利用两束同色激光场与中红外场形成的组合场驱动氦原子产生单个阿秒脉冲

Single attosecond pulse generated by helium atom exposed to the combined field of two laser pulses with the same color and midinfrared intense laser pulse

提出了使用两束同色激光场与中红外场形成的组合场驱动一维氦原子产生单个阿秒脉冲的方法.通过数值模拟研究了氦原子在组合场驱动下发射高次谐波的特点,谐波谱的截止位置可以拓展到Ip+12.6Up,对第二平台区域不同范围内高次谐波叠加均能得到单个阿秒脉冲,最短脉宽达42as,尤其是对平台区域的前端进行叠加,不仅可以得到单个阿秒脉冲,而且与截止位置附近高次谐波构造的阿秒脉冲相比,强度提高了3个数量级.经过经典和小波分析发现,中红外场的加入不仅使高次谐波谱平台区域得到了扩展,同时还抑制了电子长路径对高次谐波的贡献.

We propose a method to generate single attosecond pulse when one-dimensional helium atom is exposed to the combination of two laser pulses with the same color and a midinfrared laser pulse. We investigate the characteristic of the high-order harmonic by numerical simulation. It is shown that the cut-off position of the harmonic spectrum is extended to Ip＋12.6Up. By superimposing some orders harmonics on different region for the second plateau, all of the pulses obtained are single attosecond ones. Minimum pulse achieves 42 as. Especially, by superimposing the lower order harmonics of the second plateau, one can not only obtain single attosecond pulse, but also the intensity of the single pulse is three order of magnitude higher, compared to the attosecond pulse obtained near cut-off of harmonics. By classical and wavelet analysis, we found that the plateau region of the high-order harmonic generation spectrum is extended greatly and the contribution of the long electron trajectory is suppressed by adding the midinfrared laser pulse.