scholarly journals Modulation Index Adjustment for Recovery of Pure Wavelength Modulation Spectroscopy Second Harmonic Signal Waveforms

Sensors ◽  
2017 ◽  
Vol 17 (12) ◽  
pp. 163 ◽  
Author(s):  
Wei Wei ◽  
Jun Chang ◽  
Qiang Wang ◽  
Zengguang Qin
Keyword(s):  
Second Harmonic ◽  
Harmonic Signal ◽  
Wavelength Modulation Spectroscopy ◽  
Modulation Index ◽  
Wavelength Modulation ◽  
Modulation Spectroscopy ◽  
Second Harmonic Signal

scholarly journals A new line-shape asymmetry model for wavelength modulation spectroscopy in gaseous flows

2018 ◽  
Vol 18 (4) ◽  
pp. 158-161 ◽  
Author(s):  
Václav Nevrlý ◽  
Vít Klečka ◽  
Michal Vašinek ◽  
Václav Válek ◽  
Jan Suchánek ◽  
...  
Keyword(s):  
Line Shape ◽  
Second Harmonic ◽  
Differential Evolution Algorithm ◽  
Wavelength Modulation Spectroscopy ◽  
Least Square ◽  
Wavelength Modulation ◽  
Modulation Spectroscopy ◽  
Shape Fitting ◽  
Fitting Procedure ◽  
Automated Line

Abstract This communication reports technical notes on the development and application of an automated line-shape fitting procedure for wavelength modulation spectroscopy (WMS). Near-infrared transitions of carbon dioxide (CO2) around 1573 nm were measured in vertical cold (nonreacting) flow of CO2 at atmospheric pressure using WMS with demodulation at second harmonic frequency. Semi-empirical model based on the set of so-called Gabor functions was developed and parameters of Lorentzian line-shape profile and its asymmetry resulting from simultaneous frequency and amplitude response of the current-modulated semiconductor laser were determined. Nonlinear least-square fitting procedure employing differential evolution algorithm was successfully utilized for performing this task. Line-shape fitting procedure enabling efficient signal de-noising and background subtraction of wavelength modulation spectra was implemented into an open-source code.

Pressure-Dependent Detection of Carbon Monoxide Employing Wavelength Modulation Spectroscopy Using a Herriott-Type Cell

2017 ◽  
Vol 71 (5) ◽  
pp. 809-816 ◽  
Author(s):  
Chuanliang Li ◽  
Yingfa Wu ◽  
Xuanbing Qiu ◽  
Jilin Wei ◽  
Lunhua Deng
Keyword(s):  
Carbon Monoxide ◽  
Detection Limit ◽  
Second Harmonic ◽  
Wavelength Modulation Spectroscopy ◽  
Wavelength Modulation ◽  
Modulation Spectroscopy ◽  
Dependent Relationship ◽  
Low Concentrations ◽  
Allan Variation ◽  
Lock In

Wavelength modulation spectroscopy (WMS) combined with a multipass absorption cell has been used to measure a weak absorption line of carbon monoxide (CO) at 1.578 µm. A 0.95m Herriott-type cell provides an effective absorption path length of 55.1 m. The WMS signals from the first and second harmonic output of a lock-in amplifier (WMS-1 f and 2 f, respectively) agree with the Beer–Lambert law, especially at low concentrations. After boxcar averaging, the minimum detection limit achieved is 4.3 ppm for a measurement time of 0.125 s. The corresponding normalized detection limit is 84 ppm m Hz–1/2. If the integrated time is increased to 88 s, the minimum detectable limit of CO can reach to 0.29 ppm based on an Allan variation analysis. The pressure-dependent relationship is validated after accounting for the pressure factor in data processing. Finally, a linear correlation between the WMS-2 f amplitudes and gas concentrations is obtained at concentration ratios less than 15.5%, and the accuracy is better than 92% at total pressure less than 62.7 Torr.

Sign in / Sign up

Export Citation Format

Share Document