Recently, the International Laboratory of Future Optics at University of Shanghai for Science and Technology, led by academicians Zhuang Songlin and Gu Min, have made another breakthrough in the field of photon orbital angular momentum. The Nano Photonics Team is the first in the world to realize the time-space wave packet with photon transverse orbital angular momentum which changes rapidly with time. The research has important applications in ultrafast optical information processing and transmission and also in the ultrafast effect of photon orbital angular momentum and micro-nano structures. The result, “Generation of ultrafast spatiotemporal wave packet embedded with time-varying orbital angular momentum”, was published as a short communication online in Science Bulletin, a top-level comprehensive journal.
The beam with vortex phase can carry photon orbital angular momentum. One revolution of vortex phase is usually at an integer of 2, which is called topological charge. The magnitude of the photon orbital angular momentum is equal to the product of the reduced Planck constant and topological charge. The orbital angular momentum of most vortex beams does not change with time. The time-varying nature of angular momentum has important applications in optical communication, information processing, and the ultrafast interaction of light and matter. Recently, Rego et al. of University of Salamanca, Spain, published a paper in Science demonstrating a beam that rapidly changes the longitudinal orbital angular momentum of photons over time, which is called a “self-torque beam”. However, the technique is based on the generation of high-order harmonics in extreme ultraviolet, and the experimental method is very complex and has a lack of controllability.
Based on the method of generating optical transverse orbital angular momentum recently published by them in Nature Photonics, the Nano Photonics Team at USST has demonstrated for the first time in experiments that it can precisely and controllably generate transverse orbits carrying photons that change rapidly with time. The spatiotemporal wave packet generated in the experiment has two spatiotemporal vortices with topological charges of +1 and -1, corresponding to the photon transverse orbital angular momentum of +1 and -1, respectively. The time interval between the two spatiotemporal vortices is precisely controllable between 0.5ps (2THz) and 1ps (1THz). Subsequent experimental studies are expected to achieve even shorter time intervals (< 100fs), more spatiotemporal vortices and higher topological charges. Such space-time wave packet carrying time-varying orbital angular momentum has potential applications in ultrafast optical switches, ultrafast optical communication, and ultrafast interaction between photon orbital angular momentum and micro-nano structures.
Source: C. Wan, J. Chen, A. Chong, and Q. Zhan, “Generation of ultrafast spatiotemporal wave packet embedded with time-varying orbital angular momentum,” Science Bulletin, https://doi.org/10.1016/j.scib.2020.04.037 (2020).