Time-of-flight study of the ionic and neutral particles produced by pulsed-laser ablation of frozen glycerol

The emitted particles from pulsed-laser ablation (PLA), lambda =193 nm and fluence=88-400 mJ/cm(2), of frozen glycerol was examined using time-of-flig ht mass spectrometry. The data are analyzed using supersonic molecular-beam theory and the result is interpreted using a thermal/fluid-dynamic model. Both intact and fragmented glycerol are emitted in the PLA process at all f luences and their concentration ratio is fluence dependent. Fragmentation o ccurs predominantly at one of the C-C bonds forming CH2-OH (31 amu) and HO- CH2-CH-OH (61 amu). CH3 is produced at the target which requires the proton ation of a CH2 fragment. At fluences higher than 250 mJ/cm(2), ions are det ected. These ions have very high velocity, > 2000 m/s, and their intensity increases with fluences. PLA is thus not suitable for glycerol transfer und er these conditions due to fragmentation. The data show that particle emiss ion proceeds as a simple thermal vaporization process at fluences < 200 mJ/ cm(2). Higher fluences will yield a Knudsen layer (KL), which is formed in front of the target surface. For fluences > 300 mJ/cm(2), particles from th e KL go through unsteady adiabatic expansion prior to free flight. Models o f particle and ion formation and interaction are proposed and discussed. (C ) 2001 American Institute of Physics.