Gain characteristics of inner-shell photoionization-pumpedL23M1transition in Ca

Abstract

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 lower lasing level ${(M}_{1}$ innershell vacancy level) is depopulated via a Coster--Kronig radiationless transition, is analyzed for Ca. The transition wavelength is 4.1 nm, which is inside the water window (the wavelength range between the K absorption edges of oxygen and carbon). The peak spectral brightness of the x-ray laser output at 4.1 nm is predicted to be as large as $5\ifmmode\times\else\texttimes\fi{}{10}^{25}{\mathrm{p}\mathrm{h}\mathrm{o}\mathrm{t}\mathrm{o}\mathrm{n}\mathrm{s}/\mathrm{s}/(\mathrm{m}\mathrm{m}}^{2}{\mathrm{}\mathrm{mrad}}^{2}\mathrm{}0.1%\mathrm{}\mathrm{bandwidth}),$ which is 4 to 5 orders of magnitude brighter than a typical undulator radiation in the similar spectral region. In addition to the high flux, the expected duration of x-ray lasing of \ensuremath{\sim}3 fs will be useful for the study of fast dynamics in physical and biological sciences.