实时补偿的宽带腔增强双光梳光谱技术研究

Spectral detection techniques with superior spectral resolution, broad bandwidth, and high sensitivity play the most important roles in the fields of trace gas sensing, spectral quantitative analysis, spectral database development, and etc. Spectrometry combined with optical frequency comb, where full advantages are taken from its unique temporal and spatial coherence, has powerfully driven the certain field forward. However, challenging barriers should be overcome in pursuing of fully exploiting the power of the comb-based spectroscopy. In this proposal, we present a high performance dual-comb spectroscopy with real-time compensation and broadband cavity enhancement, aiming at detection of high-quality absorption features. A quantitative model linked the parameters of the combs and the sampling system to the performance of the spectrum will be set up by the Monte Carlo method. The simulated results could promote the parameters optimization of real-time compensation. Beating two pairs of comb teeth from each with two CW-lasers in separate region, enables to extract the offset and scaling factor in the uncorrected spectra owing to the relative jitters of the repetition rates and carrier-envelope-offset frequencies. Spectral distortion could be fully eliminated by operating the real-time compensation algorithm developed on the FPGA platform. Thus, high spectral resolution and high SNR can be achieved. Moreover, to achieve broadband and high sensitivity detection, one comb has to be locked to an optimally designed high finesse cavity via two-band PDH technique. To demonstrate the capability of the proposed scheme, an experimental system will be set up. The expected quantifications are listed as: spectral resolution: 0.02 cm-1, sensitivity: 4E-10 cm-1Hz-1/2, spectral bandwidth: 300cm-1 (6300cm-1~6600cm-1), spectral line position uncertainty: <1MHz, and absorption length: >600m.

高分辨、宽带、高灵敏度的光谱探测技术在痕量气体分析、光谱数据库构建等领域具有重要应用价值。光梳光谱技术凭借其优良的时频特性正成为这一领域的宠儿，但要发挥其潜力，仍极具技术挑战。本申请提出一种实时补偿的宽带腔增强双光梳光谱探测原理和方法，通过腔增强技术和实时补偿的双光梳光谱技术的结合，实现高性能探测。研究时域扫描和频率转换过程中光梳光源、采样特性对光谱性能影响的定量模型，指导实时补偿参数优化。采用CW激光器提取双光梳光源重频和偏频的相对抖动，分离出光谱的平移和缩放因子，通过基于数字逻辑算法进行实时补偿，实现高分辨、高信噪比探测。通过增强腔参数优化和双波段PDH协调锁定，将一个光梳相对于增强腔宽带稳定锁定，实现宽带高灵敏度探测。本申请拟构建一套实验系统，实现光谱分辨率0.02波数，探测灵敏度4E-10cm-1Hz-1/2，光谱带宽300波数，谱线位置不确定度<1MHz，吸收光程>600m。

双光梳光谱技术作为独具宽带、高分辨、高灵敏度的激光光谱技术在呼吸气体分析、大气环境、燃烧诊断等微量、痕量气体分析领域具有重要应用潜力。本研究瞄准高性能双光梳光谱探测的实现，从探测信号动态补偿、信号增强、光源优化和应用探索等方面开展了深入研究。经四年努力，圆满完成项目预期目标。完成的主要研究工作和重要技术指标包括：1）从多外差光谱信号形成机制入手建立了数学分析模型，完成了直接射频基准参考和光学频率基准参考下光谱性能的变化特性研究，为数字化补偿方案实现提供了支撑。2）采用光频链接探测和数字补偿算法提取出独立的偏频和重频抖动信号，实现将无补偿时半宽度0.36MHz的抖动信号补偿到3.5Hz（0.34ms）的近变换极限宽度，进而实现了梳齿分辨光谱探测，获得梳齿半宽度达650kHz。3）提出一种自适应腔增强双光梳光谱探测技术，通过腔对光梳的重频和梳相对腔的偏频锁定实现腔梳自适应耦合。构建了一套自适应腔增强光谱探测系统，实现测量光谱范围6300~6650cm-1（超过350cm-1），增强因子大于1200，效吸收光程~700m，光谱信噪比大于440:1（@1s），光谱元素数量达40000，噪声等效吸收达2.0×10-10 cm-1Hz-1/2的高分辨、高灵敏、宽带气体光谱探测。4）结合时域复用技术，提出一种具备探测视线内多分段的光谱和吸收长度同步探测能力段分辨双光梳光谱技术，实验验证了三个分段内无串扰探测，路径探测单次测量标准差为0.6μm，气体浓度反演偏差约为1%。5）拓展提出了一种双波段光频梳链接的腔衰荡测量技术，实现衰荡腔长和测量用激光器同时向同一基准源的溯源，改进了光开关驱动及拟合算法，实现噪声等效吸收7.9×10-12 cm-1∙Hz-1/2。6）针对双光梳光谱探测速度与光梳重频差之间的强耦合限制，提出一种光源重频调制技术，通过对双光梳脉冲对相对延迟的探测与反馈控制，实现特定延迟域的扫描，将双光梳互扫描频率从重复频率差（<100Hz）提升至重频调制频率的两倍（>10kHz）。本项目在研期间在Photonics Researh，ACS Photonics，Optics Express等本领域学术期刊发表论文（含已接收）10篇，其中SCI论文9篇，封面论文1篇；获得发明专利授权4项，软件著作权1项。