Simultaneous water vapor concentration and temperature measurements using 1.31-mu m diode lasers

This paper reports the development of a compact, inexpensive sensor for simultaneous water vapor concentration and temperature measurements suitable for aeropropulsion exhaust applications. High sensitivity is achieved with an electronically balanced dual detector strategy that circumvents requirements for custom-fabricated lasers operating at specific wavelengths or high-frequency modulation techniques. Using widely available, broadly tunable InGaAsP diode lasers near 1.31 mu m, simultaneous measurements are demonstrated in a fiber-coupled, wavelength multiplexed configuration with a limiting density sensitivity of 10(15) cm(-3) in a 50-cm path and an rms standard deviation of 42 K over a range from 300 to 1300 K. Initial results suggest the possibility of extending this temperature range to 1900 K and above using other line pairs.