Multiphoton physics in the x-ray domain

1. 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

2. AMO Physics Bertold Krässig Steve Southworth Bob Dunford Conny Höhr Emily Peterson Linda Young Elliot Kanter Christian Buth Nina Rohringer

3. Outline • Introduction • Nonresonant multiphoton absorption • Resonant nonlinear processes

5. 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.

6. 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.

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

8. 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?

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

10. 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)

11. Charge-state distribution as a function of x-ray energy(1013 photons, 1 m, 230 fs) Rohringer, Santra, Phys. Rev. A 76, 033416 (2007)

12. Competition between PAP and PPA:single shot Rohringer, Santra, Phys. Rev. A 76, 033416 (2007)

13. 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).

14. PAP vs. PPADependence of Auger yield on intensity: ensemble average Rohringer, Santra, Phys. Rev. A 76, 033416 (2007)

15. Ion yield as a function of intensity: ensemble average Rohringer, Santra, Phys. Rev. A 76, 033416 (2007)

16. 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?

17. Photoabsorption spectrum of Ne at low x-ray intensity Coreno et al., Phys. Rev. A 59, 2494 (1999)

18. Resonant Auger effect

19. Resonant Auger-electron spectrum at 1s-3p resonance O. Hemmers et al., Rev. Sci. Instrum. 69, 3809 (1998).

20. 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)

21. Total resonant Auger yield after exposure to a Gaussian pulse, as a function of peak intensity Rohringer, Santra, Phys. Rev. A 77, 053404 (2008)

22. Resonant Auger line profile for a 2-fs Gaussian pulse Rohringer, Santra, Phys. Rev. A 77, 053404 (2008)

23. Resonant Auger line profile (LCLS parameters) a) Single shot b) Ensemble average Rohringer, Santra, Phys. Rev. A 77, 053404 (2008)

24. 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