Ultrafast broadband spectroscopic studies of GaAs under intense laser excitation

An ultrafast broadband spectroscopic technique (350 to 900 nm) is employed to measure the dielectric function of GaAs in response to a 70-fs laser pulse excitation. We observe drastic changes in the dielectric function within 1ps of the excitation, which we attribute to an ultrafast non-thermal structural transition. These broadband measurements provide extensive information on the initial electronic excitation and the dynamics of the subsequent phase transition.