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

where P is in torr. The lifetime of atoms in our magnetic trap is ∼ 30 s,
suggesting that the background pressure is ∼ 3 × 10 −10 torr.
2.5 Interaction of Light with Atoms
Interactions of light with atoms fall into two very broad regimes. In
the first, the so called far-detuned regime, the frequency of light is far from
any atomic resonance. The primary effect of the light is to mix states of
opposite parity, inducing a dipole moment in the atom [58]. The induced
dipole moment can then interact with an optical intensity gradient present in
the dipole inducing beam. As will be discussed, this situation can lead to an
almost completely conservative optical trap for neutral atoms. In the second,
near-resonant regime, light interacts with atoms primarily through forces due
to photon scattering. As will be explored in some detail, this regime can be
used to cool and trap atomic ensembles.
2.5.1 The Optical Dipole Force
The use of the optical dipole force for confining atoms was first consid-
ered by Askar’yan in 1962 [59]. Eight years later Ashkin trapped micron-sized
particles with a laser using a combination of radiation pressure and the opti-
cal dipole force [60]. He later suggested a 3-D trap for neutral atoms based
on his previous work [61]. In 1978 Bjorkholm experimentally demonstrated
the dipole force by focusing a beam of neutral atoms [62]. These ideas and
work culminated in 1986 with the first optical dipole trap for neutral atoms
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