Nonsecond pulsed-laser annealing of semiconductors is widely believed to be a simple thermal melting and recrystallization effect. We have examined subthreshold-irradiated arsenic-implanted silicon wafers in cross section by conventional transmission and scanning transmission electron microscopy. Both microdiffraction and high-resolution microscopical techniques were found to be very useful. There is evidence for both thermal melting and at a deeper level partial solid-state regrowth. The origin of this nucleation is thought to be thermal but it may be influenced by ionization or stress effects.