Orientation-dependent High Harmonic Generation from h-BN(Invited)
The absorption and emission of light by matter plays a crucial role in the development of science and technology.High Harmonic Generation(HHG)presents an extremely nonlinear optical radiation induced by the interaction of intense laser fields with matter.Over the past two decades,HHG in gaseous materials has been extensively studied and regarded as a vital tool for advancements in ultrafast science.The fundamentals of gaseous HHG can be explained by the semi-classical three-step model,the understanding of microscopic processes in HHG has laid the foundation for atto-second physics and metrology,including the ability to probe atomic structure and dynamics and molecular systems.Recently,there have been reports of HHG occurring in various solid-phase materials,the targets of solid-state high harmonic studies have been extended from bulk metals,semiconductors,and insulators to low-dimensional nanostructures.Two-dimensional materials can neglect the propagation effects in the direction of laser propagation,and thus become ideal materials for the study of high-harmonic carrier dynamics.An important phenomenon of HHG in solids is the anisotropy.Due to the modulation of the lattice symmetry,the harmonic signals generated by the driving light polarized along the different directions of the crystal are quite different,it has shown potential applications such as reconstructing crystal band structure,measuring Berry curvature,and investigating topological phase transitions.In this paper,we have investigated the process of HHG from monolayer h-BN by using the tight binding energy band and solving the two-band SBEs.We show that the yield of harmonics displays a periodicity of 60° as the azimuthal angle between the h-BN and driving field are varied,consistent with the symmetry of the laser and the crystal.Notably,an intriguing pattern in the orientation-dependent HHG is observed.Specifically,we decompose the high harmonics into components parallel and perpendicular to the driving light,the parallel component of the odd-order harmonics in the cut-off region exhibits an angular shift of 30° compared to the other orders,and this angular shift is independent of the change of driving light intensity.Comparison of the harmonic spectra of the driving light polarization along the zigzag direction and the armchair direction reveals that the harmonic spectrum has a sharp decrease(cut-off region)for harmonics above H17 when the driving field is along the zigzag direction.The harmonic intensities below the H17 are stronger in the zigzag direction than in the armchair direction,and the sharp decrease in the zigzag direction harmonics at the H17 results in the harmonic intensities being less than those in the armchair direction harmonics.Therefore,we believe that the angular shift of the intensity modulation of odd-order harmonic parallel components are related to the cut-off of the zigzag directional harmonic spectrum.Furthermore,we found the energy at which this angle shift occurs is strongly correlated with the bandgap energy of h-BN,especially when close to the M-momentum channel bandgap.Through detailed analyses,we determine that the phase shift in the intensity modulation of H17 arises due to the interference of different momentum channels and the interference of different polarity half-periods.We believe that this phenomenon is not coincidental,that the effect of energy band structure on harmonics is significant.The angular shift of odd-order harmonics holds important potential for developing techniques to probe the energy band structure of solids through HHG.
High harmonic generationStrong-field dynamicsTwo-dimensional materialOrientation-dependentAngular shift
郑文洋、刘灿东、白亚、刘鹏、李儒新
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中国科学院上海光学精密机械研究所 强场激光物理国家重点实验室,上海 201800
中国科学院大学,北京 100049
张江实验室,上海 201210
高次谐波 二维材料 强场动态 方向依赖 角度偏移
National Natural Science Foundation of ChinaNational Natural Science Foundation of ChinaNational Natural Science Foundation of ChinaYouth Innovation Promotion Association of the Chinese Academy of SciencesScientific Instrument Developing Project of the Chinese Academy of SciencesCAS Project for Young Scientists in Basic Research
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