利用可调谐半导体激光吸收光谱(TDLAS)技术对气体进行长时间实时监测时，激光器波长的漂移会给测量精度造成较大的影响。为了消除这种影响，利用Lab-VIEW设计的数字比例积分微分（PID）算法和软件数字锁相，将激光频率锁定在待测气体的吸收峰上。采用1.653 μm的分布式反馈（DFB）半导体激光器作为光源，结合100 m离散型Herriot吸收池，选择空气中的甲烷作为研究对象，对系统性能进行了测试和分析。结果表明，该系统可以将激光器稳定在±0.001 cm-1范围内，对激光器的漂移起到了很好的抑制作用。系统使用二次谐波测量时1 s积分时间内检测限约为1.8×10-8体积分数，可以满足环境空气中甲烷的长时间监测。该方法可以直接应用于其他痕量气体探测、燃烧诊断等领域。

The fluctuation of laser brings many troubles when tunable diode laser absorption spectroscopy (TDLAS) is used in the real-time measurement of gases. For eliminating this influence, a novel method, in which a digital proportion integration differentiation (PID) algorithm and a software lock-in amplifier designed by using Lab-VIEW are employed, is introduced to lock the laser to the center of the absorption line. In order to test the system, three intimate absorption lines of methane near 1.653 μm are chosen by using fiber-coupled distributed feedback (DFB) diode laser. A 24-hour continuous measurement is implemented. Relative results are presented and discussed. The detection limit is lower than 1.8×10-8 while the second harmonic signal measurement is utilized. This method can be applied to the detection of trace gases by using other long path length cells (CEAS) or combustion diagnosis.