The use of virtually lossless topologically isolated edge states may lead to
a novel class of thresholdless lasers operating without inversion. One needs
however to understand if topological states may be coupled to external
radiation and act as active cavities. We study a two-level topological
insulator and show that self-induced transparency pulses can directly excite
edge states. We simulate laser emission by a suitable designed topological
cavity, and show that it can emit tunable radiation. For a configuration of
sites following the off-diagonal Aubry-Andre-Harper model we solve the
Maxwell-Bloch equations in the time domain and provide a first principle
confirmation of topological lasers. Our results open the road to a new class of
light emitters with topological protection for applications ranging from
low-cost energetically-effective integrated lasers sources, also including
silicon photonics, to strong coupling devices for studying ultrafast quantum
processes with engineered vacuum
