Thermal manipulation of plasmons in atomically thin films

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.

Plasmonics: photothermal modulation

A new breed of ultrafast light modulators that operate across the visible to terahertz regions may be possible by harnessing photothermal control of plasmons in graphene and thin-metal films. Theoretical analysis performed by Eduardo Dias and coworkers from the ICFO research institute in Barcelona, Spain suggests that ultrafast optical excitation of thin gold/silver-graphene structures can significantly raise the electron temperature in the carbon layer and as a result dramatically modify the plasmonic response. Calculations indicate that strong changes (>70%) in the optical reflection of such structures are possible, with a strength that increases with the fluence of the excitation pulses. Importantly, the fluence is below the damage threshold of the materials. The photothermal modulation approach could have useful applications ranging from all-optical light modulation to optical sensing.