Continuous superradiant laser based on a simple hot atomic beam*

We will report on our recent work that aims to experimentally demonstrate continuous superradiance on the ¹S₀-³P₁ transition of ⁸⁸Sr. Our approach employs a simple architecture based on a hot atomic beam of excited atoms passing through a cavity that was recently proposed [1,2]. Superradiant lasing in the bad-cavity regime decreases cavity pulling reducing sensitivity to environmental perturbations. Due to the promise of cavity noise suppression, superradiant lasers have been proposed as a next generation optical frequency reference for atomic clocks [3].

To achieve sufficient atomic flux through the cavity mode we use an oven with an elongated aperture aligned to the cavity axis and employ transverse cooling to reduce the transverse velocity of the atoms to below 1 m/s. Atoms with a velocity along the cavity axis below 0.5 m/s are selectively stored in the metastable ³P₀ state. This allows remaining ground-state atoms to be Doppler shifted away from the bare atomic resonance preventing interaction with the collective cavity mode. Immediately before the velocity-selected atoms enter the cavity, they are optically pumped to the ³P₁ state. This architecture shows potential as a compact, robust and simple, optical frequency reference with microwatt power levels and linewidths of about 10 Hz, ideal for a wide range of industrial and scientific applications.

[1] Jingbiao Chen, arXiv:physics/0512096 (2005).

[2] Liu et al, Phys. Rev. Lett. 125, 253602 (2020).

[3] Meiser et al., Phys. Rev. Lett. 102, 163601 (2009).