Heating of conduction band electrons by intense femtosecond laser pulses

We present photoelectron spectra for $\chem{CsI}$ excited by intense femtosecond $\chem{Ti}$-Sapphire laser pulses. A high-energy plateau is detected in the spectra, at excitation intensities above 0.5$\un{TW/cm^2}$. This plateau extends up to 24$\un{eV}$ at 3$\un{TW/cm^2}$ and 90% of the emitted electrons have energy higher than twice the laser photon energy. Such intensive electron heating in solids cannot be explained in terms of phonon-assisted transitions. A model of direct interbranch transitions in the conduction band is used for the simulation of the heating process.