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

Area of Science:

• Geochemistry
• Environmental Science
• Spectroscopy

Background:

• Volcanic emissions contain trace gases crucial for monitoring geological activity.
• Cavity-Enhanced Absorption Spectroscopy (CEAS) offers high sensitivity for gas analysis.
• Extended-wavelength diode lasers enable probing of specific absorption lines.

Purpose of the Study:

• To apply extended-wavelength Distributed Feed-Back (DFB) diode lasers to in-situ trace measurements of geothermal gases.
• To monitor carbon monoxide (CO) and methane (CH4) concentrations in volcanic emissions in real-time.
• To assess the potential for detecting other volcanic gas species.

Main Methods:

• Utilized a GaSb-based DFB diode laser emitting around 2.33 µm (4300 cm⁻¹).
• Employed Cavity-Enhanced Absorption Spectroscopy (CEAS) for trace gas analysis.
• Analyzed volcanic gas from the Solfatara volcano fumarole after drying and cooling.

Main Results:

• Simultaneously monitored CO and CH4 absorption lines using a single DFB laser.
• Measured CO concentration at approximately 3 ppm and CH4 at approximately 75 ppm.
• Achieved detection limits around 1 ppb, highlighting the system's high sensitivity.

Conclusions:

• Extended-wavelength DFB diode lasers are effective for in-situ trace gas monitoring in volcanic environments.
• The developed method allows for real-time analysis of key volcanic gas species.
• Further applications for monitoring other geochemically relevant gases are feasible.