Resonant Cavity Light Emitting Diodes for Infrared Gas Spectroscopy

The predictive skill of reactive transport models of hydrobiogeochemical processes currently being used to simulate the coupled interactions of complex subsurface systems (soils, rhizosphere, sediments, aquifers, the vadose zone and groundwaters) is limited by the accuracy of the model parameters that represent subsurface system structure and intrinsic properties. Robust field testing to validate these increasingly-complex models requires accurate, highly-selective, sensitive, and rugged in situ devices for low-cost field deployment in remote locations in order to enhance our ability to monitor processes at finer levels of resolution and over broader areas. The key elements to be measured include carbon, nitrogen, sulfur and phosphorus. Isotopes such as 2H, 18O and molecular species including CH4, CO2, and nitrogen compounds such as N2O are also important markers of relevance to hydrologic and biogeochemical systems.Statement of How this Problem or Situation is Being Addressed This program is aimed at developing a new light source for in situ, fieldable technology improving gas detection sensitivity while also reducing system cost and complexity. The key innovation of this program is use of a resonant-cavity (RC) infrared (IR) light-emitting diode (LED) to replace costly, complicated quantum cascade lasers (QCL) typically used in these applications. Development of this technology will provide a manufacturable solution for monitoring N2O and other gases with similar IR absorption characteristics. The resulting gas monitoring sensor will be small and low cost so that multiple sensors can be placed throughout the terrain to be monitored. The individual gas sensors will be based on a novel RC-LED IR source coupled directly with a proven IR detector, where both LED and detector can be tuned by design to source and detect specific wavelengths. The information collected from the sensor network can then be sent to a base station for concentration analysis, data recording and additional processing. What is being done in Phase II In the Phase II program Amethyst Research will develop a resonant cavity infrared LED optimized to source wavelengths in and around 4.4715 m to detect the 14N14N16O isotope of N2O. The Phase II program will also pair the source with an IR detector centered at the same wavelength and will develop a breadboard test system for the entire RC-LED-based N2O sensing system. Commercial Application and Other Benefits: Amethyst is developing a high-sensitivity, paired infrared resonant cavity source and detector for use in monitoring subsurface gaseous species. This technology can be translated to other applications including monitoring of greenhouse gases, IR imaging and IR tomography.