Development of an automated diode-laser-based multicomponent gas sensor

The implementation and application of a portable fiber-coupled trace-gas sensor for the detection of several trace gases, including CO2, CH4, and H2CO, are reported. This particular sensor is based on a cw fiber-amplified near-infrared (distributed Bragg reflector) diode laser and an external cavity diode laser that are frequency converted in a periodically poled lithium niobate crystal to the mid-IR spectroscopic fingerprint region (3.3-4.4 mu m). A continuous absorption spectrum of CH4 and H2CO from 3.37 to 3.10 mu m with a spectral resolution of 40 MHz (similar to 0.0013 cm(-1)) demonstrated the spectral performance that can be achieved by means of automated wavelength tuning and phase matching with stepper motor control. Autonomous long-term detection of ambient CO2 and CH4 over a 3- and 7-day period was also demonstrated. (C) 2000 Optical Society of America OCIS codes: 190.2620. 300.6340.