▎ 摘　　要

We present a unique scheme to efficiently enhance terahertz third harmonic generation (THG). By exploiting the high-order guided-mode resonance of graphene plasmonic grating, the off-plane transverse localized field can be suppressed, which enables the electromagnetic energy to be tightly concentrated and significantly enhanced in the monolayer graphene. Meanwhile, high density of in-plane hot spots can be excited to form a quasi-continuous enhanced-field profile called as hot surface. This can bring about the giant nonlinearity enhancement of terahertz field-graphene interaction, greatly pushing forward the enhanced THG in monolayer graphene to breakout the limitation of various patterned metamaterials. It is anticipated that the graphene plasmonic grating has promising application for nonlinear terahertz spectroscopy, imaging and communication.