  Topology describes properties that remain unaffected by smooth distortions.
Its main hallmark is the emergence of edge states localized at the boundary
between regions characterized by distinct topological invariants. This feature
offers new opportunities for robust trapping of light in nano- and micro-meter
scale systems subject to fabrication imperfections and to environmentally
induced deformations. Here we show lasing in such topological edge states of a
one-dimensional lattice of polariton micropillars that implements an orbital
version of the Su-Schrieffer-Heeger Hamiltonian. We further demonstrate that
lasing in these states persists under local deformations of the lattice. These
results open the way to the implementation of chiral lasers in systems with
broken time-reversal symmetry and, when combined with polariton interactions,
to the study of nonlinear topological photonics.
