Laser-induced field emission from a tungsten nanotip by circularly polarized femtosecond laser pulses

Abstract

We have investigated emission patterns and energy spectra of electrons from a tungsten nanotip induced by circularly polarized femtosecond laser pulses. Variations of emission patterns were observed for different helicities of circular polarization while the energy spectra remained almost identical. The physics behind this difference in emission patterns is the change in propagation directions of surface electromagnetic waves on the tip apex. The energy spectra showed the same spectroscopic signatures as the linearly polarized laser in a strong-field regime, which are a low-energy peak and a plateau feature. The low-energy peak is due to a delayed electron emission with respect to a prompt emission. The experimental data and plasmonic simulations support our previous conclusion, where the observed delayed emission processes originate from an inelastic rescattering process. This work demonstrates that the use of circular polarization is an easy means to add extra knobs to control the spatial and temporal emission from a nanotip at the nanometer and femtosecond scale. It could find applications as a helicity-driven subcycle optical switch.We have investigated emission patterns and energy spectra of electrons from a tungsten nanotip induced by circularly polarized femtosecond laser pulses. Variations of emission patterns were observed for different helicities of circular polarization while the energy spectra remained almost identical. The physics behind this difference in emission patterns is the change in propagation directions of surface electromagnetic waves on the tip apex. The energy spectra showed the same spectroscopic signatures as the linearly polarized laser in a strong-field regime, which are a low-energy peak and a plateau feature. The low-energy peak is due to a delayed electron emission with respect to a prompt emission. The experimental data and plasmonic simulations support our previous conclusion, where the observed delayed emission processes originate from an inelastic rescattering process. This work demonstrates that the use of circular polarization is an easy means to add extra knobs to control the spatial and temporal emission from a nanotip at the nanometer and femtosecond scale. It could find applications as a helicity-driven subcycle optical switch.

Subnanometeric optical modulation of a single-molecule electron source

“…The electrons are emitted from the hot spots of optical elds that are created by plasmonic effects and localised at the geometrical inhomogeneities of nano-objects, such as nanometric gaps [11] or sharp tips [12,13] , as schematically depicted in Figures 1(a)-1(c). The plasmonic effects modulate the spatial distribution of the local elds by varying optical parameters such as laser incident angle [14] , polarisation [11,13,15] , and the temporal [11,12] pro les of laser pulses. Thus, for instance, one could select the A or B emission site, as indicated in Figures 1(a)-1(c).…”

“…The optical modulation of the electron source makes it possible to probe and control the coherent electronic and plasmonic dynamics in space [5,6,[11][12][13][14][15][16] . Moreover, since each emission site can be used as a switch, the modulation practically realises the integration of multiple ultrafast switches into a nanoobject [11][12][13] .…”

A tunable photo-electric co-excited point electron source: low-intensity excitation emission and structure-modulated spectrum-selection

“…), [34][35][36] transition metals (tungsten, molybdenum, etc. ), 19,37,38 and carbon-based materials (carbon nanotubes, graphene, diamond, etc.). 15,20,31 Among them, tungsten (W) shows advantages of high electric and thermal conductivities, excellent high-temperature stability, as well as large-current and high-current-density output properties.…”

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

“…It is typically argued that the small dimension of the nano-emission site leads to highly divergent trajectories, justifying the neglect of charge interaction [9,30,31]. On the other hand, for certain parameter ranges the electron kinetic energy spectrum from nanometric needle tips with large apex radii (r∼100 nm) seems to be completely dominated by Coulomb interaction [32,33]. Clearly, the miniscule emission area makes nanometric needle tips highly susceptible to space charge effects close to the emission surface.…”