Multiple ionization of rare gas atoms by intense free electron laser radiation at 51 and 61 nm

We have studied multiple ionization of rare gas atoms (Ne, Ar, Kr, Xe) by intense 51 nm and 61 nm radiation delivered by the EUV-FEL at SPring-8 Compact SASE Source (SCSS) Test Accelerator. Charge states as high as Ar7+ and Kr8+ have been observed. We present intensity dependent yields of multiply charged ions providing benchmark data for theory, and discuss the role of direct, sequential and resonant ionization channels.