We propose a new x-ray laser mechanism that uses radiation from the st
rongest 3d --> 2p Ne-like resonance line in an optically thick plasma
to radiatively drive population from the Ne-like ground state to the 3
d state, which then lases to two 3p states. Collisional mixing of the
3p states with nearby 3s and 3d states depopulates the lower laser sta
tes. Modeling is presented for this mechanism in Ne-like Ar, and in ex
periments we observe one potential 3d --> 3p lasing transition at 45.1
nm in Ne-like Ar. (C) 1996 Optical Society of America