Single-Photon Atomic Cooling - Raizen Lab - The University of ...
Single-Photon Atomic Cooling - Raizen Lab - The University of ...
Single-Photon Atomic Cooling - Raizen Lab - The University of ...
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where I/Isat ≪ 1 has been assumed. Clearly for damping to occur α > 0 so<br />
the detuning ∆ = ω − ω0 < 0 is negative, in agreement with the qualitative<br />
picture presented earlier.<br />
<strong>The</strong>re are two features <strong>of</strong> optical molasses that warrant explicit state-<br />
ments. First, optical molasses only confines atoms in velocity and not config-<br />
uration space. In other words, it is a cooling and not a trapping technique.<br />
Second, even though Eq. 2.80 suggests that after sufficient time v → 0 hence<br />
T → 0 this is clearly not a physical result. This discussion ignored heating<br />
effects due to the random nature <strong>of</strong> the absorption and spontaneous emission<br />
process. <strong>The</strong> heating and cooling effects <strong>of</strong> optical molasses reach a balance<br />
at the Doppler temperature [70]<br />
TD = Γ<br />
. (2.82)<br />
2kB<br />
This temperature is the lowest value that one expects to cool a two-level<br />
system. However, due to magnetic substructure the temperature achieved<br />
in experiments are much lower. <strong>The</strong> effect responsible for this is the topic <strong>of</strong><br />
the next section.<br />
2.5.2.3 Sisyphus <strong>Cooling</strong><br />
As discussed in Sec. 1.1, many groups, most notably the group <strong>of</strong> W.<br />
Phillips, measured temperatures <strong>of</strong> atomic clouds cooled by optical molasses to<br />
be well below the Doppler limit given in Eq. 2.82. This cannot be understood<br />
in terms <strong>of</strong> the simple two-level system used in that discussion. Jean Dalibard<br />
59