Xray emission from highZ plasmas for Xray absorption fine spectroscopy of WDM

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X-ray emission from high-Z plasmas for X-ray
absorption fine spectroscopy of WDM

• M. Harmand, F. Dorchies, C. Fourment, J.J.
  Santos,
• O. Peyrusse
• CELIA, Université Bordeaux I - CEA - CNRS,
  Talence, France

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Context

• Ultrafast X-ray sources for absorption
  spectroscopy (ps or sub-ps)
• Pump (fs laser) / probe (X) experiments
• Scientific goals
• X-ray absorption fine spectroscopy
• (XANES EXAFS)
• Warm Dense Matter (0.1 - a few eV)
• Phase transitions (solid-solid-liquid-plasma)
• gt X-ray absorption fine spectroscopy (XAFS)
  leads to short-range order structural data

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EXAFS / XANES
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Requirements for XAFS

• XAFS basic requirements
• Broadband X-ray source over a few 100 eV
• High spectral resolution 1 eV
• Energy range fitted with the K- or L-edge
  considered
• High Signal / Noise is required
• A few 10 spectral modulations for XANES
• A few for EXAFS
• Duration requirement for WDM studies
• ?tX lt 10 ps expansion time of solid matter _at_ 1
  eV

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Thermal X-rays from high Z plasma
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Experimental set-up
High resolution spectrometer 1.3 - 1.7 keV
Near edge absorption spectroscopy Al K-edge
CCD
E (keV)
CCD
Broadband spectrometer 2 - 10 keV
KAP crystal
CCD
Mica crystal
Plast. / Plast. Al
Shielding
E (keV)
Magnets
Aurore TiSa laser 5 mJ _at_ 1 kHz 30 fs - 5
ps up to 1017 W/cm2 on target
Rotating target fresh target _at_ 1 kHz
f 200 mm
X-rays
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The best target for Al K-edge ?

• Study of X-ray emission from Sm, Gd, Dy, Er, Yb
• (Z 62, 64, 66, 68, 70)

Calculations
Measurements
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Signal to Noise ratio optimization
2000 shots (2s) accumulated Signal optimization
Background noise hard X-rays
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kHz X-ray source stability
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Static XANES of cold Aluminum

• A single crystal used both for reference
  transmitted spectra

CCD
Ex (keV)
KAP
Plast. / Plast. Al
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XANES measurements calculations

• XANES modulations resolved with 1000 Å thickness
• (compatible with WDM laser heating)
• Reproduced by calculations

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What about EXAFS ?

• Clear XANES difference between 2000 Å Al and
  Al2O3
• EXAFS resolution limited by crystal defects

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WDM experiment aimed at CELIA

• Two separated crystals reference/transmitted
  (higher S/N ratio)
• Sample closer to X-ray source uniformly thick
  probed area

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Conclusion

• Development of broadband ultra-short X-ray source
  
• Based on thermal emission from high Z plasma
• M-shell X-ray spectroscopy of Sm, Gd, Dy, Er, Yb
  (Z 62 to 70)
• High Signal / Noise achieved with a few ps laser
  pulse
• Time resolved (ps) measurements (next week)
• XAFS experiments on cold Al sample
• Achievement of useful K-edge XANES spectra
• Sample thickness down to 1000 Å
• Modulations reproduced by MS calculations

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Perspectives

• XAFS measurements of WDM (Al)
• Al laser heating and characterization ( 0.1 - 1
  eV, solid)
• Pump (fs laser) /probe (X-ray) experiment
• Single-shot to be compatible with other heating
  beams
• Laser generated proton beam (large homogeneous
  heated volume)
• Laser driven shocks (higher densities)
• Extend the field of applications
• Ultrafast phase transitions
• Biology

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Reach higher energy K-edge (Fe)