An electrostatic light shutter for atomic fountain clocks

Most cesium fountain clocks built today operate in sequential steps where an atomic cloud is trapped, launched, interrogated and detected. Except for the interrogation, every other step requires laser beams to illuminate the atoms and produce fluorescence. The microwave interrogation is, on the other hand, severely disturbed by any fluorescence which produces a light shift on the atoms. Since it is desirable to minimize the dead time between the interrogation of the atoms, it is tempting to try to operate the fountain with many steps occurring simultaneously. In that case, the fluorescence light produced by the trap and the detection must be blocked before it enters the interrogation region. This is accomplished in some fountains by a using various shutters or by deflecting the trajectory of the atomic cloud with a non-uniform magnetic field. We propose here a new type of shutter that operates using an electrostatic force to move a rotor. A hole in the rotor lines up with the axis of the fountain at regular intervals to let the atomic cloud through, but then the shutter is closed when the laser beams are turned on. We give here the details of the operations of such a shutter and present the results of attenuation measurements.