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 µm. A measurement sensitivity of 2.4 × 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 109) for the strong H2O lines near 1.4 µm. The shot-to-shot noise of the decay time constant τ was approximately 0.3–0.7%, and ringdown acquisition rates as great as 900 Hz were achieved.
© 2000 Optical Society of America
Original Manuscript: August 12, 1999
Revised Manuscript: January 6, 2000
Published: April 20, 2000
Gerhard Totschnig, Douglas S. Baer, Jian Wang, Franz Winter, Hermann Hofbauer, and Ronald K. Hanson, "Multiplexed continuous-wave diode-laser cavity ringdown measurements of multiple species," Appl. Opt. 39, 2009-2016 (2000)