Dual diode-laser fiber-optic diagnostic for water-vapor measurements.

We present a novel diode-laser diagnostic for water-vapor measurements based on absorption spectroscopy. Two InGaAsP diode lasers were used to record H(2)O absorption line shapes near 1395 nm at a 3-kHz repetition rate along a single path through a water-vapor flow field generated in a shock tube. The use of two lasers permits simultaneous line-shape measurements in different spectral regions and facilitates the selection of appropriate line pairs for thermometry. The wavelength tuning rate was determined by use of a fiber-optic device known as a ring interferometer. Flow-field conditions (1320 K, 0.3 atm) inferred from measured line shapes compared favorably with calculated values.