Gong Zheng, Chen Jialin, Chen Ruoxi, Zhu Xingjian, Wang Chan, Zhang Xinyan, Hu Hao, Yang Yi, Zhang Baile, Chen Hongsheng, Kaminer Ido, Lin Xiao
Interdisciplinary Center for Quantum Information, State Key Laboratory of Extreme Photonics and Instrumentation, ZJU-Hangzhou Global Scientific and Technological Innovation Center, Zhejiang University, Hangzhou 310027, China.
International Joint Innovation Center, The Electromagnetics Academy at Zhejiang University, Zhejiang University, Haining 314400, China.
Proc Natl Acad Sci U S A. 2023 Sep 19;120(38):e2306601120. doi: 10.1073/pnas.2306601120. Epub 2023 Sep 11.
Cherenkov radiation occurs only when a charged particle moves with a velocity exceeding the phase velocity of light in that matter. This radiation mechanism creates directional light emission at a wide range of frequencies and could facilitate the development of on-chip light sources except for the hard-to-satisfy requirement for high-energy particles. Creating Cherenkov radiation from low-energy electrons that has no momentum mismatch with light in free space is still a long-standing challenge. Here, we report a mechanism to overcome this challenge by exploiting a combined effect of interfacial Cherenkov radiation and umklapp scattering, namely the constructive interference of light emission from sequential particle-interface interactions with specially designed (umklapp) momentum-shifts. We find that this combined effect is able to create the interfacial Cherenkov radiation from ultralow-energy electrons, with kinetic energies down to the electron-volt scale. Due to the umklapp scattering for the excited high-momentum Bloch modes, the resulting interfacial Cherenkov radiation is uniquely featured with spatially separated apexes for its wave cone and group cone.
切伦科夫辐射仅在带电粒子以超过该介质中光的相速度的速度运动时才会发生。这种辐射机制在很宽的频率范围内产生定向光发射，并且除了对高能粒子难以满足的要求外，还可能促进片上光源的发展。从与自由空间中的光没有动量失配的低能电子产生切伦科夫辐射仍然是一个长期存在的挑战。在这里，我们报告了一种通过利用界面切伦科夫辐射和倒逆散射的联合效应来克服这一挑战的机制，即来自具有特殊设计（倒逆）动量转移的连续粒子 - 界面相互作用的光发射的相长干涉。我们发现这种联合效应能够从动能低至电子伏特尺度的超低能电子产生界面切伦科夫辐射。由于对激发的高动量布洛赫模式的倒逆散射，产生的界面切伦科夫辐射的独特特征是其波锥和群锥在空间上分离的顶点。
