数值研究了He+在啁啾场与单极场下发射高次谐波及阿秒脉冲的特点.计算结果表明,当He+的初始波函数布局在基态与激发态的叠加态时,其谐波强度比单基态时增强7个数量级.随后在啁啾场及单极控制场的作用下,谐波发射的截止能量明显增强,谐波的干涉结构也明显减小.引入空间非均匀效应,谐波截止能量得到进一步延伸,形成一个320 eV的平台区.通过叠加谐波,可获得3个持续时间在45～48 as的X射线脉冲.其强度比单基态输出的脉冲增强5～6个数量级.%The generations of the high-order harmonic and the attosecond pulse from He + ion driven by the chirped pulse combined with the unipolar pulse have been numerically investigated .The results show that by preparing the initial state as the coherent superposition of the ground and the first excited states of He + ion ,the harmonic yield is enhanced by 7 orders of magnitude in comparison with the single ground initial state case .Further ,by introducing the laser chirp and the unipolar controlling pulse ,the cutoff energy of harmonic spectrum is remarkably enhanced ,and the interference structure of harmonic is also reduced .With the introduction of the spatial inhomogeneous effect ,the harmonic cutoff can be further extended ,resulting in a super-bandwidth of 320 eV .By superposition of harmonics ,three at-tosecond X-ray pulses with durations from 45 as to 48 as can be obtained ,which is 5 ～ 6 orders of magni-tude improvement in comparison with the single ground initial state case .
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