Nonlinear Thermoplasmonics in Graphene Nanostructures

The linear electronic dispersion
relation of graphene endows the
atomically thin carbon layer with a large intrinsic optical nonlinearity,
with regard to both parametric and photothermal processes. While plasmons
in graphene nanostructures can further enhance nonlinear optical phenomena,
boosting resonances to the technologically relevant mid- and near-infrared
(IR) spectral regimes necessitates patterning on ∼10 nm length
scales, for which quantum finite-size effects play a crucial role.
Here we show that thermoplasmons in narrow graphene nanoribbons can
be activated at mid- and near-IR frequencies with moderate absorbed
energy density, and furthermore can drive substantial third-harmonic
generation and optical Kerr nonlinearities. Our findings suggest that
photothermal excitation by ultrashort optical pulses offers a promising
approach to enable nonlinear plasmonic phenomena in nanostructured
graphene that avoids potentially invasive electrical gating schemes
and excessive charge carrier doping levels.