Ultrafast electron and lattice dynamics in semiconductors at high excited carrier densities Original Research Article

We directly measure ultrafast changes in the dielectric function of GaAs over the spectral range from the near-IR to the near-UV caused by intense 70-fs laser excitation. The dielectric function reveals the nature of the ultrafast phase transformations generated in the material, including a semiconductor-to-metal transition for the strongest excitations. Although the electron and lattice dynamics are complex when large carrier densities are excited — between 1 and 20% of the valence electrons — the dominant processes and their timescales can be deduced.