Gain characteristics of inner-shell photoionization-pumped L23M1 transition 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 Ii 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 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 spectral region. In addition to the high flux, the expected duration of x-ray lasing of similar to3 fs will be useful for the study of fast dynamics in physical and biological sciences.