Improvement of Concentration Inversion Model Based on Second Harmonic Valley Spacing in Wavelength Modulation Spectroscopy

Pan, Yun; Li, Yang; C, Yan; Yuan, Jing; Ren, Yongmao

doi:10.1109/access.2020.3045587

Cited by 5 publications

(2 citation statements)

References 31 publications

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“…The modulation of laser emission frequency is achieved by changing the injection current, which actually modulates the laser frequency and light intensity simultaneously, and this produce a gas independent background signal called residual amplitude modulation (RAM). And there is a phase delay between the frequency modulation and the intensity modulation [17][18][19]. The intensity of the light emitted by the diode laser can be expressed as:…”

Section: Theory Of Tdlasmentioning

confidence: 99%

TDLAS second harmonic demodulation based on Hilbert transform

Chen

Kang

et al. 2022

PLoS ONE

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A demodulation method for tunable diode laser absorption spectroscopy (TDLAS) second harmonic based on the Hilbert transform is proposed in this paper. The second harmonic of the TDLAS signal can be easily obtained without a reference signal. The TDLAS signal is firstly processed by band-pass filtering, then the envelope of the processed signal is obtained with Hilbert transform. And finally, the second harmonic is extracted from the 1f component of the envelope. The validity of the proposed method is confirmed by simulation and verified by experiment, and the result shows that the error is acceptable under the cases of weak absorbance, which indicates that the proposed method is applicable to practical trace gas detection.

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Section: Theory Of Tdlasmentioning

confidence: 99%

TDLAS second harmonic demodulation based on Hilbert transform

Chen

Kang

et al. 2022

PLoS ONE

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“…Tunable diode laser absorption spectroscopy (TDLAS) is widely used for trace gas detection because of its characteristics, such as non-contact measurement, high sensitivity, and fast response time [ 1 , 2 , 3 , 4 ]. As two main techniques of TDLAS, the variation of line shape has an important effect on both direct absorption spectroscopy (DAS) and wavelength modulation spectroscopy (WMS) [ 5 , 6 , 7 , 8 , 9 ]. Normally, the shapes can be described as Gaussian profiles, Lorentzian profiles and the convolution of these two profiles.…”

Section: Introductionmentioning

confidence: 99%

A Width Measurement Method of Line Shape Based on Second Harmonic Peak and Modulation Amplitude

Lin

Chang

Sun

et al. 2023

Sensors

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The line width of different line shapes is a very important parameter in absorption spectroscopy sensing techniques. Based on the high sensitivity and low noise properties of wavelength modulation spectroscopy, we report a novel line width measurement method. After theoretically proving the relationship between line width, modulation amplitude and the amplitude of the second harmonic at the center frequency, the absorption lines of CH4 near 6046.96 cm−1 and CO2 4989.97 cm−1 were chosen for simulation, and the relative errors of the line width between our method and theoretical data were kept at about 1%. A distributed feedback laser diode operating near 1653 nm with three different concentrations of CH4 was used for experimental validation, and the results were consistent with the numerical simulation. Additionally, since only the peaks of second harmonic need to be measured, the advantages of wavelength modulation can be utilized while reducing the difficulty of data acquisition.

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