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高次谐波是获得阿秒紫外光源最主要的方法之一, 是强场超快领域研究的热点问题, 具有非常广泛的应用前景. 本文围绕如何产生超连续高次谐波平台及单个超短阿秒脉冲面临的问题, 概述了这方面研究的进展, 并从理论上展示了一种有效可行的方案, 即将强激光场中的含时薛定谔方程与非约束优化算法相结合, 以扩展谐波平台最宽为目标函数, 分别优化双色和三色组合激光场并驱动氦原子产生超连续高次谐波谱. 优化后的双色组合激光场驱动氦原子产生的超连续谐波谱平台达到了100阶, 叠加获得了最短25 as的单个阿秒脉冲; 优化后的三色组合激光场驱动氦原子产生的超连续谐波谱平台宽度达到了170阶, 叠加获得最短17 as的单个阿秒脉冲, 同时谐波转换效率也有所提高. 为了给实验提供切实可行的参考, 本文以优化的双色组合激光场情况为例, 基于同时求解含时薛定谔方程和麦克斯韦方程, 进一步考虑了介质宏观演化效应对单原子层次产生阿秒脉冲的影响, 发现利用远场轴外量子通道的空间选择性可以获得更短的单个阿秒脉冲.High-order harmonic generation, which is a hot topic of strong ultrafast fields, is one of the most important ways for obtaining the ultraviolet attosecond sources, and has a very wide application prospect. This work focuses on the challenges of the generation of either short or high attosecond pulses. We present the research progress of the high-order harmonics and attosecond pulse generation, and propose an effective and feasible method, and show some results. Specifically, combining the time-dependent Schrödinger equation and new unconstrained optimization algorithm, the objective function with the aim of the widest supercontinuum plateau of He atom is designed and the optimized two-color and three-color laser fields are obtained. The supercontinuum spectra extend up to 100 harmonic orders for the case of the optimized two-color laser field. As a result, a single ultrashort attosecond pulse of 25 as is produced. For the three-color case, the supercontinuum spectra reach up to 170 harmonic orders, and the width of single shortest attosecond pulse obtained by superposing pulses from low order (110 order) to high order (280 order) is obtained to be 17 as . Taking the optimized two-color laser field for example, the macroscopic medium propagation is discussed by solving the Maxwell equation. The results show that the selectivity of quantum trajectories from far-field space distribution can obtain the single ultra-short attosecond pulse.
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Keywords:
- high-order harmonic generation/
- attosecond pulse generation/
- strong laser field/
- macroscopic media propagation
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$ l $ $ \alpha $ $r_{\rm{c}}$ S $ A_1 $ $ A_2 $ $ B_1 $ $ B_2 $ $ 0 $ $ 0.28125 $ $ 2.0 $ $ -7.9093912 $ $ -10.899664 $ 0 $ 1.7 $ $ 3.8 $ $ 1 $ $ 0.28125 $ $ 2.0 $ $ 1.50094970 $ $ 0.11297684 $ 0 $ 1.3 $ $ 3.8 $ $ 2 $ $ 0.28125 $ $ 2.0 $ $ 0.88294766 $ $ -0.032043029 $ 0 $ 1.3 $ $ 3.8 $ $ 3 $ $ 0.28125 $ $ 2.0 $ $ 0.41193110 $ $ -0.129391180 $ 0 $ 1.3 $ $ 3.8 $ $ \geqslant 3 $ $ 0.28125 $ $ 2.0 $ $0$ $0$ 0 $ 1.3 $ $ 0 $ 
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