Two-line atomic fluorescence flame thermometry using diode lasers

This paper reports on the first application of diode laser based LIF for pointwise temperature measurements in flames. The technique is based on two-line atomic fluorescence (TLAF) thermometry of indium atoms seeded at trace levels into the flame. Two novel extended cavity diode laser systems (ECDLs) were developed, providing tunable single-mode radiation around 410 and 451 nm, respectively, to excite the temperature sensitive 5P(1/2)-6S(1/2) and 5P(3/2)-6S(1/2) transitions of indium. The wide tuning range of the ECDLs allowed scans over the entire pressure broadened hyperfine structure of both transitions to be performed with signal-to-noise ratios exceeding 50 on single wavelength sweeps (at 20 Hz). We present a modified TLAF detection scheme that requires only a single detector and obviates the need for detection system calibration. Spatially resolved temperature profiles were obtained from a laminar premixed CH4/air flame and found to be in excellent agreement with temperatures obtained from high-resolution OH LIF scans. The accuracy and spatial resolution of the technique makes this an attractive alternative to traditional, more complex, and expensive, temperature measurement techniques of similar or better precision. Finally, we demonstrate that PLIF imaging of atom distributions in flames is possible using low power diode lasers. (c) 2004 The Combustion Institute. Published by Elsevier Inc. All rights reserved.