Engineered disorder and light propagation in a planar photonic glass.

Sergei G Romanov,Daniel Ploss,Clemens K Weiss,Nicolas Vogel,Ulf Peschel,Sergej Orlov

doi:10.1038/srep27264

Abstract

The interaction of light with matter strongly depends on the structure of the latter at wavelength scale. Ordered systems interact with light via collective modes, giving rise to diffraction. In contrast, completely disordered systems are dominated by Mie resonances of individual particles and random scattering. However, less clear is the transition regime in between these two extremes, where diffraction, Mie resonances and near-field interaction between individual scatterers interplay. Here, we probe this transitional regime by creating colloidal crystals with controlled disorder from two-dimensional self-assembly of bidisperse spheres. Choosing the particle size in a way that the small particles are transparent in the spectral region of interest enables us to probe in detail the effect of increasing positional disorder on the optical properties of the large spheres. With increasing disorder a transition from a collective optical response characterized by diffractive resonances to single particles scattering represented by Mie resonances occurs. In between these extremes, we identify an intermediate, hopping-like light transport regime mediated by resonant interactions between individual spheres. These results suggest that different levels of disorder, characterized not only by absence of long range order but also by differences in short-range correlation and interparticle distance, exist in colloidal glasses.

Highlights

One of the most important goals of material science in contemporary photonics is developing materials with manageable light-matter interaction
The typical spectral features of photonic crystals, which are based on the collective interaction between all the scatterers, fade away and are replaced by an optical response which is merely based on that of single particles: Diffraction resonances disappear completely in photonic glasses, while Mie resonances of individual spheres become the dominating optical effect[13]
Such adjustment of disorder properties is enabled by the two-dimensional nature of the crystal, with which we mitigate the necessity for touching spheres that is typically found in three-dimensional colloidal photonic glasses

Summary

Introduction

One of the most important goals of material science in contemporary photonics is developing materials with manageable light-matter interaction. Ordered colloidal photonic crystals are characterized by long-range order of the individual scattering elements[1] resulting in a periodic lattice This order gives rise to quasi-ballistic propagation of light[9] through the crystal and to the formation of noticeable diffractive resonances[10,11], visible for certain frequencies and angles of incidence as spectrally narrow dips in transmission. Colloidal photonic glasses have emerged as a completely new and very interesting class of disordered optical materials[12]. Similar to their crystalline counterparts they consist of monodisperse colloidal particles, but lack long-range periodicity. Structural stability of three-dimensional photonic glasses requires individual scatterers to be touching, impeding the realization of free and controlled variation of interparticle distances

Methods

Results

Conclusion