Active Hyperuniform Disordered Materials
Creators: name: SPALDING, RICHARD JOHN
Publisher: name: University of Surrey
Year: 2022

description: Hyperuniform disordered structures are a class of artificial structures that, despite a
description: random visual appearance, contain a hidden order that arises from their uniform distribution of geometric features and constrained correlations in the reciprocal space.
description: Hyperuniform disordered photonic materials have highly tunable scattering characteristics and can exhibit large, isotropic photonic band gaps, which make them attractive to
description: many areas of research in photonics.
description: This thesis explores the photonic characteristics of hyperuniform disordered structures
description: which, combined with the dynamics of active materials, gives rise to complex functionalities in a number of photonic devices. Foremost, we argue that spatial correlations
description: — in any structure — are central in establishing a fundamental link between geometric
description: and optical properties. As such, we assemble a toolbox of analytical techniques that
description: can extract important geometric features from arbitrary structures, such as average
description: separation of structural features, uniformity, and strength of both long- and short-range
description: order, which we subsequently deploy in exploring the physics of hyperuniform disordered
description: photonic materials.
description: Hyperuniform disordered structures are first employed in the design of a thin solar
description: cell architecture, where a light trapping technique is devised to attain large absorption
description: enhancements up 85% over the visible spectrum. This is predicated on understanding
description: the interplay between two key physical phenomena: the efficient coupling of light to the
description: guided modes of the absorbing material, and diffraction via a patterned surface layer. By
description: analysing the absorption spectra of several types of hyperuniform disordered structures,
description: photonic crystals, and quasicrystals, using finite-difference time-domain computational
description: simulations, we explore the presence of fundamental correlations not only between the
description: structures and their optical response, but also between visually contrasting structures
description: that have similar absorption spectra.
description: We subsequently probe the transport of electromagnetic waves through a hyperuniform
description: disordered photonic slab, in which the patterning is two-dimensional but the structure
description: has a finite vertical thickness. The behaviour of the transmission points towards several
description: transport regimes that are present in hyperuniform disordered materials: a) complete
description: suppression in the photonic band gaps, b) Anderson-like localisation in close spectral
description: proximity to the photonic band gap, c) unimpeded transmission in a “stealthy” region,
description: where the structure appears transparent to waves below a certain wavevector, and d)
description: diffusive transport everywhere else. The individual guided resonances that photonic
description: hyperuniform disordered materials support are also investigated at great depth, particularly those in close spectral proximity to the bandgap. These modes are naturally
description: localised — the lower frequency band edge modes of the hyperuniform disordered photonic slab exhibit very large quality factors up to 26,000, due to their excellent in-plane
description: confinement and their localisation within the dielectric material. The spatial extents,
description: quality factors and robustness of the modes (against a reduction in the expanse of the dielectric structure that surrounds them) are explored using finite-difference time-domain
description: simulations.
description: Using this knowledge, we design a laser that utilises a single mode of a hyperuniform
description: disordered photonic slab to achieve efficient laser action. Employing finite-difference
description: time-domain simulations, we observe and analyse the lasing dynamics of two lasing
description: devices: one that utilises hyperuniform disordered structuring and another that uses
description: periodic structuring.
description: Our results indicate that hyperuniform disordered materials show a promising future for
description: implementation in such functionalities, with novel and interesting features that can be
description: exploited in other applications.