Experiments to Control Atom Number and Phase-Space Density in ...

trough, see section 4.3.2, is placed below the ensemble, where the initial atomic density
is negligible. The demon beam, see section 4.3.1.4, slightly detuned below the |F =
2〉 → |F ′ = 1〉 transition, is focused down to a final waist of 8 µm inside the trough.
This setup is shown in figure 5.1.
A schematic of the implementation of single-photon cooling in rubidium using
the gravito-optical trap is shown in figure 5.2. The figure shows the potentials along
the gravitational axis. Atoms in the magnetic trap are predominantely trapped in the
|F = 2,mF = 2〉 state. Only the most energetic atoms have enough energy to reach the
demon beam (near their classical turning points), at which point they have lost most of
their kinetic energy and gained potential energy.
Energy
gravity
F=1, m F =1
F=2, m F =2
F=1, m F =0
F=1, m F =1
Position
5 2 P 3/2
5 2 S 1/2
m -1 0 1
F F’=1
m F
m F
.02
.42
.05
.42
.10
-2 -1 0 1 2
Figure 5.2: Implementation of single-photon cooling in rubidium. Near their classical
turning points, atoms in the |F = 2,mF = 2〉 state are excited to the |F ′ = 1,m ′ F = 1〉
state and spontaneously decay. The probability to decay into the |F = 1,mF = 0〉 and
|F = 1,mF = 1〉 states are given by the branching ratios (shown to the right). In these
states the atoms are trapped in the gravito-optical trap.
When the atoms encounter the demon beam, they undergo spontaneous Raman
scattering and about 84% of the atoms, as dictated by the branching ratios, are trans-
69
F=2
F=1