Dispersions and light-matter interactions in plasmonic lattices of different geometries
A metallic nanoparticle array with a periodicity comparable to the single particle resonance can show extremely narrow resonances in its extinction spectrum. This phenomenon is known as the surface lattice resonance (SLR) of the array. In this dissertation we show how the SLRs can influence the emission of light from nearby emitters, leading to amplified spontaneous emission, lasing, or even condensation. In particular, we focus on the effects of the local density of states (LDOS) and of the lattice geometry. In Chapters 2 the interactions between SLRs and quantum dots (QDs) are studied. We developed a hybrid lithography-functionalization method to efficiently deposit silica-coated QDs onto the near-field regions of plasmonic nanoarrays. The emission from randomly-oriented QDs were found to couple with the collective SLR mode of the plasmonic lattice, resulting in amplified spontaneous emission (ASE) and a directional light source. The high LDOS of the SLRs, especially at the Gamma-point, significantly enhanced the spontaneous emission rate of the QDs by a factor of 30. In Chapter 3, we demonstrate for the first time Bose-Einstein condensation (BEC) of SLRs. SLRs can be considered as bosonic excitations, enabling, under suitable conditions, a macroscopic occupation of given modes. We employed a unique measurement scheme that allows to probe the evolution of the SLRs upon propagation. We showed that the interactions between propagating SLR excitations and organic molecules result to gradual decrease in energy of the SLR excitations and, finally, to BEC. Chapters 4 and 5 of this dissertation introduce work on geometry dependence of the SLRs. We proposed a simple theoretical framework to interpret the dispersions of nanoparticle arrays with different lattice geometries, such as square, hexagonal, and Lieb lattice. This framework allows designing the lattice parameters and tailoring the dispersion. Based on this we fabricated gold nanopartice arrays in a honeycomb lattice and measured the dispersions at the K-point in the first Brillouin zone edge. Previous works on lasing in plasmonic nanoparticle arrays rely on feedback at the Gamma-point. For the first time, we have observed lasing at the K-points in a plasmonic lattice, with specific polarization properties originating from the lattice geometry.
|Tila||Julkaistu - 2018|
|OKM-julkaisutyyppi||G5 Tohtorinväitöskirja (artikkeli)|