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www.rle.edu
Large-Scale and Long-Term Stable Timing Distribution For Free-Electron Lasers
and Terahertz-Driven Linear Accelerators
Franz X. Kärtner Center for Free-Electron Laser Science (CFEL), DESY, Hamburg, Germany
Ultrafast Optics and X-Rays Division
Department of Physics and The Hamburg Center for Ultrafast Imaging,
University of Hamburg, Germany and
Department of Electrical Engineering and Computer Science and
Research Laboratory of Electronics, MIT, USA
BIOXFEL: January 14, 2015
Acknowledgement
Students:
Kemal Safak, Aram Kalaydzyan,
Michael Peng, Patrick Callahan, Ravi Koustuban, Ronny Huang,
Sergio Carbajo, Jan Schulte, Anne-Laure Calendron, Frederike Ahr
Postdocs:
Ming Xi, Amir Nedjadmalayeri, Emilio Nanni, Xiaojun Wu, Damian Schimpf,
Huseyin Cankaya, M. Hemmer, F. Reichert
Research Scientists: Kyung-Han Hong, Luis Zapata, Oliver Mücke
Collaborators:
OFS: Eric Monberg, Man Yan,
Lars Grüner-Nielsen,
John Fini
Contributors:
DESY: Holger Schlarb and Cezary Sydlo
CFEL: Dwayne Miller
2
3
Outline
Progress in timing distribution for X-ray FELs
Timing jitter of femtosecond lasers
Timing distribution over stabilized fiber links
km-scale sub-fs timing (European XFEL)
Compact: Terahertz-driven linear accelerators
Motivation
Efficient THz generation
Demonstration of THz acceleration
X-Ray FELs operating and under construction
4
LCLS 2009 FERMI 2010
European XFEL 2016
SACLA 2011
5
Free-electron laser schematic
Today long-term sub-10 fs synchronization over entire facility desired.
300 m - 3 km
Tomorrow sub-fs synchronization will be required.
fs x-ray
pulses
Seeding with various schemes demonstrated!
X-ray crystallography
6 H. Chapman, et al. Nature 470, 73, 2011
Optical
Pump
X-ray
Probe
(time resolved)
Imaging before destruction Molecular movie
7
Pulse femtosecond timing distribution
J. Kim et al, FEL 2004.
fs x-ray
pulses
Other approaches: R. Wilcox, LBNL,
cw-distribution, or post stamping
Timing and synchronization
8
Kilometer – Scale Facilities
with
Femtosecond Lasers
9
10 -6
Femtosecond Laser
TR
time
t
Dt
Optical Cavity
Electronic Oscillator
time
am
plitu
de
T0 Dt
Timing jitter of femtosecond lasers
J. Kim et al., Laser & Phot. Rev., 1–25 (2009).
H. A. Haus et al., IEEE JQE 29, 983 (1993).
10 -4
kTc 50~
2 2 1 cML
pulse cav
dt
dt W
t
t D
pulse width
~100fs
ħωc = photon energy
Dissipation-Fluctuation
Theorem
2 2
0
mod
1RF
e cav
d kTt T
dt W t D
cavity
lifetime
period
~100ps
kT = thermal energy
How do we measure low jitter?
10
Sensitive Time Delay Measurements
by
Balanced Optical Cross Correlation
Single-crystal balanced cross-correlator
11
Reflect fundamental
Transmit SHG Transmit fundamental
Reflect SHG
Type-II phase-matched PPKTP crystal
J. Kim et al., Opt. Lett. 32, 1044 (2007)
T. Schibli et al, OL 28, 947 (2003)
Single-crystal balanced cross-correlator
12
In comparison:
Typical microwave mixer
Slope ~1 mV/fs @ 10 GHz
Greatly reduced thermal drifts!
80 pJ, 200 fs
1550nm input pulses
at 200 MHz rep. rate
Timing jitter of fiber lasers
13
Modelocked
Laser 1
Modelocked
Laser 2
HWP
PBS Single crystal
balanced
cross-
correlator
Oscilloscope
RF-pectrum
analyzer
-1
0
1
-800 0 800
Time delay (fs)D
ete
cto
r outp
ut
(V)
Loop
filter
J. Kim, et al. , Opt. Lett. 32, 3519 (2007).
Phase detector method Timing Detector method
Timing jitter of OneFive:Origami Laser
14
1k 10k 100k 1MFrequency (Hz)
Jitte
r S
pe
ctr
al D
en
sity (
fs2/H
z)
10-9
Ph
ase
No
ise
@ 1
0G
Hz (
dB
c/H
z)
-180
10-7
10-5
10-3
-160
-140
-120
Inte
gra
ted
Jitte
r a
t [f,1
MH
z] (f
s)
0
0.1
0.2
0.3
f>15
kHz
Two 10-fs Ti:Sapphire lasers synchronized within 13 as
15
13 as
Ref @ 10 GHz
A. Benedick, et al. Nat. Ph. 6, 97-100, 2012
16
Timing - Stabilized
Fiber Links
17
Timing-stabilized fiber links
PZT-based fiber
stretcher
Mode-locked laser
Fiber link ~ several
hundreds meters
to a few kilometers
SMF/DCF
isolator
Timing
Comparison Faraday
rotating
mirror
Cancel fiber length fluctuations slower than the pulse travel time (2nL/c).
1 km fiber: travel time = 10 μs ~100 kHz BW
1-week operation with SMF/DCF
18
0 50 100 150-5
0
5
10
15
20
25
Tim
ing
Lin
k D
rift
(fs
)
Time (hours)0 50 100 150
-15
-10
-5
0
5
10
15
Fib
er
Flu
ctu
ati
on
s (
ps)
Timing Link System Performance
5 fs (rms) drifts over one week of operation
FLASH, FERMI, and tests at PAL and LCLS
Jointly with idestaQE
19
Clocking the European XFEL
3.5 km
Injector laser Probe laser
M. Y. Peng et al. Opt. Exp. 21, 19982 (2013).
High precision PM-link developed jointly with OFS
Dispersion-compensating PM Fiber
D = -102.5 ps/nm∙km @1550nm, slow axis
D’ = -0.33 ps/nm2∙km, slow axis Splice
Fiber 1
Std. PM 1550
Length: 4m
Fiber 2
Std. PM 1550
Length: 2946m
Fiber 3
Bridge Fiber
Length: 2m
Fiber 4
PM DCF
Length: 511m
Fiber 5
Bridge Fiber
Length: 2m
Fiber 6
Bridge Fiber
Length: 19m
Fiber 7
Std. PM 1550
Length: 3m
20
Europen XFEL PM-link test bed
21
High precision PM-link results
3.5 km
Injector
laser Probe laser
0 4 8 12 16 20 24 28 32-1
-0.5
0
0.5
1
Ou
tlo
op
Drift (
fs)
36 40 44
0 4 8 12 16 20 24 28 32Time (hours)
36 40 4444
45
46
47
50
Re
l.T
em
pe
ratu
re (
K)
-0.6
-0.4
-0.20
0.6
Re
l. H
um
idity (
%)
0.2
0.4
48
49
Laser-to-Laser Remote Synch.: 100 as RMS & 0.6 fs Pk-Pk drift (< 1Hz) over 44 h
M. Xi et al. Opt. Exp. 22, 14904 (2014)
Compact: THz driven linear accelerator
22
• High-gradient accelerators: reduced size and improved
electron beam quality
• Increasing operational frequency: reduced pulse energy ~ V3, pulsed heating, breakdown and average power load
• Optical THz generation: Commercial IR laser: 20 MW THz
• Proof of concept: accelerate 60 keV electrons with THz pulse
THz LINAC
Nanni, E.A., et al. arXiv preprint arXiv:1411.4709 (2014).
Other Work
23
Peralta, E. A., et al., Nature 503.7474 (2013): 91-94. Thompson, M. C., et al., Phys. Rev.
Lett. 100.21 (2008): 214801.
Laser-Driven Acceleration
Demonstrated 190 MV/m
Dielectric Wakefield Acceleration
Demonstrated 5.5 GV/m
Single cycle THz pulse (~2 ps) centered at 0.45 THz
From a 1 mJ commercial regenerative amplifier
10 µJ pulse measured ~1 m from source (1 % 2 %)
Electric Field from EO Sampling Transverse Intensity Profile
Efficient THz Generation
S.-W. Huang et al., Opt. Lett. 38:(5), 796-798 (2013). 24
Dielectrically Loaded Metal Waveguide
25
Traveling wave structure: best for coupling broad-
band single cycle pulse
Phase-group-velocity matching: THz-phase to
electron velocity with thickness of dielectric
Dispersion Relation
w/ dielectric
w/o dielectric
Copper Inner Diameter = 940 µm
Fused Silica Inner Diameter = 400 µm
~1-5 cm
L.J. Wong et al., Opt. Exp. 21, 9792 (2013).
26
DC Ceramic
UV Input
Focusing Solenoid
THz Input
MCP
Zoom Next Slide
DC Gun and THz LINAC (D. Miller)
Steering Dipole
27
DC Gun and THz LINAC
THz Input
THz LINAC
60 kV DC Bias
Electron Beam Tunnel
100 µm Pinhole
Aperture
UV Input
Focusing Solenoid
10 mm
28
MCP Image of Accelerated Beam
Signal integrated over 3 sec. with 1 kHz repetition rate
Alignment with co-propagating guide laser
Temporal scans to optimize timing
THz Off THz On
29
Energy Spectrum
Measured energy spectrum for 59 keV start energy
Modeled on-axis gradient of 4.9 MeV/m
Electron bunch σz = 45 µm
THz Off THz On
www.cfel.de
www.rle.edu
Ralph Assmann
DESY, Hamburg
Petra Fromme
Arizona State
University, DESY
Franz Kärtner
DESY, CFEL and
University of Hamburg
Henry Chapman
DESY, CFEL and
University of Hamburg
Frontiers ERC Synergy Grant: Open Positions MSU
& Assoc. Scientists from Mid-Sweden University,
DESY and MIT
Frontiers in Attosecond X-ray Science:
Imaging and Spectroscopy
AXSIS
Frontiers in Attosecond X-ray Science:
Imaging and Spectroscopy
AXSIS
1
_MG_1344 _MG_1346
_MG_1355 _MG_1360
Summary
31
km-scale sub-fs timing distribution with PM-fiber links
Compact Terahertz-driven linear electron acceleration
THz Off THz On
Laser-to-Laser Remote Synch.: 100 as RMS & 0.6 fs Pk-Pk over 44 h
3.5 km
Injector
laser Probe laser
Thank You!
