Hyperbolic phonon polaritons (HPhPs) are hybrid excitations of light and coherent lattice vibrations that exist in strongly optically anisotropic media, including two-dimensional materials (e.g., MoO 3 ). These polaritons propagate through the material’s volume with long lifetimes, enabling novel mid-infrared nanophotonic applications by compressing light to sub-diffractional dimensions. Here, the dispersion relations and HPhP lifetimes (up to ≈12 ps) in single-crystalline α-MoO 3 are determined by Fourier analysis of real-space, nanoscale-resolution polariton images obtained with the photothermal induced resonance (PTIR) technique. Measurements of MoO 3 crystals deposited on periodic gratings show longer HPhPs propagation lengths and lifetimes (≈2×), and lower optical compressions, in suspended regions compared with regions in direct contact with the substrate. Additionally, PTIR data reveal MoO 3 subsurface defects, which have a negligible effect on HPhP propagation, as well as polymeric contaminants localized under parts of the MoO 3 crystals, which are derived from sample preparation. This work highlights the ability to engineer substrate-defined nanophotonic structures from layered anisotropic materials.

中文翻译：

---

MoO3 中基底介导的双曲声子极化激元

双曲声子极化激元 (HPhPs) 是存在于强光学各向异性介质（包括二维材料（例如，MoO 3 ））中的光和相干晶格振动的混合激发。这些极化子以长寿命传播通过材料的体积，通过将光压缩到亚衍射尺寸来实现新颖的中红外纳米光子应用。在这里，单晶 α-MoO 3 中的色散关系和 HPhP 寿命（高达 ≈12 ps）是通过对使用光热诱导共振 (PTIR) 技术获得的真实空间、纳米级分辨率的极化子图像进行傅立叶分析来确定的。沉积在周期性光栅上的 MoO 3 晶体的测量显示更长的 HPhPs 传播长度和寿命 (≈2×)，以及更低的光学压缩，与与基板直接接触的区域相比，在悬浮区域。此外，PTIR 数据揭示了 MoO 3 亚表面缺陷，其对 HPhP 传播的影响可以忽略不计，以及位于部分 MoO 3 晶体下方的聚合物污染物，这些污染物源自样品制备。这项工作突出了从层状各向异性材料设计衬底定义的纳米光子结构的能力。