Visible fluorescence of liquid oxygen excited by a Q-switched Nd:YAG laser

Abstract

Liquid oxygen and oxygen-argon mixtures were excited by 1.06-µm Q-switched Nd:YAG laser light. Fluorescence spectra were observed at wavelengths of 481, 637, 704, and 764 nm. Emission intensities showed a cubic dependence on the exciting Nd:YAG laser power for 481-nm fluorescence and a quadratic dependence on it for fluorescence at other wavelengths. These dependences are understood qualitatively to be a result of pair transitions of the oxygen molecule excited by the Nd:YAG laser light through single-molecule absorption (and/or pair-molecule absorption). The emissions at 637 and 704 nm were observed to decay exponentially with time, whereas the emissions at 481 and 764 nm showed time dependences composed of two exponential terms. The measured quenching coefficients of the 1Δg state by ground-state oxygen and by argon are in good agreement with values reported previously.