Volker Schlott SV84, LL-RF Workshop, CERN, October 11th, 2005

Femto-Second StableTiming 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

Volker Schlott SV84, LL-RF Workshop, CERN, October 11th, 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

Volker Schlott SV84, LL-RF Workshop, CERN, October 11th, 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 15 kly 25 kly 31kly 1 kly 2 kly 3 kly 4

RF-gun / injector 23rd harm. structure

bunch compression 1 / 2

mainSC LINAC

collimationdiagnostics

switchyard,beam distribution

undulator sections

beam dumps towardsbeam lines

collimation /diagnostics

multiple

experimental stations

gun

lase

r

SC boosterRF-gun / injector 1

~ 3.5 km

diagn. 1 diagn. 2 diagn. 3 diagn. 4seed laserpump-probe laser

RF-

sign

al

RF-

sign

al

RF-

sign

al

RF-

sign

al

RF-

sign

al

RF-

sign

al

RF-

sign

al

RF-

sign

al

SYN

C-s

igna

l

SYN

C-s

igna

l

SYN

C-s

igna

l

SYN

C-s

igna

l

SYN

C-s

igna

l

SYN

C-s

igna

l

SYN

C-s

igna

l

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

Volker Schlott SV84, LL-RF Workshop, CERN, October 11th, 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

Volker Schlott SV84, LL-RF Workshop, CERN, October 11th, 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 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!

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)

Volker Schlott SV84, LL-RF Workshop, CERN, October 11th, 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 microwaveoscillator

diagnostics 1…n

photo-injectordrive 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

Volker Schlott SV84, LL-RF Workshop, CERN, October 11th, 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 microwaveoscillator

seed laser

experiment

RF optical sync-moduleand / or pulse picker

photo-injectordrive 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)

Volker Schlott SV84, LL-RF Workshop, CERN, October 11th, 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

outputisolator

Er-fiber (normal dispersion)

single mode fiber withanomalous 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 GHzA. Winter et. al, to be published in NIM-A

Volker Schlott SV84, LL-RF Workshop, CERN, October 11th, 2005

Femto-Second Stable Timing and Synchronization Systems

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

Volker Schlott SV84, LL-RF Workshop, CERN, October 11th, 2005

Femto-Second Stable Timing and Synchronization Systems

RF Distribution – Photo-Detection to Extract RF from Laser Pulse Train

f… ..

fR 2fR nfR (n+1)fR

optical pulse train(time domain)

TR = 1/fR

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

fnfR

t

TR/n

LNA

• any suitable harmonics (nfR) can be extracted

Volker Schlott SV84, LL-RF Workshop, CERN, October 11th, 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 microwaveoscillator

laser master oscillator

(mode-locked Er-fiber laser)

fine opticalcross-correlator

ultimate stabilization < 1 fs

“coarse” RF stabilization ~ 20 fs

phase noisemeasurement

isolator50:50

coupler

cont

rolle

rpi

ezo

driv

er

piezo controlledfiber stretcher

SMF link (1 - 5 km)

output coupler

photo-detection

FaradayMirror

Volker Schlott SV84, LL-RF Workshop, CERN, October 11th, 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

Volker Schlott SV84, LL-RF Workshop, CERN, October 11th, 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)

Volker Schlott SV84, LL-RF Workshop, CERN, October 11th, 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…!