基于连续量子级联激光器的1103.4cm–1处NH3混叠吸收光谱特性研究

NH3 aliasing absorption spectra at 1103.4 cm–1 based on continuous quantum cascade laser

由于NH3在大气气溶胶化学中具有重要作用,所以快速和精确反演NH3浓度对环境问题非常重要.本文以9.05μm的室温连续量子级联激光器(quantum cascade laser,QCL)作为光源,采用波长扫描直接吸收可调谐二极管激光吸收光谱(tunable diode laser absorption spectroscopy,TDLAS)技术,研究了QCL在1103.4 cm–1的光谱特性,获得了激光器控制的温度电流与波长的关系.设计了QCL二级温控的低压实验平台,测量氨气在1103.4 cm–1处的6条混叠吸收线,在降低压强的情况下谱线展宽变小,使混叠光谱分离,由此计算各条吸收线的线强,进一步对测量不确定度进行分析.针对混叠严重的光谱提出了低压分离单光谱精确反演气体浓度的方法,并进行了实验验证.通过与HITRAN数据库进行结果对比,得出氨气在1103.4 cm–1的实验测量线强值与数据库偏差为2.71%-4.71%,实验测量线强值的不确定度在2.42%-8.92%,极低压条件下反演浓度与实际值的偏差在1%-3%.

Due to the important role of NH3 in atmospheric aerosol chemistry,rapid and accurate inversion of ammonia concentration is very important for environmental issues.In this paper,a 9.05μm continuous quantum cascade laser(QCL)is used as the light source at room temperature,and the scanned-wavelength direct-absorption tunable diode laser absorption spectroscopy(TDLAS)is used to study the spectral characteristics of the QCL at 1103.4 cm-1.A low-pressure experimental platform based on two-level temperature control was designed to measure the six aliasing absorption lines of ammonia at 1103.4 cm-1.The broadening of spectral line becomes smaller under the condition of reducing the pressure,and the aliasing spectra are separated.The line strength of each absorption line is calculated,and the measurement uncertainty is further analyzed.A method for accurate inversion of single-spectrum gas concentration by low-pressure separation was proposed for severely aliased spectra,and experimental verification was performed.By comparing the results with the HITRAN database,it is concluded that the experimental measured line strength of ammonia gas at1103.4 cm-1 has a deviation from the database of.The uncertainty of the line intensity measurement is mainly related to the separation and extraction of aliasing absorbance,which is about 2.42%-8.92%.The deviation between the inversion concentration and the actual value under the condition of extreme low pressure is between 1%and 3%,while the calculated deviation of the line intensity value in the 2.71%-4.71%HITRAN database is about 3%to 5%.The results above indicate that the experimental data are reliable.The nonseparative aliasing spectral line method is used to invert the concentration at normal pressure,and the lowpressure separated single spectral line method is used to invert the concentration at low pressure.The results of the two are compared.The analysis results show that the low-pressure separation single-spectrum spectral line inversion concentration value has smaller deviation and higher accuracy from the original concentration.The study of this method provides reference for future inversion of gas concentrations inversion in the atmospheric environment and other fields.