激光强度依赖的阈下谐波产生机制  

Mechanism of laser intensity-dependent below-threshold harmonic generation

作　　者：郭春祥 焦志宏[1] 周效信[1] 李鹏程[1] Guo Chun-Xiang;Jiao Zhi-Hong;Zhou Xiao-Xin;Li Peng-Cheng(College of Physics and Electronic Engineering,Northwest Normal University,Lanzhou 730030,China)

机构地区：[1]西北师范大学物理与电子工程学院,兰州730030

出　　处：《物理学报》2020年第7期60-67,共8页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:11674268,11764038,91850209);西北师范大学青年教师科研能力提升计划(批准号:NWNULKQN-17-1)资助的课题.

摘　　要：利用广义伪谱方法精确数值求解了氢原子在强激光场中的三维含时薛定谔方程,获得了强激光中氢原子的含时波函数,利用时间依赖的偶极矩的傅里叶变换得到了高次谐波谱,研究了氢原子在强激光场中发射低于电离阈值的谐波谱对激光强度的依赖性.研究发现,激光强度在低于电离阈值的谐波产生的通道选择的过程中扮演着重要角色,主要有两种量子通道对阈下谐波的产生有贡献,即广义的短轨道和长轨道,其中长轨道对激光场强度比较敏感.结合小波时频变换、经典轨道分析、以及强度依赖的量子通道选择分析,本文阐明了其背后的物理机制.High-order-harmonic generation(HHG)is a fundamental atomic and molecular process in strong laser fields and plays a crucial role in the development of ultrafast science and technology.The essential features in HHG,such as the above-threshold harmonic plateau and cutoffs,can be well understood by the semiclassical threestep model.The HHG cutoff occurs approximately at the energy 3.17 U_p+I_P,where I_p is the atomic ionization potential,and U_p is the ponderomotive potential.In the past,most studies focused on the HHG above the ionization threshold,and the general pattern of the HHG spectrum can be qualitatively explained by means of the strong field approximation(SFA)and the quantum treatment of three-dimensional time-dependent Schr?dinger equation(TDSE).However,the SFA results in inadequate description for the process in the harmonic generation below the ionization threshold since it neglects the Coulomb potential and the detailed electronic structure of atoms.Recently,as a promising method to produce vacuum-ultraviolet frequency comb,the HHG in the near-and below-ionization threshold has been increased considerably.However,the dynamical origin of in these lower harmonics is less understood and largely unexplored.Here we perform an ab initio quantum study of the near-and below-threshold harmonic generation of hydrogen atom by means of the time-dependent generalized pseudospectral method.We study the intensity dependence of the harmonic spectra below the ionization threshold of hydrogen atom in the intense laser field.The high-order harmonic spectra are calculated by the Fourier transform of the atom induced dipole moment in the laser field.The below-threshold harmonic spectra yield is scaled as a function of the laser peak intensity.We find that the spectra yield in below-threshold harmonic generation(BTHG)dependents on the light intensity in the multiphoton ionization regime.And the laser intensity plays an important role in the channel selection process for BTHG.There are mainly two kinds of quantum channels to

关 键 词：强激光场 高次谐波 电离阈值 量子通道 

分 类 号：O562[理学—原子与分子物理] TN24[理学—物理]