Lasing action in Fano-resonant superlattice metagratings

A proposal of Fano lasing spaser is demonstrated in a superlattice meta-grating, in which the spatial-temporal lasing dynamics is investigated by a semiclassical model that involves the coupling between full-wave electromagnetic equations and electronic rate equations. The out-of-phase dark mode and in-phase bright mode supported by the meta-grating can be independently tailored by the width of the thin strip and the fat strip in each supercell of the meta-grating. It provides a facile way to alter the dark/bright mode to overlap the emission/absorption window of a given four-energy-level gain medium simultaneously, in which case the system exhibits the optimal lasing characteristic. Our findings may provide a useful guideline to design low-threshold and high-efficient miniaturized lasers.