The polar nature of calcite results in lattice vibrations that can be stimulated through gratings and nanostructures to design spatially and spectrally coherent thermal radiation patterns. In order to obtain optimal design control over such patterned materials, it is first necessary to understand the fundamental emissivity properties of the lattice vibrations themselves. Because calcite is a uniaxial material, when the optic axis (OA) is tilted with respect to the crystal surface, the surface wave solutions to Maxwell’s equations and vibrational modes that are permitted will change due to the crystal’s structural anisotropy. This implies that the OA orientation can play a critical role in dictating which modes can be harnessed when designing a narrowband or angular thermal emitter. Here we explore the angle and polarization dependence of the bulk far-field emissivity of unpatterned calcite with tilted OA. We show that by manipulating the OA orientation via crystallographic off-cut, polarization, and sample rotation, the emissivity at a given frequency can vary by as much as 0.8. These results suggest that, in addition to serving as a basis for modifying the behavior of the relevant phonon polaritons, OA orientation can be used to alter the thermal emission pattern without the need for complex lithographic patterning.

中文翻译：

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通过光轴重新定向在块状方解石中定制热发射

方解石的极性性质导致晶格振动，可以通过光栅和纳米结构激发晶格振动，以设计空间和光谱相干的热辐射模式。为了获得对这种图案化材料的最佳设计控制，首先需要了解晶格振动本身的基本发射率特性。由于方解石是单轴材料，当光轴（OA）相对于晶体表面倾斜时，由于晶体的结构各向异性，允许的麦克斯韦方程和振动模式的表面波解将发生变化。这意味着在设计窄带或角度热发射器时，OA 方向可以在决定可以利用哪些模式方面发挥关键作用。在这里，我们探讨了具有倾斜 OA 的未图案化方解石的体远场发射率的角度和偏振依赖性。我们表明，通过晶体切割、极化和样品旋转来操纵 OA 方向，给定频率下的发射率可以变化多达 0.8。这些结果表明，除了作为修改相关声子极化激元行为的基础外，OA 取向还可用于改变热发射模式，而无需复杂的光刻图案化。