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Quadruple-enhanced four-wave mixing in nanometer plasmonic hotspots: classical theory and experiments

Efficiency is a critical factor limiting the applications of nonlinear plasmonic devices. We show by theory and experiments that high efficiency four-wave mixing (FWM) is achieved in nanometer size plasmonic hotspots, which open up opportunities for nanoscale light manipulation. First, we present a classical calculation on the efficiency of frequency conversion by quadruple-enhanced FWM for a Kerr nonlinear material loaded in the plasmonic hotspot of a gold nanosphere dimer. The results indicate the viability to achieve over 10% efficiency in a nanometer volume under milliwatts of pump power consumption or less. Next, we present experimental results which show around 10% linewidth broadening of a 100 fs pulsed laser by a monolayer graphene in a gold nanosphere-plane junction. Such a high efficiency, low power, and nanoscale nonlinear process is a promising candidate for making ultra-compact and high-speed nonlinear optical devices.