Soft%20X-Rays%20for%20the%20Future

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Soft X-Rays for the Future
Joachim Stöhr Stanford
Synchrotron Radiation Laboratory
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What are Soft X-Rays ?
Soft X-Rays
VUV
Hard X-Rays
30 eV
3000 eV
285 eV
C K-edge
grazing incidence optics
vacuum
wavelength is a few nanometers
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Closing the Soft X-ray Gap gt 285 eV 1975 - 77
Stanford
Hamburg
Flipper monochromator
Grasshopper monochromator
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Why are X-Rays so Useful?
X-ray diffraction
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Why are Soft X-Rays so Useful?
X-ray spectroscopies photoemission, x-ray
absorption, x-ray emission
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Synchrotron Radiation Facilities Around the World

• 54 in operation in 19 countries
• (including Brazil, China, India, Korea,
  Taiwan, Thailand)
• 8 in construction
• Armenia, Australia, China, France, Jordan,
  Russia, Spain, UK
• 11 in design/planning
• For a list of SR facilities around the world see
• http//ssrl.slac.stanford.edu/SR_SOURCES.HTML

All provide soft x-rays a broad basis for
future research
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Soft X-Rays A Look into the Future

• Storage rings will continue to serve most soft
  x-ray users

• Linac based sources offer specific exciting
  opportunities

• enhanced peak power
• enhanced brightness (coherence)
• shorter pulse length

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The Future Soft and Hard X-RAY FELs
X-Rays LCLS (Stanford) - 2008 TESLA
(Hamburg)
VUV and Soft X-Rays BESSY
LINAC COHERENT LIGHT SOURCE
TESLA
20 1000 eV
500 eV - 15 keV lt 20
fs controlled through seeding
1 - 100 fs
Spectroscopy electron and spin distributions
Scattering atomic positions
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The Future Soft and Hard X-RAY FELs
X-Rays LCLS (Stanford) - 2008 TESLA
(Hamburg)
VUV and Soft X-Rays BESSY
LINAC COHERENT LIGHT SOURCE
Sources are complementary
TESLA
20 eV to 1 keV
500 eV to 15 keV lt 20
fs controlled through seeding
1- 100 fs
Spectroscopy electron and spin distributions
Scattering atomic positions
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So, what is the excitement all about?
BESSY-II
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Some scientific dreams

• High peak power Making hollow atoms
• Ultrashort pulses
• coherence Ultrafast snapshots
  of matter

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Electrons and Spins in High Photon Fields
For x-rays, electrons and spins only quiver in
fields - no field ionization
Optical lasers can strip valence electrons
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Stripping atoms from the inside hollow atoms
X- ray absorption selects core electrons
No field ionization of valence electrons
Core
Ionization Cross Section
Valence
Formation of Hollow Atoms
Ne Photoionization
Unfocussed beam
2.5 of atoms have multiple core holes per pulse
(8x107 atoms)
hn 900eV
K-edge
tAuger 2.5fs
Focussed beam (100nm)
All atoms have multiple core holes per pulse (105
atoms)
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Rule of thumb the smaller the faster!
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not enough intensity need to repeat over
and over
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Present Pump/Probe Experiments
laser pump pulse
x-ray probe pulse delayed by time ?
sample
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Present Pump/Probe Experiments
laser pump pulse
x-ray probe pulse after ?
sample
over and over

• Can produce various pump pulses
• photon
• current (laser electro-optical switch)
• pressure (lattice heating)

Process has to be reversible Not enough
intensity for single shot experiments
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Imaging dynamics began 1878 at Stanford
40 milliseconds
0.5m
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Today X-ray Microscopy
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Toward single-shot imaging soft x-ray
spectro-holography
coherent x-ray beam
S. Eisebitt, J. Lüning, W. F. Schlotter, M.
Lörgen, O. Hellwig, W. Eberhardt, J. Stöhr,
Nature (to be publ.)
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Does it work ?
FT Hologram
STXM
W. F. Schlotter Y. Acremann
Reference hole ? 100 nm
Resolution 30 - 40 nm
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Motion pictures with multiple pulses
mirror
mirror
Pulse 1
Pulse 1
CCD 2
CCD 2
XFEL
XFEL
CCD 1
CCD 1
beam splitter
beam splitter
Pulse 2
Pulse 2
sample
sample
delay - change of optical path length
Present detectors not fast enough for multiple
images
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Summary

• Soft x-rays offer complementary capabilities to
  hard x-rays
• Future work has solid foundation in synchrotron
  radiation sources worldwide
• FELs promise to be extraordinary scientific tools
• Forefront science requires availability of
  various complementary sources