基于差频中红外激光的痕量气体高分辨光谱检测研究

Research on the High Resolution Trace Gas Detection Based on the Difference-frequency Mid-infrared Spectrometer

研究了基于差频光源的高分辨中红外激光光谱检测系统,差频中红外光源使用两台近红外半导体激光器作为种子光源,采用PPLN晶体作为非线性混频器件,结合准相位匹配技术实现了3.2～3.7μm中红外相干光源输出,最大差频输出功率约为1μW.以CH4为例检验了系统的高分辨红外光谱检测特性,选择CH4分子3028.751cm-1 v3基频吸收线作为分析谱线,10cm光程的检测限为0.8ppm.光谱数据分析表明,系统检测限主要受到标准具光学噪音的限制.

Mid-infrared spectral region is favorable for high sensitivity trace gas detection.The development and characterization of a compact mid-infrared laser spectrometer for high resolution spectroscopic detection of trace gases is reported.Continuous-wave mid-infrared radiation is generated by difference-frequency mixing of outputs of two commercial narrow linewidth diode lasers.A maximum mid-infrared radiation power of 1 μW at 3.31 μm is generated,and the wavelength tuning region is around 3.2 μm to 3.7 μm.The high-resolution spectroscopy capability of this spectrometer is evaluated by trace CH4 measurement,the line at 3 028.751 cm-1 of v3 fundamental vibrational band of CH4 is chosen as target analysis line for this line is relatively free of interference by other gas species.The detection sensitivity for CH4 is estimated to be 0.8 ppm for 10 cm optical path length at atmospheric pressure,and the limitation is supposed mainly from the etalon noise of optical surfaces.