Density measurement in compressible flows using off-resonant laser- induced fluorescence

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Abstract
Measurement of molecular number density in compressible flows using laser‐induced fluorescence is complicated by collisional quenching of the excited state. It is shown that by exciting the fluorescence off‐resonance the signal becomes proportional to number density and independent of collisional effects. Quantitative measurement of density in an underexpanded jet of nitrogen is demonstrated using off‐resonant fluorescence from iodine seed molecules irradiated with the 514.5 nm line of the argon‐ion laser.