design of single- shot time/energy-resolved xes spectrometer for the lcls
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Design of single-shot time/energy-resolved XES spectrometer for the LCLS
Katherine SpothDennis Nordlund, mentor
August 11, 2011
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Surface Chemistry
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X-ray Emission Process (XES)
1s
2s
2p
1s
2s
2p
1s
2s
2p
Ener
gy
Ground State Excitation Decay
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Resonant X-ray Emission (RIXS)
1s
2s
2p
1s
2s
2p
1s
2s
2p
Ener
gy
Ground State Excitation Decay
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Basic Spectrometer Design
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Non-Dispersive Imaging:Time Resolved XES
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Non-Dispersive Imaging:Variable-Energy RIXS
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Design Goals
• Optimize for study of Oxygen at 520 eV• Best energy resolution (grating) of 0.25 eV– Also allow high-throughput resolution up to 1 eV
for certain applications• Imaging resolution (mirror):– Time-resolved XES: 10 um on source,
corresponding to 30 fs– Variable-energy RIXS: 200 um on source,
corresponding to 0.25 eV
Ray tracing - SHADOW• Simulated spectrometer’s performance:
– Mirror position, shape, incidence angle– Illumination distance of mirror, grating
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Final Design
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Results of Ray-Tracing
• 1:10 imaging, ideal elliptical shape are best choices for non-dispersive focusing mirror
• Determine maximum length on grating, mirror that can be illuminated keeping required resolution
• Large source sizes (sample footprints) are not imaged well
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Monochromator
Dispersion on sample for θ=12°LCLS SXR: 1 eV/mm SSRL BL 13: 10 eV/mm
Ideally, want higher eV/mm at smaller angle θ
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Conclusions
• This design is capable of:– Time-resolved XES– Variable-energy RIXS • SXR at normal incidence (bulk measurements)• BL 13 SSRL, grazing incidence (allows surface chemistry
experiments)
• To observe surface reactions using RIXS at LCLS SXR, need modifications to monochromator or new BL at LCLS-II
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Acknowledgements
• My mentor, Dennis Nordlund• SLAC and the DOE for supporting the SULI
program• The staff at SLAC which make this program
possible• My fellow interns!
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