可调谐二极管激光吸收光谱(TDLAS)技术利用二极管激光器波长调谐特性，获得被测气体的特征吸收光谱范围内的吸收光谱，从而对污染气体进行定性或者定量分析，这种方法不仅精度较高，选择性强而且响应速度快，已经被用于大气痕量气体监测以及工业控制。在对空气中的痕量气体进行检测中，由于气体浓度较低，需要和长吸收光程技术相结合。将可调谐二极管激光吸收光谱与经过108次反射后达到27 m光程的多次反射池相结合研制了用于地面环境空气中甲烷含量监测的便携式吸收光谱仪，并结合了用于微弱信号检测的二次谐波检测技术，从而达到了体积分数低于1×10-7的检测限，并利用不同体积分数的甲烷气体对系统进行了测试，得到了很好的测试结果。

Tunable diode laser absorption spectroscopy (TDLAS) is a new method to detect trace gas qualitively or quantitavely, based on the tunable characteristic of the diode laser, by obtaing the absorption spectroscopy in the characteristic absorption region. For the significant advantage in sensitivity， selectivity and rapidity of response, it has been widely used in atmospheric trace gas measurements and industrial control. In air trace gas measurements, TDLAS should be combined with the long absorption path technique due to the low concentration. Based on the combination of TDLAS and 27 m absorption path after 108 times reflection a portable absorption spectrometer is developed for monitoring the ambient methane, and the detection limit is below 1×10-7 by second harmonic detection which is usually used to detect low signals. The system is tested by the gas with different concentration， and the result is very well.