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Title: Resonant two-photon absorption of extreme-ultraviolet free-electron-laser radiation in helium

Abstract

We have investigated the nonlinear response of helium to intense extreme-ultraviolet radiation from the free-electron laser in Hamburg (FLASH). We observe a spectral feature between 24 and 26 eV electron kinetic energy in photoemission which shows a quadratic fluence dependence. The feature is explained as a result of subsequent processes involving a resonant two-photon absorption process into doubly excited levels of even parity (N=5 and 6), radiative decay to the doubly excited states in the vicinity of the He{sup +} (N=2) ionization threshold and finally the photoionization of the inner electron by the radiation of the next microbunches. This observation suggests that even-parity states, which have been elusive to be measured with the low pulse energy of synchrotron radiation sources, can be investigated with the intense radiation of FLASH. This also demonstrates a first step to bring nonlinear spectroscopy into the xuv and soft-x-ray regime.

Authors:
; ; ; ; ; ; ; ;  [1]; ; ;  [2]
  1. Institute fuer Experimentalphysik Universitaet Hamburg, Luruper Chaussee 149, 22761 Hamburg (Germany)
  2. HASYLAB at DESY, Notkestrasse 85, 22607 Hamburg (Germany)
Publication Date:
OSTI Identifier:
20982446
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. A; Journal Volume: 75; Journal Issue: 5; Other Information: DOI: 10.1103/PhysRevA.75.051406; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; ABSORPTION; ATOMS; ELECTRONS; EV RANGE; EXCITED STATES; EXTREME ULTRAVIOLET RADIATION; FREE ELECTRON LASERS; HELIUM; HELIUM IONS; MULTI-PHOTON PROCESSES; NONLINEAR PROBLEMS; PHOTOEMISSION; PHOTOIONIZATION; PHOTON-ATOM COLLISIONS; PHOTONS; PULSES; RADIATIVE DECAY; SOFT X RADIATION; SPECTROSCOPY; SYNCHROTRON RADIATION SOURCES

Citation Formats

Nagasono, Mitsuru, Suljoti, Edlira, Pietzsch, Annette, Hennies, Franz, Wellhoefer, Michael, Hoeft, Jon-Tobias, Martins, Michael, Wurth, Wilfried, Foehlisch, Alexander, Treusch, Rolf, Feldhaus, Josef, and Schneider, Jochen R. Resonant two-photon absorption of extreme-ultraviolet free-electron-laser radiation in helium. United States: N. p., 2007. Web. doi:10.1103/PHYSREVA.75.051406.
Nagasono, Mitsuru, Suljoti, Edlira, Pietzsch, Annette, Hennies, Franz, Wellhoefer, Michael, Hoeft, Jon-Tobias, Martins, Michael, Wurth, Wilfried, Foehlisch, Alexander, Treusch, Rolf, Feldhaus, Josef, & Schneider, Jochen R. Resonant two-photon absorption of extreme-ultraviolet free-electron-laser radiation in helium. United States. doi:10.1103/PHYSREVA.75.051406.
Nagasono, Mitsuru, Suljoti, Edlira, Pietzsch, Annette, Hennies, Franz, Wellhoefer, Michael, Hoeft, Jon-Tobias, Martins, Michael, Wurth, Wilfried, Foehlisch, Alexander, Treusch, Rolf, Feldhaus, Josef, and Schneider, Jochen R. Tue . "Resonant two-photon absorption of extreme-ultraviolet free-electron-laser radiation in helium". United States. doi:10.1103/PHYSREVA.75.051406.
@article{osti_20982446,
title = {Resonant two-photon absorption of extreme-ultraviolet free-electron-laser radiation in helium},
author = {Nagasono, Mitsuru and Suljoti, Edlira and Pietzsch, Annette and Hennies, Franz and Wellhoefer, Michael and Hoeft, Jon-Tobias and Martins, Michael and Wurth, Wilfried and Foehlisch, Alexander and Treusch, Rolf and Feldhaus, Josef and Schneider, Jochen R.},
abstractNote = {We have investigated the nonlinear response of helium to intense extreme-ultraviolet radiation from the free-electron laser in Hamburg (FLASH). We observe a spectral feature between 24 and 26 eV electron kinetic energy in photoemission which shows a quadratic fluence dependence. The feature is explained as a result of subsequent processes involving a resonant two-photon absorption process into doubly excited levels of even parity (N=5 and 6), radiative decay to the doubly excited states in the vicinity of the He{sup +} (N=2) ionization threshold and finally the photoionization of the inner electron by the radiation of the next microbunches. This observation suggests that even-parity states, which have been elusive to be measured with the low pulse energy of synchrotron radiation sources, can be investigated with the intense radiation of FLASH. This also demonstrates a first step to bring nonlinear spectroscopy into the xuv and soft-x-ray regime.},
doi = {10.1103/PHYSREVA.75.051406},
journal = {Physical Review. A},
number = 5,
volume = 75,
place = {United States},
year = {Tue May 15 00:00:00 EDT 2007},
month = {Tue May 15 00:00:00 EDT 2007}
}