Photoelectric Measurements of Doublet Intensity Ratios in Cesium
The effects of the spin-orbit perturbation on the alkali fine-structure doublets have a number of manifestations that have been reviewed recently by zu Putlitz.1 These include the non-zero minimum, as a function of energy, of the photoionization cross sections, polarization of the photoelectrons obtained near this cross-section minimum, and the departure, in the discrete spectrum, from the value 2 of the doublet intensity ratio. The value 2 is expected simply on the basis of the ratio of the statistical weights of the excited 2P3/2 and 2P1/2 states. The interest in these phenomena was renewed after the theoretical prediction by Fano,2 based on the perturbation effects by the spin-orbit interaction, that circularly-polarized light could orient the spins of electrons ejected in the photoionization process in cesium. The potential application of the phenomenon to make polarized electron sources was to be exploited soon thereafter.3,4 The two experimental efforts that were thus made to produce polarized electrons, and to measure the degree of polarization, relied on related, but different, techniques. The photoionization results, extrapolated into the discrete spectrum, made different predictions for the behavior of the resonance-line doublet intensity ratios: in one case3 the ratio would pass through a maximum, as the principal quantum number, n, of the excited P states increases toward infinity; in the other4 the ratio would continue to increase as the ionization potential is approached.
KeywordsDiscrete Spectrum Principal Quantum Number Perturbation Effect Photo Ionization Photoionization Process
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