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Single-shot, Sub-picosecond, EO bunch measurements at FELIX

Single-shot, Sub-picosecond, EO bunch measurements at FELIX. Steven Jamison, Giel Berden, Allan MacLeod Allan Gillespie, Jingling Shen, Dino Jaroszynski, Britta Redlich, Lex van der Meer School of Computing and Advanced Technologies, University of Abertay, Dundee, UK

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Single-shot, Sub-picosecond, EO bunch measurements at FELIX

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  1. Single-shot, Sub-picosecond, EO bunch measurements at FELIX Steven Jamison, Giel Berden, Allan MacLeod Allan Gillespie, Jingling Shen, Dino Jaroszynski, Britta Redlich, Lex van der Meer School of Computing and Advanced Technologies, University of Abertay, Dundee, UK Department of Physics, University of Strathclyde, Glasgow, UK FOM Institute for Plasma Physics “Rijnhuizen”, Nieuwegein, The Netherlands

  2. Single-shot electro-optic detection of ultra-short bunches- spectral-decoding - temporal decoding • FELIX electron bunch measurementsreal time bunch profile adjustment bunch timing jitter charge dependence EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004

  3. Electro-optic detection of Coulomb field: Spectral decoding method 1.7ps Temporal decoding method 450fs EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004

  4. Time-resolution of spectral decoding. Time domain Fouriertransform Frequency domain Mixing of optical spectrum with neighbouring frequencies w  W approximate temporal limitation based on bandwidth EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004

  5. Time-resolution function NOT a smoothing function. Can cause artifacts!! Should be considered as temporal limitation e.g balanced detection: measure change in probe spectrum… EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004

  6. Lab-bench test-bed for EO techniques able to produce mimic of Coulomb field with unipolar THz pulse from GaAs emitter Single-shot spectral decoding Multi-shot scanning optical delay EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004

  7. Observe oscillating features on shorter time scale than usual “time resolution” Jamison et al. Opt. Lett. 18 1710 (2003) EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004

  8. Temporal decoding • Same chirped pulse encoding of Coulomb field information. • Decode information through time-domain measurement of probe intensity Cross-correlation of EO modulated pulse, IOpt(t) ~ EOpt2(t) with transform limited “gate” pulse, Igate(t) (balanced detection example) Time resolution set by gate pulse duration (<50fs) EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004

  9. Temporal decoding at FELIX ~100mJ 30 fs ~1mJ 21 ps Chirped probe focussed on ZnTe in beamline (sampling field at single point) Probe expanded and collimated forcross-correlator (for temporal-spatial mapping) EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004

  10. 30-50MeV electron beam measurements FELIX FEL facility, Rijnhuizen, Netherlands EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004

  11. Second-harmonic generation (single shot) cross-correlation Time window, t: • Beam diameter, D • Angle of incidence F t ~ 9ps for D=5mm, F~15o Symmetric crystal geometry: 400nm walk-off orthogonal to time-axis Phase matching in BBO achievable for incident angles F < 33o Able to choose time window from fs → 30ps for 1cm beam (outside beamline!) EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004

  12. Single-shot “temporal decoding” of optical probe Temporal profile of probe pulse→ Spatial image of SHG Symmetrical optical arrangement No temporal blurring with crystal thickness EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004

  13. FELIX FEL facility, Rijnhuizen, Netherlands CCD camera short pulse chirped probe EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004

  14. ZnTe Electron bunch 5mm Chirped probe pulse EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004

  15. EO without any upstream mirror … ZnTe Reflection geometry…. High frequency signal components • cancel during counter-propagating path • sampled during co-propagating path Low frequency components • “averaged” during counter-propagating path • sampled during co-propagating path doubled retardation Have applied this technique to single-shot laser-plasma EO bunch measurements (May & August 2003) EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004

  16. Early temporal decoding measurements at FELIX (July 2003) 30MeV→110fs resolution (at 1mm from beam) ~800fs Berden et al. Proceedings of FEL2003 ~600fs 28 July, 2003 EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004

  17. Temporal decoding measurements at FELIX December 2003 450fs FWHM G. Berden, S.P. Jamison et al. Accepted for Phys. Rev. Lett. EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004

  18. Temporal decoding measurements at FELIX December 2003 Bunch timing jitter EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004

  19. Bunch profile versus EO signal… • Zero background signal • Signal ~ E2 “Crossed-polarisers” • Small modulation on large background • Signal ~ E “Balanced detection”

  20. Determining Coulomb field from EO signal Using “crossed-polariser” configuration  EO signal  [Coulomb Field]2 Ecoulomb = [EO signal]1/2 Quadratic dependence of EO signal on field confirmed by varying bunch charge ( EO signal  Q2 ) EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004

  21. Confirmation of time-resolution and quadratic EO dependence with monochromatic FEL radiation EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004

  22. Temporal decoding, spectral decoding comparison temporal decoding measurement NOT time-resolution limited (crossed polarisers configuration) EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004

  23. Real time beam adjustment (beam-steering towards crystal) EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004

  24. Real time monitoring and bunch profile modification… .  450 fs FWHM Coulomb field on sub peak Bunch profile modified by changing the buncher and accelerator phase. EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004

  25. Need even better time-resolution…. (measuring sub-200fs bunches) . Spectrum-envelope interdependence (spectral-decoding) >300fs bunch duration limitation Solved by temporal decoding ~30-50fs possible >200fs limitation for undistorted measurement Rigorous retrieval of true field possible EO phase matching EO crystal absorption Alternative EO materials. (GaP, GaSe, DAST…) Approximate interpolation… ~30fs possible (?) Time resolution approx. optical pulse duration. ~30 fs. Improvements through X-FROG, ….? Optical bandwidth EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004

  26. CONCLUSIONS FOR TEMPORAL DECODING….. • Demonstrated non-destructive longitudinal profile measurement with 650fs FWHM bunches • ~450fs FWHM substructure observed • Estimated time resolution ~300fs (2.8THz), due to ZnTe response and low g of bunch • Real-time bunch shape monitoring and adjustment EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004

  27. Supported by EPSRC Basic Technology Programme (alpha-X project on wavefield accelerator driven FEL) Allan MacLeod Allan Gillespie Steve Jamison Jingling Shen Dino Jaroszynski (Capital Normal University, Beijing) Giel Berden Britta Redlich Lex van der Meer EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 2004

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