激光吸收光谱中谱线重叠干扰的解析方法

Analytical Method of Spectral Overlapping Interference Using Laser Absorption Spectroscopy

激光吸收光谱常被用于测量大气痕量气体,但某些气体在某波长附近会出现多条谱线重叠的现象,导致吸收信号产生重叠峰。以NH3气体为例,研究6529cm-1附近的4条重叠谱线,通过Voigt线型模拟不同压强下的谱线,搭建直接吸收光谱测量实验系统。实验发现,低浓度NH3气体的谱线峰值并没有随着压强的减小而减小,反而逐渐增大。由于NH3存在吸附性,因此,采用无吸附性的CH4气体进行验证。结果表明:当气体压强为0.18atm(≈18kPa)时,实验谱线与模拟谱线相差最小,NH3的最大吸收峰吸光度与气体浓度成正比。研究结果为后续多气体测量过程中的干扰问题提出了解决方法。

Laser absorption spectroscopy is widely used for monitoring trace gases in the atmosphere.However,some gases have several overlapping absorption lines.Therefore,the peak signals overlap;this affects the measured results.For example,the NH3peak near 6529cm-1 includes four overlapping absorption lines.Absorption spectra at different pressures are simulated to obtain four absorption lines separated by Voigt-line profiles.First,the experimental platform is established by the direct absorption method.The experiment demonstrates that the peak value of the NH3spectra at low gas concentration does not decrease.However,the peak value increases at a lower gas pressure.The phenomenon may be attributed to the absorbability of NH3.Therefore,the CH4gas,which does not exhibit absorbability,is used to verify this assumption.Finally,by analyzing the NH3absorption lines at different pressures,it is determined that the difference between the experimental and simulated spectra is the smallest when the gas pressure is 0.18atm(≈18kPa)and the maximum absorption peak of NH3is proportional to the gas concentration.This result solves the interference problem,which will improve future gas-detection approaches.