Femtosecond time-resolved measurements of interband transition in ultrathin gold foils under ultrafast excitation

Summary form only given. The advance in ultrafast laser technology has enabled the observation of transient processes in many areas. One interesting phenomenon is laser-induced phase transition from solid to plasma. A detailed study of this could bridge the gap between condensed matter physics and plasma physics. A recent experiment on femtosecond laser heating of ultrathin freestanding gold foils revealed a quasi-steady-state behavior before the onset of hydrodynamic expansion. Further investigations with frequency domain interferometry (FDI) yielded the time scale of such a state, which agrees well with the electron-phonon coupling time calculated from a simple Two-Temperature Model (TTM). To provide further insight into the processes of electron-electron and electron-phonon relaxation, a fs wavelength-tunable probe generated by an optical parametric amplifier is used to follow the temporal evolution of interband transition in gold (5d-6s/p) under intense laser excitation through transient reflectivity and transmissivity measurements. The comparison of the measurements and the model calculation will be discussed.