Ultrafast dielectric function dynamics in bismuth

The time-dependent reflectivity at two angles from a fs-laser-excited single crystal of Bi were simultaneously measured up to 25 ps after a 50-fs pump pulse excitation. We demonstrate that bismuth did not have transition to liquid state even at the absorbed energy twice the equilibrium enthalpy of melting. We attribute this to the fast electrons transport that carries the excess energy away from the heated surface before the thermalisation of electrons and phonons has occurred.