6 September 2021
Nina Rohringer, DESY Hamburg, Germany
Stimulated X-Ray Emission – Opportunities for new x-ray sources and nonlinear spectroscopy
Stimulated emission following electronic inner-shell ionization or resonant excitation is a basic building block for nonlinear x-ray spectroscopy, or can serve as a novel source for phase-stable, ultrashort bright x-ray pulses. In this tutorial I will give an overview over experimental activities in this area. I will explain the basics of x-ray superfluorescence and stimulated emission following core ionization by discussing the first proof-of-principle experiments in gaseous Neon that demonstrated x-ray K-a stimulated emission with high amplification gain starting from spontaneous emission. An extension of these first experiments to the hard x-ray range in Mn containing liquids and solids will be presented, opening the perspective of stimulated x-ray emission spectroscopy for chemical analysis. More detailed chemical information of a compound can be obtained by stimulated resonant inelastic x-ray scattering. This process is key to several suggested nonlinear x-ray pump probe techniques: if resonant inelastic x-ray scattering is stimulated by broad bandwidth (ultrashort) x-ray pulses in molecular targets, localized valence-electron wave packets can be launched with unique characteristics. In solids these wave packets could be created with well-defined momentum, opening possibilities of launching directed electronic wave packets, but have not been experimentally realized. I will discuss the underlying experimental challenges and limitations that precluded demonstration of this process and will give a perspective for future experiments in the field of nonlinear x-ray pump-probe spectroscopy.