Multi-frequency coherent emission from superstructure thermal emitters

Long-range spatial coherence can be induced in incoherent thermal emitters by embedding a periodic grating within material supporting propagating polaritons or dielectric modes. However, only single spatially coherent mode is supported purely emitters. While various designs have been proposed for the purpose of allowing arbitrary emission profiles, limitations associated with partial are not known. Here, we explore superstructure gratings (SSGs) to control and spectral properties SSGs long-range periodicity but employ unit cell that provides multiple Bragg vectors interact light. These allow simultaneous launching different frequencies/wavevectors grating, manifesting as additional modes profile. still well-defined period, which allows us assess role finite plays We find length defines maximum possible SSG period used. This fundamental limit on degree emitter has broader implications use techniques such inverse design structure optimization.