At present, the ellipticity and orientation dependence of solid harmonic yield have been widely studied, but the influence of excitation mechanism on them remains relatively unexplored. Here, taking graphene as an example, we investigate the ellipticity and orientation dependence of harmonic yield at different laser frequencies by solving the semiconductor Bloch equations. Our results reveal a transition from anomalous to normal in the ellipticity dependence as the laser frequency increases. Simultaneously, the structure of the orientation dependence undergoes a transformation. By analyzing the conduction-band electron populations, we attribute these changes to the transformation of the dominant excitation mechanism. At low frequencies, tunneling ionization dominates, whereas at high frequencies, multiphoton ionization prevails. Furthermore, the limitation of the solid Keldysh parameter is discussed. These findings underscore the crucial role of the dominant excitation mechanism in solid high-order harmonic generation.

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• High-order harmonic generation
• Light-matter interaction