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FIP Seminar Student Speaker Awardee: From Radiative to Nonradiative Mie-tronics with the Topology of Light and Matter

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Wednesday, March 29, 2023
12:00 pm - 1:00 pm
Hooman Barati Sedeh, PhD Candidate, ECE, Duke University

Structured light with an asymmetric phase distribution emerges as an enabling tool to control the light-matter interactions in optical nanostructures. In this work, we first investigate structured light interactions with the all-dielectric meta-atoms of different geometries and aspect ratios and demonstrate that the phase asymmetry of Laguerre-Gaussian (LG) beams of various orders facilitates the excitation of higher-order radiative modes that are not accessible via conventional Gaussian beam or plane wave as shown schematically in Figure 1 (a). In particular, we show that the use of an LG beam not only can excite the quadrupole moments within the designed nano-resonators but can alter the strength of the induced moments. It is also demonstrated that the geometry and orientation of the meta particles, as well as the illumination angle of the LG beam, can strongly affect the magnitude and spectral location of the induced radiative modes within the subwavelength meta-atom. Figure 1. (a) Mie resonance manipulation using structured light beams carrying an orbital angular momentum. By utilizing a spatial light modulator to change the structural features of the incoming light beam, the excited multipole moments within the meta-atom can be manipulated and turned on and off on demand. (b) The formation of a non-radiating electric anapole state as the result of destructive interference between electric and toroidal dipoles.

Figure 1. (a) Figure 1. (b)

Next, we demonstrate the design of a meta-atom that supports new non-radiative states, called anapoles, formed due to the destructive interference between waves generated by certain multipoles, as shown in Figure 1(b). While a majority of existing studies focused on the electric anapoles, here we design and demonstrate an all-dielectric cuboid meta-atom that support magnetic and hybrid anapoles that are formed due to the overlap of electric and magnetic multipoles with their toroidal counterparts. In addition, we demonstrate that with a careful design, such meta-atom can support non-radiative states up to quadrupole moments. We also show that various anapole orders can be excited and manipulated by changing the angle of illumination. Furthermore, by changing the topology of the cuboid meta-atom to a pyramid particle, we demonstrate the satisfaction of different Kerker's condition, such as unidirectional scattering, and the establishment of superscattering regime.

Contact: August Burns