DESIGN OF AN OPEN-PATH NEAR-INFRARED DIODE-LASER SENSOR - APPLICATIONTO OXYGEN, WATER, AND CARBON-DIOXIDE VAPOR DETECTION

An open path diode laser sensor was constructed with near-infrared dio de lasers and two-tone frequency-modulation spectroscopy. The sensor i ncorporates novel features (such as digital signal-processing algorith ms, a computerized line-locking routine, and discontinuous wavelength scanning) that are important in a field instrument. The sensor was use d to monitor oxygen, water, and carbon dioxide in the near-infrared sp ectral range. For oxygen an absorbance detection sensitivity of 2 x 10 (-6) in a 10-Hz bandwidth was demonstrated with a GaAlAs laser at 760. 56 nm. The stability of the sensor was 0.1% over a period of 10 h when an absorbance of 6 x 10(-3) was monitored.