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Depletion effect in high-order harmonic generation with coherent superposition state
Journal of the Optical Society of America B ( IF 1.9 ) Pub Date : 2020-01-14 , DOI: 10.1364/josab.382154
Ngoc-Loan Phan , Thanh-Tuynh Nguyen , Hirobumi Mineo , Van-Hung Hoang

Enhancement of the conversion efficiency of high-order harmonics (HHG) generated from an atom in the superposition of two quantum states instead of the ground state is essential because of the recent application in the generation of ultrashort isolated attosecond pulses. In this study, we first confirm the enhancement for a more real system with full three-dimensional geometry and then investigate an interesting effect—the influence of the depletion on the HHG cutoff. For this purpose, we prepare a hydrogen atom initially in the coherent superposition of the ground and the first excited states and calculate the HHG by numerically solving the three-dimensional time-dependent Schrödinger equation (TDSE)—the TDSE method. We find that the plateau of HHG spectra with the coherent superposition state ends earlier than that of the ground state, which can be attributed to the depletion of the excited state. We justify this link by adopting the classical simulation and time-dependent ionization rate. Besides, we show that the conversion efficiency is sensitive to the existence of the excited state. Particularly, for some values of laser field intensity, the excited state population of about 1% increases HHG intensity by more than 5 orders. However, after a critical excited state population, the HHG intensity is stable with continuously increasing initial population of the excited state that is meaningful for experimental setups.

中文翻译:

具有相干叠加态的高次谐波产生中的耗尽效应

由原子在两个量子态而不是基态的叠加中产生的高次谐波(HHG)的转换效率的提高是必不可少的,因为最近在超短隔离阿秒脉冲的产生中得到了应用。在这项研究中,我们首先确认具有完整三维几何形状的更真实系统的增强,然后研究一个有趣的效果-损耗对HHG截止的影响。为此,我们首先在基态和第一激发态的相干叠加中制备氢原子,然后通过数值求解三维时变薛定ding方程(TDSE)(TDSE方法)来计算HHG。我们发现具有相干叠加状态的HHG光谱的平稳期早于基态的平稳期,这可以归因于激发态的耗尽。我们通过采用经典的模拟和随时间变化的电离速率来证明此链接的合理性。此外,我们表明转换效率对激发态的存在很敏感。特别是,对于某些激光场强度值,大约1%的激发态种群将使HHG强度增加5个数量级以上。但是,在临界激发态种群之后,HHG强度随着激发态初始种群的不断增加而稳定,这对于实验设置是有意义的。对于某些激光场强度值,大约1%的激发态种群将使HHG强度增加5个数量级以上。但是,在临界激发态种群之后,HHG强度随着激发态初始种群的不断增加而稳定,这对于实验设置是有意义的。对于某些激光场强度值,大约1%的激发态种群将使HHG强度增加5个数量级以上。但是,在临界激发态种群之后,HHG强度随着激发态初始种群的不断增加而稳定,这对于实验设置是有意义的。
更新日期:2020-02-03
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