Engineering Strongly Chiral Plasmonic Lattices with Achiral Unit Cells for Sensing and Photodetection

Abstract

Although the concept of chirality has its origin in chemistry, the field of photonics is actively exploring and utilizing it. A new family of 2D chiral lattices constructed from fully achiral unit cells is introduced here. This type of chiral structure differs fundamentally from previously reported arrays made of chiral unit cells. In this system, circular dichroism (CD) appears due to the electromagnetic interaction between unit cells and the formation of lattice plasmons (LP). Importantly, the CD is strongly enhanced for anisotropic rectangular lattices, whereas the chiral signal in square lattices is found to be relatively weak. The results cover two configurations. The first has an index‐matched environment, and the second includes an asymmetric arrangement of refractive indices. The index‐matched model is preferable and supports ultrasharp LP resonances. Overall, excellent control of the spectral position and broadening of the CD peaks is also demonstrated by tuning the geometry and matrix refractive indices. These results can be useful for engineering polarization filters and chiral biosensors.

Manipulation of Fluid Convection by Surface Lattice Resonance

“…For the absorption spectra of the SLR-based metasurface in Figure 2a, a narrow absorption peak with a peak value of 0.97 is located around 812 nm. This resonance wavelength is close to the Rayleigh anomaly (RA) wavelength of (0, ±1) and (±1, 0) orders for the normal incidence, which is given by [15,36]…”

“…Recently, the high potential of SLRs in chiroptical applications has also been reported. [15,26,27] Predominantly, for a normal angle of the impinging light, the strong asymmetry between superstrate and substrate can destroy the radiative coupling between the nanoparticles and affect the formation of SLR. A common solution to achieve a homogeneous environment is to replace the air superstrate with an index matching oil, glycerol, or water.…”

“…The SLRs are well known for overcoming the damping of LSPs and minimizing scattering losses from gratings, resulting in very narrow bandwidth. Considering that SLRs for noble metal lattices have very high Q-factors with respect to LSPs, the plasmon dephasing time is several orders of magnitude longer for SLRs, [15] allowing long-life light trapping.The capability of plasmonic metasurfaces (PMs) under illumination to generate heat and induce fluid convection is a promising building approach for optofluidic applications. However, the low quality (Q)-factor in PMs introduced into optofluidic applications remains a challenging problem.…”

“…The SLRs are well known for overcoming the damping of LSPs and minimizing scattering losses from gratings, resulting in very narrow bandwidth. Considering that SLRs for noble metal lattices have very high Q-factors with respect to LSPs, the plasmon dephasing time is several orders of magnitude longer for SLRs, [15] allowing long-life light trapping.…”

Circular Dichroism Induced by the Coupling between Surface Plasmon Polaritons and Localized Surface Plasmon Resonances in a Double-Layer Complementary Nanostructure

“…Planar chiral nanostructures composed of lattice nanoparticles exhibit optical chirality by the asymmetrical arrangement. For example, a chiral system consisting of square spiral nanoparticles generated the CD effect by the difference of interplay between the LSPR and the lattice plasmon modes under LCP and RCP light illuminations . Planar chiral nanostructures exert the CD effect under an oblique incidence of circularly polarized light due to the phase difference of nonparallel electric dipoles produced in different parts of the nanostructures.…”