Degenerate four-wave mixing (DFWM) is a nonlinear optical process that has been developed for making quantitative measurements of gasdynamic properties in reactive environments. This technique can be used to measure temperature and species concentration in both flames and plasma environments. The resulting coherent signal beam makes DFWM particularly attractive for luminous and harsh environments, compared to incoherent techniques, such as laser-induced fluorescence (LIF). Furthermore, DFWM can probe non-fluorescing species. We describe methods for measuring velocities of gas flows using nearly-DFWM and translational temperatures using DFWM.
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