Partial Order Colloidal Phases as Photonic Solids

非技术描述：本研究项目的目的是制备由非球形胶体粒子组成的偏序光子中间相，并表征其光学性质。这些新型材料表现出晶体和玻璃之间的结构有序，有望强烈地改变光的光谱和角输运（类似于晶体），并促进具有高各向同性的带隙（类似于玻璃）。该研究有助于阐明各种光子介质中光子带隙的形成机制，并寻求新的光学特性，如超高分辨率透镜的负折射和增强非线性光学的低光速。该项目的教育活动包括在伊萨卡科学中心开展非正式的科学学习活动；通过让代表性不足的少数群体和妇女参与研究，扩大她们对科学的参与；并为扩大参与研究所编写的本科研究最佳做法手册作出贡献。特别是，研究生辅导员要接受向包括儿童在内的公众传播科学的培训。技术描述：本项目利用形状各向异性胶体的热力学捕获有序无序共存的新型光子材料光子介相，并研究其光子特性。该研究旨在了解促进重要光子特性（即光子带隙、负折射、慢光）的有序类型和边界，以及通过低成本、大面积自组装为光子板制造光子中间相材料的能力。具体地说，我们绘制了各向异性胶体和形状二元混合物在楔胞约束下的自组织，以阐明稳定光子中间相的条件。利用具有精确时空分辨率的定量共聚焦显微成像技术研究了约束高度可达五层、系统密度和粒子间相互作用的变化和自组织。计算了模场、透射（反射）光谱和态密度的空间分布，阐明了结构和光性的相关性。利用角分辨镜面反射测量来探测色散关系来表征光子中间相。通过分析带隙边缘的频率轮廓和计算带隙边缘的群速度，确定了偏阶对折射和慢光传播特性的影响。对具有全角负折射和有效折射率为负1的光子中间相进行了折射率模拟和点源平面透镜成像。

Nontechnical Description: The objective of this research project is to fabricate partial order photonic mesophases made of non-spherical colloidal particles and characterize their optical properties. These novel materials exhibit structural ordering between those of crystals and glasses and hold promise to strongly modify spectral and angular transport of light (similar to crystals) and also to promote bandgaps with high isotropy (similar to glasses). The research helps clarify the mechanisms for the formation of photonic band gaps in various photonic media and seeks novel optical properties such as negative refraction for ultrahigh resolution lenses and low speed of light for enhanced nonlinear optics. The education activities of this project include developing informal science learning activities at the Ithaca Sciencenter; broadening participation of underrepresented minorities and women in science through involving them in research; and contributing to a manual of the best practices for undergraduate research developed by the Institute for Broadening Participation. In particular, graduate student facilitators are trained in science communication to public audiences including children.Technical Description: This project exploits the thermodynamics of shape-anisotropic colloids to capture photonic mesophases, a new class of photonic materials in which order and disorder cohabit, and to study their photonic properties. The research aims to develop an understanding of the types and bounds of order that promote significant photonic properties (i.e., photonic band gaps, negative refraction, slow light) and an ability of fabricating photonic mesophase materials for photonic slabs via low-cost, large-area self-assembly. Specifically, the self-organization of anisotropic colloids and shape-binary mixtures is mapped out under wedge-cell confinement to elucidate the conditions for stabilizing photonic mesophases. Confinement height up to five layers, system density and interparticle interactions are varied and the self-organization is studied using quantitative confocal microscopy imaging with precise spatial and temporal resolution. The spatial distributions of the mode fields, transmission (reflection) spectra and density of states are calculated to elucidate the structure and optical property correlations. The photonic mesophases are characterized using angle-resolved specular reflectance measurements to probe the dispersion relations. The effects of partial order on refraction and slow-light propagation properties are determined from the analysis of equifrequency contours and the calculation of the group velocity at the band gap edges, respectively. Simulations of the refraction and the flat lens imaging of a point source are performed for photonic mesophases that exhibit all-angle negative refraction and effective refractive index of negative one.