The background radiation disturbance in luminous environments has been compared for degenerate four-wave mixing (DFWM) and laser-induced fluorescence (LIF) for OH radical detection in a sooty propane/ oxygen flame. The LIF signal generally was considerably stronger than the DFWM signal, but in strongly sooty environments the LIF signal was accompanied by a significant background signal, while the DFWM signal was background-free under all soot loads tested.
S. Kröll, C. Löfström, and M. Aldén, "Background-Free Species Detection in Sooty Flames Using Degenerate Four-Wave Mixing," Appl. Spectrosc. 47, 1620-1622 (1993)