GaAs under Intense Ultrafast Excitation: Response of the Dielectric Function

Abstract

We used a new broadband spectroscopic technique to measure the dielectric function of GaAs over the spectral range of 1.5--3.5 eV following intense 70-fs laser excitation. The results provide the most detailed information thus far on the electron and lattice dynamics both above and below the fluence threshold for permanent damage, ${F}_{\mathrm{th}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.0\phantom{\rule{0ex}{0ex}}\mathrm{kJ}/{\mathrm{m}}^{2}$. There are three distinct regimes of behavior: lattice heating $(<{0.5F}_{\mathrm{th}})$, lattice disordering (0.6--0.8) ${F}_{\mathrm{th}}$, and a semiconductor-to-metal transition $(>{0.8F}_{\mathrm{th}})$. Below ${F}_{\mathrm{th}}$, the changes are completely reversible.