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

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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.