OP: Hyperbolic nano-optical tweezers

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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.