Recently, under the leadership of academician Zhizhan Xu, the State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences has made latest progress in relativistic vortex laser physics.

The classical optical reflection law states that the reflected beam of a light is in the same plane of incidence with the incident beam and the normal, and the reflection angle is equal to the incident angle. However, in the relativistic regime of vortex-laser-plasma interaction, this basic principle is facing its new challenge. The intense vortex beam reveals significant new nonlinear propagation in reflection.

Through fully there-dimensional numerical simulation, researchers of Group Baifei Shen in the State Key Laboratory of High Field Laser Physics clearly demonstrated a new deflection effect deviating the reflection law caused by the symmetry-breaking of the reflection surface, which is beyond our routine recognition. When an intense vortex laser obliquely impinges onto an overdense plasma target, the reflected beam deflects out of the plane of incidence with an experimentally observable deflection angle. This process of the relativistic vortex beam, because of the orbital angular momentum it carries, is analogous to that of a table-tennis ball flying towards us with very intense left or right rotation that jumps swiftly to the left or right after it bounces from the paddle.

By using the Maxwell stress tensor, a more general tool describing the electromagnetic forces, researchers successfully revealed the substantial physics underlying this new effect. They found unsymmetrical shear stress components in the vortex beam acting on  the plasma foil, which breaks the rotational symmetry of the reflecting surface and dominating the deflection of the reflected intense vortex beam.

This work was published in journal of Physical Review Letters [Phys. Rev. Lett. 117, 113904(2016)].

Prior to this work, Prof. Shen’s group has achieved fruitful achievements in the relativistic vortex laser regime, such as Light fan driven by a relativistic laser pulse [Phys. Rev. Lett. 112, 235001(2014)] and Generation of intense high-order vortex harmonics [Phys. Rev. Lett. 114, 173901(2015)], which were all chosen as the Research Highlights by Nature Photonics.

This work was supported by the National Natural Science Foundation of China, the Ministry of Science and Technology, and the Strategic Priority Research Program of the Chinese Academy of Sciences.

Fig. Relativistic vortex beam deflecting the plane of incidence when reflected by the plasma foil.(Image by Lingang Zhang)

Contact:
Lingang Zhang
Shanghai Institute of Optics and Fine Mechanics
E-mail: lgzhang@siom.ac.cn