Space-time wave packets (STWPs) constitute a broad class of pulsed optical fields that are rigidly transported in linear media without diffraction or dispersion, and are therefore propagation-invariant in the absence of optical nonlinearities or waveguiding structures. Such wave packets exhibit unique characteristics, such as controllable group velocities in free space and exotic refractive phenomena. At the root of these behaviors is a fundamental feature underpinning STWPs: their spectra are not separable with respect to the spatial and temporal degrees of freedom. Indeed, the spatiotemporal structure is endowed with non-differentiable angular dispersion, in which each spatial frequency is associated with a single prescribed wavelength. Furthermore, controlled deviation from this particular spatiotemporal structure yields novel behaviors that depart from propagation-invariance in a precise manner, such as acceleration with an arbitrary axial distribution of the group velocity, tunable dispersion profiles, and Talbot effects in space–time. Although the basic concept of STWPs has been known since the 1980s, only very recently has rapid experimental development emerged. These advances are made possible by innovations in spatiotemporal Fourier synthesis, thereby opening a new frontier for structured light at the intersection of beam optics and ultrafast optics. Furthermore, a plethora of novel spatiotemporally structured optical fields (such as flying-focus wave packets, toroidal pulses, and spatiotemporal optical vortices) are now providing a swath of surprising characteristics, ranging from tunable group velocities to transverse orbital angular momentum. We review the historical development of STWPs, describe the new experimental approaches for their efficient synthesis, and enumerate the various new results and potential applications for STWPs and other spatiotemporally structured fields, before casting an eye on a future roadmap for this field.

中文翻译：

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时空波包

时空波包 (STWP) 构成了一类广泛的脉冲光场，它们在线性介质中刚性传输，没有衍射或色散，因此在没有光学非线性或波导结构的情况下是传播不变的。这种波包表现出独特的特性，例如自由空间中的可控群速度和奇异的折射现象。这些行为的根源是支撑 STWP 的基本特征：它们的光谱在空间和时间自由度方面不可分离。实际上，时空结构具有不可微分的角色散，其中每个空间频率与单个指定波长相关联。此外，与这种特定时空结构的受控偏差产生了以精确方式偏离传播不变性的新行为，例如具有群速度的任意轴向分布的加速度、可调谐色散分布和时空中的 Talbot 效应。尽管 STWP 的基本概念自 1980 年代就已为人所知，但直到最近才出现了快速的实验发展。时空傅里叶合成的创新使这些进步成为可能，从而在光束光学和超快光学的交叉点开辟了结构光的新前沿。此外，大量新颖的时空结构光场（如飞焦波包、环形脉冲和时空光学涡旋）现在提供了一系列令人惊讶的特性，从可调群速度到横向轨道角动量。我们回顾了 STWPs 的历史发展，描述了其有效合成的新实验方法，并列举了 STWPs 和其他时空结构领域的各种新结果和潜在应用，然后着眼于该领域的未来路线图。