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Progress in femtosecond timing distribution and synchronization for ultrafast light sources. John Byrd Lawrence Berkeley National Laboratory. John Staples, LBNL Russell Wilcox, LBNL Larry Doolittle, LBNL Alex Ratti, LBNL Franz Kaertner, MIT Omar Illday, MIT Axel Winter, DESY

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progress in femtosecond timing distribution and synchronization for ultrafast light sources

Progress in femtosecond timing distribution and synchronization for ultrafast light sources

John Byrd

Lawrence Berkeley National Laboratory

acknowledgements
John Staples, LBNL

Russell Wilcox, LBNL

Larry Doolittle, LBNL

Alex Ratti, LBNL

Franz Kaertner, MIT

Omar Illday, MIT

Axel Winter, DESY

Paul Emma, SLAC

John Corlett, LBNL

Mario Ferianis, ST

Jun Ye, JILA

David Jones, U of B.C.

Joe Frisch, SLAC

Bill White, SLAC

Ron Akre, SLAC

Patrick Krejcik, SLAC

Acknowledgements

John Byrd, BIW2006

a great intro to fsec lasers
A great intro to fsec lasers

Femtosecond Optical Frequency Comb: Principle, Operation and Applications

Jun Ye (Editor), Steven T. Cundiff (Editor)

John Byrd, BIW2006

synchronicity
Synchronicity

Stabilized link

Stabilized link

Stabilized link

FEL seed laser

Stabilized link

PC drive laser

user laser

Stabilized link

EO laser

LLRF

  • Next generation light sources require an unprecedented level of remote synchronization between x-rays, lasers, and RF accelerators to allow pump-probe experiments of fsec dynamics.
    • Photocathode laser to gun RF
    • FEL seed laser to user laser
    • Relative klystron phase
    • Electro-optic diagnostic laser to user laser

Master

John Byrd, BIW2006

overview
Overview
  • Motivation: LCLS example
  • Ultrastable clocks
  • Stabilized distribution links
  • Synchronizing techniques
  • Measuring synchronization

John Byrd, BIW2006

lots of fel activity
Lots of FEL activity

John Byrd, BIW2006

small things
Small things

A gnat’s ass

100 femtoseconds

  • 100x10-15 sec
  • 30 microns
  • 0.8 mrad@1.3 GHz
  • 0.045 deg@1.3 GHz
  • 1.8 mrad@2856 MHz
  • 0.1 deg@2856 MHz
  • (10 TeraHertz)-1
  • 20*(1.5 micron)

John Byrd, BIW2006

motivation lcls
Motivation: LCLS
  • Final energy 13.6 GeV (stable to 0.1%)
  • Final peak current 3.4 kA (stable to 12%)
  • Transverse emittance 1.2 mm (stable to 5%)
  • Final energy spread 10-4 (stable to 10%)
  • Bunch arrival time (stable to 150 fs)

Critical LCLS Accelerator Parameters

P. Emma

(stability specifications quoted as rms)

John Byrd, BIW2006

electron bunch compression
Electron Bunch Compression

d DE/E

d

d

under-compression

szi

‘chirp’

z

z

z

sz

sdi

Dz = R56d

V = V0sin(kz)

P. Emma

RF Accelerating

Voltage

Path-Length Energy-

Dependent Beamline

John Byrd, BIW2006

compression stability
Compression Stability

d

RF phase jitter becomes bunch length jitter…

Compression factor:

Df

d

z

P. Emma

John Byrd, BIW2006

lcls machine schematic
LCLS Machine Schematic

250 MeV

z  0.19 mm

  1.6 %

4.30 GeV

z  0.022 mm

  0.71 %

13.6 GeV

z  0.022 mm

  0.01 %

6 MeV

z  0.83 mm

  0.05 %

135 MeV

z  0.83 mm

  0.10 %

Linac-X

L =0.6 m

rf= -160

rf

gun

Linac-1

L 9 m

rf  -25°

Linac-2

L 330 m

rf  -41°

Linac-3

L 550 m

rf  0°

23-m

Linac-0

L =6 m

undulator

L =130 m

21-1b

21-1d

21-3b

24-6d

25-1a

30-8c

X

...existing linac

BC1

L 6 m

R56 -39 mm

BC2

L 22 m

R56 -25 mm

DL1

L 12 m

R56 0

LTU

L =275 m

R56  0

1 X-klys.

3 klystrons

1 klystron

26 klystrons

45 klystrons

research yard

SLAC linac tunnel

P. Emma

John Byrd, BIW2006

optical metrology
Optical metrology
  • A revolution is going on in optical metrology due to several coincident factors:
    • development of femtosecond comb lasers
    • breakthroughs in nonlinear optics
    • wide availability of optical components

2005 Nobel Prize in Physics awarded to John L. Hall and Theodor W. Hänsch "for their contributions to the development of laser-based precision spectroscopy, including the optical frequency comb technique"

This technology is nearly ready for applications in precision synchronization in accelerators

John Byrd, BIW2006

a brief history of timekeeping
A brief history of timekeeping
  • 1949 Ramsey's separated oscillatory field technique
  • 1955 First caesium atomic clock
  • 1960 Hydrogen maser
  • 1967 Redefinition of the second in terms of caesium
  • 1975 Proposals for laser cooling of atoms and ions
  • 1978 Laser cooling of trapped ions
  • 1980s GPS satellite navigation introduced
  • 1985 Laser cooling of atoms
  • 1993 First caesium-fountain clock
  • 1999 First optical-frequency measurement with femtosecond combs
  • 2001 Concept of an optical clock demonstrated

John Byrd, BIW2006

mode locked lasers
Mode-locked Lasers

Locking the phases of the laser frequencies yields an ultrashort pulse.

John Byrd, BIW2006

locking modes
Locking modes

Intensities

John Byrd, BIW2006

femtosecond combs
Femtosecond combs

diode detection

John Byrd, BIW2006

example ti sapph mll
Example:Ti:Sapph MLL

Repetition rate given by round trip travel time in cavity. Modulated by piezo adjustment of cavity mirror.

Passive mode locking achieved by properties of nonlinear crystal

Modern commercial designs include dispersion compensation in optics

Comb spectrum allows direct link of microwave frequencies to optical frequencies

John Byrd, BIW2006

self referencing stabilizer
Self-referencing stabilizer

CEO frequency can be directly measured with an octave spanning spectrum and stabilized in a feedback loop. This allows direct comparision (and or locking) with optical frequency standards.

John Byrd, BIW2006

master oscillator passively mode locked er fiber lasers
Master Oscillator: Passively Mode-Locked Er-fiber lasers

Ippen et al. Design: Opt. Lett. 18, 1080-1082 (1993)

  • diode pumped
  • sub-100 fs to ps pulse duration
  • 1550 nm (telecom) wavelength for fiber-optic component availability
  • repetition rate 30-100 MHz

John Byrd, BIW2006

master oscillator timing jitter
Master Oscillator Timing Jitter

Agilent Signal Analyzer 5052a

f0=1 GHz

  • Scaled to 1 GHz
  • Limited by photo
  • detection
  • Theoretical limit ~1 fs

Very stable operation

over weeks !

John Byrd, BIW2006

why fiber transmission
Why fiber transmission?
  • Fiber offers THz bandwidth, immunity from electromagnetic interference, immunity from ground loops and very low attenuation
  • However, the phase and group delay of single-mode glass fiber depend on its environment
    • temperature dependence
    • acoustical dependence
    • dependence on mechanical motion
    • dependence on polarization effects
  • These are corrected by reflecting a signal from the far end of the fiber, compare to a reference, and correct fiber phase length.
  • Two approaches: CW and pulsed

John Byrd, BIW2006

slide23

Stabilized fiber link

Frequency-offset Optical Interferometry

Principle: Heterodyning preserves phase relationships

1 degree at optical = 1 degree RF

1 degree at 110 MHz = 0.014 fsec at optical

Gain 105 leverage over RF-based systems in phase sensitivity

Technique used at ALMA

64 dishes over 25 km footprint, 37 fsec requirement

John Byrd, BIW2006

detailed configuration
Detailed configuration

Control channel

Monitor channel

  • Phase errors,drifts in 110 MHz RF circuits insignificant
  • Reflections along fiber don't contribute: only frequency-shifted reflection beats with outgoing laser line to produce error signal
  • Low power cw signals, linear system, commodity hardware

John Byrd, BIW2006

drift results
Drift Results

Compare phase at the end of fiber with reference to establish stability.

Measure slow drift (<1 Hz) of fiber under laboratory conditions

Compensation for several environmental effects results in a linear drift of 0.13 fsec/hour and a residual temperature drift of 1 fsec/deg C.

Lab AC cycle

Environmental factors

  • Temperature: 0.5-1 fsec/deg C
  • Atmospheric pressure: none found
  • Humidity: significant correlation
  • Laser Wavelength Stabilizer: none
  • Human activity: femtosecond noise in the data

John Byrd, BIW2006

laser standard clock
Laser Standard Clock
  • Laser provides absolute standard for length of transmission line
    • Narrow-line (2 kHz) Koheras Laser (coherence length > 25 km)
    • For single fringe stabilization over 150 m, laser frequency must be stabilized to better than 1:108
    • Use frequency lock with acetylene cell

Frequency lock loop on acetylene (C2H2) 1530.3714 nm absorption line

John Byrd, BIW2006

thermal control of critical components
Thermal control of critical components

Peltier Coolers

Baseplate

Aluminum Chamber

Some components

Complete

Insulating Jacket

John Byrd, BIW2006

rf signal transmission
RF signal transmission

RF (S-band) may be modulated directly onto the optical carrier with a zero-chirp Mach-Zehnder modulator and recovered directly at the far end of the fiber. Any modulation pattern is acceptable.

Critical to minimize added phase noise at demodulation. Modulation of CW carrier has signal S/N advantages over pulsed modulation.

John Byrd, BIW2006

an advantage of am
An advantage of AM

pulse train spectrum

RF out

optical in

f

150ps

t

100MHz

T

two methods

3GHz

1/f

  • Diode has an average current limit before saturation
    • At saturation, high frequencies drop in power
  • Diode bandwidth is chosen to be equal to RF frequency, and pulse width is 1/bandwidth
  • For t=150ps, T=10ns and f=3GHz, AM has 15db more power in the transmitted frequency

John Byrd, BIW2006

group and phase velocity correction
Group and Phase Velocity Correction

Interferometric technique stabilizes phase delay at a single frequency . At a fixed T, simple a 1.6% correction for 1 km cable.

Possible fixes: measure group velocity from the differential phase velocity at two frequencies.

Correction can be applied dynamically or via a feedforward scheme.

John Byrd, BIW2006

pulsed distribution system
Pulsed distribution system

Low-noise

microwave

oscillator

low-bandwidth lock

1

4

3

fiber couplers

Optical to RF

sync module

Master laser

oscillator

2

stabilized fibers

Low jitter

modelocked laser

Optical to RF

sync module

5

low-level RF

Optical to optical

sync module

Laser

Demonstration of complete link with ~ 50fs jitter (1-4) and ~ 20fs jitter from (2-4)

John Byrd, BIW2006

stabilized fiber links pulsed
Stabilized Fiber Links: pulsed

PZT-based fiber stretcher

SMF link 500 km

50:50 coupler

Master Oscillator

isolator

OC

coarse

RF-lock

<50 fs

fine cross-

correlator

ultimately < 1 fs

Optical cross correlator enables sub-femtosecond length stabilization,

if necessary

John Byrd, BIW2006

rf transmission over stabilized fiber link
RF-Transmission over Stabilized Fiber Link
  • Passive temperature stabilization of 500 m
  • RF feedback for fiber link
  • EDFL locked to 2.856 GHz Bates master oscillator

John Byrd, BIW2006

rf synchronization module
RF-Synchronization Module

John Byrd, BIW2006

summary so far
Summary so far

RF: Jitter: Dtrms[10Hz,1MHz]

Drift: Dtp-p[>8hours]

Optical: Jitter: Dtrms[10Hz,1MHz]

Comparison of RF phase over independent transmission lines now in progress for CW and pulsed approaches

John Byrd, BIW2006

rf transmission design
RF transmission design
  • RF transmission has looser requirements on jitter
  • LLRF system can integrate between shots to reduce high frequency jitter

John Byrd, BIW2006

synching mode locked lasers
Synching mode-locked lasers

Trep

Trep

slave

master

n*frep

n*frep

BP

BP

ML Laser

m*frep+fceo

n*frep

Df

H

Detection and bandpass filter

carrier/envelope

offset

repetition rate

0

frequency

Shelton (14GHz)

Bartels (456THz)

Shelton et al, O.L. 27, 312 (2002)

Bartels et al, O.L. 28, 663 (2003)

present

work (5THz)

ML Laser

John Byrd, BIW2006

idealized example
Idealized example

80 th harmonic

Achieved 4.3 fsec jitter over 160 Hz BW for 10 seconds.

John Byrd, BIW2006

two frequency synch scheme
Two-frequency synch scheme

m-n2s

m- s

s

s

m- s) - m- s) = 0

m- m) - s- s) = 0

m

m

master

clock

frequency

transmitted

frequencies

synched

laser

}

}

5THz

5THz

Lock two frequencies within the frequency comb separated by 5 THz. For a 1degree error in phase detection, temporal error is <0.6 fsec

John Byrd, BIW2006

two frequency synch layout
Two-frequency synch layout

frep

CW

2

frep

interferometer

CW

1

master

clock

split

interferometer



mux

stabilized fiber

+

interferometer

synched

laser

demux

interferometer

John Byrd, BIW2006

direct seeding laser systems
Direct seeding laser systems

Amplification to high energy at low repetition frequency

a) All fiber: ~1 J @ 1550 nm

b) Grating compressor: ~10 J @ 1550 nm

c) OPCPA: ~100 J – 1mJ @ 1550 nm

pump coupler

air-core photonic crystal fiber (< 1 uJ)

input pulse

a) 1 uJ, ~100 fs

Er-doped fiber

stretcher fiber

b) 10 uJ, ~100 fs

975 nm pump diode

bulk grating compressor (high energy)

c) 100mJ-1mJ, ~20 ps

OPCPA

1 um, 1mJ, 20ps

Regen. Ampl.

John Byrd, BIW2006

PPLN

conceptual system design
Conceptual system design
  • Laser synch for any popular modelocked laser
  • RF transmission via modulated CW, and interferometric line stabilization
  • RF receiver is integrated with low level RF electronics design

John Byrd, BIW2006

details details
Details, details…
  • Actual performance depends on many technical details:
  • thermal and acoustic environment of cable layout
  • design of feedback loops
    • gain limited by system poles (i.e. resonances in the system)
    • multiple audio BW feedback loops suggests flexible digital platform
    • feedback must deal with drift and jitter (separate loops?)
  • AM/PM conversion in photodiode downconversion

John Byrd, BIW2006

example menlo edfl
Example: Menlo EDFL

plate

piezo

mirror

motorized stage

old

new

amplitude

  • Piezo driven cavity end mirror controls reprate
  • Was a 10mm long piezo on a light Al plate
  • Replaced with 2mm piezo on steel plate

phase

John Byrd, BIW2006

am to pm conversion in a photodiode
AM-to-PM conversion in a photodiode

var.

atten.

CW

laser

modulator

var.

delay

EDFA

1.1Vpp

power

meter

network analyser

  • Measured at 3GHz using a network analyser
  • Modulation was 100% AM on 1530nm CW carrier
  • From 1mW to 0.5mW on a 15GHz photodiode, phase shift was 87fs/mW
  • In this test, phase noise from 10Hz to 3kHz was 92fs p-p. The noise was averaged over 100ms to determine AM/PM shift
  • CW power stability through 100m fiber <10% p-p variation over 16h (low polarization dependent loss)
    • This variation results in 8.7fs p-p
  • Conclusion: for RF transmission, AM-to-PM is not an issue

John Byrd, BIW2006

measurement techniques
Measurement techniques
  • How do we characterize the achieved synchronization on the electron or photon beam?
  • Use “classic” approaches:
    • time to angle or position
    • time to frequency
    • time to amplitude
  • Deflecting cavity
  • Electro-optic sampling
  • Streak camera
  • Laser tagging
  • X-ray/laser cross correlator

John Byrd, BIW2006

time to position
Time to Position

RF

‘streak’

2.44 m

V(t)

sy

e-

sz

D 90°

bc

bp

Electron bunch measurements using a transverse RF deflector

P. Emma

S-band

V0 20 MV

sz 50 mm, E 28 GeV

John Byrd, BIW2006

eo sampling
EO Sampling

Electro-Optic Sampling encodes electron pulse shape on a laser pulse

A. Cavalieri

EO Crystal

John Byrd, BIW2006

slide49

time

polarizing

beamsplitter

integrated intensity

time; space

time

integrated intensity

John Byrd, BIW2006

slide50

EOS data from SPPS

A. Cavalieri

Timing Jitter Data

(20 Successive Shots)

Single-Shot

w/ high frequency filtering

iCCD counts

shot

time (ps)

color representation

time (ps)

John Byrd, BIW2006

x ray streak camera
X-ray streak camera

V

time

View from side

Photocathode

Streaked image

Magnetic lens

2-D Detector

Time

X-rays

Sweep

Space

Sample

Anode Mesh)

View from top

Voltage gradient

on deflector 5V/psec

Space

Time

Electron guns with a twist!

Convert time to vertical deflection

  • Deflection triggered by synchronous laser.
  • Each image uses 3rd harmonic laser fiducial.

John Byrd, BIW2006

spps sc and eo measurements
SPPS SC and EO Measurements

SC and EO sampling measurements show good correlation.

Measurement of centroid can be done to higher resolution than separating time events. Good for relative timing measurement.

John Byrd, BIW2006

laser tagging
Laser tagging

imprint optical pattern on beam

allows adoption of many optical pulse characterization techniques:

FROG, GRENOUILLE, SPIDER, etc.

John Byrd, BIW2006

attosecond measurements
Attosecond measurements!

R. Kienberger, et al., Nature 427, 26 February 2004

Optical field modifies energy spectrum of ionized electrons

Requires very fine synchronization of x-rays and laser.

Techniques like these are the Rosetta stone for understanding

FEL performance.

John Byrd, BIW2006

summary
Summary
  • Accelerators are ready to take advantage the revolution in optical metrology
    • femtosecond lasers can be synchronized to RF oscillators
    • distribution links can be (optically) stabilized to fsec level
    • results expected soon in synching remote mode-locked lasers
  • Fiber-based systems under development
    • TTF-DESY
    • LCLS
    • FERMI/Sincrotrone Trieste
    • All subsequent 4th generation light sources
    • Applications for large machines (ILC)
  • Synchronization diagnostics have a bright future

John Byrd, BIW2006

slide56

If we share this nightmare

Then we can dream

Spiritus mundi

If you act as you think

The missing link

Synchronicity

We know you, they know me

Extrasensory

Synchronicity

A star fall, a phone call

It joins all

Synchronicity

It's so deep, it's so wide

You're inside

Synchronicity

Effect without cause

Sub-atomic laws, scientific pause

Synchronicity

With one breath, with one flow

You will know

Synchronicity

A sleep trance, a dream dance

A shaped romance

Synchronicity

A connecting principle

Linked to the invisible

Almost imperceptible

Something inexpressible

Science insusceptible

Logic so inflexible

Causally connectable

Yet nothing is invincible

Thank you for your attention

John Byrd, BIW2006