Establishing nonlinearity thresholds with ultraintense X-ray pulses.
X-ray techniques have evolved over decades to become highly refined tools for a broad range of investigations. Importantly, these approaches rely on X-ray measurements that depend linearly on the number of incident X-ray photons. The advent of X-ray free electron lasers (XFELs) is opening the ability to reach extremely high photon numbers within ultrashort X-ray pulse durations and is leading to a paradigm shift in our ability to explore nonlinear X-ray signals. However, the enormous increase in X-ray peak power is a double-edged sword with new and exciting methods being developed but at the same time well-established techniques proving unreliable. Consequently, accurate knowledge about the threshold for nonlinear X-ray signals is essential. Herein we report an X-ray spectroscopic study that reveals important details on the thresholds for nonlinear X-ray interactions. By varying both the incident X-ray intensity and photon energy, we establish the regimes at which the simplest nonlinear process, two-photon X-ray absorption (TPA), can be observed. From these measurements we can extract the probability of this process as a function of photon energy and confirm both the nature and sub-femtosecond lifetime of the virtual intermediate electronic state.
Paul Scherrer Institut, Villigen, Switzerland.|Institute of Physics, Jan Kochanowski University, Kielce, Poland.
Jakub
J
Szlachetko
Department of Physics, University of Fribourg, Fribourg, Switzerland.
Joanna
J
Hoszowska
Department of Physics, University of Fribourg, Fribourg, Switzerland.
Jean-Claude
JC
Dousse
Paul Scherrer Institut, Villigen, Switzerland.
Maarten
M
Nachtegaal
Department of Physics, University of Fribourg, Fribourg, Switzerland.
Wojciech
W
Błachucki
Paul Scherrer Institut, Villigen, Switzerland.
Yves
Y
Kayser
Department of Chemistry, Uppsala University, Uppsala, Sweden.|Institute of Physical Chemistry, Polish Academy of Sciences, Warsaw, Poland.
Jacinto
J
Sà
Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park, USA.|NSF BioXFEL STC, 700 Ellicott Street, 14203 Buffalo, USA.
Marc
M
Messerschmidt
Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park, USA.
Sebastien
S
Boutet
Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park, USA.|Brookhaven National Laboratory, Upton NY 11973 USA.
Garth J
GJ
Williams
Paul Scherrer Institut, Villigen, Switzerland.
Christian
C
David
Paul Scherrer Institut, Villigen, Switzerland.
Grigory
G
Smolentsev
Paul Scherrer Institut, Villigen, Switzerland.|Institute for Chemical and Bioengineering, ETH Zürich, Zürich, Switzerland.
Jeroen A
JA
van Bokhoven
Paul Scherrer Institut, Villigen, Switzerland.
Bruce D
BD
Patterson
Paul Scherrer Institut, Villigen, Switzerland.
Thomas J
TJ
Penfold
Paul Scherrer Institut, Villigen, Switzerland.
Gregor
G
Knopp
Institute of Physics, Jan Kochanowski University, Kielce, Poland.
Marek
M
Pajek
Paul Scherrer Institut, Villigen, Switzerland.
Rafael
R
Abela
Paul Scherrer Institut, Villigen, Switzerland.
Christopher J
CJ
Milne