PhD Thesis Defense | Carlos Alberto Maciel Escudero

Probing nanoscale light-matter interactions with fast electrons and near-field optical probes

February 9, 11:00

CFM Auditorium

Candidate: Carlos Alberto Maciel Escudero

Supervisors:  Javier Aizpurua and Rainer Hillenbrand

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Summary

Polaritons are hybrid light-matter electromagnetic waves that result from the coupling between photons and dipolar excitations in matter, such as phonons in polar materials, plasmons in metals, or excitons in semiconductors. Polaritons provide a way to overcome the limitations imposed by the diffraction limit, making them promising building blocks for nanoscale light manipulation and control. A major challenge of polariton physics, however, stems from their large momentum mismatch with free-space photons, thus preventing their excitation using conventional far-field optical techniques.

This thesis aims at investigating the excitation of polaritons in the near field using a fast electron beam or light localized at a metallic tip. Specifically, we focus on the excitation of polaritons arising in anisotropic phononic media as well as polaritons that result from the coupling between electromagnetic modes and excitonic, or molecular vibrational modes. To this end, we introduce the fundamentals of polaritons and their near-field probing and analyze polaritonic systems in different scenarios.

Figure 1. Exciting nanoscale light-matter interactions with fast electrons and near-field optical probes. Schematic representation of a fast electron (green ray) and a nanotip (gray conical structure) interacting in the near field with a polaritonic medium (gray hexagonal pattern). The near-field interaction leads to the excitation of hybrid light-matter electromagnetic waves, i. e., polaritons (blue wavy arrows and concentric wavy lines) within the medium. The red wavy arrow represents the incident illumination focused onto the nanotip.