Widely Tunable Infrared Laser Spectrometer for Measurement of Isotopic Ratios of Carbon Cycle Gases

60520 The atmospheric abundance of carbon dioxide and methane have increased dramatically during the industrial era. Since these increases can perturb the global climate, it is vital to understand and quantify the factors controlling them. This is difficult because CO2 and CH4 have a wide range of complex surface sources and sinks, which have both natural and anthropogenic components. However, since the sources (and sinks) produce (and remove) the isotopic forms of these species at varying rates, atmospheric measurements of the isotopic composition of the carbon cycle gases provide a powerful tool for quantifying their sources and sinks. Most measurements are currently performed with large, expensive mass spectrometers using complex and time consuming analytical methods. This project will develop a compact, deployable, easy to use isotopic monitor using Tunable Infrared Laser Differential Absorption Spectroscopy (TILDAS). During Phase I, a novel optical design was demonstrated for isotope measurements, and isotopic ratios with precisions as small as 0.2% were obtained with a very simple instrument. The optical design compensates for the large difference in concentration between major and minor isotopes by measuring them with vastly differing path lengths within the same multipass cell. An infrared difference frequency source was also designed, and it was shown that using a built-up cavity to produce the difference frequency radiation would increase output power by a factor of 40. Phase II will design and build a prototype isotopic monitor for CO2 and CH4. The infrared source will be produced using a build-up cavity to produce sufficient power and will be widely tunable in frequency. The source will be integrated into a prototype isotopic monitor which employs the novel optical and signal processing methods. Finally, standard isotopic gas samples will be tested to validate the instrument¿s performance. Commercial Applications and Other Benefits as described by the awardee: The instrument should compete with existing mass spectrometric isotope instruments which are expensive, large, and relatively slow. In addition, the infrared source should have application to the measurement of many other gas species and also should have wide application in atmospheric monitoring, industrial process control, and medical research.