On the gain media uniformity in controlled expansion cooled high gain recombination x-ray lasers

We investigate the uniformity of the plasma column produced on a multifin target which is designed for implementing a high gain recombination x-ray laser based on the controlled adiabatic expansion cooling scheme. It is shown that a plasma column, which is as uniform as that produced on a flat slab target, can be generated on a segmented target under an appropriate laser irradiation condition, and an enhancement of the on-axis emission of lasing lines is observed simultaneously, which can be attributed to an increase in laser gain. For the Li-like Al 4f-3d laser system, an increase of gain from 1.8 to 2.4 cm−1 was evaluated by comparing the on-axis emission from the multifin target with that from the flat-slab target. However, a large nonuniformity is also observed when the laser condition is so changed that strong ion collisions between the neighboring plasmas appear. The extension of this target design to the shorter wavelength laser regime appears to be promising provided that both the target parameter and the driving laser condition are optimized.