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Abstract:
The ability to control the light–matter interaction and the simultaneous tuning of both the structural
order and disorder in materials, although important in photonics, remain major challenges. In this
paper, we demonstrate that path length dictates light–matter interaction for the same crystal structure,
formed by the ordering of magnetic nanoparticle self-assembled columns inside magnetic nanofluid
under applied field. When the path length is shorter (L = 80 m , m ) the condition for maintaining
temporal coherencefor the constructive interference is therefore satisfied, resulting in the formation of
a concentric diffraction ring pattern; while for a longer path length (L = 1 mm ,) only a corona ring of
scattered light is observed. Analysis of diffraction ring pattern suggests the formation of 3D hexagonal
crystal structure, where the longitudinal and lateral inter-column spacings are 5.281 μm and
7.344 μm, respectively. Observation of speckles and diffuse scattering background within the
diffraction ring pattern confirms the presence of certain degree of crystal disorder, which can be tuned
by controlling the applied field strength, nanoparticle size and particle volume fraction. Our results
provide a new approach to develop next generation of tunable photonic devices, e.g. tunable random
laser, based on simultaneous harnessing of the properties of disordered photonic glass and 3D
photonic crystal.
