Hot-electron relaxation in quartz using high-order harmonics

Using ultrafast time-resolved ultraviolet photoelectron spectroscopy, we have followed the energy relaxation kinetics of conduction electrons in quartz, for energies of the order of 30 eV above the conduction-band minimum. We measure energy-loss rates three orders of magnitude lower than those estimated for energies close to this minimum. Likewise, the impact ionization rate obtained (1/40 ${\mathrm{ps}}^{-1})$ is much lower than the values generally assumed in optical breakdown models.