Mechanism of Intact Adsorbed Molecules Ejection Using High Intensity Laser Pulses

A novel universal mechanism for the ejection of intact, neutral molecules from thin films into the gas phase initiated by high intensity ultrashort laser pulses is described. The proposed mechanism is substantiated by detailed reactive molecular dynamics simulations. In the present study, 2,4,6-trinitrotoluene (TNT) and cryogenic benzene are used as thin film targets. According to the proposed mechanism, the laser pulse, absorbed by the substrate, forms a hot plasma plume which in turn generates a shock wave that moves across the deposited thin film. The simulations indicate that the shock wave propagates through the thin film without dissipation and eventually ejects molecules from the free surface. It is revealed that the proposed mechanism is feasible only in a limited range of shock velocities. The results compare well qualitatively with recent experimental findings of femtosecond, nonresonant, laser-induced desorption. Simple experimental measurements are outlined to validate the proposed mechanism.