Kinsler P, McCall M W
Blackett Laboratory, Imperial College, Prince Consort Road, London, United Kingdom.
Phys Rev Lett. 2008 Oct 17;101(16):167401. doi: 10.1103/PhysRevLett.101.167401. Epub 2008 Oct 15.
Using the principle of causality as expressed in the Kramers-Kronig relations, we derive a generalized criterion for a negative refractive index that admits imperfect transparency at an observation frequency omega. It also allows us to relate the global properties of the loss (i.e., its frequency response) to its local behavior at omega. However, causality-based criteria rely on the group velocity, not the Poynting vector. Since the two are not equivalent, we provide some simple examples to compare the two criteria.
利用克拉默斯-克勒尼希关系中所表达的因果律原理，我们推导出了一种针对负折射率的广义判据，该判据允许在观测频率ω处存在不完全透明性。它还使我们能够将损耗的全局特性（即其频率响应）与其在ω处的局部行为联系起来。然而，基于因果律的判据依赖于群速度，而非坡印廷矢量。由于二者并不等效，我们提供了一些简单示例来比较这两种判据。
