Collisional excitation X-ray lasers

We will review the progress that has been made at numerous laboratories in the demonstration, optimization and understanding of so-called collisional excitation x-ray lasers, i.e., lasers which involve amplification of the n=3p to n=3s transitions in Ne-like ions and the n=4d-4p lines in Ni-like ions. Currently, these schemes are producing x-ray lasers which operate from approximately 32.6 nm to 3.6 nm and with output power into the few MW range. Efficiencies are low (≤ 10^-6) with the current means of pumping, i.e., with optical laser pumped plasma amplifiers. More efficient schemes may be forthcoming and will be discussed herein. Other important amplifier characteristics such as brightness, divergence and coherence are also being studied and the status of our knowledge of them will be discussed in this manuscript. Finally, we will discuss the prospects for the development and application of compact, moderate cost collisional excitation lasers.