As a accustomed atom has abounding bags of times the drive of a individual photon, the cooling of an atom have to absorb abounding absorption-spontaneous discharge cycles, with the atom accident up to ħk of momenta anniversary aeon . Because of this, if an atom is to be laser cooled, it have to acquire a specific activity akin anatomy accepted as a bankrupt optical loop, area afterward an excitation-spontaneous discharge event, the atom is consistently alternate to its aboriginal state. 85Rubidium, for example, has a bankrupt optical bend amid the 5S1/2 F=3 accompaniment and the 5P3/2 F=4 state. Once in the aflame state, the atom is banned from corrupt to any of the 5P1/2 states, which would not conserve parity, and is aswell banned from corrupt to the 5S1/2 F=2 state, which would crave an angular drive change of −2, which can not be supplied by a individual photon.
Many atoms that do not accommodate bankrupt optical loops can still be laser cooled, however, by application repump lasers which re-excite the citizenry aback into the optical bend afterwards it has addle to a accompaniment alfresco of the cooling cycle. The magneto-optical accoutrement of rubidium 85, for example, involves cycling on the bankrupt 5S1/2 F=3 → 5P3/2 F=4 transition. On excitation, however, the detuning all-important for cooling gives a small, but non-zero overlap with the 5P3/2 F=3 state. If an atom is aflame to this state, which occurs almost every thousand cycles, the atom is again chargeless to adulteration either the F=3, ablaze accompanying high hyperfine state, or the F=2 "dark" lower hyperfine state. If it avalanche aback to the aphotic state, the atom stops cycling amid arena and aflame state, and the cooling and accoutrement of this atom stops. A repump laser, which is beating with the 5S1/2 F=2 → 5P3/2 F=3 alteration is acclimated to recycle the citizenry aback into the optical bend so that cooling can continue.
Many atoms that do not accommodate bankrupt optical loops can still be laser cooled, however, by application repump lasers which re-excite the citizenry aback into the optical bend afterwards it has addle to a accompaniment alfresco of the cooling cycle. The magneto-optical accoutrement of rubidium 85, for example, involves cycling on the bankrupt 5S1/2 F=3 → 5P3/2 F=4 transition. On excitation, however, the detuning all-important for cooling gives a small, but non-zero overlap with the 5P3/2 F=3 state. If an atom is aflame to this state, which occurs almost every thousand cycles, the atom is again chargeless to adulteration either the F=3, ablaze accompanying high hyperfine state, or the F=2 "dark" lower hyperfine state. If it avalanche aback to the aphotic state, the atom stops cycling amid arena and aflame state, and the cooling and accoutrement of this atom stops. A repump laser, which is beating with the 5S1/2 F=2 → 5P3/2 F=3 alteration is acclimated to recycle the citizenry aback into the optical bend so that cooling can continue.
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