Interference effects and Stark broadening in XUV intrashell transitions in aluminum under conditions of intense XUV free-electron-laser irradiation

Abstract

Quantum mechanical interference effects in the line broadening of intrashell transitions are investigated for dense plasma conditions. Simulations that involved $LSJ$-split level structure and intermediate coupling discovered unexpected strong line narrowing for intrashell transitions $L$-$L$ while $M$-$L$ transitions remained practically unaffected by interference effects. This behavior allows a robust study of line narrowing in dense plasmas. Simulations are carried out for XUV transitions of aluminum that have recently been observed in experiments with the FLASH free-electron laser in Hamburg irradiating solid aluminum samples with intensities greater than ${10}^{16}$ W/cm${}^{2}$. We explore the advantageous case of Al that allows, first, simultaneous observation of $M$-$L$ transitions and $L$-$L$ intrashell transitions with high-resolution grating spectrometers and, second, has a convenient threshold to study interference effects at densities much below solid. Finally, we present simulations at near solid density where the line emission transforms into a quasicontinuum.