Magneto-optical-trap loading in a large optical-access experiment

Abstract

We present an experimental, numerical, and analytical study of strontium magneto-optical trap (MOT) loading from a cold atomic beam in a configuration optimized for high numerical aperture optical tweezers. Our approach orients the beam flow along the MOT symmetry axis to reduce the experimental complexity and maximize the overall optical access into the scientific region of study. We use a moving molasses technique to enable this configuration and show that its performance depends critically on metastable-state shelving (to 5s5p 3P2) during the atom transfer to the three-dimensional (3D) MOT. Furthermore, we find that the parameters for optimal transfer efficiency are bounded by dark-state loss (to 5s5p 3P0) in the trap region where repumping is present. These observations are verified to great degree of accuracy using both our developed analytical and numerical models. The corresponding 3D simulation tool is used to perform a comprehensive study of the trap loading dynamics, beginning at the oven exit and ending at the 3D MOT, demonstrating its effectiveness in optimizing an effusive oven experiment.

Figures (3)

• Figure : Figure 2: (a) Schematic view of the experimental vacuum chamber (OM: optical molasses; ZS: Zeeman slower; MOT: magneto-optical trap). The inset displays a top view of a high numerical aperture (NA) tweezer setup; the 3D MOT side beams are mirrored with respect to the radial axis perpendicular to the objectives axis at a $25\,^{\circ}$ angle. Note that the permanent magnets and the coils producing, respectively, the 2D and 3D MOT magnetic fields are not shown. (b) The corresponding numerical setup, including the 2D OM, ZS, 2D and 3D MOTs. The blue dots are superparticles. A video version of this figure is available as online Supplemental Material 2:0.
• Figure : Figure 4: Diagrams showing the 3D MOT atom numbers (normalized; see text for absolute) using our loading technique connecting the 2D and 3D MOTs via moving molasses, obtained analytically, experimentally, and numerically. The experimental and numerical data points are obtained at the values seen on the axes, with the contours enhancing the features. The vertical dashed line marks the fixed bottom beam detuning ($-46$ MHz), and the slanted dashed line delineates approximately the sloped analytical feature. The cross and the dotted circle highlight respectively the location with the greatest analytical atom number ($44.8$ G/cm gradient at $-7.3$ MHz top beam detuning) and the greatest experimental as well as numerical atom number ($48$ G/cm gradient at $-10$ MHz top beam detuning).
• Figure : Figure 7: Diagrams showing the normalized 3D MOT atom numbers obtained using our analytical model describing the 3D MOT loading using the moving molasses technique discussed in the main text (Sec. \ref{['sec:MainResults']}). The left diagram uses the full Eq. \ref{['eq:N']} of our model, while the right one excludes the loss to the dark state $5s5p\,^3\!P_0$ ($\Gamma_\text{loss}$ is held at a fixed positive value in Eq. \ref{['eq:N']}). The left dashed line and the cross are as in Fig. \ref{['fig:4']}, while the right dashed line indicates the boundary where the sign of the confinement is flipped. Note that the diagrams span over a larger parameter space than in Fig. \ref{['fig:4']}.