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!