We report on the development and performance of a gas sensor based on a quantum cascade laser operating at a wavelength of ~10 μm to measure ethylene (C<sub>2</sub>H<sub>4</sub>) concentrations by use of a rotational component of the fundamental ν<sub>7</sub> band. The laser is thermoelectrically cooled and operates in a pulsed mode. The influence of pulse-to-pulse fluctuations is minimized by use of a reference beam and a single detector with time discriminating electronics. Gas absorption is recorded in a 100-m optical path-length astigmatic Herriott cell. With a 10-kHz pulse repetition rate and an 80-s total acquisition time, a noise equivalent sensitivity of 30 parts per billion has been demonstrated. The sensor has been applied to monitor C<sub>2</sub>H<sub>4</sub> in vehicle exhaust as well as in air collected in a high-traffic urban tunnel.
© 2004 Optical Society of America
(140.5960) Lasers and laser optics : Semiconductor lasers
(280.1120) Remote sensing and sensors : Air pollution monitoring
(280.3420) Remote sensing and sensors : Laser sensors
(300.6320) Spectroscopy : Spectroscopy, high-resolution
Damien Weidmann, Anatoliy A. Kosterev, Chad Roller, Robert F. Curl, Matthew P. Fraser, and Frank K. Tittel, "Monitoring of Ethylene by a Pulsed Quantum Cascade Laser," Appl. Opt. 43, 3329-3334 (2004)