An improved method for the investigation of high-order harmonic generation from graphene  

作　　者：Zhong Guan Lu Liu Guo-Li Wang Song-Feng Zhao Zhi-Hong Jiao Xiao-Xin Zhou 管仲;刘璐;王国利;赵松峰;焦志宏;周效信(College of Physics and Electronic Engineering,Northwest Normal University,Lanzhou 730070,China;Department of Physics,College of Science,National University of Defense Technology,Changsha 410073,China)

机构地区：[1]College of Physics and Electronic Engineering,Northwest Normal University,Lanzhou 730070,China [2]Department of Physics,College of Science,National University of Defense Technology,Changsha 410073,China

出　　处：《Chinese Physics B》2020年第10期268-275,共8页中国物理B（英文版）

基　　金：Project supported by the National Natural Science Foundation of China (Grant Nos. 11764038, 11864037, 11765018, and 11664035);the Science Foundation of Northwest Normal University, China (Grant No. NWNU-LKQN-17-1).

摘　　要：High-order harmonic generation (HHG) of bulk crystals in strong laser field is typically investigated with semiconductor Bloch equations (SBEs). However, in the length gauge, it suffers from the divergence for the crystals with a zero band gap, such as graphene, using both Bloch- and Houston-states expansion methods. Here, we present a method of solving the SBEs based on time-dependent Bloch basis, which is equivalent to semiconductor Bloch equations in the velocity gauge. Using this method, we investigate the HHG of a single-layer graphene. It is found that our results for population are in good agreement with the other results. For a initial condition py = 0, we find the electrons just move in single valence band or conduction band, which are in accord with classical results. Our simulations on the HHG dependence of polarization of driving laser pulse confirm that 5th, 7th, and 9th harmonic yields increase to the maximal value when laser ellipticity ε ≈ 0.3. What is more, similar to the case of atoms in the laser field, the total strength of 3rd harmonic decrease monotonically with the increase of ε. In addition, we simulate the dependence of HHG on crystallographic orientation with respect to the polarization direction of linear mid-infrared laser pulse, and the results reveal that for higher harmonics, their radiation along with the change of rotation angle θ reflects exactly the sixfold symmetry of graphene. Our method can be further used to investigate the behaviors of other materials having Dirac points (i.e., surface states of topological insulators) in the strong laser fields.

关 键 词：high-order harmonic generation GRAPHENE velocity gauge DIVERGENCE 

分 类 号：TQ127.11[化学工程—无机化工]