The design of nano-antennas is so far mainly inspired by radio-frequency technology. However, material properties and experimental settings need to be reconsidered at optical frequencies, which entails the need for alternative optimal antenna designs. Here a checkerboard-type, initially random array of gold cubes is subjected to evolutionary optimization. To illustrate the power of the approach we demonstrate that by optimizing the near-field intensity enhancement the evolutionary algorithm finds a new antenna geometry, essentially a split-ring/two-wire antenna hybrid which surpasses by far the performance of a conventional gap antenna by shifting the n=1 split-ring resonance into the optical regime.PACS numbers: 84.40. Ba, 73.20.Mf, 78.67.Bf Light-matter interaction, i.e. absorption and emission of light as well as the control of its spectral and directional properties, can be optimized by means of antennalike plasmonic nano structures [1, 2]. This is of immediate importance in diverse fields of research ranging from solar energy conversion [3], photocatalytic [4] and sensing applications [5] to single-particle manipulation [6,7] and spectroscopy [8] as well as quantum optics and communication [9][10][11][12].RF-antenna designs are usually optimized for thin, infinitely good conducting wires that only support surface currents and are typically fed by transmission lines connected by infinitely narrow gaps [13]. For antennas at optical frequencies the general operation conditions deviate substantially from such ideal behaviour: (i) Antenna wire diameters are comparable to the electromagnetic penetration depth into the wire material leading to volume currents [14]. In the case of noble metals, such wires therefore exhibit plasmon resonances in the visible spectral range resulting in a reduced effective wavelength of wire waves [15]. (ii) Feeding (excitation) of optical antennas is often achieved by focused laser beams or quantum emitters. (iii) high-frequency-related effects such as the 'kinetic inductance' become significant [16]. It can therefore not be taken for granted that RF-inspired antenna designs, like dipole [17], bow tie [18,19] and Yagi-Uda antennas [20,21], represent 'optimal' geometries also at optical frequencies, although they provide a reasonable performance.Evolutionary algorithms (EAs) find optimized solutions to highly complex non-analytic problems by creating subsequent generations of individuals coded by their respective genomes that compete for the right to pass on their properties, according to a fitness parameter [22]. These optimized solutions can then be analyzed to foster the understanding of underlying physical principles. Evolutionary optimization has successfully been applied in various fields of research, including pulse shape optimization in coherent control of chemical reactions [23] and field localization in plasmonic structures [24,25]. Furthermore, evolutionary optimization has been used to aid the development of radio-wave antennas [26,27]. First attempts to employ such met...
This work compares two popular MC simulation frameworks ROSI (Roentgen Simulation) and GEANT4 (Geometry and Tracking in its fourth version) in the context of X-ray physics. The comparison will be performed with the help of a parameter study considering energy, material and length variations. While the total deposited energy as well as the contribution of Compton scattering show a good accordance between all simulated configurations, all other physical effects exhibit large deviations in a comparison of data-sets. These discrepancies between simulations are shown to originate from the different cross sectional databases used in the frameworks, whereas the overall simulation mechanics seem to not have an influence on the agreement of the simulations. A scan over energy, length and material shows that the two parameters energy and material have a significant influence on the agreement of the simulation results, while the length parameter shows no noticeable influence on the deviations between the data-sets.
Most currently studied optical antenna geometries are based on radio wave antenna designs. However, material properties at optical frequency largely differ from the perfect metal case at radio frequencies. Recently, evolutionary algorithms (EA) [1] were used in the field of Plasmonics to find novel geometries however with strongly limited configuration space [2]. We developed an EA capable of handling complex multiparticle geometries. In a first application we optimized near-field intensity enhancement produced by antenna structures in a single point [3]. We found a novel geometry, i.e. a nano antenna/split-ring hybrid antenna for which the near-field intensity enhancement is strongly increased. Yet these structures are not suitable for experimental realization. Here we show the results of an adapted EA which uses primitive elements that are compatible with an experimental fabrication step using FIB. The performance of the realized structures is characterized by means of confocal two-photon-photoluminescence-(2PPL)-microscopy. We find that the hierarchy of performances found in individuals taken from sequential generations of the EA can be reproduced in fabricated structures.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.