Abstract
Nanoscale photothermal effects enable important applications in cancer therapy, imaging and catalysis. These effects also induce substantial changes in the optical response experienced by the probing light, thus suggesting their application in all-optical modulation. Here, we demonstrate the ability of graphene, thin metal films, and graphene/metal hybrid systems to undergo photothermal optical modulation with depths as large as >70% over a wide spectral range extending from the visible to the terahertz frequency domains. We envision the use of ultrafast pump laser pulses to raise the electron temperature of graphene during a picosecond timescale in which its mid-infrared plasmon resonances undergo dramatic shifts and broadenings, while visible and near-infrared plasmons in the neighboring metal films are severely attenuated by the presence of hot graphene electrons. Our study opens a promising avenue toward the active photothermal manipulation of the optical response in atomically thin materials with potential applications in ultrafast light modulation.
Highlights
Heat generation driven by light absorption in nanostructures has proven useful for photothermal therapy[1,2,3], nanoscale imaging[4,5], data storage[6], photocatalysis[7] and photodetection[8,9]
Photothermal excitation has been proposed as a way to reach the visible and near-infrared (vis-NIR) plasmonic regime[37], but experimental attempts in this direction have only been limited to the mid-IR38,39
The manipulation of the graphene conductivity is possible through electrical gating or chemical doping, these methods cannot reach the ultrafast regime that might become necessary for future applications
Summary
Heat generation driven by light absorption in nanostructures has proven useful for photothermal therapy[1,2,3], nanoscale imaging[4,5], data storage[6], photocatalysis[7] and photodetection[8,9]. As an alternative approach to extrapolate the appealing plasmonic properties of graphene to vis-NIR, both monolayer noble metals[40] and hybrid systems formed by graphene in close proximity to few-nanometer metal films[41] have been predicted to display relatively low losses and a large electrical tunability in the vis-NIR domain. Progress in this direction has been recently made with the experimental demonstration of plasmons in laterally patterned sub-2-nm crystalline silver[42] and thicker amorphous gold[43] films. Epitaxially grown silver films serve as a novel platform for ultracompact nanophotonic devices that can further benefit from the comparatively high quality factor of plasmons in defect-free crystalline silver samples[42]
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