Multiplexed continuous-wave diode-laser cavity ringdown measurements of multiple species

Rapid cavity ringdown measurements of multiple broadband absorbing species (methanol and isopropanol) in gas mixtures have been recorded with two multiplexed continuous-wave distributed-feedback diode lasers operating near 1.4 mu m. A measurement sensitivity of 2.4 x 10(-9) cm(-1) for a 4.3-s averaging time was achieved in a 39.5-cm-long static cell with 99.94% reflectivity mirrors. This corresponds to a water-vapor detection limit of less than 2 ppb (parts in 10(9)) for the strong H2O lines near 1.4 mu m. The shot-to-shot noise of the decay time constant tau was approximately 0.3-0.7%, and ringdown acquisition rates as great as 900 Hz were achieved. (C) 2000 Optical Society of America.