Wavelength-dependent interband contributions to high-order harmonics in MgO crystals

By numerically solving semiconductor Bloch equations under the three-band model, we investigate the highorder harmonic emission of bulk MgO crystals irradiated by linearly polarized laser pulses. Our results reveal that as the laser wavelength increases, interband polarization dominates over intraband current near the minimum band gap (7.8eV) in the ‹001› orientation, with contributions shifting toward lower-energy regions. This shift arises from enhanced electron density accumulation at the Brillouin zone boundary and increased interband harmonics between conduction bands. The findings highlight the critical role of laser wavelength in shaping harmonic contributions and deepen our understanding of high-order harmonic generation in crystalline materials.