Progress towards realizing a cw superradiant laser

Superradiant lasers are a promising path towards realizing a narrow-linewidth, high-precision and high-bandwidth active frequency reference [1]. They shift the phase memory from the optical cavity, which is subject to technical and thermal vibration noise, to ultra-narrow optical atomic transitions of cold atoms trapped inside the cavity. Our previous demonstration of pulsed superradiance on the mHz transition in ⁸⁷Sr [2,3] achieved a fractional Allan deviation of 6.7·10^-16 at 1s of averaging. Moving towards continuous-wave superradiance shows promise to improve the short-term frequency stability by orders of magnitude. A key challenge in realizing a cw superradiant laser is the continuous supply of cold atoms that act as the laser's gain and phase memory. We will present continuous loading of cold ⁸⁸Sr atoms into a ring cavity in the strong collective atom-cavity coupling regime, after several stages of laser cooling and slowing. We will further present progress towards transporting the atoms within the ring cavity using a travelling wave optical lattice.

[1] D. Meiser, J. Ye, D. R. Carlson, M. J. Holland, Prospects for a millihertz-linewidth laser. Phys. Rev. Lett. 102, 163601 (2009).

[2] M. A. Norcia, M. N. Winchester, J. R. K. Cline, J. K. Thompson "Superradiance on the millihertz linewidth strontium clock transition." Science Advances 2, e1601231 (2016)

[3] M. A. Norcia, J. R. K. Cline, J. A. Muniz, J. M. Robinson, R. B. Hutson, A. Goban, G. E. Marti, J. Ye, J. K. Thompson, "Frequency Measurements of Superradiance from the Strontium Clock Transition" PRX 8, 021036 (2018)