Abstract
An infrared absorption spectrometer has been constructed to measure the stable isotopic composition of atmospheric methane samples. The spectrometer employs periodically poled lithium niobate to generate of tunable difference-frequency radiation from two near-infrared diode lasers that probe the ν3 rotational–vibrational band of methane at . To enhance the signal, methane is extracted from 25 l of air by use of a cryogenic chromatographic column and is expanded into the multipass cell for analysis. A measurement precision of is demonstrated for both and δD.
© 2006 Optical Society of America
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