Bridging infrared and visible light with nano-optics

Abstract

If human vision extended to the infrared (IR) spectrum, we would witness a world teeming with vibrant and distinct color combinations, each corresponding to unique molecular vibrations that absorb and emit IR light. Instruments allowing us to look at the world in the IR enable medical diagnoses, pigment dating, greenhouse gas monitoring, and help us resolve the birth of stars by peering deeper into space than ever before with the James Webb Space Telescope. However, the detection of IR photons presents significant challenges, with existing technologies being inefficient, prohibitively expensive, and impractical. To overcome these limitations, I develop nanophotonic tools are used to convert IR into visible light, leveraging the efficiency and widespread availability of visible light detectors. Plasmonics exploits the collective oscillations of electrons to funnel light to the nanoscale. In my thesis, I demonstrate the confinement of both IR and visible light using self-assembled plasmonic nanostructures, resulting in the first measurement of the IR absorption spectrum of a single dye molecule, using mid-infrared vibrationally-assisted luminescence. I then design layered metafilms, composed of gold nanoparticles with precise gap separations defined by nanometer-sized molecules, which support resonances in both the visible and IR ranges through ultra-strong coupling of collective plasmons with light. Such metafilms exhibit record-breaking enhancements in IR optical properties and enable the development of chip-scale visible-IR sensors. Finally, my research explores the use of simple gratings to achieve local ultrastrong coupling of IR-vibro-polaritons, leading to the discovery of the first conclusive Raman scattering signatures of vibro-polaritons. The development of dual IR and visible wavelength resonant nanostructures presents a new platform for ubiquitous IR sensing in point-of-care diagnostics and expands the possibilities for manipulating molecular vibrations in chemistry. The discoveries made in this thesis advance the field of IR sensing and deepen our understanding of how molecules can be controlled through IR light.