Opt Express. 2021 Jun 21;29(13):20863-20871. doi: 10.1364/OE.430376.
Recent studies of optical reflectors as part of the vision apparatus in the eyes of decapod crustaceans revealed assemblies of nanoscale spherulites - spherical core-shell nanoparticles with radial birefringence. Simulations performed on the system highlighted the advantages of optical anisotropy in enhancing the functionality of these structures. So far, calculations of the nanoparticle optical properties have relied on refractive indices obtained using ab-initio calculations. Here we describe a direct measurement of the tangential refractive index of the spherulites, which corresponds to the in-plane refractive index of crystalline isoxanthopterin nanoplatelets. We utilize measurements of scattering spectra of individual spherulites and determine the refractive index by analyzing the spectral signatures of scattering resonances. Our measurements yield a median tangential refractive index of 1.88, which is in reasonable agreement with theoretical predictions. Furthermore, our results indicate that the optical properties of small spherulite assemblies are largely determined by the tangential index.
最近对十足目甲壳动物眼睛视觉器官中的光反射器的研究发现，纳米级球晶 - 具有径向双折射的球形核壳纳米粒子 - 的组装体。对该系统进行的模拟突出了光学各向异性在增强这些结构功能方面的优势。到目前为止，对纳米粒子光学性质的计算依赖于使用从头算计算获得的折射率。在这里，我们描述了对球晶切向折射率的直接测量，该折射率对应于结晶异黄质纳米薄片的面内折射率。我们利用单个球晶的散射光谱测量，并通过分析散射共振的光谱特征来确定折射率。我们的测量结果得出的切向折射率中位数为 1.88，与理论预测相当吻合。此外，我们的结果表明，小的球晶组装体的光学性质主要由切向指数决定。
