Phase space manipulation of free-electron pulses from metal nanotips using combined terahertz near fields and external biasing

This work studies the manipulation of photoelectron emission from metallic nanostructures by intense single-cycle terahertz transients. Specifically, the authors employ streaking spectroscopy to study the kinetic energy of photoelectrons emitted from metal nanotips exposed to tailored static and terahertz electrical fields. Supported by detailed numerical simulations, the measurements provide quantitative information on the temporal and spatial properties of terahertz near fields at metal nanotips. The study illustrates far-reaching control over the trajectories and phase-space density evolution of photoelectron wavepackets acted upon by strong static and dynamic near fields. The results are relevant for applications of nanoscopic photoelectron sources employed in ultrafast electron diffraction and microscopy.