涡旋正交双色场驱动N2-Ar混合气体高次谐波及新型阿秒脉冲产生

Generation of High-Order Harmonics and Novel Attosecond Pulses from N2-Ar Gas Mixture Driven by a Vortex Orthogonal Two-Color Field

  • 摘要: 本文基于二维含时薛定谔方程,系统研究并对比了正交双色场与涡旋正交双色场驱动下 N₂ 分子(HOMO 与 HOMO-1 混合态)、Ar 原子(基态)及其混合气体的高次谐波产生特性。研究结果表明,在正交双色场作用下,N₂ 分子 与 Ar 原子均能够产生明显的偶次谐波,且混合气体在平台区大多数谐波阶次上表现出显著的协同增强现象。在涡旋正交双色场中,23 阶之前 Ar 原子的谐波强度高于 N₂ 分子,而在 23 阶之后二者的强度关系发生反转;混合气体谐波谱整体呈现出向优势组分靠拢的特征。进一步研究发现,通过优化混合比例至 N₂ : Ar = 1: 9,并结合相对相位调控,可在特定谐波阶次实现相长干涉,从而有效提升目标谐波的辐射强度。时频分析结果显示,在涡旋场驱动条件下,短轨迹电子对谐波发射起主导作用。对 9–21 阶谐波进行频谱合成后,混合气体可产生脉宽约 506 as、椭偏率达 0.42 的阿秒脉冲,其综合性能优于单一 N₂ 分子所产生的阿秒脉冲(540 as,0.23)以及单一 Ar 原子所产生的阿秒脉冲(480 as,0.35)。此外,经过远场传播后,谐波光束的环形空间分布进一步演化为更加纯净的“甜甜圈”型结构,同时阿秒脉冲的椭偏率得到进一步提高。上述结果表明,利用混合气体与涡旋光场的协同作用,可实现对高次谐波及阿秒脉冲时空特性的有效调控,为发展新型可控超快光源提供了理论依据和可行途径。

     

    Abstract: Based on the two-dimensional time-dependent Schrödinger equation, this paper systematically investigates and compares the high-order harmonic generation (HHG) characteristics of N2 molecules (in a mixed state of HOMO and HOMO-1), Ar atoms (in the ground state), and their gas mixture driven by an orthogonal two-color field and a vortex orthogonal two-color field. The results show that under the orthogonal two-color field, both N2 molecules and Ar atoms can generate pronounced even-order harmonics, and the gas mixture exhibits significant synergistic enhancement for most harmonic orders in the plateau region. In the vortex orthogonal two-color field, the harmonic intensity of Ar atoms is higher than that of N2 molecules before the 23rd order, whereas the intensity relationship reverses after the 23rd order. The harmonic spectrum of the gas mixture overall tends to resemble that of the dominant component. Further studies reveal that by optimizing the mixing ratio to N2: Ar = 1: 9 and adjusting the relative phase, constructive interference can be achieved at specific harmonic orders, thereby effectively enhancing the radiation intensity of the target harmonics. Time-frequency analysis indicates that under the vortex field, short-trajectory electrons dominate the harmonic emission. After synthesizing the 9th–21st harmonics, the gas mixture produces an attosecond pulse with a pulse duration of approximately 506 as and an ellipticity of 0.42, whose overall performance is superior to that of pure N2 molecules (540 as, 0.23) and pure Ar atoms (480 as, 0.35). Furthermore, after far-field propagation, the annular spatial distribution of the harmonic beam evolves into a purer "donut" structure, while the ellipticity of the attosecond pulse is further improved. These results indicate that the synergistic effect of gas mixtures and vortex light fields can effectively control the spatiotemporal characteristics of high-order harmonics and attosecond pulses, providing a theoretical basis and a feasible approach for developing novel controllable ultrafast light sources.

     

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