Electron transitions in conduction band of wide-band insulators under high-power ultra-short laser pulses

Electron heating in the crystal conduction band under high-power femtosecond laser pulses has been studied. It is demonstrated that the electron heating mechanism in the insulator conduction band based on multiple electron—photon— phonon scatterings may become ineffective in exciting some insulators (in particular, Csl) by ultrashort laser pulses with intensity higher than $10^{11}$ W/cm$^2$. To describe electron heating by these pulses to an energy of several tens of electron-volts, a mechanism that accounts for direct interbranch transitions in the conduction band is proposed.