DETECTION OF H2O AND CO2 WITH DISTRIBUTED-FEEDBACK DIODE-LASERS - MEASUREMENT OF BROADENING COEFFICIENTS AND ASSESSMENT OF THE ACCURACY LEVELS FOR VOLCANIC MONITORING

We reproduced the chemical-physical conditions of fumarolic emission a t Phlaegrean Fields, Pozzuoli, Italy, and we measured the CO2 and H2O concentrations using an absorption spectrometer based on two distribut ed feedback laser diodes at wavelengths of 1.578 and 1.393 mu m. We di scuss the accuracy levels of the different methods used. Furthermore, we measured the broadening coefficients for H2O (self-broadening, 28.2 +/- 0.6 MHz/Torr; CO2 broadening, 6.0 +/- 0.4 MHz/Torr) and CO2 (self -broadening, 3.2 +/- 0.1 MHz/Torr; H2O broadening, 4.0 +/- 0.1 MHz/Tor r). Using the present data, we evaluated a minimum detectable variatio n of 9% for H2O and 1% for CO2. (C) 1997 Optical Society of America.