Interaction of Complex Interaction of Complex Beams with Epsilon-Near-Zero Media

Student thesis: Doctoral ThesisDoctor of Philosophy

Abstract

Structured optical beams offer new degrees of freedom for achieving unusual wavefronts, polarisation and optical angular momentum. These are demanded in many fields like microscopy, optical trapping, information encoding and more. Metasurfaces, initially developed for controlling the phase of light and its reflection and transmission beyond Snell’s law, provide a rich playground for generation and manipulation of structured beams. This work is at the intersection of these two fields, investigating the interaction of complex beams with plasmonic metamaterials. The latter consist of two-dimensional arrays of gold nanorods and exhibit a strong resonance in an epsilon-near-zero dispersion regime, that can be optically excited by an electric field parallel to the axis of the nanorods. The coupling to these plasmonic modes can hence be achieved with a change in the angle of incidence of illuminating light, or by its strong focusing. Here, we theoretically and experimentally investigate the coupling between the longitudinal field of complex vector beams and metamaterials in various dispersion regimes, including elliptic, hyperbolic and epsilon-near-zero. In particular, the modification of vectorial polarisation states upon interaction with metamaterials is investigated, and the control of the modal structure and diffraction properties of the vector beams is demonstrated as an effect of the metamaterial tailoring the longitudinal field. The theoretical model here developed allows an estimation of every quantity which is experimentally probed for different dispersion regimes of interactions and any vectorial structured beam. The obtained results may pave the way to a transformative development for the applications of complex vector beams and metasurfaces in optical communications, displays, security, biological or chemical sensing, and optical trapping.
Date of Award1 Jun 2024
Original languageEnglish
Awarding Institution
  • King's College London
SupervisorAnatoly Zayats (Supervisor) & Francisco Rodriguez Fortuno (Supervisor)

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