Investigation of laser induced phosphorescence and fluorescence of acetone at low pressure for molecular tagging velocimetry in gas microflows

Abstract

Laser-induced fluorescence and phosphorescence properties of gaseous acetone in argon are measured and analyzed in a pressure ranging from 10(5) to 10(2) Pa, with the aim of analyzing by molecular tagging velocimetry gas microflows in rarefied regimes which requires operation at low pressure. Acetone is excited at a wavelength of 266 nm and immediately emits short lifetime fluorescence rapidly followed by long lifetime phosphorescence. At atmospheric pressure, the early phosphorescence intensity is more than 600 times lower than the fluorescence one. The phosphorescence signal is rapidly decreasing with time, closely following a power law. Both fluorescence and phosphorescence signals are decreasing with pressure. The systematic analysis of fluorescence and phosphorescence of acetone molecules shows that although the signal is dramatically reduced at low pressure, the on-chip integration technique and the optimization of the acquisition parameters provide an exploitable signal for molecular tagging velocimetry in rarefied microflows, in a Knudsen number range corresponding to the early slip flow regime.