Hyperfine optical pumping of cesium with a CW GaAs laser

Efficient and stable hyperfine pumping of Cs
¹³³
vapor has been achieved for extended periods of time with the use of a CW single-mode GaAs diode laser. Static matching of either hyperfine component of the 8521-Å D
2
line was performed by adjusting the dc injection current. As the pumping-beam intensity was increased continuously, the population of the depleted hyperfine level was monitored by the fluorescence caused by a weak, modulated probing beam. For the first time, it has been possible to display a complete depopulation of either one of the two ground-state hyperfine levels. These results provide new possibilities for cesium frequency standards, such as atomic-beam clocks without deflecting magnets. The construction of a cesium maser now becomes feasible.