研究目的
To measure the linestrengths, self-broadening and narrowing coefficients for 8 absorption transitions of CO2 near 1.43 μm using the wavelength modulation direct absorption spectroscopy (WM-DAS) at 300-1000 K and 5-20 kPa.
研究成果
The linestrengths and the parameters of various lineshape models were measured for 8 spectral lines of CO2 near 1432 nm at 300-1000 K. The WM-DAS method was used to recover the absorbance profile and retrieve the self-broadening and -narrowing coefficients and their temperature dependent exponents for the VP, GP, RP and qSDVP. The SNR is increased to 1500 around the peak absorbance of 5% and remains at 550 when the peak absorbance is around 1% by using the WM-DAS method.
研究不足
The disturbance by the H2O is enhancing at temperatures higher than 700 K due to the significantly increased H2O linestrength and the much weaker CO2 absorbance. The limited range of γC/ γD at high temperatures, as well as the disturbance by the H2O desorption off the cell walls both likely increase the errors.
1：Experimental Design and Method Selection:
The WM-DAS method was used to recover the absorbance profiles for the 8 spectral lines of CO2 around 1432nm at temperatures from 300 K to 1000 K. The Voigt, Rautian, Galatry and quadratic speed-dependent Voigt profiles were used to recover the absorbance and retrieve the best-fit spectroscopic parameters and their temperature dependence.
2：Sample Selection and Data Sources:
Pure CO2 gas was used to measure the self-parameters. The absorbance profiles were least-squares fit with VP, GP, RP and qSDVP to determine the spectroscopic parameters.
3：List of Experimental Equipment and Materials:
A continuous-wavelength distributed-feedback tunable diode laser with a wavelength near 1432 nm and a linewidth of 2 MHz was used. The laser was driven by a commercial diode laser controller (Thorlabs ITC4001). The laser wavelength was modulated by scanning both the temperature and current with sinusoidal or triangle waves produced by a function generator (Keysight 33220A).
4：1). The laser wavelength was modulated by scanning both the temperature and current with sinusoidal or triangle waves produced by a function generator (Keysight 33220A).
Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: The laser beam was split into three parts using a 1×3 fiber splitter. The first part (30%) was collimated using a fiber collimator and propagated through the heated static cell. The second part (20%) was used as a reference light to eliminate the effect of ambient air. The last beam propagated through an etalon (Thorlabs SA210-12B) with a free spectral range (FSR) of 0.05 cm-1 to calibrate the laser frequency.
5：05 cm-1 to calibrate the laser frequency.
Data Analysis Methods:
5. Data Analysis Methods: The absorbance profile and baseline were recovered simultaneously using a Levenberg–Marquardt nonlinear fitting procedure.
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