DETECTION OF METHANE IN AIR USING DIODE-LASER-PUMPED DIFFERENCE-FREQUENCY-GENERATION NEAR 3.2 MU-M

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 mu m 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 mu W probe power. Methane has also been detected using a 3.2 mu m confocal build-up cavity in conjunction with an intracavity absorption cell. The best methane detection limit observed was 12 ppb m (Hz.)(-1/2).