Cherenkov radiation1,2,3,4 has played a key role in the discovery of some fundamental particles and physical phenomena, including anti-protons5, J particles6 and neutrino oscillations4. The electron energy (velocity) threshold required to generate Cherenkov radiation in a natural medium is greater than hundreds of keV (refs 3,4). Although various approaches have been adopted, high-energy electrons (tens of keV)7 are still required to generate Cherenkov radiation experimentally. Here, we demonstrate, in hyperbolic metamaterial, that the electron velocity threshold for Cherenkov radiation can be eliminated. Based on this threshold-less Cherenkov radiation, the first integrated free-electron light source has been realized. Cherenkov radiation covering λ0 ≈ 500–900 nm is obtained with an electron energy of only ∼0.25–1.4 keV, which is two to three orders of magnitude lower than in previous reports3,7,8,9. This work provides a way to achieve threshold-less Cherenkov radiation, opens up the possibility of exploring high-performance integrated free-electron light sources and optoelectronic devices, and offers a platform to study the interaction of flying electrons with nanostructures on chip.
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The authors thank J. Feng, G. Bai and X. Li in Beijing Vacuum Electronics Research Institute for help in testing the chip. The authors also thank Y. Zhang and A. Lambert for polishing the English. This work was supported by the National Basic Research Programs of China (973 Program) under contract no. 2013CBA01704 and the National Natural Science Foundation of China (NSFC-61575104 and 61621064).
The authors declare no competing financial interests.
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Liu, F., Xiao, L., Ye, Y. et al. Integrated Cherenkov radiation emitter eliminating the electron velocity threshold. Nature Photon 11, 289–292 (2017). https://doi.org/10.1038/nphoton.2017.45
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