Copyright by Kirsten Viering 2006 - Raizen Lab - The University of ...

a quadrupole field with a magnetic field gradient in radial (ρ-) and axial (z-) direction,
where
dBz
dz
= 2dBρ . (4.5)
dρ
In addition to the magnetic field gradient there are three pairs of counter-propagating
beams, red-detuned from the resonance at zero magnetic field; a schematic of the
alignment is shown in fig. 4.2. If a trapped atom moves out of the zero magnetic field
at the center of the trap, the magnetic sublevels will split according to the magnitude
Figure 4.2: Schematic of the beam configuration in a magneto optical trap (MOT), the
current in the Anti-Helmholtz-coils (red) flows opposite, the MOT beams are represented
by the blue arrows
of the magnetic field. Therefore the detuning decreases with an increasing distance
from the center of the magnetic field. If the polarizations of the two opposing beams
are aligned correctly, there will be more light scattered from one than from the other
and the atom driven back towards the center of the trap, i.e. an atom moving to the
right scatters more σ − -polarized light. In fig. 4.3 we have shown a schematic for the
magnetic detuning in a 1-D-MOT, which can easily be extended to three dimensions.
The beams in our setup are 20MHz red detuned from the 3 2 S1/2(F = 2) →
3 2 P3/2(F ′ = 3) transition; the magnetic field gradient in the axial direction is 15G/cm.
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