Evaporation of an atomic beam on a material surface

We report on the implementation of evaporative cooling of a magnetically guided beam by adsorption on a ceramic surface. We use a transverse magnetic field to shift locally the beam towards the surface, where atoms are selectively evaporated. With a $5\text{−}\mathrm{mm}$-long ceramic piece, we gain a factor of $1.5\pm 0.2$ on the phase-space density. Our results are consistent with a 100% efficiency of this evaporation process. The flexible implementation that we have demonstrated, combined with the very local action of the evaporation zone, makes this method particularly suited for the evaporative cooling of a beam.

Figure 1

(a) Section cut of the four copper tubes that generate the two-dimensional quadrupole of the magnetic guide, with the cross-shaped ceramic piece. (b) Deflection of the minimum of the magnetic confinement using a pair of coils. (c) Typical atomic trajectory that precesses around the minimum of the magnetic potential because of the nonharmonic confinement.

Figure 2

Fraction of remaining atomic flux $\phi$ for a transverse shift of the position of the beam by $\delta$ mm towards the edge of the ceramic surface: experimental points (∎) and numerical simulation (solid line).

Figure 3

Gain in phase-space density resulting from the evaporation on a ceramic surface after rethermalization. Dashed lines: $D^{\prime }∕D$ deduced from the Monte Carlo numerical simulation for a surface length $\ell =0.01\mathrm{mm}$ (a), $5\mathrm{mm}$ (b), $10\mathrm{mm}$ (c), and $50\mathrm{mm}$ (d). Solid line: two-dimensional evaporation where all atoms with a maximum distance from the center axis above the radius $R-\delta$ are removed [10]. ∎ is the experimental point which corresponds to a gain in phase-space density of $1.5\pm 0.2$.