Surface polaritons are fundamentally interesting for different technological applications, but their coupling to light is generally weak due to their momentum mismatch. In this work, we show that coupling plane-waves into polaritons is a fundamentally inefficient process. We show nevertheless that a small scatterer placed at a suitable distance from a given surface can couple light completely into the surface modes supported by the surface, under illumination by an adequately modulated field. We corroborate the analytical results by performing fully-numerical simulations using realistic setups, which exhibit a very strong enhancement of the absorption into surface plasmons under the prescribed optimal conditions.
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, via the spatial patterning of the temperature of electrons in a graphene film, which can diffract a probe beam and directly excite plasmons.
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.
Polaritons in 2D materials are fundamentally interesting for different technological applications, but their coupling to light is generally weak due to their momentum mismatch. In this work, we remarkably show that a small scatterer placed at a suitable distance from a given surface can couple light completely into the surface modes supported by the surface, under illumination by a modulated field. We present rigorous closed-form prescriptions for the modulation of the incident light beam which maximizes this coupling, depending on the characteristics of the scatterer and surface, and use the derived expressions to provide a rigorous theoretical analysis of the extremal light coupling to plasmons in different 2D materials (namely thin metals and graphene). We corroborate the analytical results by performing fully-numerical simulations using realistic setups, which exhibit a very strong enhancement of the absorption into surface plasmons under the prescribed optimal conditions.
Polaritons in 2D materials have been extensively studied over the past decade due to their fundamental interest and as a platform for applications in telecommunications and sensing. We quantify the coupling strength between light and 2D polaritons in thin films, using point and line scatterers, and find universal constraints that limit its fundamental maximum allowed values.
Nanoscale photothermal effects induce substantial changes in the optical response experienced by probing light. 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. We demonstrate the ability of graphene and thin metal films to undergo ultrafast photothermal optical modulation under pump-probe conditions, with depths as large as >70% over a wide spectral range.
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.
Polaritonic modes in two-dimensional van der Waals materials display short in-plane wavelengths compared with light in free space. However, such large confinement is accompanied by poor in/out optical coupling, which severely limits the application of polaritons in practical devices. Here, we quantify the coupling strength between light and 2D polaritons in thin films using accurate rigorous analytical methods. In particular, we obtain universal expressions for the cross sections associated with photon−polariton coupling by point and line defects, as well as with polariton extinction and scattering processes. Additionally, we find closed-form constraints that limit the maximum possible values of these cross sections. Our results bear fundamental interest for the development of 2D polaritonics and the design of applications based on these excitations.
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 address some fundamental limits in the coupling of radiation to 2D polaritons using free-propagating plane-waves. We study the scattering properties of 0D and 1D scatterers over a 2D or finite-thickness layer and quantify the coupling of light-to-polaritons cross-section for this process as a function of the scatterer effective polarizability. We formulate our results for both 0D and 1D scatterers, including material edges, and present them in simple closed-form expressions. We finally propose coupling light to plasmons using a graphene edge as a configuration which maximizes the coupling efficiency. Furthermore, we show that the adequate shaping of the impinging radiation can be used as a strategy to overcome the limitations of using plane-waves, and we demonstrate how to optimize this shaping for several different purposes.
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, 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. We further 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.
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