Optical skyrmion serves as a crucial interface between optics and topology. Recently, it has attracted great interest in linear optics. Here, we theoretically introduce a framework for the all-optical generation and control of free-space optical skyrmions in extreme ultraviolet regions via high harmonic generation (HHG). We show that by employing full Poincaré beams, the created extreme ultraviolet fields manifest as skyrmionic structures in Stokes vector fields, whose skyrmion number is relevant to harmonic orders. We reveal that the generation of the skyrmionics structure is attributed to spatial-resolved spin constraint of HHG. Through qualifying the geometrical parameters of full Poincaré beams, the topological texture of extreme ultraviolet fields can be completely manipulated, generating the Bloch-type, Néel-type, anti-type, and higher-order skyrmions. We promote the investigation of topological optics in optical highly nonlinear processes, with potential applications toward ultrafast spintronics with structured light fields.

The generation of power- and wavelength-scalable few optical cycle pulses remains one of the major challenges in modern laser physics. Over the past decade, the development of table-top optical parametric chirped pulse amplification-based systems was progressing at amazing speed, demonstrating excellent performance characteristics in terms of pulse duration, energy, peak power and repetition rate, which place them at the front line of modern ultrafast laser technology. At present, table-top optical parametric chirped pulse amplifiers comprise a unique class of ultrafast light sources, which currently amplify octave-spanning spectra and produce carrier-envelope phase-stable, few optical cycle pulses with multi-gigawatt to multi-terawatt peak powers and multi-watt average powers, with carrier wavelengths spanning a considerable range of the optical spectrum. This article gives an overview on the state of the art of table-top optical parametric chirped pulse amplifiers, addressing their relevant scientific and technological aspects, and provides a short outlook of practical applications in the growing field of ultrafast science.

We demonstrated a scheme to differentiate the high-harmonic generation (HHG) originating from the surface states and bulk states of the topological insulator Bi2Se3. By adopting two-color mid-infrared laser fields on Bi2Se3, we found that the nonlinear response sensitively depends on the relative phase of the driving fields. The even harmonics arise from the surface states with a clear signature, whose modulation period equals the cycle of the second-harmonic generation (SHG) field. We reveal that the weak SHG perturbs the nontrivial dipole phase of the electron-hole pair in surface states, and thus leads to the modulation of HHG. It provides a means to manipulate the ultrafast dynamics in surface states through adopting a weak perturbing laser field.

采用第一性原理的含时密度泛函理论方法，从理论上研究了在少周期飞秒脉冲辐照下的氩晶体中孤立阿秒脉冲产生的最优控制。系统地研究了相对于晶体的不同激光偏振方向对孤立阿秒脉冲产生的影响，研究表明相对于晶体的激光偏振方向是产生孤立阿秒脉冲的敏感控制参数。对于Ar晶体，在最佳激光偏振方向上产生的孤立阿秒脉冲强度最大，约为相同激光脉冲驱动下Ar原子的11倍。本文研究结果对于理解强驱动脉冲激光下晶体中的阿秒电子动力学也有重要的意义。

We propose and numerically demonstrate a simple and background-free all-optical chiral spectroscopy technique for gas molecules. Our approach is based on high harmonic generation driven by a new type of laser beam that is produced by one linearly polarized single-color beam passing through a lens and a prism. It is shown that chiral and achiral signals are completely separated in frequency, indicating strong background-free and highly sensitive chirality detection. We believe this all-optical method can open new opportunities for ultrafast detection for chiral dynamics in the femtoseond to attosecond time scale.

The interest in tailoring light in all its degrees of freedom is steadily gaining traction, driven by the tremendous developments in the toolkit for the creation, control and detection of what is now called structured light. Because the complexity of these optical fields is generally understood in terms of interference, the tools have historically been linear optical elements that create the desired superpositions. For this reason, despite the long and impressive history of nonlinear optics, only recently has the spatial structure of light in nonlinear processes come to the fore. In this review we provide a concise theoretical framework for understanding nonlinear optics in the context of structured light, offering an overview and perspective on the progress made, and the challenges that remain.The interest in tailoring light in all its degrees of freedom is steadily gaining traction, driven by the tremendous developments in the toolkit for the creation, control and detection of what is now called structured light. Because the complexity of these optical fields is generally understood in terms of interference, the tools have historically been linear optical elements that create the desired superpositions. For this reason, despite the long and impressive history of nonlinear optics, only recently has the spatial structure of light in nonlinear processes come to the fore. In this review we provide a concise theoretical framework for understanding nonlinear optics in the context of structured light, offering an overview and perspective on the progress made, and the challenges that remain.

利用红外超快涡旋激光脉冲与气体介质相互作用可以产生携带轨道角动量的极紫外高次谐波。采用含有径向节点的拉盖尔-高斯（LG）光束作为驱动光，利用定量重散射模型计算单原子响应，通过求解谐波场在介质中传播的三维麦克斯韦方程以及在傍轴近似下的惠更斯积分，分别获得近场和远场高次谐波的强度和相位分布。结果表明：随着驱动光的径向节点数增加，高次谐波的强度分布呈现多环结构，相位分布上出现节点结构，强度分布的空间范围在近场减小，而在远场增大。相位匹配分析显示，短轨道和长轨道高次谐波的空间相干长度分布图对驱动激光的模式非常敏感，与高次谐波场在气体介质内的演化图像定性一致，解释了有径向节点的LG光束作用下产生的涡旋高次谐波的特征。

超快激光脉冲整形技术是基础研究和应用研究中广泛使用的重要实验手段，将其升级为亚周期激光脉冲光场整形技术是当今超快激光研究最前沿的重要课题之一。亚周期光场整形技术意味着对激光脉冲的完全控制，也标志着通过任意波形光场直接操控强场物理过程成为可能。亚周期光场整形技术的实现与亚周期光脉冲的产生建立在同样的技术基础之上，即超宽带光谱的产生与精确控制。实验上，用于产生亚周期光脉冲的光场相干合成技术同时也是亚周期激光脉冲光场整形有效且几乎唯一的实现手段。本文将综述介绍亚周期激光脉冲光场整形的研究进展，主要描述亚周期光场整形的技术基础、光场相干合成光源的实验结果及其在强场物理实验中的应用。