Extreme confinement of light on the nanoscale is today at the heart of many technological applications: confining light means confining optical energy to high densities, and this ultimately leads to drastically improved light-matter interaction. This is true, for instance, in non-linear systems, such as Raman scattering, which is proportional to the fourth power of the local electric field, and which is at the base of spectroscopic sensing of bio-molecules or gas traces. Or in photocatalysis, where high density of optical energy may lead to the splitting of stable molecules, such as water, into its constituents. In specific cases, however, light-matter interaction may also lead to exotic behaviors, such as the strong coupling regime, where photons (light) and matter excitations (such as excitons in semiconductors, i.e. transitions between valence and conduction band) may couple together to form mixed quasi-particles, called polaritons. In this particular situation, when the two excitations approach the same resonance frequency, a characteristic repulsion of modes splits the energy levels in two distinct values, yielding a gap of forbidden energy states.
The work carried out within this fellowship revolves around the study of sub-wavelength light-matter interaction in a specific environment: III/V semiconductors, and more specifically, heterostructures hosting quantum wells. Light interacting with such artificial materials can be absorbed at given frequencies, to promote a transition of an electron in the conduction band from an energy level to another: such discrete absorption mechanisms are called intersubband (ISB) transitions.
By patterning metallic nanoantennas directly on engineered heterostructures, thus achieving high electric field confinement within the active region, this MSCA Individual Fellowship addresses this last field of applied physics for both fundamental and applicative optoelectronic studies, investigating the interaction between light in the mid-infrared (mid-IR) range and the intersubband (ISB) transition in highly doped quantum wells. The goal of this proposal is to fully develop and exploit the potential of nanoantenna-enabled light confinement, funneling energy with unprecedented efficiency onto optically active materials. By taking advantage of a recently introduced novel class of vertical metallic nanoantennas, which have optimized energy harvesting properties (light is trapped and exchanged within arrays of 3D antennas in the form of oscillating ensembles of electrons), efficient layout (the out-of-plane character inherently provides a strong and conveniently oriented electric field) and a very small interaction volume (few hundreds of nanometers in diameter, which means extreme subwavelength energy confinement), this fellowship tackles two main objectives.
From one side, it explores a more fundamental aspect – the possibility of triggering and detecting strong coupling from a single nanoantenna optical resonator; from the other side, it exploits extreme subwavelength confinement to explore novel and efficient optoelectronic devices, such as quantum well infrared detectors (QWIPs) and second harmonic generation (SHG).
A new class of devices can stem from this action, yielding improved infrared cameras and detectors, or improved frequency up-conversion in non-linear optically active materials.
