Optical Bound States and Non-linearity in Geometrically-Modulated Dielectric Nanowires

光与微观尺寸的球形或圆柱形粒子的相互作用经常被用来理解光如何与不同尺寸和形状的物质相互作用的一般原理。例如，与光的波长相当或小于光的波长的微观颗粒可以引起令人惊讶的强光散射和吸收。最近，已经有可能使微观粒子的形状超越简单的圆柱体，而是在其大小上具有周期性调制。在适当的条件下，这些几何调制会导致粒子以一种新的方式与光相互作用，从而产生所谓的“连续介质中的光学束缚态”或BIC。该项目使用理论，计算，合成和测量的组合来理解微观粒子的几何形状如何用于控制BIC的属性。BIC是令人兴奋的，因为它们大大增加了光与粒子相互作用的程度。在某些情况下，这种相互作用足够强，导致粒子将红光或红外光转换为蓝光或紫外光，这是一种“非线性”效应。该项目的结果提供了控制几何调制粒子中BIC的一般原理，从而提供了在微观尺度上控制各种颜色的光的基本原理。研究工作涉及本科生，研究生和博士后学生在一个项目，桥梁之间的接口化学，物理学和工程-提供经验的广度在纳米材料合成，微细加工，光谱学，显微镜，和modeling.Technical Description在圆柱形介电粒子，米氏共振可以引起令人惊讶的强烈的光散射和光吸收，米氏共振的重要性和相互作用，先前已经研究了这些结构中的漏模共振和导模。一种相对较新的共振类型，BIC，已经被确定，理论上可以在理想系统中无限长时间捕获光。本计画主要研究奈米尺度之介电圆柱体中BIC之光散射、光吸收及非线性特性。硅结构是通过自下而上的气-液-固工艺合成的，该工艺使用原位掺杂剂调制结合湿化学蚀刻来创建精确定义的形态。介电圆柱体的直径的周期性调制示出引入一系列的BIC的不同的顺序，极化，和对称类型。控制几何形状的单纳米线的光谱测量进行比较，理论模型，提供验证的理论预测。还评估了硅纳米线中的BIC通过使入射光的频率加倍或三倍来实现非线性效应的能力。总体而言，拟议的研究揭示了基本特征的BIC在介电圆柱体，并突出了重要的实际应用，这些BIC modes.This奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

Nontechnical descriptionThe interaction of light with spherical or cylindrical particles of microscopic size has frequently been used to understand the general principles of how light interacts with matter of different sizes and shapes. For example, microscopic particles that are comparable to or smaller than the wavelength of light can give rise to surprisingly strong light scattering and absorption. Recently, it has become possible to make microscopic particles with shapes that go beyond simple cylinders to instead have periodic modulations in their size. Under the right conditions, these geometric modulations cause the particles to interact with light in a new way, giving rise to what is termed an “optical bound state in the continuum,” or BIC. This project uses a combination of theory, computation, synthesis, and measurement to understand how the geometry of microscopic particles can be used to control the properties of BICs. BICs are exciting because they dramatically increase the extent to which light interacts with particles. In some cases, the interaction is sufficiently strong to cause the particles to convert red or infrared light into blue or ultraviolet light, a “non-linear” effect. The results of this project provide the general principles for controlling BICs in geometrically-modulated particles, thus providing the fundamental principles for controlling light over a broad range of colors at a microscopic scale. The research effort involves undergraduate, graduate, and postdoctoral students in a project that bridges the interface between chemistry, physics, and engineering—providing breadth of experience in nanomaterial synthesis, microfabrication, spectroscopy, microscopy, and modeling.Technical DescriptionIn cylindrical dielectric particles, Mie resonances can cause surprisingly strong light scattering and light absorption, and the importance and interplay of Mie resonances, leaky-mode resonances, and guided modes in these structures has previously been studied. A relatively new class of resonance, the BIC, has been identified and can theoretically trap light for an infinite time in an ideal system. This project studies the fundamental light scattering, light absorption, and nonlinear properties of BICs in dielectric cylinders with nanoscale lateral size. The silicon structures are synthesized by a bottom-up vapor-liquid-solid process using in situ dopant modulation combined with wet-chemical etching to create precisely-defined morphology. Periodic modulation of the diameter of a dielectric cylinder is shown to introduce a range of BICs of different order, polarization, and symmetry type. Spectroscopic measurements on single NWs of controlled geometry are compared to theoretical models, providing validation of theoretical predictions. The capacity of BICs in silicon NWs to enable nonlinear effects by doubling or tripling the frequency of incoming light is also evaluated. Overall, the proposed study reveals the fundamental characteristics of BICs in dielectric cylinders and highlights important practical applications of these BIC modes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.