Phase-matching and Peak Nonlinearity Enhanced Third-Harmonic Generation in Graphene Plasmonic Coupler

Abstract

Optical third-harmonic generation (THG) is important for various applications in nanomedicine, photocatalysis, and biosensing, but advances are held back due to small third-order nonlinear susceptibility ${\ensuremath{\chi}}^{(3)}$ and phase mismatch between the fundamental and third-harmonic waves. This work uses a graphene plasmonic coupler to achieve tunable, highly efficient THG through combining phase matching with resonant three-photon transitions. The study not only offers understanding and guidance for the problem at hand, but also points to further exploration of tunable, subwavelength coherent sources and ultracompact signal processing in the midinfrared and terahertz spectral regimes.