Comparison of pumping a cesium beam tube with D1 and D2 lines

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Abstract
The operation of a cesium beam tube optically pumped with cesium D1 and D2 lines is theoretically and experimentally investigated. In a single laser diode configuration using the D2 line, the most efficient excitation scheme is found to be the 3→3σ(D2) scheme leading to a clock signal-to-noise ratio equal to 15 000 in a one-hertz bandwidth. In the case of the D1 line, the predicted best excitation schemes are the 4→3π(D1) and the 4→3σ(D1) schemes. However, these two configurations lead to an extra fluorescence noise presumably due to unpumped atoms. The 3→4π(D1) scheme is experimentally found to be the best with S/N performances comparable to the 3→3σ(D2) configuration. Nevertheless, in the case of the 3→3σ(D2) scheme, optical pumping efficiency decreases when the magnetic field is too low whereas 3→4π(D1) features are independent of the magnetic-field amplitude. Moreover, the well-separated fluorescence lines in the case of the D1 line allow a more accurate locking of the laser frequency on the top of the fluorescence line than in the case of the D2 line. A perfectly symmetrical microwave spectrum results when the 3→4π(D1) scheme is used.