Self photo-pumped neon-like and nickel-like X-ray lasers

摘要

A new x-ray laser mechanism is presented which uses radiation trapping of the strongest 3d -> 2p neon-like resonance line in an optically thick plasma to create an intense radiation field which radiatively drives population from the neon-like ground state to the 3d state, which then lases to a pair of 3p states. Collisional mixing of the 3p states with nearby 3s and 3d states depopulates the lower laser states. Modeling is presented for this mechanism in neon-like argon. Strong gain is predicted on the two 3d -> transitions at 45.1 nm and 46.5 nm, the first of which has been observed in recent x-ray laser experiments using an argon gas puff. The 3d -> 3p line has also been observed at 60 and 30 nm, respectively, in x-ray laser experiments recently done on sulfur targets using the prepulse technique and on titanium targets driven by a nsed pulse followed by a psec pulse. This pumping mechanism also enhances the gain of the two 3p -> 3s, J = O -> 1 transitions which are at 43.1 and 46.9 nm in argon. This generic scheme can also work in other ionization stages. In nickel-like ions, the analogous process of lasing on the 4f -> 4d transitions due to photo-pumping by the strong 4f -> 3d lines will be discussed.