Fig. 1. Basic structure information of graphene and transition path of Dirac cone under linearly polarized laser

Fig. 2. HHG from graphene and its anomalous ellipticity dependence

Fig. 3. Transition dipoles of graphene and gapped graphene

Fig. 4. Transient electron population and harmonic generation of graphene and gapped graphene under different ellipticity

Fig. 5. Ellipticity dependence of HHG from graphene， gapped graphene and the surface state of Bi₂Te₃

Fig. 6. Laser ellipticity for the largest harmonic yield vs. bandgap of gapped graphene