Collisional ionisation probabilities of highly excited S1/2, D3/2 and D5/2 states of caesium

The authors present experimental results on the ionisation probabilities of highly excited Rydberg S and D states of caesium in collisions with ground-state Cs atoms. The measurements were done in a thermionic diode using two-photon excitation of Rydberg states with principal quantum numbers in the range 18 to 60. Over the investigated range (0.17 to 12 mTorr) a simple exponential dependence of the ionisation probabilities on binding energy and pressure was found. The authors also measured the intensity ratios of the fine-structure doublets in 6S1/2 to nD two-photon transitions and find good agreement with theoretical calculations. From the results they conclude that the collisional ionisation probabilities are independent of orbital and total angular momentum.