High harmonic generation from GaSe in a deep-UV range well above the bandgap

Abstract

We demonstrate high harmonic generation from GaSe in the deep-UV range with its photon energy reaching three times the bandgap energy. The harmonic spectrum represents a clear dependence on the crystal orientation with respect to the incident field, reflecting the 6̄2m point group. This reflection indicates the possibilities of high harmonic spectroscopy and high harmonic waveform control at frequencies well above the bandgap. The 3D time-dependent density matrix simulations reveal that the interband polarization mechanism dominates over the intraband current mechanism at frequencies above the bandgap and can generate attosecond bursts with characteristic sine-like waveforms.