Magnetic Nanoantennas Made of Plasmonic Nanoclusters for Photoinduced Magnetic Field Enhancement

Abstract

We focus on a category of nanoantennas called magnetic nanoantennas, made of a circular cluster of gold nanospheres, that leads to enhanced local magnetic field oscillating at optical frequency. We elaborate on the magnetic field enhancement and the magnetic to electric field ratio, i.e., the local field admittance, when the nanoantenna is illuminated by a single plane wave and by superposition of two plane waves to maximize the magnetic-only response. Single dipole approximation (SDA) is used to analyze magnetic nanoantennas and verified by our findings with full wave simulations. We derive a formula that estimates the natural frequency associated to the magnetic resonance of a circular plasmonic cluster with an arbitrary number of plasmonic nanospheres. Lastly, we classify clusters based on their quality factor, their ability to enhance the magnetic field, and discuss the surface area with strong magnetic field provided by the plasmonic cluster.

Unscrambling Structured Chirality with Structured Light at the Nanoscale Using Photoinduced Force

“…in which w0 is called the beam parameter and controls the spatial extent of the beam in the transverse plane, i.e., the beam waist (w0 tends to be the same as the beam waist for non-sharply collimated beams 31,32,49 to describe the magnetic to electric field ratio compared to that of a plane wave, since this is an important parameter when light interacts with magnetic dipoles.…”

“…( 6) clearly demonstrates that the differential force depends linearly on the electric polarizability of the tip-apex, hence, the material, size and shape of the tip-apex play crucial roles in determining the differential force. Specifically, in a previous study 27 the importance of the shape and material of the tip-apex has been further discussed 49,50 . For example, as discussed previously 27 , by choosing a plasmonic tip-apex, we get stronger electric dipolar response and hence observe more pronounced differential force on the tip-apex.…”

“…However, we emphasize that our technique, in contrast to conventional chiroptical techniques, is capable of detecting nanosamples in the order of ~50-100nm. The detection of chiral samples with smaller chirality parameter requires some extra considerations, like increasing the incident power which is possible in cryogenic conditions 59 or in liquids[60][61][62] or using nanotips with stronger electric polarizability, or even explore nanotips able to express magnetic response49 . However, as we have already discussed, it would be interesting to investigate the capability of our proposed excitation scenario (RCP/LCP waves) in distinguishing between the transverse and longitudinal components of the magnetoelectric polarizability.…”

In pursuit of photo-induced magnetic and chiral microscopy

“…Since natural magnetism fades at optical frequencies, an important aspect under investigation is the use of an engineered structure to provide artificial magnetism (i.e., magnetic dipoles) at optical frequencies that has become the focus of attention in recent years [20][21][22][23][24][25][26][27][28][29][30][31][32][33]. The building block in engineering artificial magnetism which is referred as magnetic nanoantenna in [17] varies from plasmonic structures [12,17,[20][21][22][23][24][25][26][27][28][29][30][31][32][33] to high density nanosphere that exhibit a Mie-like magnetic resonance [34][35][36][37][38][39][40][41][42][43][44][45][46][47]. Magnetic nanoantennas, as nanoengineered structures to enhance the magnetic field at optical frequencies, host resonant modes with circulating electric currents or electric fields which giv...…”

“…Using this configuration, we characterize a tightly focused APB in the near-field by using PiFM to confirm the dominant magnetic field in the proximity of the optical axis [8]. Next, we discuss various designs of magnetic nanoprobes that support magnetic resonances [17][18][19] based on plasmonic and dielectric nano-structures . We put particular emphasis on a Si nanodisk structure, and discuss PiFM measurements of the electric field distribution under APB illumination.…”