Lasing in the superradiant crossover regime

A new class of laser, which harnesses coherence in both light and atoms, is possible with ultracold alkaline-earth-metal atoms trapped in an optical lattice inside an optical cavity. Different lasing regimes, including superradiance, superradiant, and conventional lasing, are distinguished by the relative coherence stored in the atoms and in the cavity mode. We analyze the physics in two different experimentally achievable regions of the superradiant lasing regime. Our calculations confirm the narrow linewidth of superradiant lasing for the doubly forbidden clock transition P-3(0) -> S- 1(0) of Sr-87 atoms. Under strong driving of the dipole-forbidden transition P-3(1) -> S-1(0) of Sr-88 atoms, the superradiant linewidth narrows further due to the coherent excitation of the cavity field.