1μm波段水分子吸收光谱双光程同步测量方法研究

Study on dual-optical paths for simultaneous measurement method of water vapor absorption spectrum in 1μm band

基于双光程气体多通吸收池,提出了一种单吸收池双光程(长光程:72.46 m;短光程:36.23 m)同步测量水分子吸收光谱的测量方法,并结合窄线宽外腔半导体激光器和高精度Fabry-Perot标准具,发展了一套1μm波段的高分辨率水分子吸收光谱双光程同步测量装置.在测量装置建立后,精确测量了Fabry-Perot标准具的自由光谱范围,并详细评估了该系统中Fabry-Perot标准具以及双光程气体多通吸收池内压力和温度的稳定性.利用该装置测量了9152.53 cm^(-1)处水分子在双光程下的吸收光谱,分别反演得到了长光程和短光程下的分子吸收线强和自加宽系数.双光程吸收线强和自加宽系数的平均值与HITRAN2016数据库相应数据的相对偏差分别为0.78%和3.8%,该结果验证了双光程同步测量方法的可行性和测量装置的可靠性.

Based on the gas multi-pass absorption cell with dual-optical paths(long optical path:72.46 m;short optical path:36.23 m),a measurement method of simultaneously detecting water vapor absorption spectra is advanced.Combining with a narrow line-width external cavity diode laser and a high-precision Fabry-Perot etalon,a high-resolution simultaneous measurement device with dual-optical paths for water vapor absorption spectra in 1μm band is developed.Since the external cavity diode laser has excellent polarization characteristics which could be combined with a half-wave plate and a polarization beam splitter to implement the laser transmissions in dual-optical paths simultaneously.Both the multi-pass absorption cell and the Fabry-Perot etalon in the measurement device have pressure and temperature control units,which are utilized for achieving ambient stability.The free spectral range of Fabry-Perot etalon is accurately measured by the method of optical comb frequency.Corresponding free spectral range with a deviation of only 0.02%from the theoretical value is obtained to be a value of 749.52 MHz,and the influence of temperature on the frequency shift of etalon is less than 1%of the measured value.The stability of the pressure and the temperature in the dual-optical path gas multi-pass absorption cell in the system are evaluated in detail,and the calculated relative errors are not more than 0.03%and 0.02%,respectively.At a temperature of 300 K,the system is used to measure the absorption spectra of water vapor at 9152.53 cm^(-1) from 400 Pa to 2000 Pa on dual-optical paths,then the integrated absorbance and Lorentzian line-width of water vapor for long optical path and short optical path are inverted by fitting absorption spectra with Voigt profile respectively.The absorption line intensities and self-broadening coefficients are acquired by performing linear fitting to the integrated absorbance and Lorentzian line-width under different pressures.And the relative deviations of the average values of the dual-optical path absorption line intensities(converted to the reference temperature of 296 K)and the self-broadening coefficients and the corresponding data of the HITRAN2016 database are 0.78%and 3.8%,respectively.Consequently,the feasibility of the dual-optical path simultaneous measurement method and the reliability of the measurement device are demonstrated by the results.