Fig. 3: Comparison of the orbital angular momentum (OAM) carried by the high-order harmonics emitted from anisotropic and isotropic targets.

OAM content of the left circularly polarized (LCP) and right circularly polarized (RCP) components of the HHG spectrum driven by a linearly polarized vector beam (LPVB) with \({{{{{{{\mathcal{P}}}}}}}}=1\)(a) and with \({{{{{{{\mathcal{P}}}}}}}}=2\)(b) in graphene. The interplay between the driving beam and crystal symmetries leads to the appearance of higher components—different from those of the driver—in the OAM content of the harmonic beams. For comparison, the OAM content obtained in argon driven by an LPVB with \({{{{{{{\mathcal{P}}}}}}}}=1\) is shown in (c). The OAM is extracted from the Fourier transform of the harmonic field along the azimuthal coordinate.