A novel instrument that employs a high-finesse optical cavity as an absorption cell has been developed for sensitive measurements of gas mixing ratios using near-infrared diode lasers and absorption spectroscopy techniques. The instrument employs an off-axis trajectory of the laser beam through the cell to yield an effective optical path length of several kilometers without significant unwanted effects due to cavity resonances. As a result, a minimum detectable absorption of ~1.4x10^-5 over an effective optical path of 4,200 meters was obtained in a 1.1-Hz detection bandwidth to yield a detection sensitivity of ~3.1x10^-11 cm^-1 Hz^-1/2. The instrument has been applied for measurements of CO, CH₄, C₂H₂, and NH₃ in the 1530-1650 nm range, and stable isotopes of CO₂ (¹³CO₂, ¹²CO₂, ¹²C¹⁶O¹⁸O) near 2052 nm.

Date Published: 23 September 2002
PDF: 10 pages
Proc. SPIE 4817, Diode Lasers and Applications in Atmospheric Sensing, (23 September 2002); doi: 10.1117/12.451461

Published in SPIE Proceedings Vol. 4817:
Diode Lasers and Applications in Atmospheric Sensing
Alan Fried, Editor(s)