FDTD analysis of anisotropic light-scattering properties induced by magnetically oriented crystals and experimental verification of their qualitative changes

The “magnetic orientation” phenomenon, where diamagnetic crystals align in response to a magnetic field, holds promise for applications that combine this behavior with optical techniques, such as non-invasive diagnostics and magnetically tunable optical micro-devices. For these applications, optimizing the optical configuration to maximize the detection sensitivity of scattered light is crucial; however, light scattering from anisotropic dielectric particles whose dimensions are comparable to or larger than the incident wavelength is difficult to analyze, and the knowledge required for such optimization remains limited. This study aims to numerically predict the light-scattering characteristics before and after crystal orientation induced by a magnetic field using the finite-difference time-domain (FDTD) method and to experimentally verify these predictions using orientable crystals. Using FDTD simulations with a cylindrical crystal model, we arranged the crystals in three patterns relative to the incident light and analyzed the relationship between orientation and scattering patterns. Based on these results, the change in light intensity between the initial random state and the magnetically oriented state was predicted; the rate of change was ∼0.4 for configurations where scattered light intensity increased compared to the pre-field state, whereas it was ∼1.1 for configurations with decreased intensity. Experiments using a suspension of orientable cellulose crystals showed good agreement with the simulated predictions for the increase or decrease in scattered light intensity observed before and after magnetic field application. These results demonstrate that the FDTD method is a powerful tool for exploring the optical configuration of detection systems that utilize magnetic orientations.