Recently, the group of Prof. Min Hu — part of Academician Shenggang Liu’s team at the Terahertz Center, School of Electronic Science and Engineering, UESTC — building on nearly a decade of theoretical and experimental work, became the first in the world to theoretically propose and investigate the “tunable optical topological transition of Cherenkov radiation”.
The result was published under the title “Tunable optical topological transition of Cherenkov radiation” in Photonics Research, a top-tier journal in optics and photonics. The School is the sole first-author and corresponding-author affiliation. Associate Prof. Tao Zhao is the corresponding author, and Tianyu Zhang, a direct-PhD student enrolled in 2018, is the first author. Co-authors also include Academician Shenggang Liu, Prof. Min Hu, Prof. Yubin Gong, Prof. Yanyu Wei, Prof. Zhaoyun Duan, and PhD students Xiaoqiuye Zhang, Zhuocheng Zhang, Xingxing Xu and Yueying Wang of the Terahertz Center.
Taking graphene hyperbolic metamaterials as an example and using free electrons as the excitation, the group revealed the fundamental principles and properties of the optical topological transition of Cherenkov radiation, and proposed two innovative and practical forms of the transition, corresponding respectively to the ultrafast photothermal effect and the nonlocal effect in graphene. Beyond providing a standard paradigm for designing and analyzing Cherenkov radiation in various novel materials and structures — especially tunable plasmonic materials — this work is expected to advance the realization and application of on-chip free-electron Cherenkov radiation devices.
Compared with the theoretical proposal first made by Academician Liu’s team in Physical Review Letters ten years ago (Physical Review Letters, 2012, 109(15): 153902), the present work represents substantial improvements in every aspect.
The associate editor handling the review was Prof. Yuri Kivshar, an internationally renowned expert in optics and photonics and a world leader in nonlinear physics, nonlinear photonics and metamaterials. All reviewers spoke highly of the work, and the entire review cycle took only two months — far below the journal’s average of 124 days.
Earlier, in 2021, the group had also been the first internationally to theoretically propose and study “high-efficiency in-plane threshold-less Cherenkov radiation in graphene hyperbolic gratings”. Using a graphene hyperbolic grating — a hyperbolic metamaterial with biaxial anisotropy — the team revealed the principles and properties of in-plane Cherenkov radiation. The results show that, compared with out-of-plane Cherenkov radiation in conventional graphene hyperbolic metamaterials, the in-plane radiation power is nearly two orders of magnitude higher. Moreover, by adjusting the structural dimensions of the grating, the chemical potential of graphene and the electron velocity, the angle and intensity of the Cherenkov radiation can be fully controlled. Combined with on-chip electron beams and graphene hyperbolic metasurfaces, this research is expected to lead to an integrated, compact, free-electron-based terahertz radiation source.
That result was published under the title “High-efficiency threshold-less Cherenkov radiation generation by a graphene hyperbolic grating in the terahertz band” in Carbon, a leading international journal in materials science. The School is the sole first-author and corresponding-author affiliation; Prof. Min Hu is the corresponding author and PhD student Xiaoqiuye Zhang the first author.
Research Background
The Terahertz Center team led by Academician Shenggang Liu has achieved a series of important advances in this direction. In addition to the two works above, representative milestones include: in 2012, the first revelation of the physical mechanism by which free electrons excite surface plasmons in metals to produce coherently enhanced Cherenkov radiation in the visible band (Physical Review Letters, 2012, 109(15): 153902) — highly praised by the editors of Nature Physics even before formal publication (Nature Physics, 2012, 8(10): 704); in 2014, the proposal to bring free-electron radiation down from the visible to the terahertz band via Smith-Purcell radiation from free electrons interacting with graphene-based dielectric grating structures (Applied Physics Letters, 2014, 104(20): 201104); in 2017, plasmonic Cherenkov radiation in the terahertz band enabled by a dielectric buffer layer breaking graphene’s intrinsic dispersion limit (Applied Physics Letters, 2017, 110(23): 231102); in 2017, the first experimental observation of reversed Cherenkov radiation using negative-index metamaterials (Nature Communications, 2017, 8(1): 14901); and in 2019, direction-controllable inverse transition radiation in the terahertz band realized with graphene hyperbolic metamaterials (Photonics Research, 2019, 7(10): 1154-1160). All of these works list UESTC as the first-author and corresponding-author affiliation.
Source: UESTC News Center Original article