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Collective coherent behavior and classical analogue of quantum phenomena in terahertz metasurfaces

Xu, Ningning
Metasurfaces made of subwavelength resonators exhibit exotic optical properties which do not exist in natural materials. Several of the unique properties of metasurfaces depend on the nearest neighbor interactions in the lattice which is important for the fundamental understanding their effective medium behavior. The collective coherent behavior influenced by the nearest-neighboring meta-atoms interactions in metasurface system has been rarely probed in the past. Therefore, in this thesis, I study the collective coherent behavior in meta-atoms dominated by the near-field and the far-field interactions in the lattice. The interaction effects have been studied in two fundamentally different metasurface systems: Lorentzian and Fano resonant meta-atoms. I identified universal behavior in both types of resonant metasurfaces, where in the Lorentzian resonator, the resonant shift due to nearest neighbor interaction decays exponentially as the lattice constant increases. While, in the Fano meta-atoms, I observed an exponential decay of the Fano resonance linewidth with a universal decay constant as the lattice constant was increased. Apart from the near-field coupling, I also studied the far-field diffraction mode mediated coupling in meta-atoms. Through diffraction mode management, I show that each of the eigenmodes of a Lorentzian resonator can be tailored by matching the fundamental diffractive mode of the lattice. Furthermore, by using these tricks to couple meta-atoms, I designed experiments to demonstrate classical analogue of quantum phenomena such as electromagnetically induced transparency and absorbance by coupling resonance modes of different Lorentzian and Fano resonators. The understanding and the discovery of the universal behavior of coupling effects in this thesis would provide future directions to design efficient metasurface lattices with applications in optical switches, narrow-band filters, modulator and quantum information processing devices across the broad electromagnetic domain extending to radio waves, microwave, terahertz, infrared and optical regimes.