Coherent control of atomic inner-shell x-ray lasing via perturbed valence-shell transitions

Atomic inner-shell x-ray lasers pumped by an x-ray free-electron laser generate ultrashort, intense, monochromatic pulses with temporal coherence. Coherent control of lasing in monovalent magnesium ions is investigated theoretically, where valence-shell transitions are driven by optical lasers. Modulated high-order sidebands and attosecond pulses are generated with quasi-continuous-wave and few-cycle control lasers, respectively. The general manipulation scheme involves fast Auger decay, limited pump coherence, diverse coupling channels, and collisions in the plasma. Our approach shows potential applications in high-resolution spectroscopy, nonlinear x-ray studies, metrology, and ultrafast science in keV regime.