Optical helicity density is usually discussed for monochromatic electromagnetic fields in free space. It plays an important role in the interaction with chiral molecules or nanoparticles. Here we introduce the optical helicity density in a dispersive isotropic medium. Our definition is consistent with biorthogonal Maxwell electromagnetism in optical media and the Brillouin energy density as well as with the recently introduced canonical momentum and spin of light in dispersive media. We consider a number of examples, including electromagnetic waves in dielectrics, negative-index materials, and metals, as well as interactions of light in a medium with chiral and magnetoelectric molecules.

中文翻译：

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复杂介质中的电磁螺旋

通常讨论自由空间中单色电磁场的光螺旋强度。它在与手性分子或纳米粒子的相互作用中起重要作用。在这里，我们介绍了各向同性分散介质中的旋光度密度。我们的定义与光学介质中的双正交麦克斯韦电磁学和布里渊能量密度以及最近引入的正则动量和色散介质中的光自旋一致。我们考虑许多示例，包括电介质，负折射率材料和金属中的电磁波，以及介质中的光与手性和磁电分子的相互作用。