Achieving strongly negative scattering asymmetry factor in random media composed of dual-dipolar particles.

Understanding radiative transfer in random media like micro/nanoporous and particulate materials, allows people to manipulate the scattering and absorption of radiation, as well as opens new possibilities in applications such as imaging through turbid media, photovoltaics and radiative cooling. A strong-backscattering phase function, i.e., a negative scattering asymmetry parameter $g$, is of great interest which can possibly achieve unusual radiative transport phenomena, for instance, Anderson localization of light. Based on the multipole expansion of Foldy-Lax equations and quasicrystalline approximation (QCA), we have rigorously derived analytical expressions for effective propagation constant and scattering phase function for a random system containing dual-dipolar particles, by taking the effect of structural correlations into account. Here we demonstrate that by utilizing structural correlations and the second Kerker condition for a disordered medium composed of randomly distributed silicon nanoparticles, a strongly negative scattering asymmetry factor ($g\sim-0.5$) for multiple light scattering can be realized in the near-infrared. As concentration of scattering particles rises, the backscattering is also enhanced. Moreover, we show that in this circumstance, transport mean free path is largely reduced and even smaller than that predicted by independent scattering approximation. We further explored the dependent scattering effects, including the modification of electric and magnetic dipole excitations and far-field interference effect, both induced by the structural correlations, for volume fraction of particles up to $f_v\sim0.25$. Our results have profound implications in harnessing micro/nanoscale radiative transfer through random media.