We have developed a field-portable optical gas sensor for the ultra-sensitive detection of ethane. The system is based on an adaptation of a commercially available system, which uses a cryogenically cooled, lead-salt laser diode at 3.34 mum and a multi-pass astigmatic Herriott sample cell. We have adapted this system to a second derivative wavelength modulation scheme giving a lower detection limit of less than 100 parts per trillion for a one second measurement time. Our custom-designed software controls every aspect of the instrument operation from spectral scanning of the laser diode, to automatic calibration, optical alignment, spectral analysis and complete data logging.
15th National Quanturn Electronics and Photonics Conference, GLASGOW, SCOTLAND, SEP 03-06, 2001