Possibilities for achieving x-ray lasing action by use of high-order multiphoton processes

We consider some possible mechanisms for producing gain in the 10-nm spectral region. They involve the creation of a population inversion in a confined plasma column by selective excitation of multiply charged ions throughabsorption of many (> 10) ultraviolet photons. Calculations of the energy-level structure of ions in the Krisoelectronic sequence show singly and multiply excited states that provide suitable strong radiative transitions inthe region of 10 nm. The potential for achieving x-ray lasing action in Kr-like ions pumped by a KrF excimer laser ismost favorable at high Z.