Abstract

Whenever light is slowed down, for any cause, two different formulas give its momentum. The coexistence of those momenta was the heart of the century-old Abraham-Minkowski dilemma, recently resolved for dielectrics. We demonstrate that this framework extends to momentum exchange in wave-particle interaction; in particular to vacuum waveguides of electron tubes (dispersive metallic slow-wave structures). In waveguides, the dilemma can be easily investigated since energy and force are well established through the use of Maxwell equations in vacuum, and since waveguides can have a strong refractive index. Our theory is assessed with simulations validated against measurements from a traveling-wave tube. In addition, we show that the dilemma resolution is not limited to discriminating between kinematic and canonical momenta but also involves a non-negligible flowing momentum from Maxwell’s electromagnetic stress. The existence of two momenta for diverse systems like materials, plasmas and waveguides, for which light velocity modification has entirely different origin, points to the universality of the Abraham-Minkowski dilemma.

Graphical abstract

中文翻译：

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真空波导中波粒系统的电磁矩

摘要

每当光线变慢时，无论出于何种原因，都会有两种不同的公式给出其动量。这些动量的共存是具有百年历史的亚伯拉罕-明科夫斯基难题的核心，最近解决了介电问题。我们证明该框架扩展到波粒相互作用中的动量交换。特别是电子管的真空波导（分散金属慢波结构）。在波导中，由于可以通过在真空中使用麦克斯韦方程很好地建立能量和力，并且由于波导可以具有很强的折射率，因此可以轻松地研究难题。我们的理论是通过对行波管测量结果进行验证的模拟进行评估的。此外，我们表明，难题的解决方法不仅限于区分运动和规范动量，还涉及麦克斯韦电磁应力引起的不可忽略的流动动量。对于诸如材料，等离子和波导之类的各种系统而言，存在着两个动量，其光速改变的起源完全不同，这表明了亚伯拉罕-明科夫斯基困境的普遍性。

图形概要