Crossed-beam slowing to enhance narrow-line ytterbium magneto-optic traps

We demonstrate a method to enhance the atom loading rate of a ytterbium (Yb) magneto-optic trap (MOT) operating on the 556 nm ¹S₀ → ³P₁ intercombination transition (narrow linewidth Γ_g = 2π × 182 kHz). Following traditional Zeeman slowing of an atomic beam near the 399 nm ¹S₀ → ¹P₁ transition (broad linewidth Γ_p = 2π × 29 MHz), two laser beams in a crossed-beam geometry, frequency tuned near the same transition, provide additional slowing immediately prior to the MOT. Using this technique, we observe an improvement by a factor of 6 in the atom loading rate of a narrow-line Yb MOT. The relative simplicity and generality of this approach make it readily adoptable to other experiments involving narrow-line MOTs. We also present a numerical simulation of this two-stage slowing process, which shows good agreement with the observed dependence on experimental parameters, and use it to assess potential improvements to the method.