Velocimetry of gas flows using degenerate four wave mixing

A method of velocimetry of gaseous flows based on resonant degenerate four-wave mixing (DFWM) is described. Spatially resolved velocity measurements are derived from Doppler shifts of DFWM signals generated in NO-seeded into flows of air or N2. Velocities in the range of 60 to 200 ms−1 have been measured with an uncertainty of ±30 ms−1.