A coupled gain calculation and output characteristics of the two Ne-like 2s and 2p hole X-ray laser lines

In most collisionally pumped X-ray lasers the lasing transitions considered are a result of collisional excitation of a Ne-like ground state 2p electron into a 3p excited level. However, there are suggestions of producing plasma conditions for collisional pumping of the inner-shell 2s electrons into highly excited 3s levels, with lasing arising as a 2p electron fills the 2s hole. Simulations on various Ne-like ions such as germanium, krypton, and yttrium, using collisional pumping, to get gain on the inner-shell transitions at 62, 50.2, and 42Å, respectively, have shown gains on the inner-shell transitions up to 30cm-1. It has been suggested that the large Doppler linewidth associated with shorter wavelengths is responsible for the smallness of the small-signal gain in the inner-shell transitions relative to than that predicted for the more usual 2p-hole transitions. However, experimental investigations of this 2s-hole inner-shell laser line, using collisional pumping technique, were unable to register any output. In this paper we report the result of calculations of the gain and the total spontaneous emission rate for the 2s-hole and the 2p-hole X-ray laser lines using a coupled four level model. It is shown that the small-signal gain of the 2s-hole inner-shell transition decreases with increasing pumping rates of the 2p-hole upper and lower levels. The output characteristics of the Ne-like inner-shell transition is simulated using this four-level model and the effects of saturation of the 2p-hole line on the 2s-hole transition is studied showing that the saturation of the former may have a severe effect on the output of the later.