Gain characteristics of inner-shell photoionization-pumped L23M1 transition in Ca - art. no. 023806

A new physical scheme for femtosecond x-ray lasers, where the upper lasing level (L-23 innershell vacancy level) is pumped by x-ray photons and the lo wer lasing level (M-1 innershell vacancy level) is depopulated via a Coster -Kronig radiationless transition, is analyzed for Ca. The transition wavele ngth is 4.1 nm, which is inside the water window (the wavelength range betw een the Ii absorption edges of oxygen and carbon). The peak spectral bright ness of the x-ray laser output at 4.1 nm is predicted to be as large as 5 x 10(25) photons/s/(mm(2) mrad(2) 0.1% bandwidth), which is 4 to 5 orders of magnitude brighter than a typical undulator radiation in the similar spect ral region. In addition to the high flux, the expected duration of x-ray la sing of similar to3 fs will be useful for the study of fast dynamics in phy sical and biological sciences.