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New X-ray laser schemes exploiting the fast (< 10 femtosecond) decay of specific inner-shell hole states via Coster-Kronig and super Coster-Kronig decay processes are analyzed. Computer simulation for Ca and Ti shows, that population inversion can be achieved by electron collisional ionization only, and also by using fast, incoherent X-ray pumping. Macroscopically observable gain requires extremely fast energy deposition: laser produced plasma on solid density target surfaces, excited by < 25 fs, Joule level optical energy. Experiments performed with the > 1 J energy, compressed pulses of a chirped pulse amplification Ti:sapphire laser system, and with specially designed multilayer metal targets containing high Z (Au) radiator and low Z (Ti) emitter show anomalous spectral line enhancement in the 2–14 nm wavelength range. Threshold conditions for gain by incoherent X-ray pumping, conversion efficiency of visible laser photons into a desired X-ray bandwidth, and the design considerations of the multilayer target structure are also discussed. [ABSTRACT FROM AUTHOR]

New keV X-ray laser schemes based on fast energy deposition (1-20 fs) and inner-shell atomic processes are analyzed. It is shown that population inversion between inner-shell vacancy levels of medium-Z elements can be created using electron collisional ionization only, or also by using fast, incoherent X-ray pumping if decay of lower level states is mediated by Coster-Kronig or super-Coster-Kronig Auger decay. Because of such fast decay of the lower state, the L[sub 2]M[sub 1] transitions of elements Z=22 to 32 are the most stable against collisional processes. We also describe here a state-of-the-art chirped pulse amplification (CPA) laser system capable to deliver >1 J optical energy in less than 25 fs with 10 Hz repetition rate. The design of sandwiched multilayer target structure and possible experimental configurations are suggested. Preliminary experimental results of ultrafast (∼25 fs), high intensity (>10[sup 19] W/cm[sup 2]) excitation of layered metal targets show anomalous enhancement of specific Ti lines in the 2–14 nm wavelength range. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]