▎ 摘　　要

Graphene is a promising material for terahertz radiation generation and has unique properties. In graphene, surface plasmon resonance (SPR) can be tuned in THz range in graphene by doping. Here we proposed a scheme of THz graphene plasmon (GP) excitation at difference frequency in graphene sheet by nonlinear mixing of two laser beams. Two laser beams that are obliquely incident, from the free space on the graphene sheet, are deposited on a dielectric substrate. These laser beams impart oscillatory velocities to electrons and exert a difference frequency ponderomotive force on the free electrons of the graphene film, the latter beats with the carrier density to produce a nonlinear current that excite THz SPs at difference frequency. The amplitude of THz graphene SPs falls monotonically because at higher frequency the coupling of SPs is weak.