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

Figure 1.2: The energy level structure of a three-level atom. An atom initially
in the ground state |g〉 is transfered by a resonant photon into the excited state
|e〉. Once there it has two possible decay channels in contrast to the two-level
system.
be removed from the cooling cycle. Because a very large number of scattering
events are necessary to cool an atom, even a small probability of decaying into
a state other than |g〉 is detrimental to the process.
Clearly no atom is truly two-level. Even hydrogen, the simplest atom,
has a rich energy level structure [18]. Of course, this fact has not rendered laser
cooling unworkable. Experimentally it means that one has to add additional
“repumping” laser beams to reintroduce atoms into the cooling cycle after they
have decayed to a state non-resonant with the cooling laser beam. For atoms
with relatively simple energy structures such as alkali metals, suitable schemes
have been developed with great success. With somewhat more effort many
Noble gases have been laser cooled by first placing them into a metastable
state. Additionally, through extreme efforts some alkaline earth metals as
well as a handful of other atoms have been cooled. But for the vast majority
of atoms and for all molecules laser cooling has not been an experimentally
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