Observation of the cesium clock transition in laser-cooled atoms

We have used the light from diode lasers to produce a nearly stationary (υ ~ 15 cm/sec) sample of atomic cesium in optical molasses that is entirely in the F = 3 hyperfine state. In this sample we excite the 9.2-GHz6S F = 3, m = 0 to F = 4, m = 0 clock transition. Most of the atoms remain for ~20 msec in the 0.4-cm³ observation region. We observe that transitions take place by monitoring the fluorescence when the atoms are illuminated with light tuned to the 6S F = 4 to 6P_3/2 F = 5 transition. Rabi resonance linewidths of less than 50 Hz are obtained.