Methane detection with a narrow-band source at 3.4 µm based on a Nd:YAG pump laser and a combination of stimulated...

We report the characterization of a 10-Hz pulsed, narrow-band source that is coincident with a fundamental ν(3) rovibrational absorption of methane at 3.43 µm. To generate this midinfrared wavelength, an injection-seeded 1.06-µm Nd:YAG laser is difference frequency mixed with first Stokes light generated in a high-pressure methane cell (1.06 ? 1.54 µm) to result in light at a wavelength of 3.43 µm, that is, the ν(1) Raman active frequency of methane (~2916.2 cm(-1)). With a modest-energy Nd:YAG laser (200 mJ), a few millijoules of this midinfrared energy can be generated with a pulse width of ~7 ns (FWHM). The methane ν(1) frequency can be pressure tuned over 8-32 atm (corresponding to ~13 GHz) and scanned across part of the ν(3)P(10) rovibrational level of methane, resulting in a peak measured methane absorption coefficient of 4.2 cm(-1) atm(-1).