Observation of Seeded Mn <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi mathvariant="normal">K</mml:mi><mml:mi>β</mml:mi></mml:mrow></mml:math> Stimulated X-Ray Emission Using Two-Color X-Ray Free-Electron Laser Pulses

\mathrm{K}\ensuremath{\beta}x-ray emission spectroscopy is a powerful probe for electronic structure analysis of 3dtransition metal systems and their ultrafast dynamics. Selectively enhancing specific spectral regions would increase this sensitivity and provide fundamentally new insights. Recently we reported the observation and analysis of \mathrm{K}\ensuremath{\alpha}amplified spontaneous x-ray emission from Mn solutions using an...