High-Order Harmonics from Interaction of Intense Laser with Solids


        Since the first observation of odd and even high-order harmonics generated from ZnO crystals (S. Ghimire et al., Nat. Phys. 2011, 7, 138), the dependence of the harmonic yields on the orientation of the laser polarization with respect to the crystal axis has never been properly interpreted. This failure has been traced to the lack of correct account of the phase of the transition dipole moment between the valence band and the conduction band. Using a two-band model based on the solution of semiconductor Bloch equations, the Atomic, Molecular & Materials Physics group (www.ammpg.net) of Professor Ruifeng Lu at Nanjing University of Science and Technology, together with the collaborator, the group of Professor Chii-Dong Lin from Kansas State University have demonstrated that the observed odd harmonics is directly related to the orientation dependence of the magnitude of the transition dipole, while even harmonics is directly related to the phase of the transition dipole (R. F. Lu, C. D. Lin and coworkers, Phys. Rev. Lett. 2018, 120, 253201, see the left figure). This theoretical work points out the essential role of complex transition dipole moment in understanding harmonic generation from solids that has long been overlooked so far, which takes an important step in strong-field dynamics in solids and will encourage such a rapidly growing community to develop more complete models. In the beginning of year 2019, the AMMP group will publish an invited review article in journal of Advances in Physics: X which summarizes recent numerical methods for high order harmonic generation in solids, please refer to DOI: 10.1080/23746149.2018.1562982 and see the right figure.