Measurement of OH rotational temperatures in a flame using degenerate four-wave mixing

Temperatures have been measured in a laminar premixed propane-air diffusion flame using degenerate four-wave mixing (DFWM) of the OH radical. The spectra were recorded simultaneously with laser-induced fluorescence through the (0, 0) band of the OH A(2)Sigma-X(2)II transition. Individual rotational lines are more clearly resolved in the DFWM spectrum than in the laser-induced fluorescence spectrum, although both are power broadened at laser intensities of 1-2 MW/cm(2) at 307 nm. Rotational temperatures have been determined from the DFWM spectra and are in close agreement with temperatures measured with coherent anti-Stokes Raman spectroscopy of nitrogen.