title: Off-axis cavity enhanced spectroscopy based on a pulsed quantum cascade laser for sensitive detection of ammonia and ethylene.
abstract: A pulsed, distributed feedback (DFB) quantum cascade (QC) laser centered at 970 cm(-1) was used in combination with an off-axis cavity enhanced absorption (CEA) spectroscopic technique for the detection of ammonia and ethylene. Here, the laser is coupled into a high-finesse cavity with an optical path length of ∼76 m. The cavity is installed into a 53 cm long sample cell with a volume of 0.12 L. The laser is excited with short current pulses (5-10 ns), and the pulse amplitude is modulated with an external current ramp, resulting in a ∼0.3 cm(-1) frequency scan. A demodulation approach followed by numerical filtering was utilized to improve the signal-to-noise ratio. We demonstrated detection limits of ~15 ppb and ∼20 ppb for ammonia and ethylene, respectively, with less than 5 s averaging time.
authors.affiliation: Electrical and Computer Engineering Department, University of Alberta, Edmonton, Alberta, Canada T6G 2V4. jmanne@ualberta.ca
authors.forename: Jagadeeshwari
authors.initials: J
authors.lastname: Manne
authors.forename: Alan
authors.initials: A
authors.lastname: Lim
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Jäger
authors.forename: John
authors.initials: J
authors.lastname: Tulip