GAS-PHASE VELOCIMETRY BY NEARLY DEGENERATE 4-WAVE-MIXING

We demonstrate a new velocimetry technique for gas flows based on Near ly Degenerate Four-Wave Mixing (NDFWM). Measurements were pet-formed o n nitric oxide in a free-jet expansion using helium and argon as carri er gases, at flow velocities on the order of 1000 m/s. We obtained vel ocities by analyzing experimental spectra from the jet using a perturb ative treatment of NDFWM that we extended to include an arbitrary bulk velocity. The results agreed with independent velocity measurements b ased on Laser-Induced Fluorescence (LIF), as well as with theoretical flow-field velocities, to better than 5% in all cases studied.