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 back-ground of this method is discussed. Experimental operation of a near mono-velocity cesium beam tube is demonstrated. The velocity distribution of a com-mercial cesium beam tube and of the pr imary labora-tory 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 distribu-t ions are discussed in detai l. The pulse method thus shows promise for the evaluation of existing labora-to ry as wel l as commerc ia l ces ium beam tubes wi th respect to these effects. Key words. Atomic beams, Cavity phase shift, Cesium beam, Frequency standard, Pulsed excitation, Second-order Doppler shift, Velocity distribution.