Study On High-resolution Water Vapor Absorption Spectroscopy In The 1μm Region

The absorption spectra of water vapor in the near infrared consist mainly of absorption bands composed of discrete spectral lines and atmospheric window regions distributed between these bands.For laser atmospheric transmission,although these windows have a high transmission rate for light,they are still affected by the weak absorption of water vapor,resulting in attenuation and thermal blooming effects during high-energy laser atmospheric transmission,which affect the laser atmospheric transmission efficiency and spot quality.As the most dominant absorption in the 1 μm atmospheric window,the accurate acquisition of the absorption spectral parameters is the fundamental scientific basis for the selection of the spectral range of the light source and the improvement of the atmospheric transmission efficiency.These absorption spectral parameters can usually be found in databases such as HITRAN and GEISA.Currently,the spectral parameters of water vapor in the 1 μm band in the HITRAN and GEISA databases are mainly derived from theoretical calculations and experimental measurements,and form the main data base for optoelectronic applications and spectral analysis.However,a comparison between HITRAN2020 and HITRAN2016 shows that most of the absorption spectral parameters of water vapor in the 1 μm band have changed considerably,so that the measurement of high-resolution absorption spectral parameters of water vapor still needs to be carried out.In addition,the Voigt profile is no longer adequate for high-resolution absorption spectroscopy and more sophisticated spectral line shapes are needed to handle these absorption spectra.The thesis addresses the demand for high-resolution absorption spectroscopy parameters for optoelectronic engineering applications.A long-range absorption spectroscopy measurement device in the 1 μm band has been established based on direct absorption spectroscopy techniques,and a study of high-resolution absorption spectroscopy parameters of water vapor in this band has been carried out.The main work of the thesis is as follows:1.An experimental measurement device for high-resolution absorption spectroscopy in the 1μm band was designed and developed based on an external cavity diode laser(ECDL)with a narrow linewidth(～100 kHz)and wide tuning range(～90 nm)and a dual-path absorption cell.A high-resolution absorption spectrum of water vapor at 9152.5356 cm-1 was carried out on the basis of this device,as well as the intensity of the absorption lines and the self-broadening coefficients of water vapor at this transition line were obtained.The results are in good agreement with the data in the HITRAN database,verifying the reliability and accuracy of the experimental setup.2.Based on a 1 μm high-resolution absorption spectroscopy experimental measurement device,the high-resolution absorption spectra of water molecules were systematically measured and the absolute line intensities and self-broadening coefficients of 119 absorption lines of water molecules in the range of 9090～9900 cm-1 were obtained.By comparing the experimentally obtained line intensities with the HITRAN2016 database data,it was found that the water molecule leap spectral lines in the 4v2+v3 vibrational band(9650～9900 cm-1)deviated significantly,and since the relative uncertainties of the data in this vibrational band in the HITRAN2016 database were mostly in the range of 10%～20%,it is assumed that The relevant data in the HITRAN2016 database are presumed to be overestimated.This conclusion is also verified in the latest HITRAN2020 database.3.The absorption spectra of water vapor in the range of 9090～9750 cm-1 were measured using a 1 μm high-resolution absorption spectroscopy experimental measurement device in combination with a fiber optic transmission system,and 31 absorption lines of water vapor in the v1+v2+v3,v2+2v3,3V2+v3 and 4v2+v3 transition bands were obtained based on the quadratic Speed-Dependent Voigt(qSDV)and Voigt profiles,respectively.The absolute line intensities,self-broadening air-broadening,nitrogen-broadening and carbon dioxide-broadening coefficients for the 31 absorption lines were compared with the HITRAN database and with data from other groups,and the measurements were in good general agreement with the HITRAN database and with data from other groups.In addition,the differences between the qSDV and Voigt profiles were compared for the inversion of the absorption spectra.It was found that the standard deviation of the residuals fitted to the qSDV profile was nearly four times smaller than that of the Voigt profile,and that there was no obvious W-shaped structure in the residuals.It is demonstrated that the qSDV profile has a higher peak and narrower linewidth than the Voigt profile under the same conditions,allowing for a better fit to the absorption spectrum.