基于中红外DFG光源的甲烷气体光谱检测方法研究

基于中红外光源的气体光谱检测是新的痕量气体监测与分析方法，在大气监测领域具有重要的应用。构建了一套基于中红外DFG光源的甲烷气体光谱检测系统。该系统以1 550 nm和1 060 nm波段可调谐半导体激光器作为基频光源，采用PPLN晶体作为差频非线性变频器件，实现了3.3 μm处的窄线宽可调谐中红外光源输出。实验结果表明，当PPLN晶体工作温度为99.5℃时，闲频光的输出功率为112 μW，差频转换效率达到1.246 mW/W2。晶体的温度接受带宽为4.3℃，泵浦光波长接受带宽为5.3 nm。在此基础上，分别利用直接吸收法和谐波检测法获得了3 028.751 cm-1处的甲烷气体吸收光谱和二次谐波检测信号。

Research on methane gas spectroscopy detection method based on mid-infrared DFG laser source

Gas spectroscopy detection based on mid-infrared laser source has been applied in the field of atmospheric monitoring as a new method for measuring and analyzing trace gases.A detection system of methane gas based on mid-infrared difference-frequency generation (DFG) laser source was constructed.The system uses a tunable semiconductor laser with 1 550 nm and 1 060 nm band as the fundamental frequency source, and uses a periodically-poled lithium niobate (PPLN) crystal as the differential frequency nonlinear inverter to achieve a narrow linewidth tunable mid-infrared source output at 3.3 μm. Experimental results show that, when the temperature of the PPLN crystal is fixed at 99.5℃, the maximum idler laser output power of 112 μW, and the nonlinear DFG conversion efficiency is 1.246 mW/W2. The acceptance bandwidth for the pump wavelength and the crystal temperature are 5.3 nm and 4.3℃, respectively. On this basis, the methane gas absorption spectrum and the second harmonic detection signal at 3 028.751 cm-1 were obtained by direct absorption method and harmonic detection method, respectively.