Some 10-fs x-ray emission switches

The transient evolution of X-ray emission from high density plasmas usually terminates with a recombination regime at low density. For matter irradiated by short pulses (< 1 ps) the accumulation of x-ray emission at low density cannot be suppressed by streak camera techniques as current time resolution is limited (> 0.5 ps). We propose intrinsically fast x-ray signals realized by the radiation emission from hollow ion states K 0 L n to temporally isolate high density information from the low density radiative recombination regime. Simulations carried out for short pulse (100 fs) intense x-ray free electron laser radiation (XFEL) interacting with dense plasmas demonstrate that the hollow ion x-ray emission "switch" has a time scale faster than 50 fs. Moreover, the time of the hollow-ion emission signal is related to the interaction time and is thus directly related only to the highest density regimes even if the usual time integrated spectroscopic techniques are employed.