High Throughput Tip-Enhanced Near Field Microscopy using Radially Polarized Fiber Modes

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Title: Tip-enhanced near-field microscopy using optical fiber vorticesNon-technical description: Optical microscopy is arguably one of the most successful techniques for non-invasive examination of the microscopic world ever created. In the last decade nanoscience, phenomena at length scales orders of magnitude smaller than the microscale, has played an increasingly larger role in the development of widespread technology such as nanoscale semiconductor devices, nanoparticle based therapies in medicine, and sensors that can measure minute forces and signals from biological as well as inanimate physical systems. Likewise, nanotechnology has also furthered our understanding of fundamental scientific phenomena at the nanoscale, such as the electronic structure of two-dimensional materials that promise to usher in the next generation of high-speed wearable electronic devices, images of intrinsic vibrational modes capable of sub-cellular classification and local presence of important proteins in biophysical systems. Probing, and in particular, optical probing at the nanoscale is thus of paramount importance to help lead the next revolution in science and technology much like the optical microscope did in the microscopic world. Our proposed optical fiber vortex light source will provide two to three orders of magnitude signal enhancement and background reduction in devices that can optically resolve nanoscale phenomena.Technical description: The goal of this proposed program is to develop a tip-enhanced near-field microscopy system that retains all the advantages of current scattering type near-field scanning optical microscopes, including the ability to probe the amplitude and phase response of materials in the nanometer scale using well-established elastic or inelastic scattering techniques, but with an increased throughput by several orders of magnitude (simulations suggest the possibility of 75% efficiencies, as opposed to 0.1-0.2% in current implementations). This will reduce background problems that have limited the application of current implementations of tip-enhanced microscopy systems. The primary intellectual significance of achieving program goals will be the realization of a nanoscale microscopy system that can probe signals orders of magnitude weaker than currently possible, aided by the dramatic reductions in background that an optical fiber-based nanoscale tip would enable. In the proposed effort we will use fiber tapering, electrochemical etching techniques, and precision metal deposition techniques to adiabatically convert the stable radially polarized optical modes in the fiber into plasmonic modes at the fiber tip, as required for tip-enhanced microscopy. The adiabatic mode transformation, as opposed to external illumination as is currently employed, will be the key differentiator between current tip-enhanced microscopy systems and the proposed device, as this is expected to yield the two-to-three orders of magnitude increase in signal throughput and corresponding decrease in background.