Solid phase of aluminum at high energy densities

Recently, there is a growing interest in using isochoric heating of solids induced by an intense, ultrafast energy source to produce gradient-free, high-energy-density matter in the laboratory. Of central importance in such an approach is the persistence of the heated material in its solid phase. In previous experiments a solid phase of gold was found to last from $\sim $20 ps after being heated by a 400 nm, 150 fs laser pulse to an energy density of 10$^{10}$ J/m$^{3}$ to $\sim $2 ps for an energy density of $\sim $4x10$^{11}$ J/m$^{3}$ [T. Ao \textit{et. al}, PRL \underline {96}, 055001 (2006); Y. Ping \textit{et. al}, PRL \underline {96}, 255003 (2006)]. In this paper, we report on observations made on aluminum isochorically heated by a 400 nm, 40 fs laser pulse. The experiment was performed at the Advanced Laser Light Source (ALLS) in Quebec. Aluminum was chosen for its free-electron like density of states in contrary to the hybridized 5d-6s/p states in gold. Interestingly, under such ultrafast laser excitation, aluminum also appeared to remain solid on a ps time scale at an energy density of $\sim $10$^{11}$ J/m$^{3}$.