ABSTRACT
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 → 3p 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 nsec pulse followed by a psec pulse. This pumping mechanism also enhances the gain of the two 3p → 3s, J = 0 → 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.
