Looking into the volcano with a Mid-IR DFB diode laser and Cavity Enhanced Absorption Spectroscopy

Abstract

We report on the first application of extended-wavelength DFB diode lasers to Cavity-Enhanced Absorption Spectroscopy in-situ trace measurements on geothermal gases. The emission from the most active fumarole at the Solfatara volcano near Naples (Italy) was probed for the presence of CO and CH(4). After passing through a gas dryer and cooler, the volcanic gas flow (98% CO(2)) was analysed in real time for the concentration of these species, whose relatively strong absorption lines could be monitored simultaneously by a single Distributed Feed-Back (DFB) GaSb-based diode laser emitting around 2.33 mum (4300 cm(-1)) at room temperature. The concentrations were found to be about 3 ppm and 75 ppm, respectively, while actual detection limits for these molecules are around 1 ppb. We discuss the possibility of detecting other species of interest for volcanic emission monitoring.

Long optical cavities for open-path monitoring of atmospheric trace gases and aerosol extinction

“…A variety of atmospheric trace constituents have been successfully detected in the field using laser-based cavity ringdown (CRD) spectroscopy [4][5][6][7]. Most CRD field instruments extract atmospheric samples [8][9][10][11][12][13], and only a few have employed an open-path configuration [14,15]. For instruments using gas extraction, inlet losses of the target species must be established in independent measurements [16].…”

Comparison of optical-feedback cavity-enhanced absorption spectroscopy and gas chromatography for ground-based and airborne measurements of atmospheric CO concentration

“…It has been demonstrated that this technique is compatible with different kinds of semiconductor lasers. Indeed, while OF-CEAS was previously developed in the NIR with distributed feedback telecom diode lasers (Morville et al, 2005;Kassi et al, 2006), it has been demonstrated that it is compatible with extended cavity diode lasers that operate in the visible (Courtillot et al, 2006;Horstjann et al, 2014) and with quantum cascade lasers (Maisons et al, 2010;Gorrotxategi-Carbajo et al, 2013) as well as more recently with interband cascade lasers (Manfred et al, 2015;Richard et al, 2016) in the mid-infrared region.…”

“…The laser spectroscopy technique going under the name of OF-CEAS was introduced by Morville et al (2005) and has been further detailed in different publications (Kerstel et al, 2006;Kassi et al, 2006;Ventrillard-Courtillot et al, 2009;Faïn et al, 2014;Maignan et al, 2014;Morville et al, 2014).…”

“…In particular the OF-CEAS instrument used in this study has been described in Kassi et al (2006). It provides in situ CO measurements with a detection limit of 0.2 ppb in 20 s (Faïn et al, 2014) with no calibration and running unattended.…”

“…The design of the spectrometer is robust and compact: the optical assembly and all the electronics, for realtime control and data acquisition, fit inside a 19 in chassis where the V-shaped cavity is placed in the diagonal as shown in Fig. 1 of Kassi et al (2006). The device is temperature stabilized around 22 • C using heating adhesive ribbons.…”