Department of Applied Physics, Nanjing University of Science and Technology, Nanjing 210094, People's Republic of China.
J. R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, Kansas 66506, USA.
Phys Rev Lett. 2018 Jun 22;120(25):253201. doi: 10.1103/PhysRevLett.120.253201.
Since the first observation of odd and even high-order harmonics generated from ZnO crystals in 2011, 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 a correct account of the phase of the transition dipole moment between the valence band and the conduction band. Using a simple one-dimensional two-band model, here we demonstrate 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. Our result points out the essential role of the complex transition dipole moment in understanding harmonic generation from solids that has long been overlooked so far.
自 2011 年首次观察到 ZnO 晶体中产生的奇数和偶数高次谐波以来，人们从未对谐波产生与激光偏振相对于晶体轴的方向之间的关系进行适当的解释。这种失败可以追溯到缺乏对价带和导带之间跃迁偶极子相位的正确解释。本文使用简单的一维两能带模型，证明了观察到的奇数谐波与跃迁偶极子大小的取向依赖性直接相关，而偶数谐波与跃迁偶极子的相位直接相关。我们的结果指出了在理解长期以来被忽视的固体谐波产生中复杂跃迁偶极子的重要作用。
