Transcript Progress in femtosecond timing distribution and synchronization for ultrafast light sources

John Byrd
Progress in femtosecond
timing distribution and
synchronization for ultrafast
light sources
John Byrd
Lawrence Berkeley National Laboratory
Fermi internal review. Nov 2005
page 1
Acknowledgements
John Byrd
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John Staples, LBNL
Russell Wilcox, LBNL
Larry Doolittle, LBNL
Alex Ratti, LBNL
Franz Kaertner, MIT
Omar Illday, MIT
Axel Winter, DESY
Paul Emma, SLAC
4 May 2006
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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
John Byrd, BIW2006
John Byrd
A great intro to fsec lasers
Femtosecond Optical
Frequency Comb:
Principle, Operation and
Applications
Jun Ye (Editor), Steven T.
Cundiff (Editor)
4 May 2006
John Byrd, BIW2006
Synchronicity
John Byrd
• 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.
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Photocathode laser to gun RF
FEL seed laser to user laser
Relative klystron phase
Electro-optic diagnostic laser to user laser
Master
PC drive laser
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
FEL seed laser
user laser
EO laser
LLRF
4 May 2006
John Byrd, BIW2006
Overview
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• Motivation: LCLS example
• Ultrastable clocks
• Stabilized distribution links
• Synchronizing techniques
• Measuring synchronization
4 May 2006
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Lots of FEL activity
John Byrd
4 May 2006
John Byrd, BIW2006
Small things
John Byrd
100 femtoseconds
= 100x10-15 sec
= 30 microns
= 0.8 [email protected] GHz
= 0.045 [email protected] GHz
= 1.8 mrad@2856 MHz
= 0.1 deg@2856 MHz
= (10 TeraHertz)-1
= 20*(1.5 micron)
4 May 2006
A gnat’s ass
John Byrd, BIW2006
Motivation: LCLS
John Byrd
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Critical LCLS Accelerator
Parameters
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)
P. Emma
(stability specifications quoted as rms)
4 May 2006
John Byrd, BIW2006
John Byrd
Electron Bunch Compression
d  DE/E
d
s zi
d
‘chirp’
z
z
sdi
V = V0sin(kz)
RF Accelerating
Voltage
4 May 2006
undercompression
z
sz
Dz = R56d
Path-Length EnergyDependent Beamline
John Byrd, BIW2006
P. Emma
Compression Stability
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d
d
Df
z
RF phase jitter becomes bunch length jitter…
Compression factor:
P. Emma
4 May 2006
John Byrd, BIW2006
LCLS Machine Schematic
John Byrd
6 MeV
sz  0.83 mm
sd  0.05 %
250 MeV
sz  0.19 mm
sd  1.6 %
Linac-X
L =0.6 m
rf= -160
4.30 GeV
sz  0.022 mm
sd  0.71 %
135 MeV
sz  0.83 mm
sd  0.10 %
rf
gun
Linac-1
L 9 m
rf  -25°
Linac-0
L =6 m
21-1b
21-1d
...existing linac
DL1
L 12 m
R56 0
3 klystrons
X
Linac-2
L 330 m
rf  -41°
Linac-3
L 550 m
rf  0°
21-3b
24-6d
25-1a
30-8c
BC1
L 6 m
R56 -39 mm
BC2
L 22 m
R56 -25 mm
1 X-klys.
1 klystron
26 klystrons
SLAC linac tunnel
4 May 2006
13.6 GeV
sz  0.022 mm
sd  0.01 %
John Byrd, BIW2006
undulator
L =130 m
45 klystrons
LTU
L =275 m
R56  0
research yard
P. Emma
Phase, Amplitude, and Charge Sensitivities
John Byrd
parameter |DE/E0| = 0.1%
1.6
Dti
46
DQ/Q0
3.5
Df0
0.32
DV0/V0
0.32
Df1
0.29
DV1/V1
5.5
DfX
2.0
DVX/VX
0.54
Df2
1.1
DV2/V2
0.35
Df3
0.15
DV3/V3
4 May 2006
|DI/I0| = 12%
4.4
5.2
0.65
0.24
0.17
0.25
1.4
1.2
0.21
1.0
24.8
5.7
John Byrd, BIW2006
|Dtf| = 100 fs
1.5
24
5.9
0.95
1.0
0.78
7.6
6.3
0.084
0.13
15
8.6
unit
psec
%
deg-S
%
deg-S
%
deg-X
%
deg-S
%
deg-S
%
P. Emma
Optical metrology
John Byrd
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
4 May 2006
John Byrd, BIW2006
John Byrd
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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
4 May 2006
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Mode-locked Lasers
John Byrd
Locking the phases of the laser frequencies yields an ultrashort pulse.
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John Byrd, BIW2006
Locking modes
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Intensities
4 May 2006
John Byrd, BIW2006
Femtosecond combs
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diode detection
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John Byrd, BIW2006
John Byrd
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
4 May 2006
John Byrd, BIW2006
John Byrd
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.
4 May 2006
John Byrd, BIW2006
Master Oscillator: Passively Mode-Locked Er-fiber lasers
John Byrd
Ippen et al. Design:
Opt. Lett. 18, 10801082 (1993)
•diode pumped
•sub-100 fs to ps pulse duration
•1550 nm (telecom) wavelength for fiber-optic component availability
•repetition rate 30-100 MHz
4 May 2006
John Byrd, BIW2006
Master Oscillator Timing Jitter
John Byrd
Agilent Signal Analyzer 5052a
f0=1 GHz




Scaled to 1 GHz
Limited by photo
detection
Theoretical limit ~1 fs
Very stable operation
over weeks !
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John Byrd, BIW2006
John Byrd
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
4 May 2006
John Byrd, BIW2006
Stabilized fiber link
John Byrd
Frequency-offset Optical Interferometry
Technique used at ALMA
64 dishes over 25 km
footprint, 37 fsec requirement
4 May 2006
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
John Byrd, BIW2006
John Byrd
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
signals, linear system, commodity
hardware
4 Maycw
2006
John
Byrd, BIW2006
Drift Results
Compare phase at the end
of fiber with reference to
establish stability.
Measure slow drift (<1 Hz)
of fiber under laboratory
conditions
Digital and Analog Phase Detector Comparison
1.5
0.5
0.0
-0.5
-1.0
-1.5
-2.0
-2.5
4 May 2006
Lab AC
cycle
-3.0
-3.5
0.0
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.
HP8405A
SR560
1.0
Phase Detector Output (fsec)
John Byrd
2.5
5.0
7.5
10.0
12.5
15.0
17.5
20.0
22.5
Hours, 24 Oct 2005
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
John Byrd,
BIW2006
data
Laser Standard Clock
John Byrd
•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
4 May 2006
John Byrd, BIW2006
Thermal control of critical components
John Byrd
Peltier
Coolers
Baseplate
Aluminum Chamber
Some
components
Complete
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John Byrd, BIW2006
Insulating Jacket
RF signal transmission
John Byrd
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.
4 May 2006
John Byrd, BIW2006
An advantage of AM
John Byrd
pulse train spectrum
RF out
optical in
150ps
t
100MHz
T
f
two methods
3GHz
t
Pn  Pav
T
1/f
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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
4 May 2006
John Byrd, BIW2006
Group and Phase Velocity Correction
John Byrd
1.48
ng  n p  
1.475
1.47
index of refraction
Interferometric technique
stabilizes phase delay at
a single frequency . At a
fixed T, simple a 1.6%
correction for 1 km cable.
dn p
d
1.465
np(w)
1.46
ng(w)
1.455
1.45
Possible fixes: measure
group velocity from the
differential phase velocity
at two frequencies.
1.445
1.44
600
800
Correction can be applied
dynamically or via a
feedforward scheme.
4 May 2006
John Byrd, BIW2006
1000
1200
wavelength, nm
1400
1600
John Byrd
Pulsed distribution system
Low-noise
microwave
oscillator
low-bandwidth
lock
1
4
3
fiber
couplers
Master laser
oscillator
Optical to RF
sync module
stabilized
fibers
2
Low jitter
modelocked laser
Optical to RF
sync module
low-level RF
5
Optical to optical
sync module
Laser
Demonstration of complete link with ~ 50fs jitter (1-4) and ~ 20fs jitter from (2-4)
4 May 2006
John Byrd, BIW2006
John Byrd
Stabilized Fiber Links: pulsed
Master Oscillator
isolator
50:50
coupler
PZT-based
fiber
stretcher
SMF link
500 km
OC
<50 fs
ultimately < 1 fs
coarse
RF-lock
fine crosscorrelator
Optical cross correlator enables sub-femtosecond length stabilization,
if necessary
4 May 2006
John Byrd, BIW2006
RF-Transmission over Stabilized Fiber Link
John Byrd
• Passive temperature
stabilization of 500 m
• RF feedback for
fiber link
• EDFL locked to
2.856 GHz Bates
master oscillator
4 May 2006
John Byrd, BIW2006
RF-Synchronization Module
John Byrd
4 May 2006
John Byrd, BIW2006
Summary so far
John Byrd
RF: Jitter: Dtrms[10Hz,1MHz]
Optical: Jitter: Dtrms[10Hz,1MHz]
Characteristic
Drift: Dtp-p[>8hours]
CW
Pulsed
RF-RF
Transmission
Jitter: <13fs 10Hz-1kHz
Drift: <50 fs over 24h
Jitter: 50fs
Drift: <50fs up to 10s
Link Stability
Jitter: 0.2 fs
Drift: 1fs/8 hours
(Phase stability)
Jitter: <22fs
Drift: < 2fs up to 10s
Opt. X-Corr:
< 0.5fs > 12 hours
Comparison of RF phase over independent transmission
lines now in progress for CW and pulsed approaches
4 May 2006
John Byrd, BIW2006
John Byrd
RF transmission design
• RF transmission has looser requirements on jitter
• LLRF system can integrate between shots to reduce
high frequency jitter
4 May 2006
John Byrd, BIW2006
John Byrd
Synching mode-locked lasers
Trep
master
n*frep
n*frep
BP
BP
ML Laser
Df
slave
ML Laser
H
Detection and
bandpass filter
carrier/envelope
offset
repetition rate
0
Trep
m*frep+fceo
n*frep
frequency
Shelton (14GHz)
Bartels (456THz)
Shelton et al, O.L. 27, 312 (2002)
Bartels
et2006
al, O.L. 28, 663 (2003)
4 May
John Byrd, BIW2006
present
work (5THz)
Idealized example
John Byrd
80 th harmonic
Achieved 4.3 fsec jitter over 160 Hz BW for 10 seconds.
4 May 2006
John Byrd, BIW2006
John Byrd
Two-frequency synch scheme
1m
master
clock
m
frequency
transmitted
frequencies
m-s
1m- 1s
synched
laser
1s
s
1m- 1s) - m- s) = 0
4 May 2006
5THz
}
}
1m- m) - 1s- s) = 0
John Byrd, BIW2006
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
Two-frequency synch layout
frep
interferometer
master
clock
CW
1
split
interferometer
CW
2
D
mux
+
frep
synched
laser
interferometer
demux
stabilized fiber
interferometer
4 May 2006
John Byrd, BIW2006
John Byrd
Direct seeding laser systems
Amplification to high energy at low repetition frequency
a) All fiber: ~1 mJ @ 1550 nm
b) Grating compressor: ~10 mJ @ 1550 nm
c) OPCPA: ~100 mJ – 1mJ @ 1550 nm
pump
coupler
input pulse
stretcher
fiber
Er-doped
fiber
air-core photonic
crystal fiber (< 1 uJ)
b) 10 uJ, ~100 fs
975 nm
pump diode
bulk grating
compressor
(high energy)
OPCPA
1 um, 1mJ, 20ps
4 May 2006
a) 1 uJ, ~100 fs
Regen. Ampl.
John Byrd, BIW2006
PPLN
c) 100mJ-1mJ,
~20 ps
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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
4 May 2006
John Byrd, BIW2006
Details, details…
John Byrd
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
4 May 2006
John Byrd, BIW2006
Example: Menlo EDFL
John Byrd
piezo
mirror
old
plate
amplitude
motorized stage
• Piezo driven cavity end
mirror controls reprate
• Was a 10mm long piezo on
a light Al plate
• Replaced with 2mm piezo
on steel plate
4 May 2006
new
John Byrd, BIW2006
phase
AM-to-PM conversion in a photodiode
John Byrd
CW
laser
var.
atten.
modulator
1.1Vpp
EDFA
var.
delay
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
4 May 2006
John Byrd, BIW2006
John Byrd
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
4 May 2006
John Byrd, BIW2006
Time to Position
John Byrd
Electron bunch measurements using a
transverse RF deflector
P. Emma
RF
‘streak’
2.44 m
V(t)
e-
sz
S-band
V0  20 MV
sz  50 mm, E  28 GeV bc
4 May 2006
sy
D  90°
John Byrd, BIW2006
bp
EO Sampling
John Byrd
Electro-Optic Sampling encodes electron
pulse shape on a laser pulse
A. Cavalieri
EO Crystal
k
k
k
v
4 May 2006
John Byrd, BIW2006
v
v
time
John Byrd
polarizing
beamsplitter
integrated intensity
time
time; space
klaser
integrated intensity
4 May 2006
John Byrd, BIW2006
200 m m
John Byrd
EOS data from SPPS
A. Cavalieri
Single-Shot
w/ high frequency filtering
Timing Jitter Data
(20 Successive Shots)
shot
iCCD counts
time (ps)
color representation
4 May 2006
time (ps)
John Byrd, BIW2006
X-ray streak camera
View from side
Photocathode
Magnetic lens
2-D Detector
Streaked image
Sweep
Time
John Byrd
X-rays
Space
Sample
Voltage gradient
on deflector 5V/psec
View from top
Space
Anode Mesh)
Time
V
time
•Deflection triggered by
synchronous laser.
•Each image uses 3rd harmonic
laser fiducial.
4 May 2006
Electron guns with a twist!
Convert time to vertical
deflection
John Byrd, BIW2006
SPPS SC and EO Measurements
John Byrd
1.5
streak
eo
1.0
1.0
0.5
Streak-jitter (ps)
Jitter (ps)
0.5
0.0
-0.5
0.0
-0.5
-1.0
-1.0
-1.5
0
1000
2000
3000
4000
5000
-1.0
-0.5
0.0
0.5
1.0
EO-jitter (ps)
Shot number
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.
4 May 2006
John Byrd, BIW2006
Laser tagging
John Byrd
imprint optical pattern on beam
allows adoption of many optical pulse characterization techniques:
FROG, GRENOUILLE, SPIDER, etc.
4 May 2006
John Byrd, BIW2006
John Byrd
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.
4 May 2006
John Byrd, BIW2006
Summary
John Byrd
• 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
4 May 2006
John Byrd, BIW2006
John Byrd
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
4 May 2006
Thank you for
your attention
John Byrd, BIW2006
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