ElectroOptic Longitudinal Profile Diagnostics for CLIC Current Status

Electro-Optic Longitudinal Profile Diagnostics for CLIC Current Status & Future Development S. P. Jamison, Accelerator Science and Technology Centre, STFC Daresbury Laboratory W. A. Gillespie, A. M. Mac. Leod , G. Berden, Carnegie Laboratory of Physics, University of Dundee University of Abertay Dundee FELIX, ‘Rijnhuizen’ FOM, Netherlands Steven Jamison, CTC, CERN September 21,

Electro-Optic Techniques. . . several different techniques • same underlying physics of electron-beam interaction • differing optical implementation • differing capability. . Choices available, based on time resolution & simplicity /robustness Spatial Encoding Temporal Decoding our CLIC proposal SLAC DESY LBNL, . . . FELIX DESY RAL(CLF) MPQ Jena, . . . Spectral Decoding FELIX DESY LBNL. . . spectral upconversion FELIX • Temporal decoding for resolution down to ~60 fs • Spectral up-conversion to be further developed & demonstrated for shorter time scale system Steven Jamison, CTC, CERN September 21,

Low time resolution. . . Spectral Decoding Attractive simplicity low time resolution measurements e. g. injector diagnostics Rely on t-l relationship of input pulse for interpreting output optical spectrum Resolution limits come from fact that EOgenerated optical field doesn't have same tl relationship Resolution related to laser parameters. . . BUT “ideal” laser systems still limited to > 1. 0 ps resolution (for all reasonable observation windows) • Laser requirement can be modest • Suitable turn-key commercial systems widely available (fibre laser) Steven Jamison, CTC, CERN September 21,

Low time resolution. . . Spectral Decoding • Laser requirement can be modest • Suitable turnkey commercial systems widely available (fibre laser) - majority of expts with complicated Ti: S systems - can be done with freq. doubled Erbium fibre lasers Could be developed to directly link to the optical timing distribution (if “pulsed” clock distribution employed) - Robust stand-alone Yb-fibre laser systems being developed by PSI & DESY low energy injector, >> 1 ps diagnostics low charge, low energy measurement on ALICE (Daresbury) Compact fiberised assembly at PSI (from Steffen et al. DIPAC 09) 40 p. C, single shot, Spectral decoding Steven Jamison, CTC, CERN September 21,

Explicit high time resolution approaches. . . Two distinct techniques demonstrated Spatial Encoding • Profile retrieval not yet adequately demonstrated - complications of specific test • Potential for moderately complex laser systems (fibre) • Potential for all-optical integration with timing distribution system Temporal Decoding • Demonstrated 120 fs FWHM, 60 fs rms resolution • Benchmarked against RF deflecting cavity • Requires high pulse energy laser system (>50 u. J per pulse) capable of explicit temporal profiles with features down to 120 fs FWHM. . . will return to definition of time resolution Further improvements face significant issues laser: - generation & transport of <30 fs pulses (physics & engineering) - ultrafast optical characterisation (physics) non-linear materials: bandwidth limitations (physics) Steven Jamison, CTC, CERN September 21,

Electro-optic experiments on FLASH. . . • Remote adjustment & alignment control required • Accelerator location required (ultrafast laser transport) - Vacuum transport of Ti: S to tunnel - Hands-on operation of amplified Ti: S CLIC context. . . • reliable remote diagnostic alignment achievable (ALICE@DL goal) • true turn-key laser systems not available now. …CLIC time scale. . ? • solution for high-power ultra-short laser transport. . ? Steven Jamison, CTC, CERN September 21,

Electro-optic experiments on FLASH high time resolution (+ wakefields ? ) realtime control-room profiles 65 mm thick Ga. P observing stabilising effect of slow feedback CDR feedback on CDR feedback off Control-room diagnostic… BUT only with laser room preparation and support Steven Jamison, CTC, CERN September 21,

Temporal decoding time resolution comparison with RF deflecting cavity Electro-optic shot-shot variations Transverse Deflecting Cavity Phys Rev Lett 99, 164801 (2007) Phys. Rev. ST, 12, 032802 (2009) not observable in (existing) EO. . . Resolution limited by both material properties & laser pulse duration Steven Jamison, CTC, CERN September 21,

Temporal resolution limits What are current limits? Coulomb field of relativistic bunch How to overcome them. ing d o c En • choices for complexity • limiting factor for “spectral decoding” probe laser D non-linear crystal (electro-optic effect) Decoding of information from laser pulse S EO E D & • Temporal resolution limits are primarily in material properties T O • Laser and “decoding” limits follow not far behind Encoding process physics: non-linear frequency mixing between Coulomb field and laser phase-velocity matching of full Coulomb spectrum with laser Constraints: (refractive index variations near phonon resonances ) Decoding physics: ultrafast optical pulse characterisation Constraints: ultrafast laser generation & transport Steven Jamison, CTC, CERN September 21,

Physics of EO encoding. . . time varying refractive index is a restricted approximation to physics Coulomb spectrum shifted to optical region Coulomb pulse replicated in optical pulse envelope optical field New concepts & understanding of very high time res techniques come from generality of frequency mixing physics description) Jamison et al. Opt. Lett 31 1753 (2006) Jamison. , Appl. Phys B. Laser & Opt. 91 241 (2008) Steven Jamison, CTC, CERN September 21,

Encoding Time Resolution. . . material response R(w) • Velocity mismatch of Coulomb field and probe laser • Frequency mixing efficiency, (2)(w) Ga. P Zn. Te • Phonon dips. . . missing data • Origin of ringing artefacts Steven Jamison, CTC, CERN September 21,

Time resolution from frequency response • Encoding “time resolution” not a RMS measure. . . • Better described as “temporal limitation” • structure on longer time scale recorded faithfully • short time scale structure not observed, PLUS ringing artefacts Steven Jamison, CTC, CERN September 21,

. . . Time resolution from frequency response 50 fs FWHM bunches, separated by 110 fs 100 um thick Ga. P 50 um thick Ga. P 10 um thick Ga. P • practical problems with 10 um thickness • ringing not solved by thinner crystals • Laser pulse duration NOT included in calculations • At sub-50 fs resolution, short pulse preservation needs to be addressed Steven Jamison, CTC, CERN September 21,

achieving even better resolution. . . ? Encoding Detector Material: – Move to new material? ( phase matching, (2) considerations ) – Could use Ga. Se, DAST, MBANP. . . or poled organic polymers? – use multiple crystals, and reconstruction process Decoding – Introduce shorter pulse lasers (<30 fs) – Use (linear) spectral interferometry – Use FROG Measurement (initially attempted at FELIX, 2004) or Alternative techniques: spectral upconversion If drop requirement for explicit time information at high frequencies, other options also become available Steven Jamison, CTC, CERN September 21,

alternative EO materials. . • alternative materials exist with higher frequency response • all materials have resonances & bandwidth limitations va polymer (MA 9 in PMMA) ryi n an g cry gle st s al Ga. Se from Cao et al Opt Lett (2002) from Ding et. al, J. non-linear Opt. materials (2003) Leads to consideration of multi-crystal EO detectors Explicit temporal reconstruction of combined crystal measurements…? removal of “ringing” from individual crystals ? ? Steven Jamison, CTC, CERN September 21,

Two approaches. . • Explicit temporal information Temporal decoding for ~60 fs resolution Higher resolution with alternative materials & reconstruction • Implicit spectral information from spectral-upconversion Full spectral information, [mm wavelength -> optical ] Robust capability [feedback. . ? ] Spectral upconversion diagnostic use long pulse, narrow band, probe laser . . . accepting loss of phase information & explicit temporal information. . . gaining potential for determining information on even shorter structure. . . gaining measurement simplicity same physics as “standard” EO. . different observational outcome. • laser complexity reduced, reliability increased • laser transport becomes trivial (fibre) • problematic artefacts of spectral decoding become solution Steven Jamison, CTC, CERN September 21,

What’s different. . . ? Spectral decoding & Temporal decoding laser bunch >> bandwidth spectral extent issues of • laser transport • laser complexity/expense/reliability • material effects (e. g. group velocity dispersion) Spectral upconversion laser bunch << bandwidth spectral extent Important: can measure non-propagating long wavelength components not accessible to radiative techniques (CSR/CTR/SP) • low power, ‘simple’ lasers OK • fibre transport now an option • simple – linear – spectral detection without artefacts of spectral decoding Steven Jamison, CTC, CERN September 21,

Spectral upconversion diagnostic experiments at FELIX For these experiments… • Free-space optical transport • Synchronised 5 -50 ps Ti: S and YAG lasers Steven Jamison, CTC, CERN September 21,

Spectral upconversion diagnostic experiments at FELIX Appl. Phys. Lett. 96 231114 (2010) FELIX temporal profile sum frequency mixing inferred FELIX spectrum difference frequency mixing

Spectral upconversion with FEL radiation. . . Explicit confirmation of frequency upconversion process with tunable, monochromatic, Far-IR and mid-IR optical side bands from l=150 mm FEL radiation Appl. Phys. Lett. 96 231114 (2010) Hig h fi Standard “EO” expectation x 10 increase in field (…charge) eld se ffec ts ! !!

Proposed spectral upconversion system fibre optic transport to optical spectrometer turn-key commercial fibre lasers commercially available link to telecoms technology (robustness) fibre optic distribution to diagnostic location in accelerator Compact crystal assembly in beam line • multiple crystals azimuthally offset • laser split and independently sent to each crystal Required development: • Short bunch testing of spectral upconversion • Testing of alternative materials, including in accelerator environment • Simultaneous testing of multiple-crystals Steven Jamison, CTC, CERN September 21,

Pathway to meeting CLIC requirements Materials investigation • Testing with laser generated THz (material properties) • FEL experiments for non-linearity and mid-IR capability EO technique development and demonstration: • Reducing laser requirements of EOTD • FROG extension of EOTD…allows sub-laser duration measurements • Multi-crystal reconstruction methods…theory -> expt test • Spectral upconversion • High field effects… Tests at short-bunch test facilities (PSI, FACET, …? ) Steven Jamison, CTC, CERN September 21,

Summary Low time resolution (>1 ps structure) • spectral decoding offers explicit temporal characterisation • relatively robust laser systems available High time resolution (>60 fs rms structure) • proven capability • significant issues with laser complexity / robustness Very higher time resolution (<60 fs rms structure) • Limited by EO material properties (& laser) • Spectral up conversion + alternative (multiple) EO materials gives implicit ultra-short bunch structure • Development & short-bunch demonstrations required (including alternative materials, Ga. Se, . . . ) Steven Jamison, CTC, CERN September 21,

S t e v e J a m i s o n , C T C , S e p t 2 0 1 0 Electro-Optic Longitudinal Profile Diagnostics for CLIC • Current capabilities & options • time resolution vs simplicity • multi-bunch operation • integration in optical timing distribution systems • Readiness for implementation • Outstanding issues • Development & Prototyping Pathways Steven Jamison, CTC, CERN September 21,

Spatial Encoding Rely on t-x relationship between laser and Coulomb field In principle: expect same/similar capabilities as TD less widely demonstrated: SPPS (SLAC) measurements SLAC and DESY expts had significant additional complications of long transport in fibre. . . FLASH (DESY) measurements from Cavaleria et al. PRL 2005 from A. Azima et. al EPAC 06 + FERMI@elettra system under test (SPARC. . . ) possible solution for simplifying laser requirements BUT. . cannot improve on temporal decoding not upgradable to FROG-like measurement without adding TD complexity (limited to laser pulse duration issues of laser transport)

Frequency domain description of EO detection. . . Electro-optic encoding is a consequence of sum- and difference-frequency mixing Coulomb field probe laser wthz wopt EO crystal (2)(w; wthz, wopt) wopt + wthz wopt - wthz wopt for arbitrary probe and Coulomb pulses. . . • convolve over all combinations of optical and Coulomb frequencies. • includes field phase (chirp), general phase matching, optical GVD etc Refractive index formalism comes out as subset of solutions (restriction on laser parameters)

alternative ways forward. . . Current limitations are from material properties Phonon-resonance at 3 -15 THz (material dependent) All materials will have some phonon resonance effects Can we use a set of crystals to cover larger range? requires (uncertain) reconstruction to find temporal profile (relative phase shifts, phase matching, efficiency between crystals) complication of system would multiply If reconstruction needed anyway, reconsider spectral techniques. . . BUT traditional spectral techniques have difficulties : long wavelength / DC component transport extreme (“ 100%”) spectral bandwidths for detection A solution : Electro-optic spectral upconversion

Steve Jamison, CTC, Sept 2010

Laser transport. . . in FLASH experiments EO Temporal decoding setup More complicated setup Less access to setup in accelerator • Vacuum laser transport from laser “hut” to tunnel. • Some relay lenses in transport • Remote adjustments on many mirrors

new slide 20 Spectral upconversion diagnostic Aim to measure the bunch Fourier spectrum. . . accepting loss of phase information & explicit temporal information. . . gaining potential for determining information on even shorter structure. . . gaining measurement simplicity use long pulse, narrow band, probe laser same physics as “standard” EO d-function different observational outcome • laser complexity reduced, reliability increased • laser transport becomes trivial (fibre) • problematic artefacts of spectral decoding become solution NOTE: the long probe is still converted to optical replica

In Summary. . . • Proven capability for explicit temporal characterisation up to ~100 fs rms electron bunch structure • high time resolution techniques have problems with reliability & necessary infrastructure. . . • . . . but there exist avenues available for improving time resolution & robustness (depending on beam diagnostics requirements) • For high time resolution, both alternative materials & spectral upconversion are under investigation

Selected References (Daresbury-Dundee Group): Free-electron laser pulse shape measurements with 100 fs temporal resolution using a 10 fs Ti: sapphire laser and differential optical gating X. Yan, A. M. Mac. Leod, W. A. Gillespie et al. Nucl. Instr. Meths. Phys. Res. Vol A 429 (1999) 7 - 9 Sub-picosecond electro-optic measurement of relativistic electron pulses X. Yan, A. M. Mac. Leod, W. A. Gillespie, G. M. H. Knippels, D. Oepts, A. F. G. van der Meer. Physical Review Letters 85 (2000) 3404 -7 Single-shot electron bunch length measurements I. Wilke, A. M. Mac. Leod, W. A. Gillespie, G. Berden, G. M. H. Knippels, A. F. G. van der Meer Phys. Rev. Lett. 88 No 12 (2002) 124801/1 -4 Real-time, non-destructive, single-shot electron bunch-length measurements G. Berden, S. P. Jamison, A. M. Mac. Leod, W. A. Gillespie, B. Redlich and A. F. G. van der Meer Physical Review Letters 93 (2004) 114802 Temporally resolved electro-optic effect S. P. Jamison, A. M. Macleod, G. Berden, D. A. Jaroszynski and W. A. Gillespie Optics Letters 31, 11 (2006) 1753 -55 Benchmarking of Electro-Optic monitors for Femtosecond electron bunches G. Berden, W. A. Gillespie, S. P. Jamison, B. Steffen, V. Arsov, A. M. Mac. Leod, A. F. G. van der Meer, P. J. Phillips, H. Schlarb, B. Schmitt, and P. Schmüser Phys. Rev. Lett. 99 043901 (2007) Electro-optic time profile monitors for femtosecond electron bunches at the soft X-ray free-electron laser FLASH B. Steffen, V. Arsov, G. Berden, W. A. Gillespie, S. P. Jamison, A. M. Mac. Leod, A. F. G. van der Meer, P. J. Phillips, H. Schlarb, B. Schmitt, and P. Schmüser Physical Review Special Topics – Accelerators and Beams 12 032802 (2009)

Temporal decoding Rely on EO crystal producing a optical temporal replica of Coulomb field measure optical replica with t-x mapping in 2 nd Harmonic Generation Temporal profile of probe pulse Spatial image of 2 nd harmonic limited by • gate pulse duration (although FROG etc could improve) • EO encoding efficiency, phase matching Practical limitations: complexity of laser systems transporting short pulse laser (gate pulse only)