Chains of Nanoparticles for Flat-Band Emission and Lasing

Controlling light-matter interactions is central to photonic technologies ranging from lasers to optical information processing. Suitably designed photonic structures give rise to flat bands, where the density of states diverges and the group velocity goes to zero, allowing light localization. These properties make flat bands attractive for lasing; however, designing photonic structures that support flat bands is challenging. Here, we introduce long-range coupled chains of nanoparticles that support totally flat bands extending over the full angular range. We demonstrate flat-band lasing in single chains and explain the transition to Γ-point lasing as the number of chains is increased. Moreover, we show partially coherent emission from square and triangular two-dimensional chain lattices. The excited modes depend on the pump power and polarization. Our results establish chain lattices as a versatile platform for exploring flat-band lasing and suggest new routes toward narrow-band, linearly polarized, and bright light sources with tailored coherence.