High harmonic generation from a two-dimensional square lattice by a circularly polarized laser pulse

We investigate the high harmonic generation from a two-dimensional square lattice driven by a circularly polarized laser field. The harmonic spectra with 4k±1 orders are obtained by numerically solving the time-dependent Schrödinger equations with a two-dimensional periodic potential. It is found that the resulting harmonics are (nearly) circularly polarized in the low orders and are elliptically polarized in the plateau. The helicities of neighboring-order harmonics are alternant. By varying the wavelength and field strength of the driving laser pulse, we find that the cutoff energy of the harmonic spectrum from solids in a circularly polarized laser field exhibits a linear dependence on both the wavelength and field strength, which is similar to the conclusion obtained from the linearly polarized laser field. Our results deepen the understanding of ultrafast electron dynamics in solids driven by circularly polarized laser fields.