Influence of AC Stark shifting on relative rates for two-colour multiphoton ionisation of Xe and Cs

An electron spectroscopic study is reported of multiphoton ionisation of Xe and Cs using two laser beams. One of the two beams is tuned to multiphoton resonance with an intermediate state and causes a considerable AC Stark shift. The second beam acts as a probe of the population and shift of the intermediate state. In Xe the authors deal with a three-photon resonance with the 6s level ( lambda approximately=440 nm); in Cs with two-photon resonances with Rydberg levels of the nd series. As probes, beams of either lambda =1064 or 532 nm have been used.