Experiments with Supersonic Beams as a Source of Cold Atoms

Atom Number
60
50
40
30
20
10
0.6 0.8 1 1.2 1.4 1.6 1.8
x 10 −3
Time (s)
Figure 5.21: Simulated time-of-flight profile for atoms arriving at the Ardara Technologies
ionizer after being ejected from the trap. The atoms are ejected by turning
off the rear trapping coil, waiting until they have passed through the coil, and then
turning the rear trapping coil back on with the opposite polarity. Of the 3,000 simulated
trapped atoms, 406 atoms entered the detection region, an efficiency of 13%,
which compares favorably with the 0.1% efficiency expected from turning off the trap.
though the calculations described are accurate for any detector at the same location
in the experiment.
The simplest method of getting atoms from the trap into the detector is to
turn off the trap. The atoms are no longer confined and will thus continue to fly
with the velocity they have when they are released. The problem with this method
is that since the atoms are moving in all directions in the trap, releasing the atoms
will distribute them in all directions. Geometric considerations give a good estimate
of the number of atoms that propagate to the detector, approximately 0.1% with
the described experimental apparatus. A better method of removing the atoms is to
switch off the rear trapping coil, while leaving the front trapping coil on. The atoms
are still repelled by the front coil, pushing them through the bore of the rear trapping
coil. Once they have passed through the rear coil, it is switched back on with the
opposite polarity, continuing to push the atoms towards the detection region. This
146