Ultrafast thermal manipulation of 2D plasmons

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Nanoscale photothermal effects enable important applications in cancer therapy, imaging, and catalysis. They also induce substantial changes in the optical response experienced by probing light, thus suggesting their application in all-optical modulation. In this work, we take advantage of the strong temperature modulation of the graphene conductivity to propose an all-optical technique of excitation and manipulation of plasmons in graphene and thin metallic films. Through spatial patterning of the temperature of electrons in a graphene film (which can be achieved from an optical grating formed by interfering two pump beams), the graphene conductivity acquires a periodic profile, enabling plasmons to be excited directly by diffraction of a probe beam in the imprinted thermal grating. We show that, when graphene is placed in the vicinity of a thin metallic film, this technique can be used to excite and manipulate the plasmons supported in this hybrid structure. Additionally, we demonstrate the ability of graphene, thin metals films, and graphene-metal hybrid systems to undergo photothermal optical modulation with depth as large as > 70% over a wide spectral range extending from the visible to the terahertz spectral 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 neighbouring metal films are severely attenuated by the presence of hot graphene electrons.