When the polarization direction of the laser beam $\hat{\mathbf{E}}$ lies on the graphene plane, the absorption spectrum $A(\omega )$ is isotropic and includes one sharp peak and some shoulders. As for $\hat{\mathbf{E}}$ along the stacking direction, $A(\omega )$ is much weaker, and shows only one broadened peak. Because of the dipole matrix element $M^{cv}$ , the optical excitations do not fully reflect the features of electronic structures [or the joint density of states (JDOS)]. $M^{cv}$ plays an important role in the relationship between $A(\omega )$ and JDOS. It is strongly dependent on $\hat{\mathbf{E}}$ , showing an anisotropic property.