Nanosecond dynamics of a gallium mirror’s light-induced reflectivity change

Transient pump-probe optical reflectivity measurements of the nano- to microsecond dynamics of a fully reversible, light-induced, surface-assisted metallization of gallium interfaced with silica are reported. The metallization leads to a considerable increase in the interface's reflectivity when solid {α}-gallium is on the verge of melting. The reflectivity change was found to be a cumulative effect that grows with light intensity and pulse duration. The reflectivity relaxes back to that of {α}-gallium when the excitation is withdrawn in a time that increases critically at gallium's melting point. It is shown that thermal processes cannot account for the effect and so a mechanism based on a nonthermal light-induced structural phase transition is proposed.