Compact light sources from free electron interaction with nanostructures and nanomaterials

• Main Author: Nussupbekov, Ayan
• Other Authors: Chong Yidong
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2023
• Subjects: Science::Physics::Optics and light
• Online Access: https://hdl.handle.net/10356/170009
• Institution: Nanyang Technological University

In the last decade, free-electron-driven light sources have had tremendous success in generating chip-scale, tunable, directional, broadband light emission. Recent research has shown the applications of such nanoscale devices in quantum computing, nanophotonics, and medical diagnostics. Further development of methods involving free electron interaction with nanomaterials and nanostructures is vital in bringing into light the rich properties of the nanoworld. This thesis reports on the development of nanostructure and nanomaterial design meth\hyp{}ods for efficient free-electron-driven light sources operating in the visible, infrared, and THz regimes. It is focused on the design of nanostructures tuned to obtain efficient light emission or light sources with tailored spectra and spatial profiles. We introduce the concept of a nanowell --- a nanostructure consisting of a metallic hole-ridge that enables efficient radiation emission when electrons pass through the nanohole. We utilize strong localized surface plasmon modes on the nanowell surface to achieve radiated power as high as 90\% of the theoretical limit. The intensity of light emission from a nanowell can exceed the radiation emission intensity of a regular nanohole by over 100 times. In addition, we demonstrate that the output radiation of such a device can be tuned over a broad spectrum of visible and near-infrared wavelengths. Next, we study the use of aperiodic sequences for efficient optimization of light emission from an electron beam's interaction with a grating. In particular, we show that the spectral and spatial profiles of light emission can be inverse designed to fit desired objective functions. Our method based on aperiodic sequences outperforms traditional periodic and customized grating optimization schemes, providing a promising approach to systematic wavefront shaping. Lastly, by utilizing the properties of carriers in two-dimensional materials, we demonstrate how free-electron-like light emission can be generated from nanomaterials placed atop periodic gratings. We show that in such a configuration, where the gap between electron-like carriers in nanomaterials and grating is minimal, near-field excitation can be exploited to generate enhanced light emission in the THz regime.