EAGER: Enhanced Optical Pressure from Nanostructured Metal Films

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Enhanced Optical Pressure from Nanostructured Metal FilmsKevin Webb and Xianfan Xu, Purdue UniversityA combined theoretical and experimental study of optical forces in nanostructured material is proposed to establish a method to control the nanometer-scale force on a small particle and to provide enhancement in the total pressure on a structured surface. Consequently, large forces on small particles and an increase in the total force on a membrane are expected. While optical tweezers are now commercially available, they are effective for moving large beads to which, for example, biological molecules are attached. Positioning nanoparticles like quantum dots requires large and local forces that can be achieved with control over the geometry of a metal surface. This would circumvent the need for the large beads in optical tweezers and provide an approach for synthesizing new materials by nano-scale optical assembly. Furthermore, the substantial increase in the relatively weak pressure provided by light will allow weaker optical signals to be used in mechanical control. The resulting optomechanical system can be simpler and more versatile than optoelectronic systems, opening communication and sensing opportunities. Specifically, while it has been recognized that all-optical networks can increase both speed and efficiency, there remain challenges as to how to provide network reconfiguration that this approach could address. At the fundamental level, this work will provide experimental force data on the nanometer scale that will be used in establishing a model that can be used for device design. The goal of this project is to design and fabricate gold films with resonant nanometer-scale slots that are expected to produce a dramatic enhancement in the overall pressure. The verification of this method for increasing the force will allow the approach to be used to mechanically control a surface using laser light in various free space and waveguide arrangements. The project will lay the design foundations for nanophotonic structures that impart substantial and controllable optical forces to actuate tuning elements in photonic networks. This will simplify switching technology and the approach has the potential to reduce energy consumption and cost. This project will facilitate sensing, allowing a molecule to be moved to a region with large field and hence large Raman dipole moment for identification. Such nanoscale traps could be used in material synthesis, allowing trapping of quantum dots in nanocavities for achieving optical sources and detectors, for instance. While optical tweezers are becoming more common, determination of the absolute force relies on macroscopic calibration procedures that do not provide access to the force on the nanometer scale. By evaluating the relationship between materials and geometry and the force, it should be possible to design tweezers with larger forces to move smaller objects or larger objects locally. There should also be new opportunities through control of the optical material properties, both electric and magnetic. At the fundamental level, the proposed work may provide an answer to a century-long debate about the description of the optical force.