Imaging energy-, momentum-, and time-resolved distributions of photoinjected hot electrons in GaAs.

Using time-and angle-resolved photoemission spectroscopy, we determine directly energy-, momentum-, and time-resolved distributions of hot electrons photoinjected into the conduction band of GaAs, a prototypical direct-gap semiconductor. The nascent distributions of photoinjected electrons are captured for different pump photon energies and polarization. The evolutions of hot electron distributions in ultrafast intervalley scattering processes are resolved in momentum space with fs-temporal resolution, revealing an intervalley transition time as short as 20 fs.