Near-infrared absorption detection in picolitre liquid volumes using amplified fibre loop ring-down detection

摘要

Cavity ring-down spectroscopy is performed using a single-mode fibre loop as an optical cavity. The loop contains absorption cells for either liquids or gases, as well as an erbium-doped fibre amplifier. The fibre amplifier is gain-clamped using a second fibre-loop. Ring-down times can be tuned to permit several hundred roundtrips by adjusting the loss ratio between the two nested loops using a variable optical attenuator. Ring-down measurements were performed either in the time domain or using phase shift measurements. Acetylene gas was detected through a ro-vibrational absorption line of the V_1-V_3 combination band at 1532 nm at a limit of detection of 50 ppm. Liquid 1-octyne and 1-dodecyne were detected in a 1 pL volume at detection limits of ～20% dilution in dodecane through their C-H stretch vibrational overtone transition.