Efficient production of a narrow-line erbium magneto-optical trap with two-stage slowing

We describe an experimental setup for producing a large cold erbium (Er) sample in a narrow-line magneto-optical trap (MOT) in a simple and efficient way. We implement a pair of angled slowing beams with respect to the Zeeman slower axis, and further slow down atoms exiting from the Zeeman slower. The second-stage slowing beams enable the narrow-line MOT to trap atoms exiting from the Zeeman slower with higher velocity. This scheme is particularly useful when the Zeeman slower is at low optical power without the conventional transverse cooling between an oven and a Zeeman slower, in which case we significantly improve the loading efficiency into the MOT and are able to trap more than ${10}^8$ atoms in the narrow-line MOT of ${}^{166}\mathrm{Er}$. This work highlights our implementation, which greatly simplifies laser cooling and trapping of Er atoms and also should benefit other similar elements.

Figure 1

Schematic of experimental apparatus for cooling and trapping Er atoms. An oven at $1200{}^{\circ }\mathrm{C}$ effuses an Er atomic beam into the intermediate chamber where laser spectroscopy is performed for the 401 nm (blue) and 583 nm (yellow) transitions. The 400-mm-long spin-flip Zeeman slower decelerates atoms and is followed by the second-stage angled slowing beams. Two recessed viewports are used in the science chamber. The 400-mm-long spin-flip Zeeman slower decelerates atoms followed by the second-stage angled slowing beams. Two recessed view ports are used in the science chamber.

Figure 2

Schematics of two-stage slowing, the science chamber, and the level diagram. (a) Layout of two-stage slowing scheme near the narrow-line MOT. Two 401-nm beams intersect 20 mm ahead of the MOT position, wherein atoms exiting from the Zeeman slower are further decelerated along the $x$ direction and slowed along the $y$ direction. (b) View of the narrow-line MOT and the recessed view ports. In the science chamber, the diameter of the MOT beam is fully maximized up to 12 mm. The gap between two recessed view ports is 13 mm. (c) Broad singlet and narrow triplet transitions are used for two-stage slowing and narrow-line MOT loading.

Figure 3

Enhanced ${}^{166}\mathrm{Er}$ MOT loading with angled slower beams atom number $N_{\text{MOT}}$ loaded in the narrow-line MOT is measured by atomic fluorescence (and absorption imaging) as a function of time at the oven temperature of $1200{}^{\circ }\mathrm{C}$. The second-stage slowing significantly improves the steady-state atom number by more than an order of magnitude. The Zeeman slower magnetic field is kept the same for both measurements. The data without angled slower beams is multiplied by 12 to simplify comparison. The blue circle (yellow triangle) is a fit result with the empirical equation $N_{\text{MOT}}\left(t\right)=R\tau (1-e^{-t/\tau })$ where $R$ is the MOT loading rate and ${\tau }^{-1}$ the loss rate from the MOT. The typical MOT loading time ($\tau$) is about 0.5 s with the angled slower beams.

Figure 4

Enhanced capture velocity of Zeeman slower with two-stage slowing. Velocity of Er atoms along the Zeeman slower with angled slower beams off (a) and on (b). The magnetic field in the Zeeman slower is separately optimized on the MOT loading in each case (a), (b). For example, the final velocities of Er atoms with an initial longitudinal speed of 200 m/s are 3.8 and 7.6 m/s after the Zeeman slower in (a) and (b), respectively. The insets show zooms of the velocity in the range between –15 and –11 cm. The MOT is located at 0 cm. The shade indicates the capture velocity of the Zeeman slower in (a), (b). (c) Maxwell-Boltzmann distribution of Er atoms at $1200{}^{\circ }\mathrm{C}$. Colored lines show different initial velocities.