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

3.2.1 Near-Resonance Lasers
Laser beams tuned near the resonance of the 87 Rb D2 transition are
used for a variety of purposes in our experiment. This includes forming MOTs
in conjunction with a magnetic field gradient. The frequency of these beams
is typically about 15 MHz to the red of the |F = 2〉 → |F ′ = 3〉 transition.
Because 87 Rb atoms occasionally decay into the |F = 1〉 manifold, where they
are no longer resonant with the MOT beams, a repump beam is introduced
into the system to place them back in the cooling cycle. The repump beam
is resonant with the |F = 1〉 → |F ′ = 2〉 transition and serves to deplete
atoms from the |F = 1〉 ground state. To cool atoms via optical molasses
(Sec. 2.5.2.2) we use beams tuned 50 MHz to the red of the |F = 2〉 → |F ′ = 3〉
transition. To image and push atoms from the upper MOT to the lower MOT
a beam resonant with the |F = 2〉 → |F ′ = 3〉 transition is used. To place
atoms in a magnetically trappable state they are optically pumped by a laser
resonant with the |F = 2〉 → |F ′ = 2〉 transition. Finally, to change the
internal state of the atoms from |F = 2,mF = 2〉 to |F = 1,mF = 0〉 during
the single-photon cooling process a depopulation beam is used. This beam is
tuned 35 MHz to the red of the |F = 2〉 → |F ′ = 1〉 transition. A diagram
of each of these beams in relation to the hyperfine structure of the 87 Rb D2
transition is given in Fig. 3.6.
To generate the required frequencies and optical powers needed to per-
form these tasks, a total of five diode lasers are used. Two of these diode lasers
are master oscillators (called the MOT and repump master) and are locked
96