Polarization-dependent thermal emission from plasmonic metasurfaces

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In the past two decades, the control of thermal radiation has attracted immense attention due to its importance in advanced energy systems, manufacturing, remote sensing, thermal management, and high-resolution thermal imaging. Thermal emission from bulk materials is typically broadband and largely diffuse. However, significant development has been made lately to construct directional-selective and wavelength-dependent emitters and absorbers using micro/nanostructured materials. The polarization state of an electromagnetic wave is determined based on how its electric field varies as the wave propagates. It is well known that polarized light detection has important applications in space and atmospheric remote sensing, target detection, surface characterization, and biomedical diagnostics. However, the polarization effect in thermal radiation has not been extensively examined. This combined theoretical and experimental project aims to model, design, fabricate, and characterize micro/nanostructured material surfaces with unique polarization-dependent thermal radiation. The study will enable a fundamental understanding of the nature of thermal emission in terms of the state and degree of polarization. The knowledge obtained will potentially benefit applications ranging from energy harvesting and surface imaging, to object recognition and biomedical sensing. Significant efforts will also be devoted to advancing student-centered pedagogy and expanding international collaboration.Metamaterials made of thin nanostructured layers, or metasurfaces, hold promise for controlling the polarization state of thermal emission. This project will employ the finite-difference time-domain method and the matrix formulation to model the reflection and absorption of metasurfaces, considering both linearly and circularly polarized incidence. Emphasis will be given to circularly polarized emitters using plasmonic metamaterials with asymmetric metallic micro/nanostructures. The localized fields will be analyzed for both linearly and circularly polarized incident waves to explore the resonance mechanisms and plasmonic local heating at the micro/nanoscales. Furthermore, the fluctuation-dissipation theorem will be employed to directly model the field components and their correlations using anisotropic dyadic Green’s functions. Both the direct and indirect methods will be used to predict the emittance components defined based on Stokes’ parameters. The results will be compared with the measured infrared reflectance and emittance of fabricated plasmonic metasurfaces. In the emittance measurements, combined retarder and polarizer arrangements will enable a characterization of all of Stokes’ parameters. The nature of thermal radiation will be explored by studying the degree of coherence, degree of polarization, directional and polarization dependence, local density of states, etc.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.