Diode-laser absorption sensor for line-of-sight gas temperature distributions

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.