可调谐二极管激光吸收光谱技术及其在大气质量监测中的应用

可调谐二极管激光吸收光谱(TDLAS)技术是利用二极管激光器的波长调谐特性,获得被选定的待测气体特征吸收线的吸收光谱,从而对污染气体进行定性或者定量分析.在大气痕量气体和气体泄漏的监测中,为了提高探测的灵敏度,一般会根据具体情况对激光器采取不同的调制技术如波长调制、振幅调制、频率或者位相调制等,同时和长光程吸收池相结合使用,并辅之以各种噪声压缩技术.TDLAS不仅精度较高,选择性强而且响应速度快,已经广泛用于大气中多种痕量气体的检测以及地面的痕量气体和气体泄漏的检测.报道了最近研制的一套可调谐二极管激光吸收光谱检测大气中甲烷浓度的实验装置,这套装置具有灵敏度高、检测限低(ppb量级)、易于集成为便携式痕量气体检测仪等优点,若激光器的调谐波长范围能覆盖1.3～1.8 μm或者在光路中装配几台窄范围可调谐激光器实现波长扫描范围覆盖1.3～1.8μm,则可同时实现对大气中诸多重要痕量气体如CO2、CH4、CO、CH2O、H2S、NH3、HCI、C2H2等的同步监测.

Tunable diode laser absorption spectroscopic technology and its applications in air quality monitoring

Tunable diode laser absorption spectroscopic(TDLAS)technology applies the wavelength tunable characteristics of diode lasers to gain the absorption spectroscopy of the selected absorption line of the target gas for the qualitative and／or quantitative analysis of the pollution gases in air．In order to get the required sensitivity in trace gas monitoring and gas leak detection,based on the idiographic requirements it generally needs to adopt diferent laser modulation techniques like wavelength m odulation amplitude m odulation ． frequency or phase modulation and so on,with combination of long path absorption cell and assistance of various noise suppression techniques．TDLAS has significant advantages not only in sensitivity and high selectivity but also in rapidity of response．It has been extensively utilized in monitoring of various pollution gases in troposphere and atm osphere． and also in location the source of toxic or hazardous gas leak．W e report a TDLAS—based instrument recently developed bv our group for the measurement of CH4 in atmosphere． This instrument possesses advantages of fast response(faster than few millisecond)and low detection limitation f<100 ppbv1,and it could be easily assembled to a portable gas monitor． Furthermore,if the laser wavelength could be tuned in covering the range of 1．3一1．8“m or installing few narrow DFB tunable lasers to cover the range of 1．3一1．8 m,simultaneous monitoring of the major atmospheric pollution gases inchlding CO2、CH4、CO、CH2O、H2S、NH3、HCI、C2H2 and s0 on could be realized．