Ultrafast Processes in Solid-State Materials 545
electronic system can exceed the lattice temperature by far. Depending on the
band structure and photon energy, intervalley scattering can occur.
Energy is transferred to the lattice (heating) by inelastic electron–phonon col-
lisions, and the carriers relax into states at the bottom of the band. The Fermi
distribution which is finally reached, can be characterized by a temperature which
is equivalent to the lattice temperature. If the excitation density is sufficiently
high, a local change in the lattice temperature can readily be observed. Extremely
high excitation can even result in melting. While the initial carrier scattering pro-
ceeds on a time scale of tens of fs or less, the intraband energy