Solidification velocities in deeply undercooled silver

We measure the solidification velocity of pure Ag as a function of undercooling temperature from the melting point (Tm=1235 K) to 0.6Tm using ultrafast, pump-probe laser experiments. The thickness of the liquid layer, while it solidifies, is measured using optical third harmonic generation. We show that velocity reaches a maximum value at 0.85Tm, and then remains nearly constant with additional undercooling. These results contradict simple collision-limited models, but they are in good agreement with molecular dynamics simulations presented here, which show that the crystallization velocity depends weakly on temperature from 0.85Tm to less than approximately 0.1Tm.