Rapid energy-level shifts in metals under intense inner-shell photoexcitation

Rapid energy-level shifts in metals due to intense near-edge photoexcitation of core electrons are investigated with the density matrix formalism. Analytic theory indicates that, as the core hole density increases, the core levels are lowered relative to the valence levels, leading to an enhancement of the band gap; its origin can be attributed to a large asymmetry between localized core and delocalized valence orbitals. The energy-level shifts are incorporated into the rate equation to compute time evolutions of near-edge photoabsorption spectra for metallic lithium irradiated by a vacuum ultraviolet laser pulse. Numerical results indicate saturable absorption due to a blue shift of the K-edge, leading to a nonlinear transmission of the laser pulse at high intensities.