以中远红外光梳为光源的精密光梳分子指纹图谱技术研究为主线，发展了非线性噪声抑制与光学频率下转换技术以及原子钟精度的中远红外双光梳光谱技术，实现了量子噪声极限的超灵敏中红外分子指纹光谱测量，并探索了其在光谱遥感、激光测距等研究中的应用潜能。项目圆满完成原定研究目标。具体研究了远红外宽频带、高相干度光梳光源的产生与时频控制技术，采用电光调制非线性频率噪声控制技术，实现了光频率的实时精确锁定；采用相位噪声自抑制的光学频率下转换技术，实现大气窗口波段的红外光梳的产生，并通过氮化硅波导有效拓宽了光梳光谱范围。项目发展了高精度、超灵敏中远红外双光梳光谱技术，实现高精度、高灵敏度、宽波段红外光梳光谱测量。在探测方面，项目结合红外光子非线性频率转换技术，将红外光子高效率的转换到近红外波段，实现了单光子水平高灵敏探测。在光谱信息取样方面，采用多模式光梳相干拍频探测的方式，获取周期性超快光学取样，在微秒时间尺度上，实现对多种气体分子的特征吸收峰的准确识别；光谱测量精度达到原子钟量级，光谱分辨达到多普勒极限；结合增强光学腔，有效地提高光场强度，增加光与物质相互作用距离，实现了超灵敏中红外分子图谱识别。项目推进了光梳光谱技术在遥感、气体监测等领域的创新应用研究。项目研制完成高功率中远红外光梳相干光源以及成双光梳光谱测量系统。此外，发表学术论文6篇，申请中国发明专利6项，申请并授权美国专利1项。