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Fluorescence imaging of gas-phase molecules produced by matrix-assisted laser desorption.

Optical spectroscopic probes based on lasers have been successfully employed for monitoring laser-generated plumes previously, providing spatial and temporal information on atoms, diatomics, and large molecules. These are based on absorption in the plume, reflection off the surface, and laser-enhanced ionization. The distinctive feature is that these probes can follow the neutral as well as the ionic forms of the vaporized species. If fragmentation involves destruction of the chromophore, one can even measure the extent of fragmentation. However, because of the substantially lower concentrations of the species of interest in MALD, the above probes are not suitable for similar studies there. In this article, the authors report the use of laser-excited fluorescence to provide spatial and temporal maps of the plumes generate by MALD. The information available is similar to that obtained by absorption probes, but with the high sensitivity needed for MALD events.