Tunable photonic crystals explained via Mie theory and discrete dipole approximation: a different light

Abstract

A novel hybrid method based on Mie theory and the Discrete Dipole Approximation (DDA) wasdeveloped to study the microscopic parameters governing the optical response of tunable photoniccrystals (PC). The method is based on a two-step process. An effective polarizability derived fromMie theory is determined by equating the extinction efficiency of an isolated nanoparticle (NP) tothe extinction efficiency of an equivalent particle considering the dipolar limit. Then, this effectivepolarizability is used in the DDA framework to compute the optical response of an interactingparticle array constituting the PC structure.As a particular example, the method was applied to a linear array of core-shell magnetite@silicaNPs to study the dependence of extinction and absorption on system parameters such as coreradius, shell thickness, total radius, interparticle separation, and size distribution. The resultsindicate that an increase in these parameters leads to a redshift of the extinction peak as wellas an increase in its FW HM. Finally, the method is applied to fitting experimental resultson reflection/transmission measurements of magnetite@silica NPs colloids subjected to differentmagnetic field strengths with very good agreement.The presented method reduces the computational cost and time for the NPs sizes considered,and can be applied to PCs responsive to different stimuli such as mechanical stress, electric fieldand temperature, inter alia.