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

We present a comprehensive experimental and numerical study of photoelectron streaking at metallic nanotips using single-cycle terahertz (THz) transients and a static bias voltage as an external control parameter. Analyzing bias voltage dependent streaking spectrograms, we explore the THz-induced reshaping of photoelectron energy spectra, governed by the superimposed static field. Numerical simulations are employed to determine the local field strengths and spatial decay lengths of the field contributions, demonstrating electron trajectory control and the manipulation of the phase space distributions in confined fields with both dynamic and static components.