Quantum-mechanical effects in photoluminescence from thin crystalline gold films.

Luminescence constitutes a unique source of insight into hot carrier processes in metals, including those in plasmonic nanostructures used for sensing and energy applications. However, being weak in nature, metal luminescence remains poorly understood, its microscopic origin strongly debated, and its potential for unraveling nanoscale carrier dynamics largely unexploited. Here, we reveal quantum-mechanical effects in the luminescence emanating from thin monocrystalline gold flakes.

Generation of entangled waveguided photon pairs by free electrons.

Entangled photons are a key resource in quantum technologies. While intense laser light propagating in nonlinear crystals is conventionally used to generate entangled photons, such schemes have low efficiency due to the weak nonlinear response of known materials and losses associated with in/out photon coupling. Here, we show how to generate entangled polariton pairs directly within optical waveguides using free electrons.

Nonlinear plasmonic response in atomically thin metal films.

Nanoscale nonlinear optics is limited by the inherently weak nonlinear response of conventional materials and the small light-matter interaction volumes available in nanostructures. Plasmonic excitations can alleviate these limitations through subwavelength light focusing, boosting optical near fields that drive the nonlinear response, but also suffering from large inelastic losses that are further aggravated by fabrication imperfections. Here, we theoretically explore the enhanced nonlinear response arising from extremely confined plasmon polaritons in few-atom-thick crystalline noble metal films.

Direct generation of entangled photon pairs in nonlinear optical waveguides.

Entangled photons are pivotal elements in emerging quantum information technologies. While several schemes are available for the production of entangled photons, they typically require the assistance of cumbersome optical elements to couple them to other components involved in logic operations. Here, we introduce a scheme by which entangled photon pairs are directly generated as guided mode states in optical waveguides.

Anisotropic second-harmonic generation from monocrystalline gold flakes.

Noble metals with well-defined crystallographic orientation constitute an appealing class of materials for controlling light-matter interactions on the nanoscale. Nonlinear optical processes, being particularly sensitive to anisotropy, are a natural and versatile probe of crystallinity in nano-optical devices. Here we study the nonlinear optical response of monocrystalline gold flakes, revealing a polarization dependence in second-harmonic generation from the {111} surface that is markedly absent in polycrystalline films.

Plasmonics in Atomically Thin Crystalline Silver Films.

Light-matter interaction at the atomic scale rules fundamental phenomena such as photoemission and lasing while enabling basic everyday technologies, including photovoltaics and optical communications. In this context, plasmons, the collective electron oscillations in conducting materials, are important because they allow the manipulation of optical fields at the nanoscale. The advent of graphene and other two-dimensional crystals has pushed plasmons down to genuinely atomic dimensions, displaying appealing properties such as a large electrical tunability.