Ph.D. Thesis - Physics

Figure 6-7: Photograph of the experimental setup for measurements on the San Quentin
trap. The spherical octagon vacuum chamber with 4 1/2 in. CF viewport is visible top
center, and the top plate PCB is seen within it. Above it is the 2 in. diameter lens tube.
Connection of the rf signal is top left, while connections to the dc electrodes and the e-gun
are on the small box (bottom right). Connection to the oven is top right. The 422 and
1092 nm lasers are collimated by Thorlabs collimation packages, are coaligned on a dichroic
mirror, and are then sent through the 1 1/3 in. CF viewport to the trap. Vacuum pumps
and the leak valve are outside the frame of this photograph.
(PI) loading, but at the same time species-specific loading is not possible, and “dark ions,”
particles other than the desired one that are trapped but do not fluoresce, are quite com-
mon. The key disadvantage of the technique for surface-electrode traps became evident in
our work; the e-gun deposits a stray electric charge on the exposed dielectric that is an
unavoidable part of the PCB trap. The stray fields resulting from this trapped charge can
become high enough to prevent any trapping in UHV conditions.
Our vacuum system includes a leak valve for introducing helium buffer gas. The colli-
sional cooling provided by the helium allows large samples (100’s of ions) to be trapped and
cooled even without stray field compensation or optimal alignment of the cooling lasers. In
this trap, a current in the oven of 8 A and a voltage across the filament of about 3.5 V was
used. The filament was also biased at -20 V with respect to ground to increase the flux of
emitted electrons. A photograph of our experimental setup is shown in Fig. 6-7.
Trapped ions were detected using both an electron-multiplying CCD camera (Princeton
Instruments PhotonMax) and a photomultiplier tube (Hamamatsu H6780-04). The 422 nm
and 1092 nm lasers used for inducing fluorescence were locked to low-finesse cavities. Typical
laser powers in this experiment were 1.2 mW of 1092 and 20-50 µW of 422. The width of
the 1092 was about 1 mm, so that the entire trap region would be illuminated by it, while
the 422 was focused to a 60 µm spot. The smaller spot size is useful in our measurement
of the position of the ion cloud. Ions were loaded prior to nulling the stray electric fields
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