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=1235K) 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 0.1Tm.