Plasmonics in Quantum region
Plasmonics is a rapidly growing field of research that has been intensely investigated in the past few decades, for its abundant underlying physics and fruitful practical applications in nanophotonics, integrated optics, optical communication and information processing. Benefiting from the ability to confine light below the diffraction limit and its ultrashort response time (~ 100 fs), a plasmonic-based optical device provides an ideal platform for the study of ultra-strong light-matter interaction and has demonstrated great promise in the strong-coupling quantum system, ultra-fast optical modulators and efficient chip-scale nonlinearities. However, the traditional plasmonic materials and nano-structures suffer from several drawbacks that hinder the further development of plasmonics, such as high optical loss and a limited nonlinear response. As a result, recent plasmonic-based devices have moved towards the quantum regime, searching for the better solution. And many recent reported results show noteworthy achievement. In this thesis, we have demonstrated that an efficient and tunable light source could be realized in delicately fabricated plasmonic nanostructures both in non-resonant and resonant conditions (with the metallic quantum well). It is done by engineering the electron wave-function coupling between plasmonic nanostructures (such as optical nano-antenna), and thus an efficient light generation is reached, which brings on-chip ultrafast and ultra-compact light sources one step closer to reality. In addition, we have shown that the nonlinear susceptibilities of ultra-thin plasmonic films could be engineered to be the state-of-the-art. It is done by introducing the quantum confinement into the plasmonic films (such as Au, Ag or TiN), so that a metallic quantum well is formed, which becomes new building blocks for the more complex plasmonic structures, such as metamaterials. This thesis starts from the theoretical investigation, followed by the nano-fabrication and experimental characterization, ends up with several interesting phenomena, their hidden physics and valuable applications. These quantum plasmonic materials and nano-structures realized in this thesis enable the further integration and functionalization of the plasmonic-based optical devices in the ultra-strong, efficient and fast light-matter interaction regime.