Simultaneous detection of multiple gas concentrations with multi-frequency wavelength modulation spectroscopy

¹ Anhui Provincial Key Laboratory of Photonic Devices and Materials, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences - Hefei 230031, China
² Department of Environmental Science and Optoelectronic Technology, University of Science and Technology of China Hefei 230026, China

Received: 18 August 2013
Accepted: 6 November 2013

Abstract

A multi-frequency wavelength modulation spectroscopy (MF-WMS) method for simultaneous monitoring multiple gas concentrations is reported. Two wavelength lasers are selected and scanned at the same sawtooth waveform and different sinusoidal modulation frequencies. Also, a 2-in-1 coupler is used to collect laser beams into a single-mode fiber to deliver the combined beams to a same optical path. The outputs from the same InGaAs detector are demodulated by a set of homemade digital lock-in-amplifiers to obtain the harmonic signals, accordingly. The new multi-pass cell was designed and filled with five different concentrations of H₂S and HCl gas mixtures for further analysis. In addition, an digital filter and a data running means method were used to further improve the stability. The results show that the signal-to-noise ratio and the anti-interference ability had been improved and the MF-WMS system gives a good performance in terms of reproducibility and feasibility.