Picosecond degenerate four-wave mixing on potassium in a methane-air flame.

We demonstrate that picosecond mode-locked laser-based degenerate four-wave mixing can be detected with good signal-to-noise ratios in an optically thin flame and that detailed turbulence statistics can be acquired by use of this technique. A regeneratively mode-locked Ti:sapphire laser was tuned to the 4(2)S((1/2))-4(2)P degrees ((1/2)) transition in atomic potassium (which was doped into the flame) at 769.9 nm. Using the all-forward degenerate four-wave mixing geometry, we achieved signal-to-noise ratios of 70:1 without the use of a spatial filter. A sensitivity curve and a method for acquiring turbulence statistics are presented.