Time Domain Velocity Selection Modulation as a Tool to Evaluate Cesium Beam Tubes

Abstract

Pulsed excitation of atomic and molecular beam devices with separated Ramsey-type interaction regions allows the observation of signals due to very narrow atomic velocity groups. The theoretical background of this method is discussed. Experimental operation of a near mono-velocity cesium beam tube is demonstrated. The velocity distribution of a commercial cesium beam tube and of the pr imary laboratory standard NBS-5 a r e obtained using the pulse method. The normal Ramsey pat terns are calculated from the velocity distribution and compared with the measured Ramsey pat terns . The pulse method al lows the direct determination of the cavity phase shift and of the second-order Doppler correction in beam devices. Velocity distributicns obtained via the pulse method allow the use of microwave power shift results for accuracy evaluat ions. These aspects as wel l as the effects of modulation and different velocity distribut ions are discussed in detai l . The pulse method thus shows promise for the evaluation of existing laborato ry as wel l as commerc ia l ces ium beam tubes wi th respect to these effects.