Generation of sub-100 Picosecond Ion Pulses by Laser-Stimulated Desorption in Ultrahigh Vacuum

Abstract

We present a method for generating ultrashort ion pulses, which is achieved through laser-stimulated desorption from a tungsten nanotip under ultrahigh vacuum conditions. A femtosecond ultraviolet laser pulse (259 nm, 280 fs, 15 nJ/pulse) is focused onto the apex of an electrochemically etched tungsten tip with a radius of ~150 nm at the apex. In the presence of background gas at partial pressures ranging from 10-9 to 10-5 mbar, adsorbates form on the tip surface. These undergo ionization through laser-triggered localized field enhancement. The nanoscopic ionization regime facilitates ion generation at moderate optical fluence. Resulting ions exhibit kinetic energies of 8.5 keV and time-of-flight pulse widths of less than 100 picoseconds. The approach is inherently synchronized with optical pulses, enabling high-precision pump-probe experiments for future studies on ultrafast ion- solid interactions. Our method permits species selection through gas exchange and emphasizes the critical role of vacuum integrity and adsorption dynamics in reliable ultrafast ion emission.