Light emission from electron-beam driven metasurfaces

Abstract

Over the last decade, free electron beams have been extensively used for characterization of nanostructures, particularly the study of plasmonic excitations using cathodo-luminescence and energy loss spectroscopy. A number of novel light sources based on electron-beam driven nano-antennas, -undulators and -gratings have also been demonstrated.

In this thesis I report on new approaches for controlling emission of light generated by electron beams interacting with nanostructured metasurfaces. In particular, I have developed the first holographic free-electron-driven light source in which emission induced by electrons injected into planar holographic pattern is controlled by the patterns design. On the platform of a conventional scanning electron microscope, using plasmonic, semiconductor and dielectric surface-relief holographic metasurface, for the first time I have experimentally demonstrated:
*  Holographic patterns designed to generate highly-collimated radiation at a given wavelength in a prescribed direction. For example, a surface relief hologram only a few tens of square microns in size milled into a plasmonic gold film and driven by 30 keV electrons emits a light beam at 800 nm with divergence of only 2.5º with an efficiency ~10^-7 photons/electron. Continuous output beam steering over ±10º in polar and azimuthal directions via nanoscale positional tuning of electron injection point has also been demonstrated.

*  Holographic patterns designed to create a source of radiation with purposely structured complex wavefronts. I have demonstrated plasmonic patterns that upon electron excitation emit light beams with prescribed topological charge, up to 30.

*  A direction-division multiplexed holographic free-electron-driven light source. The source comprises a microscopic array of plasmonic surface-relief holographic domains, each tailored to direct electron-induced light emission at a selected wavelength into a collimated beam in a prescribed direction. Emission direction is switched by µm-scale repositioning of the electron injection point among domains. I show that cross-talk between adjacent and overlapping domains can be as low as -3 dB at a only 2 µm injection point separation, thereby allowing for small arrays (typically ~40 µm across) and rapid switching of the emission direction.

I also conducted computational studies of free-electron driven Smith-Purcell emission from composite gratings containing multiple slits per period, showing that the relative efficiency of resonant modes can be attenuated or enhanced with the addition and removal of narrow slits.

In summary, the nanoscale electron-driven light sources developed in this work offer an unprecedented level of control over the spectral characteristics, divergence, directionality and topological charge of emitted light. They may find application in lab-on-a-chip and sensor technologies, field-emission and surface-conduction electron emission display technologies, optical signal multiplexing, and charged-particle-beam position metrology.

More information

Identifiers

ORCID for Nikolai Zheludev: orcid.org/0000-0002-1013-6636

ORCID for Kevin MacDonald: orcid.org/0000-0002-3877-2976

Catalogue record

Export record