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

• Published in: Optical fiber technology 2013-12, Vol.19 (6), p.822-827
• Main Authors: Andrews, Nicholas L.P., Litman, Jessica, Stroh, Daniel, Barnes, Jack A., Loock, Hans-Peter
• Format: Article
• Language: English
• Subjects: Absorption spectroscopy; Acetylene gas detection; Cavity ring-down; Fiber (fibre) loop; Liquid sensing; Picoliter (picolitre) volume
• ISSN: 1068-5200; 1095-9912
• DOI: 10.1016/j.yofte.2013.07.012

•Use amplified cavity ring-down setup with commercial equipment.•Gain-clamping of EDFA to enhance stability.•Near-infrared detection of weak overtones and combination bands.•Detection of acetylene gas to from 50ppm to 1000ppm.•Detection of liquid 1-alkynes in 1picolitre volume. 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 ν1–ν3 combination band at 1532nm at a limit of detection of 50ppm. Liquid 1-octyne and 1-dodecyne were detected in a 1pL volume at detection limits of ∼20% dilution in dodecane through their C–H stretch vibrational overtone transition.