Influence of electron Coulomb explosion on photoelectron spectra of dielectrics irradiated by femtosecond laser pulses

The photo-emission of electrons from dielectric surfaces induced by intense femtosecond laser pulses with a wavelength of 800 nm is addressed. The energy distribution of electrons emitted from SiO2 and Al2O3 samples is presented for various laser intensities. It appears that the maximum kinetic energy may reach unexpected values up to roughly 3 keV even at moderate intensities. This observation may be explained by invoking electron Coulomb explosion occurring at the surface of the material. Simple modelling calculations support this physical scenario.