Coherence-assisted superradiant laser with hertz-level linewidth and 10-10 -W power

The superradiant laser, based on the clock transition between the electric ground state 1S0 and the metastable state 3P0 of fermionic alkaline-earth-metal-like atoms, has been proposed to be a new promising light source with linewidth of the order of millihertz. However, due to the small 1S0 to 3P0 transition strength, the steady-state power in that system is relatively low (approximately 10-12W). In this work we propose an alternative superradiant laser scheme based on a Raman-transition-induced coupling between the 3P0 and 3P1 states in bosonic alkaline-earth-metal-like atoms and achieve a laser with narrow linewidth (less than approximately 2π×1Hz) and high power (greater than approximately 10-10W, approximately 103 photons in steady state) at a small pumping cost (less than approximately 2π×10kHz). The Raman beams play two significant roles in our scheme. First, the coherence between the dark and bright states induced by the Raman beams produces a new local minimum in the pumping-linewidth curve with pumping rate lower than 2π×10kHz, which is beneficial for continuous output. Second, the Raman beams mix the long-lived 3P0 state into the lasing state and thus make the laser linewidth tunable. Our work greatly improves the output performance of the superradiant laser system with coherence induced by Raman transitions and may offer a firm foundation for its practical use in the future.