posted on 2016-03-15, 00:00authored byMohammad M. Jadidi, Jacob
C. König-Otto, Stephan Winnerl, Andrei
B. Sushkov, H. Dennis Drew, Thomas E. Murphy, Martin Mittendorff
Subwavelength
graphene structures support localized plasmonic resonances in the
terahertz and mid-infrared spectral regimes. The strong field confinement
at the resonant frequency is predicted to significantly enhance the
light-graphene interaction, which could enable nonlinear optics at
low intensity in atomically thin, subwavelength devices. To date,
the nonlinear response of graphene plasmons and their energy loss
dynamics have not been experimentally studied. We measure and theoretically
model the terahertz nonlinear response and energy relaxation dynamics
of plasmons in graphene nanoribbons. We employ a terahertz pump–terahertz
probe technique at the plasmon frequency and observe a strong saturation
of plasmon absorption followed by a 10 ps relaxation time. The observed
nonlinearity is enhanced by 2 orders of magnitude compared to unpatterned
graphene with no plasmon resonance. We further present a thermal model
for the nonlinear plasmonic absorption that supports the experimental
results. The model shows that the observed strong linearity is caused
by an unexpected red shift of plasmon resonance together with a broadening
and weakening of the resonance caused by the transient increase in
electron temperature. The model further predicts that even greater
resonant enhancement of the nonlinear response can be expected in
high-mobility graphene, suggesting that nonlinear graphene plasmonic
devices could be promising candidates for nonlinear optical processing.