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 2.33μm (4300cm -1 ) at room temperature. The concentrations were found to be about 3 ppm and 75ppm, 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. © 2006 Optical Society of America.