Single-Photon Atomic Cooling - Raizen Lab - The University of ...

of 22 ◦ C. The expected vapor pressure is therefore ≈ 3 × 10 −7 torr. This
pressure is sufficiently high to rapidly load a MOT in the upper chamber. This
MOT serves as a reservoir of atoms which are pushed through the differential
pumping tube and recaptured in the lower MOT.
The differential pumping tube maintains a pressure differential between
the upper and lower chamber allowing long magnetic trap lifetimes in the lower
chamber. The differential pumping tube is formed from a 6-3/4 ′′ long 304
stainless steal tube with an outer diameter of approximately 1/2 ′′ . The inner
diameter increases in five steps from 1/8 ′′ at the top to 3/8 ′′ at the bottom.
This internal taper was made to allow room for the push beam to diverge
while still maintaining a sufficiently low conductance, which is calculated to
be C ≈ 52 mL/s for this tube [87]. The pumping speed in the lower chamber
is 75 L/s resulting in a pressure differential of approximately 1500 between the
upper and lower chambers [87]. The expected pressure in the lower chamber
is therefore approximately 2 × 10 −10 torr.
The top of the differential pumping tube is cut at 20 ◦ to allow diagonal
MOT beams to pass unclipped. A MOT is formed in the upper chamber
from three pairs of counter-propagating near-resonant beams and two current
carrying wire coils, as discussed in Sec. 2.5.2.4.
3.1.2 Middle Chamber
The middle-chamber is located directly below the upper-chamber and
serves as a hub to attach the vacuum equipment needed to pull, maintain,
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