Line-of-sight diode-laser absorption techniques have been extended to enabl
e temperature measurements in nonuniform-property flows. The sensing strate
gy for such flows exploits the broad wavelength-scanning abilities (>1.7 nm
approximate to 30 cm(-1)) of a vertical cavity surface-emitting laser (VCS
EL) to interrogate multiple absorption transitions along a single line of s
ight. To demonstrate the strategy, a VCSEL-based sensor for oxygen gas temp
erature distributions was developed. A VCSEL beam was directed through path
s containing atmospheric-pressure air with known (and relatively simple) te
mperature distributions in the 200-700 K range. The VCSEL was scanned over
ten transitions in the R branch of the oxygen A band near 760 nm and option
ally over six transitions in the P branch. Temperature distribution informa
tion can be inferred from these scans because the line strength of each pro
bed transition has a unique temperature dependence; the measurement accurac
y and resolution depend on the details of this temperature dependence and o
n the total number of lines scanned. The performance of the sensing strateg
y can be optimized and predicted theoretically. Because the sensor exhibits
a fast time response (similar to 30 ms) and can be adapted to probe a vari
ety of species over a range of temperatures and pressures, it shows promise
for industrial application. (C) 2001 Optical Society of America.