OP: Hyperbolic nano-optical tweezers

光对小颗粒的操纵在生物工程和纳米技术中有许多应用，包括分子、细胞和微/纳米物体的捕获和精确定位。这些应用依赖于光照射粒子时产生的光力。由于这种力的强度通常很弱，因此需要非常高功率的激光束来有效地控制粒子的位置和运动。最近，通过将粒子定位在金属表面（如金或银）附近，在纳米尺度上作用的光力得到了增强，这些金属表面支持某些类型的电磁波。已经证明，感应力的强度在很大程度上取决于这些电磁波的受限程度。该项目旨在通过用工程双曲超表面取代这些金属表面来实现巨大的光学力，双曲超表面是一种先进的复合表面，能够支持极端受限的电磁波。由此产生的设备将能够使用低功率激光束以非常高的精度定位纳米颗粒。教育和推广工作将侧重于吸引从K-12到大学的西班牙裔学生学习科学、技术、工程和数学。具体来说，几名本科生将积极参与拟议的研究，为他们提供通往研究生院的道路。K-12的活动包括参加加州州立数学和科学暑期学校，以及一系列关于萨克拉门托地区西班牙裔学校的讲座。本项目旨在理论建模，数值模拟和优化，并通过实验实现和表征一类新型双曲纳米光镊，其工程近场能够产生比各向同性等离子体表面大几个数量级的巨大光力。所提出的器件是基于双曲和各向异性超薄超表面中光子自旋霍尔效应与超约束表面等离子激元极化子的结合。基于这一概念，该项目的目标是：(i)揭示通过设计极各向异性薄膜的近场可以获得的光学力的基本限制和最大强度；（ii）分析和设计具有接近最佳性能的现实双曲镊子，能够实现亚衍射纳米颗粒定位、光学捕获和绑定等功能；以及（iii）制备和表征由纳米结构银制成的双曲型纳米光学镊子。由此产生的宽带设备将(i)在纳米尺度上提供前所未有的吸引力和排斥力；（ii）降低所需激光束的强度，从而避免因光加热而损坏粒子；（iii）增强态的局部密度，从而提高捕获粒子的拉曼光谱和光致发光；它们在单个和多个纳米结构的操作、捕获、组装和表征、力测量和生物系统方面具有变革性的潜力。该技术计划将与一系列旨在将等离子镊子整合到本科/研究生教育中的推广和教育活动相结合，重点关注代表性不足的西班牙裔社区。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The manipulation of small particles with light has enabled many applications in bioengineering and nanotechnology, including the trapping and accurate positioning of molecules, cells, and micro/nano-objects. These applications rely on the optical forces induced on the particles when they are illuminated by light. Since the strength of such forces is usually weak, laser beams with very high power are required to effectively control the position and motion of the particles. Recently, optical forces acting at the nano-scale have been enhanced by locating the particles near metallic surfaces, such as gold or silver, that support certain types of electromagnetic (EM) waves. It has been shown that the strength of the induced forces strongly depends on how confined these EM waves are. This project aims to achieve giant optical forces by replacing these metallic surfaces with engineered hyperbolic metasurfaces, which are advanced composite surfaces able to support extremely confined EM waves. The resulting devices will be able to route nanoparticles with very high accuracy using low-power laser beams. The educational and outreach efforts will focus on engaging Hispanic students, ranging from K-12 to college, in science, technology, engineering and math. Specifically, several undergraduate students will actively participate in the proposed research, providing them a path towards graduate school. K-12 activities include the participation in the California State Summer School for Mathematics and Science, as well as a set of talks on Hispanic schools in the Sacramento area. Technical description This project aims to theoretically model, numerically simulate and optimize, and experimentally realize and characterize a novel class of hyperbolic nano-optical tweezers with engineered near-fields able to generate giant optical forces several orders of magnitude larger than those attainable in isotropic, plasmonic surfaces. The proposed devices are based on combining the photonic spin Hall effect with ultra-confined surface plasmon polaritons in hyperbolic and anisotropic ultrathin metasurfaces. Rooted in this concept, the project objectives are to (i) reveal the fundamental limits and maximum strength of optical forces that can be attained by engineering the near-field of extremely anisotropic films; (ii) analyze and design realistic hyperbolic tweezers with near-optimal performance able to realize functionalities such as sub-diffractive nanoparticle positioning, optical trapping and binding; and (iii) fabricate and characterize hyperbolic nano-optical tweezers made of nanostructured silver. The resulting broadband devices will (i) provide attractive and repulsive forces of unprecedented strength at the nanoscale; (ii) reduce the intensity of required laser beams, thus avoiding damage to the particles due to photoheating; and (iii) enhance the local density of states, thus boosting the Raman spectroscopy and photoluminescence of trapped particles; and they have the potential to be transformative in the manipulation, trapping, assembly, and characterization of individual and multiple nanostructures, force measurement, and biological systems. The technical program will be combined with a number of outreach and educational activities aimed at integrating plasmonic tweezers into undergraduate/graduate education, with strong emphasis on the underrepresented Hispanic community.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.