Defence of dissertation in the field of engineering physics, Rui Guo, M.Sc.
Manipulating the properties of metal nanoparticle arrays via lattice geometry
Rui Guo, M.Sc., will defend the dissertation "Dispersions and light-matter interactions in plasmonic lattices of different geometries" on 20 September 2018 at 12 noon at the Aalto University School of Science, lecture hall H304, Otakaari 1, Espoo. In this dissertation the collective modes supported by metal nanoparticle arrays were investigated systematically, focusing on the effects of lattice geometries. A new type of nanolaser was presented based on the geometrical effects.
Metal nanoparticle arrays show collective resonances, that is to say, under proper conditions the electromagnetic field surrounding the whole array will oscillate in coherence. This appealing property can be observed by spectral measurements where the dispersions indicate the collective modes; and can be implemented for different purposes from efficient LED lighting to lasing and Bose-Einstein condensation.
The collective modes, called surface lattice resonances (SLRs) can be tuned by different parameters. Here we emphasize the effects caused by the lattice geometries of the nanoparticle arrays. We are able to design and fabricate different lattice types – square, rectangular, rhombus, hexagonal, honeycomb and Lieb lattices. Spectral measurements reveal their different dispersions and polarization dependences, we also provide a simple way to interpret the dispersions even for the more complicated lattices.
By increasing the detectable angle, we can dig into the dispersions into the boarder of a region called the first Brillouin zone, where interesting phenomena can be observed. Especially, a honeycomb lattice immersed into a dye solution was found to be lasing at the K-points of the momentum space, namely, emitted six off-normal laser beams in a hexagonal configuration, upon a proper pumping condition. The six laser beams show different polarization dependences, from which we can conclude that they are all stemming from a singlet mode, one of the eigenstates supported by a honeycomb lattice. These new findings have especially promising applications as new light sources and in further studies in topological properties in nanophotonic systems.
Opponent: Professor Bill Barnes, University of Exeter, UK
Custos: Professor Päivi Törmä, Aalto University School of Science, Department of Applied Physics