为了研究免校准波长调制光谱技术对激光光强变化及外界干扰的免疫能力, 采用基于免校准波长调制技术的多光程吸收光谱, 以乙炔为测量目标, 进行了理论分析和实验验证。结果表明, 不同激光功率下得到的波长调制二次谐波信号幅值发生明显变化, 但通过免校准的方法得到的信号变化较小, 且受气流影响、部分遮光、系统振动等外界干扰影响较小; 采用免校准方法实验得到的体积分数在5×10-6 ～9×10-5范围内的光谱信号拥有较好的线性度, 相关系数达0.9997; 采用Allan方差分析得到该实验系统的最小探测极限可达1.2×10-8。免校准波长调制光谱技术能较好地避免光强抖动、气流干扰、系统振动等干扰, 从而提高系统稳定性和探测灵敏度。

In order to study the immunity of calibration-free wavelength modulation spectroscopy to laser intensity change and external interference, multi-path absorption spectra based on calibration-free wavelength modulation technology were adopted. Taking acetylene as the measurement target, theoretical analysis and experimental verification were carried out. The results show that, the amplitude of wavelength modulated second harmonic signal varies significantly under different laser power. But the signal obtained by the calibration-free method changes little. It is less affected by external disturbance such as airflow, partial shading and system vibration. The spectral signals with volume fraction in the range of 5×10-6 ～9×10-5 obtained by calibration-free method have good linearity. The correlation coefficient is 0.9997. Allan variance analysis shows that the minimum detection limit of the experimental system can reach 1.2×10-8. This study shows that calibration-free wavelength modulation spectroscopy can avoid the interference of light intensity jitter, air flow and system vibration. The system stability and detection sensitivity are improved.