This study reports the gate-tuning of graphene plasmons using infrared nano-imaging. Graphene, a two-dimensional material, allows for the tuning of its electronic and optical properties via gate voltage. The researchers used infrared nano-imaging to demonstrate that graphene/SiO₂/Si back-gated structures support propagating surface plasmons. The wavelength of these plasmons is approximately 200 nm at infrared frequencies, and they can propagate several times this distance. The amplitude and wavelength of these plasmons can be altered by gate voltage. The researchers also investigated plasmon losses using plasmon interferometry, revealing that the losses are linked to the exotic electrodynamics of graphene. The plasmonic figures of merit of their tunable graphene devices surpass that of common metal-based structures. Surface plasmons can exist in any material with mobile charge carriers whose response to electric fields remains reactive. In graphene, high-momentum plasmons are expected to appear in the terahertz and infrared domains. The researchers used a scattering-type scanning near-field optical microscope (s-SNOM) to access these high-momentum plasmons by illuminating the tip of an atomic force microscope (AFM) with a focused infrared beam. The spatial resolution of s-SNOM is set by the tip curvature radius and is an order of magnitude smaller than the plasmon wavelength. The direct observable of their method—the scattering amplitude s(ω)—is a measure of the electric field strength inside the tip-sample nanogap. This technique enables spectroscopy and infrared nano-imaging of graphene plasmons without the need for specialized periodic structures. The researchers observed interference patterns in graphene plasmons, which can be manipulated by gate voltage. They also demonstrated that the plasmon wavelength is directly determined by the carrier density. By imaging under gate bias, they showed that the plasmon wavelength decreases with the reduction in hole density. The plasmon damping rate was found to be roughly constant across different gate voltages. The researchers also found that the real part of the conductivity of graphene is as high as σ₁ ≈ 0.5e²/h, which is much higher than theoretical estimates but comparable to IR spectroscopy results for back-gated graphene. The study shows that graphene/SiO₂/Si structures are a potent plasmonic medium that enables voltage control of both the plasmon wavelength and amplitude. The plasmon wavelength in graphene is one of the shortest for any material, and the propagation length is comparable to that of gold in experiments monitoring strongly confined plasmons launched by AFM tips. The figure of merit λ_IR/λ_p = 50-60 for their back-gated devices surpasses that of conventional Ag-based structures. The intrinsic plasmonic losses in graphene can be reduced or eliminated through population inversion. The study also highlights the potential of graphene for active infrared plasmonics, withThis study reports the gate-tuning of graphene plasmons using infrared nano-imaging. Graphene, a two-dimensional material, allows for the tuning of its electronic and optical properties via gate voltage. The researchers used infrared nano-imaging to demonstrate that graphene/SiO₂/Si back-gated structures support propagating surface plasmons. The wavelength of these plasmons is approximately 200 nm at infrared frequencies, and they can propagate several times this distance. The amplitude and wavelength of these plasmons can be altered by gate voltage. The researchers also investigated plasmon losses using plasmon interferometry, revealing that the losses are linked to the exotic electrodynamics of graphene. The plasmonic figures of merit of their tunable graphene devices surpass that of common metal-based structures. Surface plasmons can exist in any material with mobile charge carriers whose response to electric fields remains reactive. In graphene, high-momentum plasmons are expected to appear in the terahertz and infrared domains. The researchers used a scattering-type scanning near-field optical microscope (s-SNOM) to access these high-momentum plasmons by illuminating the tip of an atomic force microscope (AFM) with a focused infrared beam. The spatial resolution of s-SNOM is set by the tip curvature radius and is an order of magnitude smaller than the plasmon wavelength. The direct observable of their method—the scattering amplitude s(ω)—is a measure of the electric field strength inside the tip-sample nanogap. This technique enables spectroscopy and infrared nano-imaging of graphene plasmons without the need for specialized periodic structures. The researchers observed interference patterns in graphene plasmons, which can be manipulated by gate voltage. They also demonstrated that the plasmon wavelength is directly determined by the carrier density. By imaging under gate bias, they showed that the plasmon wavelength decreases with the reduction in hole density. The plasmon damping rate was found to be roughly constant across different gate voltages. The researchers also found that the real part of the conductivity of graphene is as high as σ₁ ≈ 0.5e²/h, which is much higher than theoretical estimates but comparable to IR spectroscopy results for back-gated graphene. The study shows that graphene/SiO₂/Si structures are a potent plasmonic medium that enables voltage control of both the plasmon wavelength and amplitude. The plasmon wavelength in graphene is one of the shortest for any material, and the propagation length is comparable to that of gold in experiments monitoring strongly confined plasmons launched by AFM tips. The figure of merit λ_IR/λ_p = 50-60 for their back-gated devices surpasses that of conventional Ag-based structures. The intrinsic plasmonic losses in graphene can be reduced or eliminated through population inversion. The study also highlights the potential of graphene for active infrared plasmonics, with