Strong-Field Control of Plasmonic Properties in Core–Shell Nanoparticles

Utilization of the plasmonic response in nanosystems
is a key component
of nanophotonics that is typically altered by varying the incident
optical frequency or the material configuration. However, in this
work we demonstrate that employing intense, femtosecond laser fields
unlock nonlinear light–matter interactions such that precise
control of the optical response is achieved solely by adjusting the
incident intensity. The plasmonic properties of Au/SiO2 nanoshells are manipulated by exploiting the nonlinear index of
refraction of gold and experimentally observed by employing photoelectrons
emitted during the interaction as a sensitive, sub-wavelength probe.
A striking transition seen in the photoelectron energy spectrum between
the weak and strong-field regime is verified by a modified Mie theory
simulation that incorporates the nonlinear dielectric nanoshell response.
The exhibited intensity-dependent optical control of the plasmonic
response in prototypical core–shell nanoparticles paves the
way toward ultrafast switching and opto-electronic signal modulation
with more complex nanostructures.