Chiral Surface Lattice Resonances

Abstract

resonances. [5,6] A collective excitation (SLR) possesses a reduced linewidth as compared to the excitation of the LSPRs in nanoparticle ensembles. [1][2][3][4] Thus, SLRs can provide high quality-factor metasurfaces with substantial impact in nanophotonic and sensing applications. [1][2][3][4] Oblique incidence on planar metasurfaces constructed of an array of split-ring resonators showed that SLRs can also selectively respond to the handedness of circularly polarized light, causing sharp lattice-mode assisted extrinsic circular dichroism. [7,8] The spectral position of these SLRs can be tuned by the angle of incidence, leading to the emergence of extrinsic chiral surface lattice resonances. [9][10][11][12] Strong optical activity can also result from plasmonic 3D nanostructures without mirror symmetry. However, SLRs from arrays of 3D building-blocks with intrinsic chirality remain unexplored, but promise decreased losses and enhanced optical activity. [1,13] The fabrication of chiral 3D nanostructures is challenging for both, bottom-up and top-down methods. [14][15][16] Recently, the excitation of SLRs was seen in self-assembled, large area colloidal systems. [17,18] Such systems offer the possibility for fast manufacturing and covering large-areas on different substrate materials. [19] Colloid-based materials allow for embedding of nanoparticle arrays into flexible free-standing polymer films, [20] enabling the design of mechanically tunable [21] and stimuliresponsive hydrogel membranes. [22] Here, we use colloidal lithography [23][24][25] to fabricate arrays of 3D crescents with a selective response to the handedness of incident circularly polarized light, and we experimentally demonstrate handedness-dependent (chiral) SLRs at normal incidence. Colloidal lithography [23][24][25] is an experimentally simple and fast process to fabricate 3D chiral plasmonic nanostructures. [26][27][28] However, a necessary condition to observe SLRs in such nanostructure arrays is that their lattice constant must be in the range of the wavelength of the LSPRs of the individual nanostructures. [1][2][3][4] For objects with resonances in the near-infrared, such as, for example, split ring resonators, this requires large interparticle distances approaching the micrometer range. For conventional colloidal lithography processes, which depend on the controlled shrinkage of a polymer particle matrix, such distances are not easily achievable. [12,[28][29][30] Therefore, we use core-shell particles with rigid cores (silica) and soft, deformable polymer shells. [31,32] The particles selfassemble into hexagonally ordered monolayers at the air/water Collective excitation of periodic arrays of metallic nanoparticles by coupling localized surface plasmon resonances to grazing diffraction orders leads to surface lattice resonances with narrow line width. These resonances may find numerous applications in optical sensing and information processing. Here, a new degree of freedom of surface lattice resonances is experimentally investigated by dem...

The Beginner's Guide to Chiral Plasmonics: Mostly Harmless Theory and the Design of Large‐Area Substrates

“…This separation can be achieved by either using randomly dispersed particles, [ 172,173 ] etching of close‐packed monolayers, [ 174,185 ] or by hard‐core/soft‐shell particle masks. [ 98,166 ]…”

“…Reproduced under the terms of Creative Commons Attribution License. [ 98 ] Copyright 2020, The Authors, Published by Wiley‐VCH.…”

“…Inspired by on‐edge lithography, [ 210,211 ] the mirror symmetry of an individual crescent is broken by introducing a dielectric step onto which the metallic crescent is evaporated under a different azimuthal angle (Figure 9c, i). [ 214 ] The direction of the twisting between the two deposition steps determines the handedness of the chiral crescents. The chiral origin and sign of CD of the two main dipolar resonances can be understood by a multipole decomposition.…”

“…The chiral origin and sign of CD of the two main dipolar resonances can be understood by a multipole decomposition. [ 214,223,254 ] The strength of the resulting circular dichroism can be controlled via the twisting angle, peaking at ±90°, or the thickness of the underlying dielectric step. [ 214 ]…”

“…[ 214,223,254 ] The strength of the resulting circular dichroism can be controlled via the twisting angle, peaking at ±90°, or the thickness of the underlying dielectric step. [ 214 ]…”