差频产生中红外光源的大气痕量成分高灵敏检测系统研究

Difference Frequency Generation Based Mid-infrared System for High Sensitive Detection of Atmospheric Gas

室温工作的连续可调谐相干光源在痕量气体检测技术中有着重要应用价值,非线性差频产生方法是获得室温工作的中红外相干光源的有效途径,是对传统激光光源的重要补充。研究了基于准相位匹配技术的差频产生基本原理和PPLN晶体的温度调谐特性;以甲醛为检测目标气体,研究了基于差频产生的大气甲醛中红外高灵敏探测系统组成,采用光通信波段半导体激光器和掺镱光纤激光器作为信号和泵浦激光,通过PPLN晶体的非线性差频过程实现3.53μm差频输出。系统具有室温工作、全光纤耦合、结构紧凑的特点,能够满足大气痕量气体实时在线检测的需要。

Room-temperature continuous-wave tunable narrow band coherent light sources emitting in the midinfrared region are valuable for trace gas sensing techniques. Nonlinear optical difference-frequency generation （DFG） scheme is a useful way to meet the requirement, and a kind of good complementarity for traditional laser technology. The basic principle of quasi-phase-matching （QPM） of DFG is depicted, the temperature tuning characteristics of periodically poled LiNbO3（PPLN） are studied based on the Sellmeier equation for the extraordinary refraction index. Setting the CH2O as target gas, a DFG based mid-infrared spectroscopic detection system is described. A telecommunication distributed-feedback（DFB） diode laser and a high power Yb fiber laser are used as signal and pump sources to generate 3.53 μm coherent light. The characteristics of this system are room-temperature, all fiber-coupled and compact. This system can meet the demands of high sensitive detection of atmospheric trace gases.