Experiments with Supersonic Beams as a Source of Cold Atoms

Figure 4.26: The temporal profile of the Faraday rotation in one of the slowing coils
used in the 64 stage slower. This is measured using a 1.4 mm TGG crystal, and the
maximal rotation observed corresponds to a 5.4 T peak magnetic field. The curve
shown is an average of 200 individual measurements.
used to reduce the dependence on the particulars of the integral described above. The
temporal profile for the 1.4mm crystal is shown in figure 4.26. Pulse lengths of 100μs
are used, instead of the 80 μs pulse lengths used in the proof-of-principle experiment.
The field follows an initial rise with a time constant of 19 μs. At switch-off, the
field first falls linearly to 20 % of its initial value over a 6 μs, and after this the field
decays exponentially with a time constant of 17 μs. This exponential decay after the
current has been switched off is most likely due to eddy currents in the Permendur
surrounding the coils.
Measurements are taken with crystals of 1.40, 2.35, and 5.00mm length. Table
4.1 shows the calculated peak field for each crystal length. These measurements give a
peak field on axis of 5.21 ± 0.20 T, which is extremely close to the field found by finite
element calculation assuming a current found by examining the total resistance of the
circuit (5.56 T). The discrepancy is probably the result of imperfect windings, where
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