利用波动电动力学对互易和非互易材料热辐射的极化分析
Polarimetric analysis of thermal emission from both reciprocal and nonreciprocal materials using fluctuational electrodynamics
摘要：
在许多具有微米/纳米结构的超材料中，已经观察到了给定偏振的相干热发射。一个完整的描述的热发射需要的光谱角发射率的所有偏振状态的充分表征。通常根据基尔霍夫定律，基于吸收率和发射率之间的等效性来获得发射率;然而，这种关系对于非互易介质可能无效。在处理磁光材料和磁性Weyl半金属时，不受光学互易性约束的更一般的方法是必要的。在这里，热发射的偏振分析进行了波动电动力学的基础上。利用相干矩阵得到了各向异性介质（包括非互易材料）多层系统的Stokes参数。结果表明，热辐射可能是圆偏振或线偏振在不同的方向和频率。研究结果与近年来几个团体提出的修改后的基尔霍夫定律的陈述是一致的，因此，证明了直接和间接方法的适当性。该研究将有助于设计所需的热发射器的能量收集和热控制。
英文摘要：
Coherent thermal emission for a given polarization has been observed in many metamaterials with micro/nanostructures. A complete description of the thermal emission requires the full characterization of the spectral angular emissivity for all polarization states. Emissivity is typically obtained based on the equivalence between the absorptivity and emissivity according to Kirchhoff's law; however, such relation may be invalid for nonreciprocal media. More general approaches without the constrain of optical reciprocity are necessary when dealing with magneto-optical materials and magnetic Weyl semimetals. Here, a polarimetric analysis of thermal emission is carried out based on fluctuational electrodynamics. The Stokes parameters are obtained using coherency matrix for a multilayered system with anisotropic media, including nonreciprocal materials. The results demonstrate that thermal emission may be circularly or linearly polarized in different directions and frequencies. The findings are consistent with the statements of the modified Kirchhoff's law provided by several groups in recent years, and therefore, justify the appropriateness of both the direct and indirect methods. This study will help the design of desired thermal emitters for energy harvesting and thermal control.
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