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Updated: Aug 7, 2026

Characterizing Far-infrared Laser Emissions and the Measurement of Their Frequencies
Published on: December 18, 2015
Stable isotopic analysis of atmospheric methane by infrared spectroscopy by use of diode laser difference-frequency
Michael E Trudeau1, Pin Chen, Guilherme de Andrade Garcia
1Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Hilo, Hawaii 96720, USA. michael.trudeau@noaa.gov
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 15 microW of tunable difference-frequency radiation from two near-infrared diode lasers that probe the nu3 rotational-vibrational band of methane at 3.4 microm. 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 12 per thousand is demonstrated for both delta13C and deltaD.
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