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

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.