ULTRAFAST HOT-ELECTRON DYNAMICS IN SILICON

Ultrafast (150 fs) time-resolved photoelectron spectroscopy is used to directly observe the energy relaxation of optically excited electrons in silicon. Conduction band electrons fit a thermal distribution by 1 20 fs pump-probe delay. The initial cooling rate of the excited distri bution is found to be extremely fast, followed by an electron-phonon t hermalization time of approximately 1 ps, and an overall much slower c ooling rate as the electrons lose energy. Here, we also report a new e ffect in two-photon photoemission unique to ultrashort laser pulses. O ur model and results demonstrate this effect to be a sensitive new mon itor of electron dynamics.