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Detection of methane in air using diode-laser pumped difference-frequency generation near 3.2 μm |
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| Authors: | K P Petrov S Waltman U Simon R F Curl F K Tittel E J Dlugokencky L Hollberg |
| Institution: | (1) Departments of Electrical and Computer Engineering, and Chemistry, Rice University, 77251-1892 Houston, TX, USA;(2) Time and Frequency Division, National Institute of Standards and Technology, 325 Broadway, 80303 Boulder, CO, USA;(3) National Oceanic and Atmospheric Administration, 325 Broadway, 80303 Boulder, CO, USA |
| Abstract: | Spectroscopic detection of the methane in natural air using an 800 nm diode laser and a diode-pumped 1064 nm Nd:YAG laser to produce tunable light near 3.2 µm is reported. The lasers were pump sources for ring-cavity-enhanced tunable difference-frequency mixing in AgGaS2. IR frequency tuning between 3076 and 3183 cm–1 was performed by crystal rotation and tuning of the extended-cavity diode laser. Feedback stabilization of the IR power reduced intensity noise below the detector noise level. Direct absorption and wavelength-modulation (2f) spectroscopy of the methane in natural air at 10.7 kPa (80 torr) were performed in a 1 m single-pass cell with 1 µW probe power. Methane has also been detected using a 3.2 µm confocal build-up cavity in conjunction with an intracavity absorption cell. The best methane detection limit observed was 12 ppb m (Hz.)–1/2. |
| Keywords: | 07 65 33 00 42 60 42 65 42 80 |
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