Recently available experimental data indicate that the solidification of
undercooled molten silicon prepared by pulsed laser melting of amorphous
silicon is a complex process. Time-resolved reflectivity and electrical
conductivity measurements provide information about near-surface melting and
suggest the presence of buried molten layers. Transmission electron
micrographs show the formation of both fine- and large-grained
polycrystalline regions if the melt front does not penetrate through the
amorphous layer. We have carried out extensive calculations using a newly
developed computer program based on an enthalpy formulation of the heat
conduction problem. The program provides the framework for a consistent
treatment of the simultaneous formation of multiple states and phase-front
propagation by allowing material in each finite-difference cell to melt,
undercool, nucleate, and solidify under prescribed conditions. Calculations
indicate possibilities for a wide variety of solidification behavior. The
new model and selected results of calculations are discussed here and
comparisons with recent experimental data are made.