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SUMMARY:Propagation and scattering of x-rays in population-inverted medium
DTSTART:20260618T140000Z
DTEND:20260618T150000Z
DTSTAMP:20260605T205200Z
UID:indico-event-406@indico.xfel.eu
DESCRIPTION:Speakers: Andrei Benediktovitch (DESY\, Hamburg\, Germany)\n\n
 When high-intensity XFEL pulses are focused onto matter\, they induce stro
 ng core-level photoionization and leave the atoms in a transient\, inner-s
 hell population-inverted state. The resulting open inner-shell transitions
  modify the resonant x-ray optical response and give rise to a range of di
 stinctive phenomena. One example is x-ray superfluorescence: spontaneous f
 luorescence is amplified along the XFEL propagation direction\, leading to
  intense\, coherent bursts of radiation. I will present the theoretical fo
 rmalism we developed to describe this process [1] and show how correspondi
 ng simulations enable interpretation of experimental observations [2].\nAn
 other manifestation of the modified x-ray–matter interaction in the pres
 ence of open inner-shell transitions is an enhancement of elastic scatteri
 ng for x-rays resonant with these transitions. In this case\, the resonant
  scattering governed by the population difference can become stronger than
  Thomson scattering set by the total electron density. I will discuss rela
 ted models and experimental observations in the soft x-ray regime\, where 
 we exploited Cu 2p–3d transitions leading to reverse saturable absorptio
 n [3]\, and in the hard x-ray regime\, where we used two-color x-ray pulse
 s to create population inversion and probe modified scattering at the Cu 1
 s–2p transition.\n \n[1] S.Chuchurka\, A. Benediktovitch\, Š. Krušič
 \, A. Halavanau\, and N. Rohringer\, “Stochastic modeling of x-ray super
 fluorescence”\, Phys. Rev. A 109\, 033725 (2024)\n[2] T. M. Linker\, A. 
 Halavanau\, T. Kroll\, A. Benediktovitch\, et al\, N. Rohringer and U. Ber
 gmann\, “Attosecond inner-shell lasing at ångström wavelengths”\, Na
 ture 642\, 934–940 (2025)\n[3] L. Mercadier\, A. Benediktovitch\, Š. Kr
 ušič\, J. J. Kas\, et al\, B. Ziaja and N. Rohringer\, “Transient abso
 rption of warm dense matter created by an X-ray free-electron laser”\, N
 at. Phys. 20\, 1564–1569 (2024)\n \n \nVirtual participation (via Zoom
 ):\nhttps://xfel.zoom.us/j/64204363232?pwd=k997wMtb2qVGdb2fVkXLHBWVSR3ajO.
 1\nMeeting ID: 642 0436 3232\nPasscode: 677625\n\nhttps://indico.xfel.eu/e
 vent/406/
LOCATION:XHV/Lighthouse (European XFEL )
URL:https://indico.xfel.eu/event/406/
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