Indexed by:期刊论文

Date of Publication:2019-04-29

Journal:OPTICS EXPRESS

Included Journals:SCIE、EI

Volume:27

Issue:9

Page Number:12137-12146

ISSN No.:1094-4087

Key Words:Absorption spectroscopy; Carbon dioxide; Harmonic analysis; Molecular spectroscopy, Decomposition methods; Detection sensitivity; High modulation frequency; High-pressure environment; Linearly proportional; Modulation amplitudes; Tunable diode laser absorption spectroscopy; Wavelength modulation spectroscopy, Frequency modulation

Abstract:Wavelength modulation spectroscopy (WMS), widely employed in tunable diode laser absorption spectroscopy (TDLAS), has been accomplished by employing the first harmonic phase angle (1f-PA) method that is immune to the laser intensity and the demodulation phase. The principle of the 1f-PA method has been demonstrated by the phasor decomposition method, which indicates that the 1f-PA is linearly proportional to the integral absorption in the approximation of weak absorption. Validation experiments have been performed to investigate the relationship between the 1f-PA and the modulation amplitude/frequency by measuring the absorption line of CO2 around 6362.5 cm(-1). The peak-to-peak value of the 1f-PA decreases with the increasing of the modulation amplitude, and is particularly apparent under small modulation amplitudes and high modulation frequencies. The 1f-PA shows good linearity with the increasing of the CO2 concentration. Comparing with the traditional first harmonic normalized second harmonic (2f/1f) method, higher detection sensitivities can be achieved at high modulation frequencies. The promising results imply that the 1f-PA method has a great potential in the applications of the WMS technique especially under high modulation frequencies or modulation-amplitude limited conditions, such as strong turbulence or high pressure environments. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement