Onset of space-charge effects in strong-field photocurrents from nanometric needle tips

Abstract

Strong-field photoemission from nanostructures and the associated temporally modulated currents play a key role in the development of ultrafast vacuum optoelectronics. Optical light fields could push their operation bandwidth into the petahertz domain. A critical aspect for their functionality in the context of applications is the role of charge interactions, including space charge effects. Here, we investigated the photoemission and photocurrents from nanometric tungsten needle tips exposed to carrier-envelope phase-controlled few-cycle laser fields. We report a characteristic stepwise increase in the intensity-rescaled cutoff energies of emitted electrons beyond a certain intensity value. By comparison with simulations, we identify this feature as the onset of charge-interaction dominated photoemission dynamics. Our results are anticipated to be relevant also for the strongfield photoemission from other nanostructures, including photoemission from plasmonic nano-bowtie antennas used in carrier-envelope phase-detection and for PHz-scale devices.

Strong-Field Control of Plasmonic Properties in Core–Shell Nanoparticles

“…The photoelectron cutoff energy, defined as the highest observable electron energy, has been established as a gold standard for probing the induced plasmonic near-fields close to various nanostructure surfaces of different materials. 12,13,36,37 This cutoff scales linearly with the cycle-averaged quiver energy of a free electron in a laser field, referred to as the "ponderomotive energy" U p = e 2 E 2 /4mω 2 ∝ Iλ 2 (e and m are electron charge and mass and E, I, ω, and λ designate the incident field strength, peak intensity, frequency, and wavelength of the laser pulse, respectively). Though near-fields are generally inhomogeneous (decreasing with distance), the fastest photoelectrons elastically rescatter and gain most of their kinetic energies near the nanoparticle surface, 17,28 well within the typical spatial range of the near-field enhancement.…”