3D Nitric Oxide Imaging by Laser-Induced Fluorescence in a Reacting Flow Using Tunable 5th Harmonic Burst-Mode Nd:YAG

We present burst-mode, volumetric laser-induced fluorescence measurements of nitric oxide in a quasi-"frozen" reacting flow with laser excitation via the 5th harmonic of a Nd:YAG laser. A tunable pulse-burst laser generated 5th harmonic radiation near 212.9 nm at 200 kHz with pulse energies of 5 mJ/pulse. The UV output beam was formed into a 55-mm tall sheet and swept across a 25-mm distance within a turbulent oxy-acetylene torch plume. The laser was tuned to overlap the gamma(1, 0) Q2 (43) transition of nitric oxide at 212.885 nm (vac.), which was formed naturally within the reacting plume. The set of PLIF images captured by a high-speed camera during the laser sweep were stacked to yield 3D renderings of the distribution of nitric oxide within the flow. The close spacing of the laser sheets led to high resolution 3D renderings with a voxel size of as small as 220 × 220 × 115 micrometers.