Radiative properties of lasing plasmonic bound state in continuum are
analyzed. The topological charge of the lasing signal is analyzed in the far
field as well as in the source plane of the finite sized plasmonic lattice. The
physical mechanism enabling the coupling of the BIC to radiation continuum is
identified. We show that while the BICs have their origin in multipolar
resonances, their far-field radiation properties are governed by the position
dependent dipole moment distribution induced by the symmetry breaking in a
finite plasmonic lattice. Remarkably, this dipole-moment enabled coupling to
radiation continuum maintains the essential topological features of the
infinite lattice BICs