BEGIN:VCALENDAR VERSION:2.0 PRODID:Icfo X-PUBLISHED-TTL:P1W BEGIN:VEVENT UID:6a972b0c8fee3 DTSTART:20260910T080000Z SEQUENCE:0 TRANSP:OPAQUE LOCATION:ICFO Auditorium SUMMARY:ICFO | LEILA ROCÍO PRÉLAT OLIVARES CLASS:PUBLIC DESCRIPTION:Free electrons provide a powerful platform to control optical e xcitations at the nanoscale because they carry electromagnetic fields that are tightly localized and contain large evanescent wave-vector components inaccessible to propagating light. Although this property makes electron beams uniquely suited to address confined optical modes\, their full poten tial for technological applications is still being actively developed. Thi s Thesis aims to contribute to this effort by exploring novel phenomena th at arise when electron beams are incorporated into different optical syste ms.\nAs an introduction to the main concepts underlying this Thesis\, Chap ter 1 summarizes the theoretical frameworks used to describe electromagnet ic excitations\, with emphasis on linear and nonlinear optical phenomena\, surface waves such as polaritons and waveguide modes\, and electron beams .\nChapter 2 explores electron-driven excitation of surface polaritons thr ough resonant scatterers placed near polariton-supporting materials. The p assing electron polarizes a small resonant particle\, which then launches surface modes with a spectrum determined by the particle&rsquo\;s response . Our semi-analytical model reveals an optimum scatterer-surface separatio n that maximizes polariton emission. This approach is extended to periodic arrays of scatterers\, leading to a polaritonic analog of the Smith-Purce ll effect\, in which surface polaritons are emitted directionally into dif fraction orders controlled by the array period\, electron velocity\, and p olariton dispersion relation. Hexagonal boron nitride nanodisks coupled to graphene plasmons are identified as a realistic mid-infrared implementati on for small resonant scatterers\, with efficiency comparable to resonant lossless particles.\nIn Chapter 3\, we introduce wave-mixing cathodolumine scence as a nonlinear spectromicroscopy technique for detecting low-freque ncy excitations through visible-range optical readout. In this mechanism\, the evanescent field of a swift electron mixes with an external optical p ump through the second-order nonlinear response of a specimen\, generating sum- and difference-frequency photons. The method up-converts far-infrare d spectral fingerprints into the visible range\, avoiding the need for low -frequency light sources or detectors. Calculations for retinal-coated sil ver nanorods show that molecular vibrational signatures can be accessed wi th nanometer-scale spatial resolution under external illumination and visi ble-range detection.\nChapter 4 explores electrostatic control of electron trajectories as a means of tuning coupling to guided modes in silicon wav eguides. By deflecting electrons into grazing trajectories using a static electron-repulsive field\, the minimum electron-waveguide separation becom es a controllable parameter that governs both coupling strength and modal selectivity. In particular\, we consider three doped silicon waveguides pl aced on a sapphire substrate\, with the two side elements acting as latera l gating structures. Including image-force effects and collision threshold s\, the analysis predicts voltage-tunable photon yields reaching several p hotons per electron in realistic integrated photonic geometries.\nIn Chapt er 5 cylindrical waveguides are studied as mediators between free electron s and nanoscale absorbers. A gate-controlled grazing electron launches a g uided wave packet that subsequently drives a nearby resonant particle. Thi s waveguide-mediated channel concentrates the broadband electron field spe ctrally and spatially\, producing strong absorption enhancements relative to direct bare-electron excitation.\nIn summary\, this Thesis establishes free-electron-nanophotonic interactions as a versatile platform for nanosc ale excitation\, spectroscopy\, and control of optical\, polaritonic\, and guided modes\, with potential applications in integrated photonics\, mole cular sensing\, and quantum nanophotonics.\nThesis Director: Prof. Dr. Jav ier Garcí\;a De Abajo DTSTAMP:20260901T194412Z END:VEVENT END:VCALENDAR