利用可调谐半导体激光吸收光谱(TDLAS)结合平衡差分探测技术测量了1.578 μm附近的CO气体3-0带P(4)跃迁在不同压强和不同浓度下的吸收光谱信号。 由于平衡差分探测方法可以有效地抑制激光光强波动、 温度漂移和机械振动等共模噪声, 从而提高了光谱探测灵敏度。 通过与直接吸收信号相比, 平衡差分的信噪比提高了3.4倍, 探测极限为87 ppmv。 测量了浓度为1%压强为40, 55, 70和85 Torr时的CO气体, 结果显示在70 Torr时其光谱信号最强。 并且, 利用直接吸收和平衡差分技术测量了不同浓度的CO气体在总压强在70 Torr时的光谱信号, 发现平衡差分技术光谱强度与浓度的关系线性度符合较好, 其测量误差小于5%。 为了进一步验证系统的稳定性, 连续采集了324 s的光谱信号, 最后通过Allan方差分析, 发现本实验系统的最佳探测时间为38 s, 探测极限为47.8 ppmv。

The P(4) line of 3-0 band for CO gas in different pressures and concentrations was measured by employing tunable diode laser absorption spectroscopy combined with balanced difference detection technology. Due to the immunization to the common-mode noise of fluctuation of laser intensity, drifts of temperature and mechanical vibrations, the sensitivity of spectroscopy can be improved by balanced difference detection technology. In comparison with the direct absorption spectroscopy (DAS), the signal to noise ratio was improved by 3.4 times, and the minimum detection limit (MDL) reached 87 ppmv. The optimum pressure for CO was 70 Torr through comparing the spectral signals at 40 Torr, 55 Torr, 70 Torr and 85 Torr of 1% CO concentration. Moreover, different concentrations of CO at 70 Torr were detected by DAS and balanced difference detection, and the results demonstrated the balanced difference detection had a more linear relationship and the deviation was less than 5%. For further testification of the stability of the system, we collected the signals within 360 s for the Allan variance analysis, which denoted the most suitable detection time was 38 s and the MDL was 47.8 ppmv.