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

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

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

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug Mixing of optical spectrum with neighbouring frequencies     Time-resolution of spectral decoding. Time domain Frequency domain Fourier transform approximate temporal limitation based on bandwidth

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

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

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 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, I Opt (t) ~ E Opt 2 (t) with transform limited “gate” pulse, I gate (t) Time resolution set by gate pulse duration (<50fs) (balanced detection example)

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

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug MeV electron beam measurements FELIX FEL facility, Rijnhuizen, Netherlands

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug Time window,  : Beam diameter, D Angle of incidence   ps for D=5mm,   Phase matching in BBO achievable for incident angles  o Second-harmonic generation (single shot) cross-correlation Symmetric crystal geometry: 400nm walk-off orthogonal to time-axis Able to choose time window from fs → 30ps for 1cm beam (outside beamline!)

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

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug FELIX FEL facility, Rijnhuizen, Netherlands

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug mm Electron bunch Chirped probe pulse

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 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 EO without any upstream mirror … Have applied this technique to single-shot laser-plasma EO bunch measurements (May & August 2003)

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

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

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

Bunch profile versus EO signal… “Crossed-polarisers” Zero background signal Signal ~ E 2 “Balanced detection” Small modulation on large background Signal ~ E

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

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

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

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

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

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

EO measurements at FELIX, Steve Jamison, XFEL2004, Aug 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  of bunch Real-time bunch shape monitoring and adjustment

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