Two-dimensional modeling of pulsed-laser irradiated a-Si and other materials

A previously developed one-dimensional (1D) computational model for heat flow and nonequilibrium phase change phenomena induced by pulsed-laser irradiation has been extended to two dimensions. The 2D modeling focuses attention on the heat flow from localized sources embedded in an otherwise planar matrix. For example, nucleation events occurring in undercooled liquids such as molten Si formed by pulsed-laser melting of amorphous Si (a-Si) and inhomogeneous absorption due to randomly occurring defects in targets used for pulsed-laser ablation can be treated. Concepts introduced in the 1D modeling, such as the state diagram and the state array, have been extended to 2D and refined. As an example of the calculations that are now possible, the laser-induced formation and propagation of buried liquid layers are followed in two dimensions for the case of a-Si on a crystalline silicon substrate. It is demonstrated how solid phase growth, though originating from individual nucleation sites, gives rise to a nearly planar liquid layer propagating through the a-Si. Two other examples briefly address questions related to the early stages of the laser ablation of insulators such as MgO, where it is believed that the absorption of the laser radiation occurs at localized but extended regions of high defect concentrations, and to particulate ejection during laser ablation of many materials.