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Future Optics International Lab makes another major breakthrough in the field of photon orbit angular momentum

March 18, 2020

Future International Optics Laboratory (FIPL), led by Academician Zhuang Songlin and Academician Gu Min, made another major breakthrough in the field of photon orbit angular momentum. The nanophotonics team, led by Professor Zhan Qiwen, demonstrated for the first time in experiment that a new type of light field with a space-time vortex phase and carrying the photon lateral orbital angular momentum creates a brand-new photon orbital angular momentum freedom. The breakthrough has great academic and application values in the fields of communication, optical information processing, quantum optics, particle manipulation, particle collision, and relativistic space physics. The research results, "Generation of spatiotemporal optical vortices with controllable transverse orbital angular momentum", were published online on February 24 in the world's top journal "Nature-Photonics".
Photons have linear momentum in the direction of beam propagation. Photons can also carry angular momentum, including spin angular momentum related to circular polarization and orbital angular momentum related to vortex phase. Generally, the spin angular momentum and the orbital angular momentum of the photon are along the beam propagation direction. Photon angular momentum has been widely studied and applied in high-speed optical communication, particle manipulation, holographic imaging, quantum optics, and so on. Taking particle manipulation as an example, the spin angular momentum of a photon can cause a particle to rotate on its own axis, and the orbital angular momentum of a photon can cause a particle to rotate around the center of the beam, similar to the rotation and revolution of the earth. In recent years, studies have shown that in the high numerical aperture focused light field and the evanescent wave light field, there is a photon lateral spin angular momentum perpendicular to the beam propagation direction. The lateral spin angular momentum of photons has received extensive attention and research in photon spin-orbit angular momentum coupling, quantum optical communication, and directional propagation of surface plasmon primitives, and the photon lateral orbit angular momentum perpendicular to the beam propagation direction has not been reported. .
The team of University of Shanghai for Science and Technology successfully generated and characterized ultra-short pulsed optical wave packets carrying lateral photon orbital angular momentum using a Fourier transform based on the space frequency-frequency surface to the space-time surface of Fourier transform. This new type of light wave packet has a transverse multicolor wave vortex phase structure. While the photon energy is rapidly propagating forward, the photon energy flow rotates around a lateral axis that moves with the wave packet, forming a photon "hurricane" similar to a fast moving photon. The angular momentum of the photon's lateral orbit can theoretically have an infinite number of values, also known as the topological charge, which can be controlled by the vortex phase of a multicolor wave.
   The research progress of photon lateral orbital angular momentum is another major breakthrough in the field of photon orbital angular momentum. This study revealed a completely new light field state, unveiled a new dimension of photon orbital angular momentum, and would have broad potential applications in the fields of light field interaction with atoms and molecules, micro nano structures and devices, macro universe and relativity research, etc.

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