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					Multiphoton physics in the x-ray domain


                            Robin Santra


            Atomic, Molecular & Optical Physics Group
                    Argonne National Laboratory


                       Department of Physics
                        University of Chicago




Workshop on “Interaction of free-electron-laser radiation with matter:
    Recent experimental achievements, challenges for theory”
                        October 8 - 10, 2008
                     DESY, Hamburg, Germany
                      Bertold
                      Krässig        Steve
        Bob
                                     Southworth
        Dunford
Conny
Höhr



                               Emily
                               Peterson
 Linda Young
               Elliot Kanter
                                                           Christian Buth

                                          Nina Rohringer




                                                                      2
Outline



  Introduction



  Nonresonant multiphoton absorption



  Resonant nonlinear processes




                                        3
4
What are the mechanisms underlying high-intensity x-ray
absorption?


  Question relevant for understanding radiation damage in matter.

  Useful tool for beam diagnostics.

  Photon energy high enough to ionize valence electrons via one-photon
   absorption.

  Inner-shell electrons, in particular, can be directly ionized.

  Inner-shell vacancies undergo a decay cascade leading to the formation of
   higher charge states.




                                                                               5
Our system of choice: neon


 LCLS will initially operate near 1 keV. The Ne K edge lies at 870 eV.



 Neon is a first-row element, which allows one to identify processes
  relevant for other first-row elements.



 Neon is nontoxic and easy to handle.



 Neon has been studied in detail at synchrotron radiation sources.




                                                                          6
 The ground-state configuration
  of Ne is 1s22s22p6. Hence, one
  can investigate the interplay
  between outer-valence, inner-
  valence, and core-shell
  processes.




                                   7
             Nonresonant multiphoton absorption



 Is x-ray absorption by inner-shell electrons fast enough to compete with
  Auger decay?

 Will this lead to enhanced double-core-hole formation?

 Will valence ionization be saturated?




                                                                             8
Multiphoton absorption in the x-ray domain:
basic “building blocks”




                                              9
Double-core-hole formation can be monitored by
measuring the KK-KLL Auger-electron hypersatellite
spectrum




                     Southworth et al., Phys. Rev. A 67, 062712 (2003)

                                                                         10
Charge-state distribution as a function of x-ray energy
(1013 photons, 1 m, 230 fs)




                      Rohringer, Santra, Phys. Rev. A 76, 033416 (2007)

                                                                          11
Competition between
PAP and PPA: single
shot




Rohringer, Santra,
Phys. Rev. A 76,
033416 (2007)




                      12
Single-shot measurements of SASE-FEL pulses




                               Field intensities and phases of
                                  the 530-nm chaotic output of
                                  the SASE-FEL at the Low
                                  Energy Undulator Testline
                                  (Argonne APS)




                       Yuelin Li et al., Phys. Rev. Lett. 91, 243602 (2003).




                                                                        13
PAP vs. PPA

Dependence of
Auger yield on
intensity:
ensemble average




 Rohringer, Santra,
 Phys. Rev. A 76,
 033416 (2007)



                      14
Ion yield as a
function of
intensity:
ensemble average




 Rohringer, Santra,
 Phys. Rev. A 76,
 033416 (2007)



                      15
                 Resonant nonlinear processes



 Step towards the development of nonlinear spectroscopy in the x-ray
  domain.

 Will x-ray-driven Rabi oscillations be fast enough to compete with Auger
  decay?




                                                                             16
Photoabsorption spectrum of Ne at low x-ray intensity




                                                 Coreno et al.,
                                                 Phys. Rev. A 59,
                                                 2494 (1999)




                                                                17
Resonant Auger effect




                        18
Resonant Auger-electron spectrum at 1s-3p resonance




                                        O. Hemmers et al.,
                                        Rev. Sci. Instrum. 69,
                                        3809 (1998).




                                                                 19
Ne ground-state population at 1s-3p resonance
(1013 photons, 1 m, 230 fs)



                                                a) Single shot




                                                b) Ensemble average




                                                Rohringer, Santra,
                                                Phys. Rev. A 77,
                                                053404 (2008)


                                                                     20
Total resonant Auger yield after exposure to a
Gaussian pulse, as a function of peak intensity




                                                  Rohringer, Santra,
                                                  Phys. Rev. A 77,
                                                  053404 (2008)


                                                                   21
Resonant Auger line profile for a 2-fs Gaussian pulse




                                                Rohringer, Santra,
                                                Phys. Rev. A 77,
                                                053404 (2008)


                                                                 22
Resonant Auger line profile (LCLS parameters)




                                                a) Single shot




                                                b) Ensemble average




                                                Rohringer, Santra,
                                                Phys. Rev. A 77,
                                                053404 (2008)


                                                                 23
Experiments at LCLS will be carried out by Argonne Atomic
Physics group in collaboration with

 Ali Belkacem, Lawrence Berkeley National Laboratory

 Nora Berrah, Western Michigan University

 John Bozek, LCLS, SLAC

 Philip Bucksbaum, PULSE Center, SLAC

 Lou DiMauro, Ohio State University

 Stephen Pratt, Argonne National Laboratory

 David Reis, PULSE Center, SLAC




                                                            24

				
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posted:3/18/2012
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