Femtosecond dynamics of the laser-induced solid-to-liquid phase transition in aluminum

We present femtosecond time-resolved measurements of the reflectivity of aluminum during the laser-induced solid-to-liquid phase transition over the 1.7-3.5 eV spectral range. Previous optical and electron-diffraction studies have shown discrepancies on the order of picoseconds in the time scale of the solid-to-liquid phase change. As a result, it is not clear if the transition mechanism is thermal or nonthermal. Our experiments conclusively show that this transition is a thermal process mediated through the transfer of heat from the photoexcited electronic population to the lattice. Our findings agree with the results of the electron-diffraction study and rule out the nonthermal mechanism proposed by the optical study.