We study light absorption by a dipolar absorber in a given environment, which can be a nanoantenna or any complex inhomogeneous medium. From first-principle calculations, we derive an upper bound for the absorption, which decouples the impact of the environment from the one of the absorber. Since it is an intrinsic characteristic of the environment regardless of the absorber, it provides a good figure of merit to compare the ability of different systems to enhance absorption. We show that, in the scalar approximation, the relevant parameter is not the field enhancement, but the ratio between the field enhancement and the local density of states. Consequently, a plasmonic structure supporting hot spots is not necessarily the best choice to enhance absorption. We also show that our theoretical results can be applied beyond the scalar approximation and the plane-wave illumination.

中文翻译：

---

使用纳米天线增强纳米体积中的光吸收：理论和优点图

我们研究给定环境中偶极吸收器的光吸收，该环境可以是纳米天线或任何复杂的不均匀介质。从第一性原理计算中，我们得出了吸收的上限，该上限将环境的影响与吸收器中的一个分开。由于无论吸收剂如何，它都是环境的固有特征，因此它提供了比较不同系统增强吸收能力的良好品质因数。我们表明，在标量近似中，相关参数不是场增强，而是场增强与状态局部密度之间的比率。因此，支撑热点的等离子体结构不一定是增强吸收的最佳选择。