engleski

Plasmonic resonances of metal nanoparticles under tightly focused illumination

The interaction of light with metal nanoparticles leads to collective electron oscillations, known as surface plasmons, resulting in strong absorption and/or scattering of light. These effects enable a large application potential of metal nanoparticles in fields like chemical and biological sensing, waveguiding, photovoltaics or cancer diagnose and therapy. From a computational point of view, the interaction of plane-wave radiation with a spherical metal nanoparticle is exactly described by the Mie theory. However, due to the increasing ability to control the light-matter interactions at the nanoscale, it is possible to illuminate metal nanoparticles with tightly focused or shaped beams. In situations where the system dimensions are comparable to the size of the focal spot, the assumption of plane wave illumination, and therefore the validity of the Mie theory, is questionable. In this work we analyze the interaction of metal nanoparticles with plane waves tightly focused by an aplanatic lens. The nanoparticles are assumed to be placed in the focal region, where illumination can be highly inhomogeneous. Using the Richards-Wolf theory for the vectorial description of focused waves, the Mie theory can be extended. The effects of numerical aperture of the system as well as of the location of the particles in the focal region are studied for different particle sizes and configurations. Overall, the simulations indicate that tight focusing of the incoming radiation allows additional tailoring of plasmonic resonances of metal nanoparticles.

surface plasmon resonance; focused illumination; nanoparticle

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