Quality Factor of a Nanobowtie Antenna

Abstract

The optimal currents on arbitrarily shaped radiators with respect to the minimum quality factor Q are found using a simple and efficient procedure. The solution starts with a reformulation of the problem of minimizing quality factor Q as an alternative, so-called dual, problem. Taking advantage of modal decomposition and group theory, it is shown that the dual problem can easily be solved and always results in minimal quality factor Q. Moreover, the optimization procedure is generalized to minimize quality factor Q for embedded antennas, with respect to the arbitrarily weighted radiation patterns, or with prescribed magnitude of the electric and magnetic near-fields. The obtained numerical results are compatible with previous results based on composition of modal currents, convex optimization, and quasi-static approximations; however, using the methodology in this paper, the class of solvable problems is significantly extended.

Reaching the Theoretical Resonance Quality Factor Limit in Coaxial Plasmonic Nanoresonators Fabricated by Helium Ion Lithography

“…Resonator critical dimensions are limited by fabrication resolution to >10 nm. In the optical regime and the quasi-static limit, the Q -factor reaches a theoretical value of up to 20 for an Au nanoantenna but typically achieves a value of 2 for cavities on the scale of 100 nm and approaches 10 for ultrasmall mode volume nanoresonators . At the dimensions in which the quasi-static approximation is not valid, the shape and the geometry of a nanoresonator strongly influence its optical performance. − Geometrical deviations from the ideal geometry, such as tapering, sidewall roughness, and corner rounding on length scales comparable to the SPP skin depth, as well as material issues, metal grain structure, effects of adhesion layers, are the reasons for the shortcomings of actual optical antennae compared to their theoretical model structure.…”

Design of a high-performance optical tweezer for nanoparticle trapping

“…Plasmonic cavities do not suffer this limitation because surface plasmon polariton (SPP) modes are strongly confined at the metal-dielectric interface, so strongly enhancing the trapping force [11]. Their very low mode volume V < 10 -4 ( /n) 3 operation enables a strong interaction between light and the target object [12] and has already been used to demonstrate the trapping of metal nanoparticles with a diameter smaller than 10 nm [13,14] and of a single bovine serum albumin (BSA) molecule with a size of 3 nm [15]. The issue with plasmonic cavities, however, is that the metallic losses cause thermal heating, which makes the traps unstable and increases the risk of damage to living matter at the nanoscale as well as increasing the risk of damage to living matter [17].…”

Tunable multipole resonances in plasmonic crystals made by four-beam holographic lithography

“…It was recognized that plasmonic losses are not entirely intrinsic and are partly caused by surface damping due to fabrication errors, metal graininess, and material loss of Cr adhesive layers. 32 To some extent, fabrication losses of EBL can be overcome using sophisticated scanning helium-ion beam lithography (HIL) of coaxial gap antennas demonstrating Q-factors up to 11 that are close to the quasi-static limit. 33 EBL and HIL fabrication techniques, however, are not readily scalable to wafer size as required for practical applications.…”