Optical Transitions and Nonreciprocity in Spatio‐Temporally Periodic Layers of Spherical Particles

Abstract An extension of the photonic layer multiple scattering methodology to dynamic spherical scatterers, which exhibit a periodic time‐varying response, is presented. The applicability of the method is demonstrated on specific examples of single‐ and bi‐layers of periodically modulated high‐refractive‐index spherical particles arranged on a square lattice. The results provide compelling evidence for strong and tunable inelastic scattering effects under the triple resonance condition, fulfilled for optical transitions between neighboring high‐Q lattice modes of the appropriate symmetry, which originate from multipolar Mie resonances. A consistent interpretation of the underlying mechanisms is provided and potential applications in the design of nonreciprocal devices are discussed.