Capillary Absorption Spectrometer for In-Situ, Underwater Gas Analysiss

We will produce a prototype Capillary Absorption Spectrometer (CAS) capable of measuring dissolved methane in water. The concept utilizes mid-infrared laser absorption spectroscopy within a hollow fiber optic capillary that both confines a gas sample and acts as an optical waveguide. A tunable laser beam propagates through the hollow fiber to a detector with near unity overlap between the beam and the analyte. The CAS can perform fast (~ 1s) and precise (isotope ratio ~ 1 0/00) measurements within the ultra-small sample volume (V ~ 1 mL) of the hollow fiber, and the concept is amenable to requirements for size, weight, and power necessary for in-situ analysis at depth. In this Phase II project, the proven concept will be developed into a field capable prototype for methane concentration and methane isotope analysis. The system will employee degassing of discrete water sample instead of a membrane, which is possible due to the ultra-small sample volume of the CAS. The concept is versatile and general and can also be applied to a wide range of other molecular species, including higher-C hydrocarbons, CO2, SO2, NOx, and a wide range of VOCs.