The monitoring of sea water content of methane and green house gas (CO2) is of great importance for correct assessment of global processes on the Earth, since due to its abundance the sea water is a major factor affecting climate. In particular, the methane content in sea water reflects general trends of methanogenesis, but it also is indicative of the local disruptive events, such as oil spills, volcanic eruptions, and plumes. Therefore, accurate measurements of the concentration of such gases can provide valuable information for monitoring these dynamical processes, even predictions of their occurrences, and quantify the amount of oil spilled
The PI requests MRI RAPID funding to develop a novel, sensitive, methane gas sensor in the near IR wavelength region. It will have the high sensitivity and a broad dynamic range required to address a large variation of the methane concentration at different depths in seawater. It will be designed to be rugged and portable. Such a sensor can be also used to detect minute amounts of methane leaking to the atmosphere, which is important for preventing possible unwanted accumulation of methane, which can result in an explosion.
Broader Impacts
This research has the potential to develop of a new instrument for gas concentration measurements with a wide range of possible applications. It includes training of participating postdoctoral associate and a graduate student, obtaining new data important for aquatic life in the gulf region and dissemination of the results through publications and participation in conferences.
The main goal of the project was to develop techniques and instrumentation for spectrally resolved, ultrafast and simultaneous measurements of methane and carbon dioxide at low concentrations with femtosecond spectrally-broadened fiber lasers. Highly nonlinear optical effects were employed to generate broadband radiation allowing for simultaneous detection of two or more gas species. We measured trace gases from ambient air and extracted from sea water, using porous membrane filters. A new instrument for gas concentration measurements with a wide range of possible applications based on frequency comb spectroscopy was developed. To enhance the sensitivity of broadband absorption spectroscopy in the near infrared we used a novel multipass cell design based on high reflecting mirrors in a confocal arrangement, which allowed to achieve long interaction lengths. To realize sensitive spectroscopy without moving parts we used two femtosecond frequency comb lasers with slightly different repetition rates to perform real-time dual frequency comb spectroscopy in the near infrared. By measuring an interferogram as pulses of the two combs passed each other and calculating the spectrum of this signal the absorption spectrum in the fingerprint spectral region was retrieved. A high-power mid-infrared frequency comb coherent source in the mid-infrared was produced through difference frequency generation in a periodically poled crystal. We employed also frequency comb vernier spectroscopy that utilizes the interaction between a frequency comb and a scanning high-finesse cavity for detecting trace amounts of gases. The project provided excellent opportunities for training of participating postdoctoral associate and several graduate students. Results of the project were disseminated through publications and presentations at conferences.
