Coster-Kronig innershell process-mediated femtosecond X-ray laser schemes

X-ray laser schemes are proposed in which the lower level of a lasing trans ition is emptied rapidly due to Coster-Kronig processes. The relevant chara cteristics of the L1M2.3. L2.3M1, M4.5N2.3, KM3, L3N1, and L3N5 transitions have been tabulated. Among these transitions, the L2M1 transition for Z = 22 to 32 has the least stringent pumping requirements for achieving inversi on in the 2- to 4- nm wavelength range. Computer simulations predict that s mall signal gains of 3.8 cm(-1) at 3.09 nm (401 eV) in Ti can be achieved f or an electron pulse of 10-fs duration and with a maximum electron density of 10(21) cm(-3). The scheme has also been applied to an innershell photoio nization pumping situation in the case of Ca (the transition wavelength is 4.1 nm, which is inside the water window). 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/sec/(mm(2) mrad(2) 0.1% bandwidth).