Rapid and sensitive trace gas detection with continuous wave Optical Parametric Oscillator-based Wavelength Modulation Spectroscopy

Abstract

A fiber-amplified Distributed Bragg Reflector diode laser is used to pump a continuous wave, singly resonant Optical Parametric Oscillator (OPO). The output radiation covers the 3-4 μm with ability of rapid (100 THz/s) and broad mode-hop-free tuning (5 cm-1). Wavelength Modulation Spectroscopy is combined with the OPO to take optimal advantage of the spectral scan speed. The sensitivity of the system was determined as 0.8 ppbv (parts-per-billion by volume) for ethane (C2H6) for the absorption peak at 2996.9 cm-1 recorded in 1.3 seconds, corresponding to a noise equivalent absorption sensitivity (NEAS) of 1.2×10 -9 cm-1/Hz1/2. A comparison between results using the 1st, 2nd and 4th harmonic derivative signal from wavelength modulation was performed. The broad continuous tunability was demonstrated by covering 35 cm-1 while recording absorption features of ethane, methane and water. © The Author(s) 2010. This article is published with open access at Springerlink.com.