Low-temperature high-density magneto-optical trapping of potassium using the open 4S→5P transition at 405 nm

Abstract

We report the laser cooling and trapping of neutral potassium on an open transition. Fermionic 40K is captured using a magneto-optical trap (MOT) on the closed 4S 1/2→4P 3/2 transition at 767 nm and then transferred, with high efficiency, to a MOT on the open 4S 1/2→ 5P 3/2 transition at 405 nm. Because the 5P 3/2 state has a smaller linewidth than the 4P 3/2 state, the Doppler limit is reduced from 145 μK to 24 μK, and we observe temperatures as low as 63(6) μK. The density of trapped atoms also increases, due to reduced temperature and reduced expulsive light forces. We measure a two-body loss coefficient of β=1.4(1)×10 -10 cm3/s near saturation intensity, and estimate an upper bound of 8×10 -18 cm2 for the ionization cross section of the 5P state at 405 nm. The combined temperature and density improvement in the 405 nm MOT is a twenty-fold increase in phase-space density over our 767 nm MOT, showing enhanced precooling for quantum gas experiments. A qualitatively similar enhancement is observed in a 405 nm MOT of bosonic 41K. Published by the American Physical Society under the terms of the http://creativecommons.org/licenses/by/3.0/ Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.