Challenges of Optics for High Repetition Rate XFEL Source

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1 Challenges of Optics for High Repetition Rate XFEL Source Liubov Samoylova, European XFEL GmbH ACTOP11, DIAMOND, April 5 th, 2011

2 2 European XFEL photon transport system - overview X-ray optics for XFEL: requirements and challenges Grazing incidence mirrors: wavefront simulations and first measurements Summary and outlook

3 European Timeline: June 5, 2007: Official funding of project by Germany and 12 international partners Nov. 2008: Award of construction contracts Oct 2009: Foundation of XFEL Company experiments (start-up 6) 27,000 pulses/sec (2-100 fs long) Å 49 Å flux: phts/(0.1% 12.3 kev 10 9 (start-up 850 M ) mid 2013: All buildings finished, start installation of components mid 2015: first beam December 2015: User operation, SASE 1

4 XFEL pulse structure s 0.6 ms 100 fs 40 W / 2 6 kw x 36,000 W/mm 2

5 European XFEL Photon Beam Systems 5 tuneable gap undulators Experimental stations: HED: High Energy Density matter experiments MID: Material Imaging and Dynamics FXE: Femtosecond X-ray Experiments SPB: Single Particle, clusters & Biomolecules SQS: Small Quantum Systems SCS: Spectroscopy & Coherent Scattering

6 Photon transport systems kev 5-24 kev kev limited performance: < 4σ transmission, damage limited

7 Requirements to Photon Transport System 7 Maximal possible transmission single pulses / full pulse train Minimal possible distortion of wavefronts Extensive/ redundant monitoring of the system status motor encoders, temperatures, bending radii of mirrors Safe operation single pulse damage, heat load damage during the pulse trains Fast change in between experiments Reliable & fast change of photon energy tuning of mirror system Stability of beam positions cp jitter of SASE Radiation protection

8 Mirror Optics Optimization 8 Diffraction effects on mirror apertures can be reduced with increasing θ inc Wave front distortions due to surface height errors ~2 h PV sin(θ inc ) grow proportional to θ inc M.Yurkov & E.Schneidmiller DESY Report Ultra smooth mirrors, <2-3 nm PV, length 800 mm Single pulse damage Heat load

9 Mirror Optics Optimization 9 Is 4 σ clear aperture sufficient? Is it possible to minimize WF distortions and provide maximum beamline transmission for whole operation ranges?

10 Wave front simulation 10 Fourier optics approach to propagation of XFEL pulses through the X-ray grazing incidence optics Alternatives ( used mostly for cross-checking): - stationary phase method - Fresnel Kirchhoff numerical integration PHASE software: HZB, J. Bahrdt SRW O. Chubar, P. Elleaume

11 z1 Fresnel number for aperture: NF = w 2 /(4λz) Wave front simulation Effect of too short mirrors 11 4σ footprint on offset mirror SASE1 SASE3 z kev SASE1: Z1=300m, z2=600m SASE kev SASE3: Z1=250m, Z2=160m SASE3 25 kev 2 mm The diffraction effects become noticeable for footprints of 4σ or less.

12 SASE1 central station (SPB) kev M1 Improving existing state-of-the-art mirrors: 2 nm Use metrology data ( F.Siewert) and: - subtract bending radius ~ km - remove slope 0.8 merror with a polynomial - M2 reduce amplitude of residual height errors by 2-5 times (provides ~2-3 nm PV) 10 kev 5 kev mm mm mm

13 SASE1 side station (FXE) 14 M2: focusing 15.5 kev M1: flat M3: flat Virtual focus M1 R = 200 km 10 kev mm 2 nm 120 km 5 kev mm M2 72 km mm

14 SASE1 side station (FXE): focused beam 15 M2: focusing M1: flat M3: defocusing Virtual focus 0.2 x 2 mm 2 10 kev ideal R2 = 120 km 4.5 σ footprint R3 = -80 km R3=-80 km R3=-70 km mm

15 Focusing conditions 16 for lowest energies z m2 z m3 z exp f R m2 R m3 round R m3 focus M central M branch SASE km flat -100 km SASE km flat -123 km SASE km -3.5 km -116 km Height difference in the center of the mirror h [ nm] = l 2 mirr [ mm] [ ] 8 R km 10% size variation of focused beam (20μm) - 3 nm stability of distribution mirror curvature 10% size variation of a round 12 kev ~30 nm of offset mirror

16 Comparison with experiment 17 Wave front analysis at LCLS XPP station, 9 kev

17 Measuring Wavefronts: Grating X-ray Interferometry 18 Differential phase contrast imaging! phase object beam-splitter phase grating analyzer amplitude grating camera interference pattern sketch courtesy of C.David, PSI First results from X-ray wavefront measurements at LCLS Project leader C. David

18 m 42 m A.Barty et al, Opt.Express (2009)

19 Wave front analysis at LCLS XPP, 9 kev Intensity distribution after two HOMs mirrors mm XPP wavefront measurements with 1D grating interferometer phase stepping mode (~100 shots per step) Calculations: Gaussian beam with far field divergence 3.5 μrad FWHM D grating interferometer data processing by Simon Rutishauser surface profiles by LLNL/Jacek Krzywinski

20 Summary 22 Photon transport systems can transmit single XFEL pulses and pulse trains with reasonable wavefronts distortions by beamline optics Design relies on novel optical components. In particular, 800 mm long mirrors, with profile errors < 2nm PV, ~20 nm slope errors and with bending control precision up to 10 nm and better. First experience with grazing incidence X-ray optics at LCLS: - coherent X-ray laser radiation brings problems, - good news: we can predict and analyze them in advance

21 and Outlook 23 precise and mechanically stable (~1 nm) active optics in-situ metrology and control are crucial! optical and X-ray grating interferometry, precision up to 10nm/10nrad user-friendly wave optics software for design, commissioning and optimisation of beamlines and instruments F. Siewert T. Noll HZB In-situ X-ray X metrology C. David, PSI J.Bahrdt HZB O.Chubar,, BNL

22 Acknowledgments: 24 Helmholtz-Zentrum Berlin Frank Siewert, Johannes Bahrdt PSI SLAC BNL Christian David, Simon Ruthhauser Jacek Krzywinski Oleg Chubar MPY, DESY Mikhail Yurkov, Evgeny Schneidmiller European XFEL: Harald Sinn Jerome Gaudin, Antje Trapp, Fan Yang, Germano Galasso, Nicole Kohlstrunk, Martin Dommach, Idoia Freijo, Shafagh Dastjani Farahani Thomas Tschentscher

23 Thank you for your attention! Wavefront propagation to the experiment: 8-fs of 100 fs SASE 1 XFEL pulse, Eph=12.4keV 25 z = 0 z = 950 m z = 950 m at undulator exit free propagation 2 flat offset mirrors, 2nm PV 100 μm 1.2 mm 1.2 mm M.Yurkov data (FAST code) SASE pulse, 2010