Self-limited underdense microplasmas in bulk silicon induced by ultrashort laser pulses

Abstract

Two-photon ionization by focused femtosecond laser pulses initiates the development of micrometer-scale plasmas in the bulk of silicon. Using pump-and-probe transmission microscopy with infrared light, we investigate the space-time characteristics of these plasmas for laser intensities up to 10¹²W/cm². The measurements reveal a self-limitation of the excitation at a maximum free-carrier density of ffi1019 cm3, which is more than one order of magnitude below the threshold for permanent modification. The plasmas remain unchanged in the 100 ps timescale revealing slow carrier kinetics. The results underline the limits in local control of silicon dielectric permittivity, which are inherent to the use of single near-infrared ultrashort Gaussian pulses. Show more