层状介质中热生电磁场的空间相关性
Spatial correlation of the thermally generated electromagnetic field in layered media
摘要：
本文推导了一种通用的互谱密度张量公式，用于计算层状介质中热产生的电磁场的空间相关性。该公式是基于波动电动力学，因此适用于近场和远场的热源。由此产生的交叉谱密度张量写在一个单一的集成方面的平行波矢量，作为角积分导致数值不稳定性的分析评估。使用这个公式，在近场的空间相关长度的碳化硅（SiC）薄膜支持表面声子极化激元（SPhPs）在红外线进行了分析。结果表明，由于SPhP耦合，SiC热源悬浮在真空中的空间相关长度大幅减少，通过减少其厚度。在10 nm厚的SiC膜的极限中，空间相关长度与黑体的空间相关长度相似。结果还表明，可以通过电介质和金属衬底控制薄SiC热源的空间相干性，分别允许和防止SPhP耦合。这表明，通过使用相变材料衬底如二氧化钒，可以通过支持红外线中的表面极化激元的薄膜对热发射进行主动调制。
英文摘要：
A general formulation for the cross-spectral density tensor enabling calculation of the spatial correlation of the thermally generated electromagnetic field in layered media is derived. The formulation is based on fluctuational electrodynamics, and is thus applicable in the near and far field of heat sources. The resulting cross-spectral density tensor is written in terms of a single integration over the parallel wavevector, as the angular integrations leading to numerical instability are evaluated analytically. Using this formulation, the spatial correlation length in the near field of a film made of silicon carbide (SiC) supporting surface phonon-polaritons (SPhPs) in the infrared is analyzed. It is shown that the spatial correlation length of a SiC heat source suspended in vacuum decreases substantially by decreasing its thickness owing to SPhP coupling. In the limit of a 10-nm-thick SiC film, the spatial correlation length is similar to that of a blackbody. The results also reveal that it is possible to control the spatial coherence of a thin SiC heat source via dielectric and metallic substrates, respectively allowing and preventing SPhP coupling. This suggests that active modulation of thermal emission via thin films supporting surface polaritons in the infrared is possible by using a phase change material substrate such as vanadium dioxide.
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