Ultrafast Control and Tailoring of Surface Plasmon Generated Electron Pulses

• Author / Creator

  Greig, Shawn R

• This thesis presents theoretical and experimental work on the generation and control of ultrashort electron pulses via surface plasmon (SP) waves. As such, new methods are presented to specifically control various beam parameters such as direction, kinetic energy, pulse duration, and current.
  Employing a single, ultrashort, terahertz (THz) electric field pulse to a standard SP based electron source provides a method for ultrafast, all-optical control of the angular directivity and kinetic energy spectra of SP generated electron pulses. By introducing a second THz pulse and controlling its delay and phase with respect to the first THz pulse, greater control over the electron’s temporal acceleration profile is afforded, allowing electrons to be accelerated to kinetic energies up to 3.5 keV.
  The design of a compact, ultrafast nanoplasmonic based electron gun is presented. Harnessing the focusing capability of radially polarized light, conical surface plasmons are able to accelerate electrons to 1.2 keV. Through the use of magnetostatic and spatial filtering, electron packets with attosecond durations can be achieved.
  Multiple methods of increasing the electron yield of surface plasmon based electron sources are studied. Reduction of the nonlinear emission order is achieved by introducing a dielectric layer beneath the plasmonic metal film. The dielectric layer allows for higher electric field confinement and thus higher acceleration gradients. To further increase the current, gating of secondary electrons generated by an external, continuous, electron beam is explored. This platform allows for an in-depth study of the interaction of free electrons with strong SP fields for the next generation of ultrafast, high current SP based electron sources.
  The knowledge gained from SP-electron interaction in a vacuum environment is transferred to a solid-state Si-based platform to investigate the next generation of optical computing devices. Utilizing the SP mode in a nanoplasmonic waveguide to accelerate electrons, and subsequently filtering them based on their energy produces a triode like behaviour useful for interfacing current nanoelectronics and nanoplasmonics. A similar effect is used to develop a solid-state detector for the carrier-envelope-phase of few-cycle pulses.
  With the understanding of the effect that free electrons within a film can have on the various properties of a plasmonic system, a method to modulate the conductivity of an ensemble of Au particles using THz electric fields was explored. By utilizing all-THz pump-probe time-resolved spectroscopy, it was demonstrated that a low THz field strength can induce a measurable change to the Au particle’s conductivity. This is the first step towards controlling the SP coupling and photoemission properties in the near-infrared, such that THz electric field enhanced photoemission can be realized.

• Subjects / Keywords

  • Ultrafast
  • Ponderomotive acceleration
  • Plasmonics
  • Electron pulse generation

• Graduation date

  Fall 2018

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R30G3HD7S

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.