1. Volker Schlott SV84, LL-RF Workshop, CERN, October 11 th, 2005 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 First Experimental Results

2. Volker Schlott SV84, LL-RF Workshop, CERN, October 11 th, 2005 Femto-Second Stable Timing and Synchronization Systems 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 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) in injector, booster and bunch compressor 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! Motivation – Future XFELs and Time Resolved Experiments on fs-Level

3. Volker Schlott SV84, LL-RF Workshop, CERN, October 11 th, 2005 Femto-Second Stable Timing and Synchronization Systems Motivation – Schematic Layout of Timing Distribution in Future XFEL Facilities Master Oscillator Timing Distribution kly 5 kly 15kly 25 kly 31 kly 1 kly 2kly 3 kly 4 RF-gun / injector 2 3 rd harm. structure bunch compression 1 / 2 main SC LINAC collimation diagnostics switchyard, beam distribution undulator sections beam dumps towards beam lines collimation / diagnostics multiple experimental stations gun laser SC booster RF-gun / injector 1 ~ 3.5 km diagn. 1 diagn. 2 diagn. 3 diagn. 4 seed laser pump-probe laser RF-signal SYNC-signal Requirements for future 4 th 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. Volker Schlott SV84, LL-RF Workshop, CERN, October 11 th, 2005 Femto-Second Stable Timing and Synchronization Systems Motivation: electron beam – laser arrival time jitter measurements Timing Jitter Data (20 successive shots) time (ps) shot EO cross-correlation-measurements performed by A.L.Cavalieri et al. @ SPPS, SLAC courtesy of A.L.Cavalieri

5. Volker Schlott SV84, LL-RF Workshop, CERN, October 11 th, 2005 Femto-Second Stable Timing and Synchronization Systems - femto-second Er-doped fiber laser locked to microwave master oscillator - transmission of RF signals ⇨ photo-detection of n th 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! Stabilized Optical Synchronization Systems – Proposed Schemes - 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 ! in general: high precision at optical frequencies and immunity of photons to noise Optical Heterodyne Technique - proposed by J. Staples and R. Wilcox, LBNL Short pulse fiber lasers - proposed by A. Winter et al. (DESY), F. Kärtner et al. (MIT)

6. Volker Schlott SV84, LL-RF Workshop, CERN, October 11 th, 2005 Femto-Second Stable Timing and Synchronization Systems ⇨ 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) Schematic Layout of Classical Synchronization System low noise microwave oscillator diagnostics 1…n photo-injector drive laser system RF fan out low level RF station 1…n Classical Synchronization Layout based on: - low noise microwave master oscillator - usually (non-) stabilized RF coaxial cable distribution

7. Volker Schlott SV84, LL-RF Workshop, CERN, October 11 th, 2005 Femto-Second Stable Timing and Synchronization Systems - other lasers (for gun, diagnostics, seeding and experiments) can be linked directly Schematic Layout of Optical Synchronization System (as proposed by Winter et al. (DESY) in collaboration with MIT) low noise microwave oscillator seed laser experiment RF optical sync-module and / or pulse picker photo-injector drive laser system pulse fan out low level RF station 1…n diagnostics 1…n laser master oscillator fiber stabilization (1 for each link) Optical Synchronization Layout based on: - low noise microwave master oscillator as stable low frequency reference (DC to < 10 kHz) - mode-locked Er-doped fiber lasers as “new” optical master oscillator - optical fiber distribution: length stabilization over kilometers achieved with fiber stretchers - RF can be re-generated locally by photo-detection (n th harmonic of laser rep.-rate)

8. Volker Schlott SV84, LL-RF Workshop, CERN, October 11 th, 2005 Femto-Second Stable Timing and Synchronization Systems 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 output isolator Er-fiber (normal dispersion) single mode fiber with anomalous dispersion pump diode laser port for diagnostics 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) single sideband noise for harmonic @ 1 GHz A. Winter et. al, to be published in NIM-A

9. Volker Schlott SV84, LL-RF Workshop, CERN, October 11 th, 2005 Femto-Second Stable Timing and Synchronization Systems Er-doped Fiber Laser (non-commercial set-up by Axel Winter)

10. Volker Schlott SV84, LL-RF Workshop, CERN, October 11 th, 2005 Femto-Second Stable Timing and Synchronization Systems RF Distribution – Photo-Detection to Extract RF from Laser Pulse Train f ….. fRfR 2f R nf R (n+1)f R optical pulse train (time domain) T R = 1/f R t RF is encoded in laser pulse repetition rate high BW (> 10 GHz) InGa As photodiode signal converted to electronic domain by photo-detector BPF f nf R t T R /n LNA any suitable harmonics (nf R ) can be extracted

11. Volker Schlott SV84, LL-RF Workshop, CERN, October 11 th, 2005 Femto-Second Stable Timing and Synchronization Systems 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 ) low noise microwave oscillator laser master oscillator (mode-locked Er-fiber laser) fine optical cross-correlator ultimate stabilization < 1 fs “coarse” RF stabilization ~ 20 fs phase noise measurement isolator 50:50 coupler controller piezo driver piezo controlled fiber stretcher SMF link (1 - 5 km) output coupler photo- detection Faraday Mirror

12. Volker Schlott SV84, LL-RF Workshop, CERN, October 11 th, 2005 Femto-Second Stable Timing and Synchronization Systems First Experimental Results by 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. Volker Schlott SV84, LL-RF Workshop, CERN, October 11 th, 2005 Femto-Second Stable Timing and Synchronization Systems First Experimental Results by 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 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)

14. Volker Schlott SV84, LL-RF Workshop, CERN, October 11 th, 2005 Femto-Second Stable Timing and Synchronization Systems Summary Acknowledgements future XFELs (and today’s fs-slicing sources at storage rings) need fs stable RF and timing distribution ⇨ excellent noise performance at high frequencies mode-locked Er-doped fiber lasers are candidates for optical master oscillators ⇨ lockable to microwave oscillators to suppress low frequency noise ⇨ high reliability and availability of pump sources and optical components (@ 1550 nm) ⇨ applying RF feedback schemes… < 20 fs stabilization of fiber optical RF and timing distribution of kilometers is possible ⇨ applying optical cross correlation… < 1 fs ⇨ applying optical heterodyne techniques… < 1 fs stabilization of RF distribution (@ 1 GHz) demonstrated in real accelerator environment @ MIT Bates to… < 50 fs jitter (0.1 Hz – 20 MHz) many thanks again to Axel Winter (DESY) for many instructive and inspiring discussions…!