Tunable Directional Scattering from High-Refractive-Index Particles Dispersed in an Anisotropic Medium

Abstract

We demonstrate the tunability of the intensity and directionality of scattered light in a soft colloidal dielectric metamaterial. The system consists of high-refractive-index sub-micrometer-sized particles dispersed homogeneously in a nematic liquid crystal. The refractive index modulation of the nematic liquid crystals achieved by the application of an ac electric field provides tunable Mie resonant forward scattering of the particles in the optical wavelength regime following Kerker’s first condition. The unique scattering properties exhibited by the system are established using the heterodyne near-field scattering (HNFS) imaging technique. The analysis of the Mie coefficients, simulation of near- and far-field scattering based on Mie theory, and finite element method elucidate the enhancement and tunability of forward scattering.

Soft‐Matter‐Based Hybrid and Active Metamaterials

“…In particular, self-assembly of both non-plasmonic and plasmonic colloidal nanocrystals into liquid crystalline matrices has immense potential to engineer composite nanostructured MMs through a bottom-up app roach. [137,139,144,145,[153][154][155][156][157][158] Indeed, self-assembly of colloidal NPs into liquid crystalline architectures is an encouraging direction to adjust the spatial configuration as well as the orientation of nanoscale building blocks over large areas. This was considered in the early work by Smalyukh et al, [145] who reported the aggregation-free elastic self-alignment of Au nanorods dispersed in LCs and their realignment by shearing and magnetic fields, and thus showed the potential for LC-mediated wellcontrolled self-assembly of bulk optical MMs with reversibly switchable properties.…”

“…[64,137] Motivated by the great likelihood of implementing tunable ultracompact on-chip devices, the development of LC-based hybrid colloidal MMs has thus become a crucial research area over the last few years. [64,137,143,[145][146][147][148][149][150][151][152][153][154][155] This section introduces and discusses LC-based self-assembling phenomena for active colloidal MMs, with particular emphasis on recent advances in the field. It then briefly considers a broad spectrum of properties and capabilities of self-organized plasmonic hybrids loaded with LCs and provide examples of active MMs which interact with electromagnetic radiation in the visible and infra-red regions.…”

“…Quite recently, the bridge between NPs and LCs has been expanded with self‐assembled hybrid MMs based on high‐index dielectrics as well as biocompatible composites. [ 151–153 ] For example, Nair et al., [ 153 ] fabricated a hybrid MM by immersing TiO 2 nanoparticles functionalized with an organic acid containing a carboxyl group in an NLC and used AC bias voltage to switch Mie resonant forward scattering of the NPs in the visible employing Kerker's postulate. Note that, the unidirectional scattering, forward or backward, was previously formulated by Kerker et al., on a theoretical molecule that reveals magnetic and dielectric dipolar resonances.…”

Dynamic Tuning and Swapping of Electric and Magnetic Dipolar Mie Resonances in High Index Dielectric Particles Dispersed in an Anisotropic Medium

“…Our previous works on similar anisotropic colloidal systems showed tunable Fano resonance arising due to the interference between a broad continuum (electric dipole) and a narrow (electric quadrupole) resonances [ 15 ] and tunability of enhanced forward scattering due interference between Mie resonant modes following Kerker's 1st condition. [ 44 ] However, the current study of the tuning and swapping of Mie resonances through random assembly of Se particles in isotropic/anisotropic media employing the ubiquitous scattering phenomena in high index dielectric particles emphasizes the role of multipolar interferences in obtaining various physical phenomena such as forward scattering and photonic nanojet formation. The manipulation of the multipolar interferences is highly dependent on the tuning of MD and swapping of ED and MD Mie resonant modes.…”

Photo-tunable epsilon-near-zero behavior in a self-assembled liquid crystal – nanoparticle hybrid material

“…On the other hand, soft materials such as polymers, colloidal dispersions, fluids, and liquid crystals offer immense scope in terms of processability and tunability. 24 Among soft materials, liquid crystals (LCs) are preferred as materials of choice to bring about tunability in metaproperties [25][26][27] due to their responsiveness to a wide range of stimuli, viz., thermal, mechanical, electrical, magnetic, and optical fields. 28,29 Liquid crystal-nanoparticle hybrid systems are interesting materials to be used for this purpose.…”