Strong-field plasmonic electron acceleration with few-cycle, phase-stabilized laser pulses
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(a) Scheme of the experimental setup with few-cycle pulses focused onto a thin silver layer on a fused silica prism (also acting as a vacuum window) to generate SPP enhanced photoemission. Electrons (with sample trajectories, solid lines) are detected in vacuum with a Hamamatsu R595 EMT the first dynodes of which are also depicted as well as a grid with retardation voltage for spectroscopic analysis. (b) Individual sample electron trajectories in the SPP enhanced electron acceleration process for different CEP values of the plasmon generating few-cycle laser pulse. As it can be seen, not just the final direction and kinetic energy of the electron is influenced by a slightly different CEP value, but also the fact that it either recollides with the surface after a half optical cycle (short-dashed-dotted trajectory) or if it can be set free (solid and dashed trajectories). (c) SPP enhanced electron acceleration spectra measured at three different focused laser intensities. (d) Long-term, in-loop CEP stability measurement of the laser output pulse train with an -to- interferometer. (e) SPP enhanced electron acceleration spectra as a function of the CEP of laser pulses with focused laser intensity. Line-outs at the dashed lines are depicted in (f) for four different CEP values with an unknown, but fixed CEP offset (, inherent to the -to- CEP stabilization technique).
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(a) STM scan of the 50 nm thick evaporated Ag surface exhibiting 2.8 nm rms roughness. (b) Computed electron spectra for a Ag surface of the same roughness as a function of the CEP of the SPP generating laser pulses. (c) Snapshot of the distribution of the absolute value of the SPP electric field strength in the vicinity of an atomically flat metal layer and accelerated test electron positions (dots) after of the beam center hitting the surface. The prism position (not to scale) and the direction of the incoming laser beam (arrow) are also indicated for easy orientation. (d) The same as (c) but for a typical evaporated metal surface with surface roughness.
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