Browsing by Author "Prasad, Ciril Samuel"

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    Thermal radiation control by engineering permittivity, symmetry and topology in thermal emitters.
    (2023-06-02) Prasad, Ciril Samuel; Naik, Gururaj V
    Thermal radiation arising from random fluctuations lack spatial and spectral coherence. Ability to control thermal radiation and render it partially coherent unlocks solutions to a host of fundamental and technological challenges in thermal imaging, thermophotovoltaics and radiative cooling. Past nanophotonic designs for thermal radiation control are limited by various trade-offs involving spectral selectivity, brightness and directionality. In this thesis, I demonstrate spatial and spectral control of thermal radiation by engineering optical losses, symmetry and topology in a nanophotonic system. First, using the principles of non- Hermitian physics, a loss asymmetric coupled resonator thermal metasurface is designed and experimentally verified to exhibit directional suppression of thermal radiation while maintaining transmission in mid-infrared. Furthermore, I experimentally demonstrate how such a metasurface can be employed to improve image contrast while performing thermal imaging in high temperature environment. Additionally, based on similar design principles, a loss engineered hybrid plasmonic-photonic resonator metasurface is designed to show strong spectral selectivity at elevated temperatures. The metasurface when employed as thermal emitter in a thermophotovoltaic system can improve the overall heat to electricity conversion efficiency. Further, the k-space of metasurface is explored to achieve angle-dependent thermal radiation. Finally, a way to enhance broadband IR absorption is proposed and demonstrated using hyperbolic aligned carbon nanotube films.
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    Unconventional nanophotonic thermal emitters for imaging and energy applications
    (2024-08-05) Prasad, Ciril Samuel; Naik, Gururaj V
    All objects above absolute zero temperature emit thermal radiation. Seamless control over this thermal radiation can unlock solutions to fundamental and technological challenges in imaging, energy harvesting, and utilization. Existing thermal emitter designs are limited by various trade-offs involving spectral selectivity, brightness, and directionality of thermal radiation. In this thesis, I demonstrate unconventional ways to achieve spectral and spatial control over thermal radiation by engineering complex permittivity of the emitter surface. First, using the principles of non-Hermitian physics, a hybrid plasmonic-photonic coupled resonator metasurface is designed and experimentally verified to exhibit strong spectral selectivity at elevated temperatures. I demonstrate that the designed selective thermal emitter on a refractory metal platform surpasses the spectral efficiency limit set by existing thermal emitter designs used in thermophotovoltaics--a solid-state scheme to convert heat into electricity. A transparent, asymmetrically emitting thermal metasurface is realized based on similar concepts. The designed metasurface enhanced the image contrast while performing thermal imaging in high-temperature environments. Further, the k-space of metasurface is explored, revealing additional tunable parameters for engineering thermal radiation. Finally, a way to achieve broadband IR emission/absorption is proposed and demonstrated using aligned carbon nanotube films with anisotropic permittivity tensor.