Abstract
Simple and double ionisation of a strontium atomic beam have been studied with a picosecond dye laser around 565 nm with intensities ranging from 10 to 1000 GW cm-2. Resonances observed on the different ion signals as well as time-of-flight electron energy spectra clearly show that double ionisation is a two-step process which can involve above-threshold ionisation followed by resonant ionisation of the ion.

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