Theory for laser photoionisation of excited atoms: n2P1/2,3/2states of Cs

The development of high-power lasers has opened the field of photoionisation experiments for short-lived excited states. The relation between experimental quantities accessible in such experiments and the transition amplitudes required to describe the photoionisation theoretically are studied with particular attention given to 'complete experiments'. It is shown, that for a complete determination of the transition amplitudes involved, three types of measurements are required: (i) one absolute and additional relative measurements of total cross sections, (ii) measurements of the angular distribution or the spin polarisation in the direction of the quantisation axis and (iii) measurements of the spin polarisation perpendicular to the reaction plane with angular resolution. A detailed analysis, including the effects of hyperfine coupling, is given for n 2 P 1/2,3/2 of alkali atoms and experimental results are quoted for the 7 2 P 1/2 state of Cs.