Theoretical study of Ni-like Ag 13.9nm TCE x-ray laser driven by two picosecond pulses

The Ni-like Ag 13.9nm x-ray laser has been previously demonstratedthat the higher gain near critical surface contributes little to theamplification of the x-ray laser because of severe refraction. Inthis paper, the transient collision excitation (TCE) Ni-like Ag13.9nm x-ray laser is simulated, driven by two 3ps short pulsepreceded by a 330ps long prepulse, optimization of the peak topeak delay time of the two short pulses is made to get the bestresults. Simulation indicates that by producing lowly ionizedpreplasma with smoothly varying electron density, it is possible todecrease electron density gradient in higher density region, andthus higher gains near this region could be utilized, and if themain short pulse is delayed by 900ps, local gains where electrondensity larger than ～ 4×10²⁰cm^-3 could be utilized.