DUAL DIODE-LASER FIBEROPTIC 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 H2O absorption line shapes near 1395 nm at a 3-kHz repetitio n 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 select ion of appropriate line pairs for thermometry. The wavelength tuning r ate was determined by use of a fiber-optic device known as a ring inte rferometer. Flow-field conditions (1320 K, 0.3 atm) inferred from meas ured line shapes compared favorably with calculated values.