Experimental investigations of quenching of ionization states in a freely expanding, recombining laser-produced plasma

The experimental measurements of the average ionization states of the plasm a produced from slab targets of carbon, aluminum, titanium, nickel, molybde num, and tantalum, using a 5 ns-Nd:YAG laser, at a laser intensity in the v icinity of 5 X 10(10) W/cm(2), are reported. The experimental results have been compared with those of the theoretically calculated ones using the ste ady state collisional radiative (CR) ionization model. It is observed that a significant difference between the two sets exists which leads to the con clusion of quenching of the ionization states through recombination. From p hysical considerations one is inclined to consider the possibility of recom bination processes quenching the ionization states faster before detection as one goes towards higher and higher values of the atomic number of the ta rget element. The limitations of the ionization model with reference to the plasmas of hydrogenlike ions, the plasma opacity and the consideration of the transient states of ionization and recombination coefficients are discu ssed. The difference between the experimentally estimated values of ionizat ion states by means of time of flight spectra and theoretical values of the se states at the center of the plasma, may provide an interesting experimen tal tool to investigate the three-body, radiative, and dielectronic recombi nation processes inside the plasma core.