We experimentally observe lasing in a hexamer plasmonic lattice and find that, when tuning
the scale of the unit cell, the polarization properties of the emission change. By a theoretical
analysis, we identify the lasing modes as quasi-bound-states in continuum of topological
charges of zero, one, or two. AT-matrix simulation of the structure reveals that the mode
quality (Q) factors depend on the scale of the unit cell, with highest-Q modes favored by
lasing. The system thus shows a loss-driven transition between lasing in modes of trivial and …

Plasmonic lattices of metal nanoparticles have emerged as an effective platform for strong
light-matter coupling, lasing, and Bose-Einstein condensation. However, the full potential of
complex unit cell structures has not been exploited. On the other hand, bound states in
continuum (BICs) have attracted attention, as they provide topologically protected optical
modes with diverging quality factors. We show that nanoparticle lattices with complex unit
cells enable lasing in quasi-BIC modes with a exceedingly high quality Q factor. By …