(a) The LLs near the K point superimposed on the electronic energy dispersion without a magnetic field E = ±v_F|p|. The magnetic field condenses the original states in the Dirac cone into discrete energies. The LLs in graphene are unequally spaced: . (b) Energy level diagram and optical transitions in a monolayer graphene interacting with probe and elliptical polarized coupling field. Graphene monolayer is a one-atom-thick monolayer of carbon atoms arranged in a hexagonal lattice, which we will treat as a perfect two-dimensional (2D) crystal structure in the x–y plane.