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The physical mechanisms and molecular-level picture of laser-induced material ejection from frozen solutions of polymer molecules in a volatile matrix are investigated in a series of coarse-grained molecular dynamics simulations. The simulations are performed for polymer concentrations up to 6 wt % and laser fluences covering the range from the regime where molecular ejection is limited to matrix evaporation from the surface up to more than twice the threshold fluence for the onset of the collective molecular ejection or ablation. The results of the simulations are related to experimental observations obtained in matrix-assisted pulsed laser evaporation ͑MAPLE͒ thin film depositions and are used to address unresolved research questions that are of direct relevance to MAPLE performance. Contrary to the original picture of the ejection and transport of individual polymer molecules in MAPLE, the simulations indicate that polymer molecules are only ejected in the ablation regime and are always incorporated into polymer-matrix clusters/droplets generated in the process of the explosive disintegration of the overheated matrix. The entanglement of the polymer molecules facilitates the formation of intricate elongated viscous droplets that can be related to the complex morphologies observed in polymer films deposited by MAPLE. Analysis of the state of the irradiated target reveals a substantial increase of the polymer concentration and complex surface morphology generated in the new surface region by the ablation process. The ramifications of the computational predictions for interpretation of experimental data and the directions for future experimental exploration are discussed based on the physical picture of molecular ejection and transport in MAPLE emerging from the simulations.

The mechanisms and kinetics of short pulse laser melting of single crystal and nanocrystalline Au films are investigated on the basis of the results of simulations performed with a model combining the molecular dynamics method with a continuum-level description of the laser excitation and subsequent relaxation of the conduction band electrons. A description of the thermophysical properties of Au that accounts for the contribution of the thermal excitation of d band electrons is incorporated into the model and is found to play a major role in defining the kinetics of the melting process. The effect of nanocrystalline structure on the melting process is investigated for a broad range of laser fluences. At high fluences, the grain boundary melting in nanocrystalline films results in a moderate decrease of the size of the crystalline grains at the initial stage of the laser heating and is followed by a rapid (within several picoseconds) collapse of the crystal structure in the remaining crystalline parts of the film as soon as the lattice temperature exceeds the limit of the crystal stability against the onset of rapid homogeneous melting (the limit of superheating). At low laser fluences, close to the threshold for the complete melting of the film, the initiation of melting at grain boundaries can steer the melting process along the path where the melting continues below the equilibrium melting temperature and the crystalline regions shrink and disappear under conditions of substantial undercooling. The unusual melting behavior of nanocrystalline films is explained on the basis of thermodynamic analysis of the stability of small crystalline clusters surrounded by undercooled liquid.