Abstract
Following the theoretical work in Part I, in this experimental study, the robustness, temporal resolution, and the narrow scan performance of the proposed wavelength modulation-direct absorption spectroscopy (WM-DAS) method are experimentally validated in a high-temperature tube furnace. The electromagnetic and other random-frequency noises can be effectively eliminated by extracting the characteristic spectra of the light intensity. The performance of WM-DAS with modulation frequencies from 0.1 to 100 kHz and scan indexes from 3.3 to 11.1 are also investigated at atmospheric pressure. The proposed method produces accurate line profile and high SNR over 500 consistently even with a weak absorption. As for real applications, the spectral line parameters of CO at 4300.6999 cm−1 including the collisional broadening, Dicke narrowing, and their dependence on temperature are measured. Furthermore, the high-speed measurement (1 ms) of the temperature and CO concentration of a McKenna flat flame are demonstrated.
Highlights
In addition to the noise robustness, the temporal resolution and compatibility with a narrow scan of tunable diode laser absorption spectroscopy (TDLAS) are in higher demand for applications in transient and high-pressure conditions
Considering the importance of the noise rejection ability, signal-to-noise ratio (SNR) and the temporal resolution of TDLAS, in Part I [33] we proposed a wavelength modulation-direct absorption spectroscopy (WM-DAS) method based on the FFT analysis of a sine wave scan
In this two-part paper, we proposed a calibration-free WM-DAS method based on the FFT analysis and the simultaneous fitting algorithm
Summary
Tunable diode laser absorption spectroscopy (TDLAS) has become one of the most important approaches in gas monitoring and has succeeded in various fields, including spectral line parameter measurements [1,2,3,4], and the diagnostic of combustion [5,6,7,8,9] and plasma [10,11,12]. In addition to the noise robustness, the temporal resolution and compatibility with a narrow scan of TDLAS are in higher demand for applications in transient and high-pressure conditions. Considering the importance of the noise rejection ability, SNR and the temporal resolution of TDLAS, in Part I [33] we proposed a WM-DAS method based on the FFT analysis of a sine wave scan This method possesses the advantages of both DAS and WMS, allowing the direct measurement on the absorbance and further gas properties. The characteristic of the proposed WM-DAS including the robustness, temporal resolution, and the narrow scan performance is experimentally validated with the CO transition in a high-temperature tube furnace. The high-speed measurement (1 ms) of the temperature and CO concentration of a McKenna flat flame are further investigated with the proposed method
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