X-ray gain in laser-produced carbon plasmas using double-layer targets

We investigate from a theoretical point of view the basic possibilities for the effect of ionizing radiation on the X-ray gain in recombining laser-produced plasmas, in particular with regard to recently performed experiments in which targets consisting of two different-material layers (double-layer targets) were used. We discuss an increase of the gain for the 3 2 transition in hydrogenic ions which is due to photoionization causing, mainly, a decrease of the Lyman- reabsorption and an increase of the population of higher levels. In our numerical simulations we consider single-material and double-layer targets, concentrating particularly on carbon and titanium. We obtain and discuss the time behaviour of the X-ray emission from the laser-produced plasma with regard to its application as pump radiation.