Multiplexed diode-laser sensor system for simultaneous H_2O, O_2, and temperature measurements

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A multiplexed diode-laser sensor system has been developed to monitor multiple species and measure multiple flowfield parameters along a single path with optical fibers and scanned-laser absorption techniques. Two InGaAsP lasers were tuned over H2O transitions near 1347 and 1392 nm, and an AlGaAs laser was tuned over an O2 transition near 760.65 nm to record fully resolved absorption concurrently at a repetition rate of 2 kHz. The system was applied to measure H2O, O2, and temperature simultaneously in a heated static cell and in room air. Wavelength modulation with second-harmonic detection, applied simultaneously in the O2 measurements, yielded a minimum detectable absorbance of 1.6 × 10−6/Hz1/2 and an O2 detectivity of 6.3 parts in 106 in a 1-m path length.