ABSTRACT
Specific proposals for excitation schemes for X-ray lasers date back to 1967, when the possibility of achieving amplification by photoionization pumping was first suggested by Duguay and Rentzepis [1]. This was followed by proposals for X-ray lasers based on the two population inversion mechanisms on which the present day’s soft X-ray lasers are based: electron impact excitation schemes [2–5] and collisional recombination [6–9].
