Highly coherent electron beam from a laser-triggered tungsten needle tip

TL;DR

This paper measures and compares the spatial coherence of electron beams emitted from a tungsten needle tip using laser-triggered photoemission and DC-field emission, demonstrating high coherence properties suitable for advanced electron imaging.

Contribution

It provides a quantitative analysis of electron coherence from a tungsten needle tip under laser-triggered and DC-field emission, highlighting the preservation of coherence in laser-induced emission.

Findings

Effective source radius of 0.80 nm in laser-triggered emission

Effective source radius of 0.55 nm in DC-field emission

Largest observed relative coherence width of 0.36

Abstract

We report on a quantitative measurement of the spatial coherence of electrons emitted from a sharp metal needle tip. We investigate the coherence in photoemission using near-ultraviolet laser triggering with a photon energy of 3.1 eV and compare it to DC-field emission. A carbon-nanotube is brought in close proximity to the emitter tip to act as an electrostatic biprism. From the resulting electron matter wave interference fringes we deduce an upper limit of the effective source radius both in laser-triggered and DC-field emission mode, which quantifies the spatial coherence of the emitted electron beam. We obtain $(0.80\pm 0.05)\,$nm in laser-triggered and $(0.55\pm 0.02)\,$nm in DC-field emission mode, revealing that the outstanding coherence properties of electron beams from needle tip field emitters are largely maintained in laser-induced emission. In addition, the relative coherence width of 0.36 of the photoemitted electron beam is the largest observed so far. The preservation of electronic coherence during emission as well as ramifications for time-resolved electron imaging techniques are discussed.