An investigation into extreme light scattering in disordered photonic networks

Abstract

Disordered photonic networks provide a unique environment to explore light scattering on the mesoscopic scale. The physical description of multiple scattering in strongly scattering random media is an ongoing field of research, with many theoretical and numerical models exploring the phase transition of light from the diffusive to the localised regime. Experimental verification of these theories is necessary to determine the validity of these results. In this thesis, a novel experimental spatio-temporal pump probe technique is used to characterise anisotropic scattering in GaP nanowire mats to determine the diffusion constant in the transverse and longitudinal directions. Coherent backscatter and total transmission and reflection spectroscopy are used to determine optical characteristics such as the transport mean free path and absorption length. Results corroborate previous independent measurements and promote the use of the pump probe technique for studying anisotropic diffusive light transport.

The multiple scattering process also forms an obstruction to optical imaging through disordered media, such as in clouds or biological tissue. The existence of correlations in the speckle of coherently transmitted or reflected light provides an opportunity to detect information of the target object through seemingly opaque media. Previous works focus on the optical memory effect and its application in such environments. The Lorentz reciprocity of scattered light in the time reverse optical memory effect allows for detection of a specific signal unique to the scattering target; which presents the opportunity for advancement in the field of imaging through scattering media. This phenomenon is explored experimentally, a phase based modulation of the process is characterised, and the principle is then demonstrated in a pulsed optical system.

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Identifiers

ORCID for Luke Burke: orcid.org/0009-0003-7343-0845

ORCID for Otto Muskens: orcid.org/0000-0003-0693-5504

ORCID for Idris Ajia: orcid.org/0000-0003-3156-4426

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