Sub-2-cycle structured light pulses and their application to all-optical control of magnetism

磁性材料对技术的发展产生了巨大的影响。控制材料中的磁性通常需要永磁体或大型且低效的电磁体。这两种磁场源都禁止在高频下对磁性进行控制，这反过来又限制了磁性设备可能进行的信息处理的带宽。激光脉冲是可用于改变和测量材料性能的最短可控事件，其在技术上的应用范围正在迅速扩大。值得注意的是，激光脉冲包含的磁场比任何永磁体或电磁体都要强得多。不幸的是，它们的实用性是有限的，因为它们对材料的影响被激光脉冲所包含的电场的更强影响所掩盖。激光的一个独特的子类被称为“结构光”。“这些激光束的形状可能与我们习惯的传统圆形光束有很大不同，某些结构光束具有纯磁场。在这项工作中，我们将开发极短的结构光脉冲，用于向磁性材料引入持续数飞秒（1飞秒为百万分之一秒的十亿分之一）的磁场。这些强大而短暂的磁场将使我们能够以前所未有的速度操纵物质的磁性状态。此外，它们将使我们能够应用超快光谱学的巨大工具箱，以时间分辨的方式读出材料的磁响应。通过探索磁性的最终速度极限，我们将提供新的基本洞察力的动力学，引起物质的磁响应，同时阐明可能是有用的高带宽磁信息处理设备的影响。

Magnetic materials have strongly influenced the course of technology. Controlling magnetism in materials has conventionally required either permanent magnets or large and inefficient electromagnets. Both of these magnetic field sources prohibit control over magnetism at high frequencies which, in turn, limits the bandwidth of information processing that is possible with magnetic devices. Laser pulses are the shortest controllable events that are available for modifying and measuring the properties of materials, and their scope of application in technology is rapidly expanding. Remarkably, laser pulses contain magnetic fields that are considerably stronger than those available from any permanent magnet or electromagnet. Unfortunately, their utility is limited because their effect on materials is masked by the much stronger influence of the electric fields that laser pulses also contain. A unique sub-class of laser light is known as "structured light." The shape of these laser beams can be considerably different from the conventional round beams we are accustomed to and certain structured light beams feature pure magnetic fields. In this work, we will develop extremely short structured light pulses, which will be used to introduce a magnetic field that lasts several femtoseconds (1 femtosecond is one billionth of one millionth of a second) to magnetic materials. These strong and brief magnetic fields will enable us to steer the magnetic state of matter at speeds that have never before been possible. Moreover, they will allow us to apply the vast toolbox of ultrafast spectroscopy to read out the magnetic response of materials in a time-resolved fashion. By exploring the ultimate speed limits of magnetism, we will provide new fundamental insight into the dynamics that give rise to the magnetic response of matter and simultaneously elucidate effects that could be useful for high-bandwidth magnetic information processing devices.