Multilayer targets as a diagnostic tool for laser-produced plasmas

A novel experimental method employing multilayer targets has been developed permitting a more detailed study of laser-produced plasmas through analysis of the spectrum emitted by a given layer as a function of its location. This method allows us to study the progression of the interaction phenomena into the interior of the target and to examine the plasma expansion phase. It could thus be demonstrated that the plasma produced at different depths within the target has essentially the same characteristic parameters and that the hot plasma region is delimited by very sharp gradients towards the interior of the target. In the expansion phase the importance of recombination phenomena has been well established up to certain limits beyond which our observations are compatible with the notion of freezing of the degree of ionization at closed-shell electron configurations in carbon and aluminum plasmas. A comparison of our experimental results with simple theoretical models is included.