Ultrafast photoelectric emission from new solid materials

We show that alkali ion implantation is a new valuable tool to improve significantly the photoelectric yield of pure metals. The enhancement by a factor ≥10 of the single-photon photoelectric sensitivity was measured in potassium ion implanted-polycrystalline-tungsten surface irradiated by subpicosecond 248 nm laser pulses with a peak intensity of a few GW/cm2. An investigation of physical and chemical properties supposed to be at the origin of this enhancement is reported. We demonstrate that the improvement of the tungsten photoelectric sensitivity is related to an effective lowering of the work function at the surface, while the nonlinear photoelectric performances of these photocathodes indicate a change in electron-electron and electron-phonon relaxation times due to alkali ions implantation.