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

where I/Isat ≪ 1 has been assumed. Clearly for damping to occur α > 0 so
the detuning ∆ = ω − ω0 < 0 is negative, in agreement with the qualitative
picture presented earlier.
There are two features of optical molasses that warrant explicit state-
ments. First, optical molasses only confines atoms in velocity and not config-
uration space. In other words, it is a cooling and not a trapping technique.
Second, even though Eq. 2.80 suggests that after sufficient time v → 0 hence
T → 0 this is clearly not a physical result. This discussion ignored heating
effects due to the random nature of the absorption and spontaneous emission
process. The heating and cooling effects of optical molasses reach a balance
at the Doppler temperature [70]
TD = Γ
. (2.82)
2kB
This temperature is the lowest value that one expects to cool a two-level
system. However, due to magnetic substructure the temperature achieved
in experiments are much lower. The effect responsible for this is the topic of
the next section.
2.5.2.3 Sisyphus Cooling
As discussed in Sec. 1.1, many groups, most notably the group of W.
Phillips, measured temperatures of atomic clouds cooled by optical molasses to
be well below the Doppler limit given in Eq. 2.82. This cannot be understood
in terms of the simple two-level system used in that discussion. Jean Dalibard
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