A novel method for online correction of light intensity fluctuation in a practical tunable diode laser absorption spectroscopy (TDLAS) system with wavelength modulation is presented. The proposed method is developed according to the linear relation between peaks at multiple frequencies of sine modulation in the power spectral density of the demodulated second-harmonic (2f) signal and the incident light intensity. Those peaks are demonstrated experimentally and explained as residual power at the first-harmonic and third-harmonic frequencies after 2f demodulation of the residual amplitude modulation signal due to the limited integrating time constant of the lock-in-amplifier. This method can achieve real-time correction of light intensity fluctuations with only little calculation. It can work well in a very large range of light intensity and has great potential applications in the wavelength modulation spectroscopy system.

在吸收光谱检测技术中，常利用多次反射池技术增加吸收气体的光程长度，以提高灵敏度，降低检测极限。通过综合传统的多次反射Herriott池和White池的优点，利用White池的三镜光学结构和Herriott池的光路传输原理，设计出了一种新型的长光程多次反射池，其结构简单、外形紧凑、光程可调、性能稳定并且小型化。将研制出的基长20 cm、光程范围10~100 m可调的新型多次反射池应用于可调谐二极管激光吸收光谱技术中进行一氧化碳气体的探测，结合数字信号处理技术可把现场检测的灵敏度提高到10^{-6量级。实验结果显示这种新型多次反射池在吸收光谱技术中应用良好，与传统同基长的反射池相比，气体检测灵敏度有了明显的提高。}