RUI: Unraveling Novel Nanophotonic Effects in Mid-Index Micro-Sized Dielectric Materials

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NON-TECHNICAL SUMMARY:When light interacts with matter, a number of things can happen – it can be absorbed, reflected, scattered, or transmitted. If matter has nanoscale features, light-matter interactions can lead to interesting phenomena. For example, optical anapoles can confine light energy within the volume of nanostructures. In the case of zero back scattering (ZBS), light is preferentially scattered in the forward direction. The emerging field of nanophotonics puts such phenomena to use in applications such as solar energy, imaging, medicine, optical communications, and data storage. However, observation of these novel nanophotonic effects is currently restricted to materials with a high refractive index, such as silicon and germanium, and requires features sizes on the nanometer scale. The research team at Illinois State University (ISU) plans to demonstrate these effects in mid-index materials, such as titanium dioxide and diamond, with micrometer scale features. This research will push the boundary in terms of availability of materials and their size well beyond the current limit for observation of these novel nanophotonic effects. In the long run, the knowledge gained from the team’s research could be used to develop more efficient optical and photonic devices, such as photodetectors and nanolasers. The PI will work to broaden the workforce in optics and photonics by training undergraduate students in research and integrating the results of this research project into the physics curriculum. Participation of underrepresented minorities in STEM will be encouraged by using existing ISU infrastructure to recruit and train underrepresented students, including outreach to local high school students.TECHNICAL SUMMARY:Resonant optical excitation of high refractive-index dielectric particles offers unique opportunities to demonstrate novel nanophotonic effects such as nonradiating anapole states, optimum forward scattering, and magnetic hotspot enhanced Purcell effects. These novel nanophotonic effects observed are related to the excitation of single dipolar modes in high-index lossless dielectric materials. These effects are inaccessible for microscale objects due to the contributions from higher order multipolar modes under plane wave illumination. Hence, observation of nanophotonic effects is currently restricted to a few relatively high-index materials in the limit of nanometer size – typically within silicon and germanium. It was recently theoretically predicted that one can unravel dipolar regimes in homogenous high-index spheres with a wide range of size parameter and refractive indices under illumination. The research team at Illinois State University (ISU) plans to experimentally unravel the dipolar regime, excite non-radiating anapole states, and demonstrate zero backscattering in mid-index (1.5 n 3.0) dielectric spheres in the micrometer range under illumination with tightly focused Gaussian beams (TFGBs). TFGBs selectively excite a few relevant Mie coefficients and control the relative weight of the different multipolar modes of the incident field. This approach will enable the investigators to unravel the dipolar regime and associated novel nanophotonic effects in microscale homogenous spheres in the mid-index regime. Understanding these phenomena opens up enormous possibilities in terms of availability of materials and objects with size parameters well beyond the current physical picture for related nanophotonic applications.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.