Figure 1
From: Origins of All-Optical Generation of Plasmons in Graphene

Illustration of electromagnetic fields (\(\overrightarrow{E}\)) (applicable to pump, probe, and DFG) propagating in the x-z plane. All the fields are p-polarized and the directions of propagation and polarizations are indicated by the red and black arrows respectively. The angles of incidence and transmission are defined in the figure as θ and ϕ.