3D-Printed Photocathodes for Resonant, Terahertz-Field-Driven Ultrafast Electron Emission

TL;DR

This paper introduces a novel 3D-printed, resonant nanoantenna design for out-of-plane, ultrafast electron emission driven by terahertz fields, enabling scalable, reproducible photocathodes with enhanced electron extraction.

Contribution

The work presents a new out-of-plane nanoantenna design fabricated via 3D printing, demonstrating improved electron emission and array-based collective effects for terahertz-driven photocathodes.

Findings

Gold-coated nanocones generate large local electric fields.

Resonant structures enhance electron emission via collective terahertz response.

Array configurations further boost photoemission efficiency.

Abstract

Ultrashort photoemitted electron bunches can provide high electron currents within sub-picosecond timeframes, enabling time-resolved investigations of ultrafast physical processes with nanoscale resolution. Non-resonant conductive nanotips are typically employed to realize nanoscale photoelectron sources with high brightness. However, such emitters require complex non-scalable fabrication procedures featuring poor reproducibility. Planar resonant antennas fabricated via photolithography have been recently investigated, also because of their superior field enhancement properties. Nevertheless, the electron emission from these structures is parallel to the substrate plane, which limits their practical use as electron sources. In this work, we present an innovative out-of-plane, resonant nanoantenna design for field-driven photoemission enabled by high-resolution 3D printing. Numerical and experimental evidences demonstrate that gold-coated, terahertz resonant nanocones provide large local electric fields at their apex, automatically ensuring out-of-plane coherent electron emission and acceleration. We show that the resonant structures can be conveniently arranged in an array form, for a further significant electron extraction enhancement via a collective terahertz response. Remarkably, such collective behaviour can also be harvested to boost photoemission from an individual nano-source. Our approach opens the path for a new generation of photocathodes that can be reproducibly fabricated and designed at will, significantly relaxing the requirement for intense terahertz drivers.