利用非局域性控制切伦科夫阈值
Controlling Cherenkov threshold with nonlocality
摘要：
由于双曲型异向介质中的光子态密度极大，在经典局域框架下，切伦科夫辐射一般被认为是无阈值的。虽然非局域性和量子效应的最新进展扩展了我们对金属纳米结构中光-物质相互作用的理解，但非局域性对无阈值切伦科夫辐射的影响仍然难以捉摸。在这里，我们从理论上证明，非局域性提供了一个不可或缺的方式灵活的工程切伦科夫阈值在金属介电层结构。特别地，非局域性导致下限速度截止，其值与电子费米速度相当。令人惊讶的是，如果超材料在ε接近零的频率附近工作，这个下限阈值可以明显小于经典预测的阈值。控制切伦科夫阈值的能力为切伦科夫辐射的实际应用开辟了许多前景，特别是对于集成的自由电子辐射源。
英文摘要：
Cherenkov radiation is generally believed to be threshold-free in hyperbolic metamaterials owing to the extremely large photonic density of states in classical local framework. While recent advances in nonlocal and quantum effects extend our understanding of light-matter interactions in metallic nanostructures, the influence of nonlocality on threshold-free Cherenkov radiation still remains elusive. Here we theoretically demonstrate that the nonlocality provides an indispensable way to flexibly engineer Cherenkov thresholds in metallodielectric layered structures. Particularly, the nonlocality results in a lower-bound velocity cutoff, whose value is comparable to the electron Fermi velocity. Surprisingly, this lower-bound threshold can be significantly smaller than the classically predicted one if the metamaterial works around epsilon-near-zero frequencies. The capability to control Cherenkov thresholds opens numerous prospects for practical applications of Cherenkov radiation, in particular, for integrated free-electron radiation sources.
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