OP: Hyperbolic nano-optical tweezers

利用光操纵小颗粒已经使生物工程和纳米技术中的许多应用成为可能，包括分子、细胞和微/纳米物体的捕获和精确定位。这些应用依赖于当粒子被光照射时在粒子上诱导的光学力。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，通过将粒子定位在支持某些类型的电磁（EM）波的金属表面（例如金或银）附近，已经增强了作用于纳米尺度的光学力。它已被证明，感应力的强度强烈依赖于如何限制这些EM波。该项目旨在通过用工程双曲超曲面取代这些金属表面来实现巨大的光学力，这些超曲面是能够支持极其有限的电磁波的先进复合表面。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路由纳米颗粒。教育和推广工作将侧重于吸引西班牙裔学生，从K-12到大学，在科学，技术，工程和数学。具体来说，一些本科生将积极参与拟议的研究，为他们提供一条通往研究生院的道路。K-12活动包括参加加州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。该项目旨在理论建模，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学力。所提出的设备是基于结合光子自旋霍尔效应与超限制表面等离子体激元在双曲和各向异性的超表面。基于这一概念，该项目的目标是：（一）揭示通过设计极端各向异性薄膜的近场可以实现的光学力的基本极限和最大强度;（二）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、光学捕获和结合等功能;以及（iii）制造和表征由纳米结构银制成的双曲纳米光镊。所得到的宽带装置将（i）在纳米尺度上提供前所未有的强度的吸引力和排斥力;（ii）降低所需激光束的强度，从而避免由于光加热而对颗粒造成的损害;以及（iii）增强局部态密度，从而增强捕获颗粒的拉曼光谱和光致发光;并且它们在单个和多个纳米结构、力测量和生物系统的操纵、捕获、组装和表征中具有变革性的潜力。该技术项目将与一些旨在将等离子体镊子融入本科/研究生教育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NSF的法定使命，并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，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.