Isolated attosecond pulses (IAPs) are generated via applying amplitude gating on high-order harmonic generation driven by carrier-envelope phase stabilized 5.2 fs pulses with 0.5 mJ pulse energy at 770 nm central wavelength at the Synergetic Extreme Condition User Facility. A continuum ranging from 70 to 100 eV that supports sub-100-attosecond pulse is extracted by Zr foil and Mo/Si multilayer mirror. We demonstrate the characterization of the IAP. The retrieved pulse duration is 86 attoseconds. The developed attosecond laser beamline with repetition rate up to 10 kHz is available for users to conduct attosecond photoelectron spectroscopy researches with a capability of coincidence measurement.

利用强场近似理论开展了正交偏振双色场与氦原子相互作用产生高次谐波和阿秒脉冲的理论研究。正交偏振双色场由少周期的4 fs钛宝石驱动脉冲激光和与它偏振方向垂直的8 fs倍频控制脉冲构成。研究发现，通过合理选择两束脉冲之间的相对相位，能够控制高次谐波发射过程中长、短电子轨道的选择。当相对相位调整为1.2π时，平台谐波主要来自短轨道电子的贡献，由于其运动时间短、波包扩散少，且没有与长轨道电子谐波产生干涉，沿驱动脉冲电场方向的高次谐波谱具有较高强度和较小调制幅度的超连续平台区，通过对第120次到第180次超连续谐波进行傅里叶变换，可产生脉宽为54 as的高强度孤立阿秒脉冲。所提方案对组合脉冲相对相位的选取要求并不严苛，在0.3π的变化范围内皆可获得脉宽较短的孤立阿秒脉冲，同时控制脉冲电场强度的变化对上述数值模拟结果的影响也很小。

The availability of ever stronger, laser-generated electromagnetic fields underpins continuing progress in the study and application of nonlinear phenomena in basic physical systems, ranging from molecules and atoms to relativistic plasmas and quantum electrodynamics. This raises the question: how far will we be able to go with future lasers? One exciting prospect is the attainment of field strengths approaching the Schwinger critical field ${E}_{\mathrm{cr}}$ in the laboratory frame, such that the field invariant ${E}^2-{c}^2{B}^2>{E}_{\mathrm{cr}}^2$ is reached. The feasibility of doing so has been questioned, on the basis that cascade generation of dense electron–positron plasma would inevitably lead to absorption or screening of the incident light. Here we discuss the potential for future lasers to overcome such obstacles, by combining the concept of multiple colliding laser pulses with that of frequency upshifting via a tailored laser–plasma interaction. This compresses the electromagnetic field energy into a region of nanometre size and attosecond duration, which increases the field magnitude at fixed power but also suppresses pair cascades. Our results indicate that laser facilities with peak power of tens of PW could be capable of reaching ${E}_{\mathrm{cr}}$ . Such a scenario opens up prospects for the experimental investigation of phenomena previously considered to occur only in the most extreme environments in the universe.

原子或分子的光电离是强场物理效应的基础。在强场近似下，对于少周期激光脉冲，实验中已证实采用双色激光脉冲场可以增强和相干控制分子的电离。同时，双色场相对相位也是非常重要的参数，借助相位结构的改变来调节分子的电离亦是控制和优化激光与物质相互作用的重要方式。基于此，本文借助Lewenstein模型计算了双色激光脉冲场中利用CO分子高次谐波获得的阿秒脉冲，分析了不同分子取向下相对相位对分子电离以及产生阿秒脉冲的影响。结果显示，平台区域的超连续展宽在任意相对相位下均可产生，但随着分子取向和激光场相对相位的变化，电离较低时易获得超短孤立阿秒脉冲。

Spatiotemporal optical vortex (STOV) pulses carrying purely transverse intrinsic orbital angular momentum (TOAM) are attracting increasing attention because the TOAM provides a new degree of freedom to characterize light–matter interactions. In this paper, using particle-in-cell simulations, we present spatiotemporal high-harmonic generation in the relativistic region, driven by an intense STOV beam impinging on a plasma target. It is shown that the plasma surface acts as a spatial–temporal-coupled relativistic oscillating mirror with various frequencies. The spatiotemporal features are satisfactorily transferred to the harmonics such that the TOAM scales with the harmonic order. Benefitting from the ultrahigh damage threshold of the plasma over the optical media, the intensity of the harmonics can reach the relativistic region. This study provides a new approach for generating intense spatiotemporal extreme ultraviolet vortices and investigating STOV light–matter interactions at relativistic intensities.

通过数值求解单电子近似下的一维含时薛定谔方程，从理论上研究了受体掺杂半导体高次谐波的产生。结果表明，受体掺杂后第二平台的谐波效率比未掺杂时提高了约3~4个数量级。理论分析发现，掺杂改变了半导体的能带结构，使价带与第一导带以及第一导带与第二导带之间的带隙变窄，电子更容易隧穿到更高导带，使高导带的电子布居数增大，从而提高了第二平台的谐波效率。

随着超快超强激光技术的发展，强激光场光与物质相互作用的研究得到了广泛的关注。与此同时，光场调控技术在经典光学领域中的快速发展为光学操控提供了一个新的自由度。近年来，这两个不同领域之间的结合——具有空间结构的强激光场与物质相互作用，成为了强场物理前沿研究的热点之一。光电离和高次谐波是传统强场科学中两个十分基本又非常重要的物理过程。本文总结和综述了涡旋强激光场对光电离过程的影响和控制方面的研究进展，以及利用涡旋光束或者柱矢量光束驱动气体高次谐波产生等方面的最新工作，最后展望了具有空间结构强激光场与物质相互作用物理和光场调控研究的发展方向。