Research On Measurements Of Molecular Absorption Spectra With High Resolution And High Precision Using A DFB-ICL

With the development of molecular absorption spectroscopy,absorption spectra with high resolution and high precision are essential in molecular structure studies and absolute spectroscopic measurement.This paper gives in-depth study on the spectral measurement technology based on the tunable laser absorption spectroscopy?TLAS?,and analyzes the influence factors of the spectral resolution and precision in measurement.Finally,this paper measured the v₂-band absorption spectra of methyl mercaptan molecular with high-resolution and high precision.The main works are summarized as follow:First,high precision optical path measurement of multi-pass cell and performance evaluation.This paper first presents a new method based on Optical Frequency Domain Reflectometer?OFDR?of high precision optical path measurement of multi-pass cell.The measurement precision is compared with the traditional method.Benefitting from the traceability procedure,the measurement uncertainty of OFDR method is reduced by 3 orders of magnitude,and the measurement precision is 10?m.This method greatly reduces the measurement uncertainty of the measurement system of optical path in TLAS.Second,optimization of the super high resolution absorption spectroscopy based on DFB-ICL.In this paper,the factors affecting the spectral resolution and measurement precision are analyzed,and the influence factors are evaluated and optimized for the TLAS technology.By measurement,the working line width of DFB-ICL3392 is less than 2×10^-5 cm^-1,and the tuning wave number of the laser is optimized and calibrated to ensure that the measurement precision of the wave number is in the order of 10^-4 cm^-1.Using the laser to measure the absorption spectrum,the spectral resolution is better than 2×10^-5 cm^-1,which is in favor of the detailed analysis of the molecular absorption spectrum.Third,measurement and evaluation of methyl mercaptan v₂-band absorption spectrum with high resolution and high precision.The methyl mercaptan v₂-band absorption spectra were measured by DFB-ICL3392,and the results were evaluated in detail.By comparing with the PNNL database,the experiment found that the spectral resolution is higher than that of the PNNL database given spectral resolution of 4orders of magnitude,and precision higher than the database by 1 order of magnitude,and the absorbance uncertainty is less than 2%comparable with the database;The molecular absorption cross-section under different pressure are calculated,and the uncertainties are evaluated.We give research on the uncertainty contribution of the gas concentration,temperature and pressure;Finally,the line strength of methyl mercaptan v₂-band absorption are calculated,and the line strengths'precision are evaluated.This paper first proposed the direct measurement method of high precision optical path of multi-pass cell based on OFDR.Use the ultra high resolution absorption spectroscopy based on DFB-ICL and measure methyl mercaptan v₂-band absorption spectra.We evaluate the resolution and precision of measurement results and confirm the importance of resolution and precision of optimization method given in this paper.