Sample laser pulse striking surface

A laser pulse strikes the surface of a sample (a), depositing energy, which leads to melting and vaporization of neutral molecules and ions from a small, confined area (b). A few nanoseconds after the pulse, the vaporized material is either pumped away or, if it is ionic, it is drawn into the analyzer of a mass spectrometer (c). 

Laser Desorption/Ablation Ionization Methods. Matrix-assisted laser desoiption ionization (MALDI) relies on the use of a solid chromophQric matrix, chosen to absorb laser light, which is co-mixed with the analyte (4). Typically, a solution of a few picomoles of analyte is mixed widi a lOO-to-5000 fold excess of the matrix in solution. A few microliters of the resulting solution are deposited on a mass spectrometer solids probe, and the solvent is allowed to evaporate before inserting the probe into the mass spectrometer. When the pulsed laser beam strikes the sample surface in the spectrometer, the sample molecules are desorbedAonized at high efficiency. The various mechanisms for matrix and non-matrix assisted laser desorption have been discussed (5,6). 

This conclusion was tested with a practical experiment in which the erosion yield of polystyrene under exposure to the effusive plasma source was measured with and without the addition of the pulsed hyperthermal Ar beam. In this experiment, the Ar beam pulse was not chopped, so the entire beam pulse produced from the laser detonation source was allowed to strike the surface. The erosion yield was determined by placing a screen over the samples during exposure and measuring the etch depth... 

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