基于光学参量振荡器的中红外NICE-OHMS光谱技术研究

In recent years, the ultrasensitive trace gas detection based on NICE-OHMS has been developed greatly since the widespread of narrow-linewidth fiber laser. However, the weak overtone transitions of gas molecular located in the infrared region restricts the improvement of detection sensitivity of NICE-OHMS. Moreover, the wavelength tuning characteristic makes it difficult to detect multiple target gases simultaneously. So it becomes a trend to develop NICE-OHMS based on the wide wavelength tuning mid-infrared laser. In this project, we plan to develop NICE-OHMS based on an optical parametric oscillator (OPO). To ensure highly efficient and stable output of the mid-infrared laser, theoretical and experimental optimization will be done, as well as the realization of the frequency stabilization of the signal laser light of OPO to an ultra-stable cavity. In frequency locking of the mid-infrared laser to the high finesse FP cavity, an acoustic optical modulator is utilized to enhance the bandwidth of frequency locking and reduce the frequency noise of the mid-infrared laser in gas detection. In addition, the balanced detection technology will be adopted to eliminate the optical interference effect to optimize the detection sensitivity. Finally, highly sensitive dispersion and absorption spectrum of C2H2, as well as other important gas components in VOCs with C-H bonds, will be studied based on NICE-OHMS, and the minimum detection sensitivity of the system will be determined.

近年来，NICE-OHMS超高灵敏痕量气体检测技术的发展得益于近红外光纤激光器的普及。然而近红外波段气体分子弱的泛频跃迁吸收限制了NICE-OHMS探测灵敏度的进一步提高，且光纤激光器的调谐特性使得NICE-OHMS很难实现多种目标气体的同时测量。因此，发展基于宽调谐中红外激光源的NICE-OHMS技术成为必然。本项目拟发展基于光学参量振荡器（OPO）的中红外NICE-OHMS技术，通过优化研究和实现OPO输出信号光到超稳腔的频率锁定来保证中红外激光的高效稳定输出。在中红外激光到高精细度FP腔的频率锁定中引入声光调制器来提高频率锁定性能，降低中红外探测光的频率噪声。此外，采用平衡探测技术消除光学干涉效应的影响提高光谱探测灵敏度。最后以C2H2为研究对象，进行高灵敏NICE-OHMS色散和吸收光谱测量，确定本光谱计的探测灵敏度，并尝试对VOCs中其它具有C-H键的重要气体成分进行检测。

近年来，NICE-OHMS超高灵敏痕量气体检测技术的发展得益于近红外光纤激光器的普及。然而近红外波段气体分子弱的泛频跃迁吸收限制了NICE-OHMS探测灵敏度的进一步提高，且光纤激光器的调谐特性使得NICE-OHMS很难实现多种目标气体的同时测量。因此，发展基于宽调谐中红外激光源的NICE-OHMS技术成为必然。本项目通过结合光学反馈和Pound-Drever-Hall（PDH）技术实现了QCL到高精细度光学腔的锁定，获得了6Hz超窄线宽中红外激光源。基于NICE-OHMS技术，通过PDH将激光锁定到高精细度FP腔，利用DVB技术将光学腔长锁定到外部射频源，得到可调谐、精准控制的激光源。基于获得的实验平台对C2H2气体的Pe(10)跃迁线进行了精密测量，得出信号信噪比达到了600。同时发展了基于线性F-P腔的光学反馈腔增强吸收光谱技术（OF-CEAS），利用透射腔模的对称性计算得到反馈相位控制的误差信号，实现了激光频率到连续101个腔模频率的锁定，对3.2×10-6的甲烷标气进行检测，得到的探测灵敏度可达0.54×10-6。本项目研究对于进一步发展中红外高灵敏光谱测量技术具有重要的参考价值。