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Femto-Second Stable Timing and Synchronization Systems Volker Schlott, PSI

Femto-Second Stable Timing and Synchronization Systems Volker Schlott, PSI. Motivation – Future XFELs and Time Resolved Experiments on fs-Level Architecture of Optical Synchronization Systems - Fiber Lasers - Optical Master Oscillator - Optical Timing Distribution

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Femto-Second Stable Timing and Synchronization Systems Volker Schlott, PSI

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  1. Femto-Second StableTiming and Synchronization SystemsVolker Schlott, PSI Motivation – Future XFELs and Time Resolved Experiments on fs-Level Architecture of Optical Synchronization Systems - Fiber Lasers - Optical Master Oscillator - Optical Timing Distribution First Experimental Results

  2. in injector, booster and bunch compressor Motivation – Future XFELs and Time Resolved Experiments on fs-Level • Stability of RF and RF Distribution - arrival time jitter of electron beam in undulator ≤ bunch length (~ 30 - 50 fs) ⇨ RF amplitude stability ~ 10-4 ⇨RF phase stability ~ 0.01 ° (21 fs @ 1.3 GHz) • Single Bunch Beam Diagnostics along Accelerator - single bunch and “sliced” beam parameters are relevant for SASE process (not rms!) - measurement locations are spread over kilometers along LINAC ⇨ highly stable timing / sync distribution on fs-level • Laser-Electron Beam and Laser-Photon Beam Interaction on a fs-Level - stable reference for seeding and HGHG generation - time-resolved (“pump-probe”) experiments at user end stations - synchronization for today’s “femto-second slicing sources” in storage rings ⇨ highly stable timing / sync distribution on fs-level but: inherent arrival time jitter of photon pulses due to stochastic SASE process!

  3. Master Oscillator Timing Distribution kly 5 kly 15 kly 25 kly 31 kly 1 kly 2 kly 3 kly 4 RF-signal RF-signal RF-signal RF-signal RF-signal RF-signal RF-signal RF-signal SYNC-signal SYNC-signal SYNC-signal SYNC-signal pump-probe laser bunch compression 1 / 2 undulator sections collimation diagnostics main SC LINAC RF-gun / injector 1 SC booster diagn. 1 diagn. 3 diagn. 2 seed laser diagn. 4 multiple experimental stations towards beam lines beam dumps gun laser collimation / diagnostics 3rd harm. structure switchyard, beam distribution RF-gun / injector 2 ~ 3.5 km • Motivation – Schematic Layout of Timing Distribution in Future XFEL Facilities SYNC-signal SYNC-signal SYNC-signal Requirements for future 4th generation light sources: - provision of highly stable reference with fs-stability ⇨ master oscillator - highly stable distribution of timing and SYNC signals with jitter < 10 fs over km-length

  4. Timing Jitter Data (20 successive shots) shot time (ps) EO cross-correlation-measurements performed by A.L.Cavalieri et al. @ SPPS, SLAC • Motivation: electron beam – laser arrival time jitter measurements courtesy of A.L.Cavalieri

  5. Stabilized Optical Synchronization Systems – Proposed Schemes Optical Heterodyne Technique- proposed by J. Staples and R. Wilcox, LBNL - single frequency Er-doped cw fiber laser as optical carrier (2 kHz LW ~ 25 km coherence length) - transmission of RF signals ⇨ amplitude modulation of cw optical carrier (wide band zero-chirp MZI) - synchronization of mode-locked lasers ⇨ phase-locking of two optical frequencies - stabilization ⇨down-conversion of optical phase shifts to RF (acousto-optical frequency shifter) ⇨applying simple, inexpensive heterodyne technique at 110 MHz - first results achieved in lab: stabilizing 100 m of optical fiber to 20 fs ! Short pulse fiber lasers- proposed by A. Winter et al. (DESY), F. Kärtner et al. (MIT) - femto-second Er-doped fiber laser locked to microwave master oscillator - transmission of RF signals ⇨ photo-detection of nth harmonics of laser rep.-rate - direct synchronization of mode-locked lasers - stabilization ⇨optical cross-correlation technique - first results achieved at MIT Bates accelerator: stabilizing 500 m of optical fiber to 12 fs! in general: high precision at optical frequencies and immunity of photons to noise

  6. low noise microwave oscillator RF fan out low level RF station 1…n diagnostics 1…n photo-injector drive laser system Schematic Layout of Classical Synchronization System Classical Synchronization Layout based on: - low noise microwavemaster oscillator - usually (non-) stabilized RF coaxial cable distribution ⇨ RF amplitude and phase stability in the order of 10-3 to 10-4 (JLAB - sc cw-RF, DESY VUV-FEL) ⇨ stability of timing / synchronization distribution typically in the order of pico-second(s)

  7. RF optical sync-module and / or pulse picker low noise microwave oscillator laser master oscillator pulse fan out fiber stabilization (1 for each link) low level RF station 1…n seed laser experiment photo-injector drive laser system diagnostics 1…n Schematic Layout of Optical Synchronization System (as proposed by Winter et al. (DESY) in collaboration with MIT) Optical Synchronization Layout based on: - low noise microwavemaster oscillator as stable low frequency reference (DC to < 10 kHz) - mode-locked Er-doped fiber lasers as “new” optical master oscillator - RF can be re-generated locally by photo-detection (nth harmonic of laser rep.-rate) - other lasers (for gun, diagnostics, seeding and experiments) can be linked directly - optical fiber distribution: length stabilization over kilometers achieved with fiber stretchers

  8. single sideband noise for harmonic @ 1 GHz A. Winter et. al, to be published in NIM-A isolator output pump diode single mode fiber with anomalous dispersion Er-fiber (normal dispersion) laser port for diagnostics Passively Mode-Locked Fiber Lasers Noise characteristics: < 10 kHz ⇨ worse than microwave oscillators due to thermal and vibrational disturbances > 10 kHz ⇨ low-pass characteristic of pump source due to long (ms) upper state lifetime of Er Er-fiber lasers ⇨ sub 100 femto-second to pico-second pulse durations ⇨ high availability of fiber-optic components @ 1550 nm (telecom) ⇨ 30 – 100 MHz repetitions rates (lockable to accelerator RF) ⇨ high reliability and long term stability (commercial systems available)

  9. Er-doped Fiber Laser(non-commercial set-up by Axel Winter)

  10. TR/n t TR = 1/fR high BW (> 10 GHz) InGa As photodiode BPF LNA t optical pulse train (time domain) … .. f nfR f (n+1)fR fR 2fR nfR RF Distribution – Photo-Detection to Extract RF from Laser Pulse Train • RF is encoded in laser pulse repetition rate • signal converted to electronic domain by photo-detector • any suitable harmonics (nfR) can be extracted

  11. SMF link (1 - 5 km) piezo controlled fiber stretcher 50:50 coupler isolator laser master oscillator (mode-locked Er-fiber laser) output coupler low noise microwave oscillator photo- detection controller piezo driver phase noise measurement Faraday Mirror “coarse” RF stabilization ~ 20 fs fine optical cross-correlator ultimate stabilization < 1 fs Optical Fiber Stabilization Scheme(as proposed by Winter et al. (DESY) in collaboration with MIT) • direct stabilization of group velocity in fiber • temperature effects and vibrations are compensated (fiber temp. coefficient ~ 5 x 10-6 m-1)

  12. First Experimental Resultsby Winter (DESY) and MIT co-workers • tests in real accelerator environment @ MIT Bates laboratory • Er-doped fiber laser locked to Bates master oscillator • laser pulses transmitted through a total fiber length of 1 km • “passive” temperature stabilization of fiber link • stabilization of fiber length by RF feedback ~ 500 meters

  13. transmited RF-signal (2.856 GHz) • phase lock jitter ⇨ 30 fs (10 Hz – 2 kHz) • total jitter added ⇨ 50 fs • overall improvement 272 fs vs. 178 fs (up to 20 MHz) • spurs are technical noise (pump diode PS) First Experimental Resultsby Winter (DESY) and MIT co-workers open / closed loop performance • open loop stability ⇨ 60 fs (0.1 Hz – 5 kHz) • closed loop stability ⇨ 12 fs (0.1 Hz – 5 kHz) • stability achieved with “simple” RF feedback • no significant noise added at high frequencies

  14. mode-locked Er-doped fiber lasers are candidates for optical master oscillators ⇨ excellent noise performance at high frequencies ⇨ lockable to microwave oscillators to suppress low frequency noise ⇨ high reliability and availability of pump sources and optical components (@ 1550 nm) • stabilization of fiber optical RF and timing distribution of kilometers is possible ⇨ applying RF feedback schemes… < 20 fs ⇨ applying optical cross correlation… < 1 fs ⇨ applying optical heterodyne techniques… < 1 fs Summary • future XFELs (and today’s fs-slicing sources at storage rings) need fs stable RF and timing distribution • stabilization of RF distribution (@ 1 GHz) demonstrated in real accelerator environment • @ MIT Bates to… < 50 fs jitter (0.1 Hz – 20 MHz) Acknowledgements many thanks again to Axel Winter (DESY) for many instructive and inspiring discussions…!

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