Limitation of single-repumping schemes for laser cooling of Sr atoms

Abstract

We explore the efficacy of two single-repumping schemes, 5s5p^{3}P_{2}−5p^{2}^{3}P_{2} (481nm) and 5s5p^{3}P_{2}−5s5d^{3}D_{2} (497nm), for a magneto-optical trap (MOT) of Sr atoms. We reveal that the enhancement in the MOT lifetime is limited to 26.9(2) for any single-repumping scheme. Our investigation indicates that the primary decay path from the 5s5p^{1}P_{1} state to the 5s5p^{3}P_{0} state proceeds via the 5s4d^{3}D_{1} state, rather than through the upper states accessed by the single-repumping lasers. We estimate that the branching ratio for the 5s5p^{1}P_{1}→5s4d^{3}D_{1}→5s5p^{3}P_{0} decay path is 1:3.9(1.5)×10^{6} and the decay rate for the transition from the 5s5p^{1}P_{1} state to the 5s4d^{3}D_{1} state is 83(32)s^{−1}. This outcome underscores the limitation on atom number in the MOT for long loading times (≳1s) when employing a single-repumping scheme. These findings will contribute to the construction of field-deployable optical lattice clocks.