generation of femtosecond x-ray pulses from the advanced ......(femto – 10-15) (atto – 10-18)...
TRANSCRIPT
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RWS Sept. 2006
Robert W. Schoenlein
Materials Sciences DivisionLawrence Berkeley National Laboratory
Generation of Femtosecond XGeneration of Femtosecond X--ray Pulsesray Pulsesfrom the Advanced Light Sourcefrom the Advanced Light Source
LBNL Instrumentation Colloquium SeriesSept. 6, 2006
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Outline
Scientific Motivation• Structural dynamics in condensed matter on femtosecond time scale• X-ray source requirements and experimental considerations
Generation of Femtosecond X-rays from 3rd Generation Synchrotrons• Manipulation of the stored electron beam with femtosecond laser pulses• Diagnostics (optical gain measurements, coherent THZ generation)• Results from proof-of-principle experiments at the ALS• Future prospects, limitations, practical issues – experimental applications
New Femtosecond X-ray Facility at the Advanced Light Source• Small-gap, in-vacuum undulator• Soft x-ray and hard x-ray branchlines• High average power (high repetition rate) femtosecond laser system
Future Femtosecond X-ray Sources
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fundamental time scale for atomic motionvibrational period: Tvib ~ 100 fs
Atomic Structural Dynamics
• ultrafast chemical reactions
• ultrafast phase transitions
• surface dynamics
• ultrafast biological processes
Ultrafast X-ray ScienceRapidly emerging field of research - Physics, Chemistry and Biology
N
N
Fe
O
Fundamental Time Scales in Condensed Matter
fundamental time scales for electron dynamicselectron-phonon interaction times ~ 1 ps
e-e scattering times ~10 fscorrelation time ~100 attoseconds (a/VFermi)
Electronic Structural Dynamics
• charge transfer
• correlated electron systemscharge/orbital orderingCMRhigh Tc superconductivity
Understanding the interplay between atomic and electronic structure- beyond single-electron band structure model – correlated systems (charge, spin, orbit, lattice) - beyond simple adiabatic potential energy surfaces
• electronic phase transitions
Fundamental Scientific Challenge in Condensed Matter:
(femto – 10-15)
(atto – 10-18)
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Femtosecond Spectroscopy
delay ∆∆∆∆t
samplepump
probe
spectrometer
CCD computer
femtosecondlaser system
∆t
- transmission- reflection- photoemission
~Iprobe(∆t)
- non-linear (probe) ~[Iprobe(∆t)]n
∆t
n-Wave Mixing
harmonic ω1±ω2
- transient four-wave mixing- photon echo
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Rhodopsin - photoreceptor for vision• cis-trans isomerization complete in 200 fs
Structural Dynamics of Ultrafast Biological Processes
• vibrationally coherent
wavelength (nm)
500 550 600 650
-150
33
100
150
200
300
400
3000
6000
dela
y (fs
)
T/T=2%−∆
Schoenlein et al. Science (1991)Wang et al. Science (1994)
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diffraction angle
time delay
time delay
x-ray probe
visible pum
patomic structure in systems with long-range order/periodicityphase transitions, coherent phonons
detector
time-resolved x-ray diffraction
delay
x-ray probe
visible pumpr
energy
time
Kedge
abso
rptio
n
Femtosecond X-ray Science
�
ω
element specificmolecular systems and reactionscomplex/disordered materials
EXAFS – local atomic structure and coordination
NEXAFS – local electronic structure, bonding geometry, magnetization/dichroism
(near-edge x-ray absorption fine structure)
time-resolved x-ray spectroscopy
(extended x-ray absorption fine structure)
surface EXAFS, µµµµEXAFS ….( )( )
2
2sin~)(
krkkr
rfφ+
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FeII Spin-Crossover Molecules
hν
low spin high spin
• ~10-15% increase in metal-ligand bond distances
• trigonal cage distortion?
• electron transfer mechanistic role in biochemical processes (cytochrome P450)
• magnetic and optical storage material
Motivation:• relationship between structure, electronic, and magnetic properties
Do the structural distortions facilitate the spin-crossover reaction?
hν
high-spin state
MLCT(charge-transfer state)
low-spin state
τ~300 fs
1A1g5T2g
∆∆∆∆S=2
(t2g)6 (t2g)4 (eg)2
Fe[tren(py)3]2+
Fe Fe
N
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NN
N
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Fe
N
N
N
N
N
N
Fe(II) Spin-Crossover X-ray Spectroscopy
M. Khalil et al., J. Phys. Chem. (2006)
flowing jet0.5 mm, ~30 mM
Ge crystal mono
chopper(2 kHz)
APDdetector
synchrotron(70 ps, 7.1 keV)
laser75 fs, 400 nm
delay
Time-resolved XAS - ALS Beamline 5.3.1)
∆µ
∆µ
∆µ
∆µ x
10-3
energy (eV)
330 ps delay
1s→→→→3d
1s→→→→4p
0.009
2.15 ±0.03
6.5 ±1
Photoexcited 5T2 (τ = 330 ps)
0.001σ (Å2)
1.94 ± 0.01R (Å)
6 ±0.5N
Reactant1A1 (τ = 0)
k (Å-1)
∆µ
∆µ
∆µ
∆µ x
10-3
τdelay = 330 ps
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Characteristics for Ideal Source
(1) temporal resolution ~ 100 fs
• synchronization to laser trigger
(2) high average flux 108-1013 photons/sec/0.1% BW
(3) tunable 0.3 keV - 10 keV
(4) rep. rate: 100 Hz - 10 kHz
• high average brightness
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MicroprobeMicroprobe
CrystallographyCrystallography
InterferometryInterferometry
MicrofabricationMicrofabrication
MicroscopyMicroscopy
3rd Generation Synchrotrons - Advanced Light Source
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3rd Generation Synchrotrons
electron storage ring:1.9 GeV500 MHz, 400 mA70 ps bunch length
12 straight sections for insertion devices
36 bend magnets
high-brightness sourceof soft x-rays 1-100 Å
wiggler
undulator
bend-magnete-
Line
ar
Acc
eler
ator
booster ring
Advanced Light Source
γθK
horiz ~∆γθ
1~vert∆
NnK 211
~2+∆
γθ
mceB
K Woπ
λ2
=
nNnn 1~
λλ∆
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laser wiggler
bendmagnet
mirrorbeamline x-rays
wiggler
femtosecond electron bunch
bend magnet beamline
70 ps electronbunch
femtosecondlaser pulse
spatial separationdispersive bend
λλλλW
electron-photon interaction in wiggler
femtosecond x-rays
e-beam
Generation of Femtosecond X-rays from the ALS
A. Zholents and M. Zolotorev, Phys. Rev. Lett., 76, 916,1996.
slit
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φωωωωω cos2),(),(~
2
R
LRLRLRL AAAAdSdrErEA ∆
∆++=+
� � ��
N
S
S
NS
SN
Nwiggler - permanent magnets
wiggler radiation
e-λw
laser
laserw
radiated K λγλλ =+= )2/1(2
22
)2/1(2/
2
2
KK
A RR +≅ ωπα
�
Energy Modulation in the Wiggler
total field energy:
wiggler radiated energy:∆E (energy mod)
Elaser
�
ωL = 1.55 eV
∆ωL = 27 period wiggler
� 36 fs laser pulse
AL = 610 µJ
ALS beam energy spread σΕ ~1.9 MeV Eo =1.9 GeVLaser requirements:
mceB
K Woπ
λ2
=0 π/2 π
optical phase
electron beam
∆E
ρ(E)
∆E
accelerated electrons
decelerated electrons
σE – rms energy spread
since σE ~ Eo2 and we want ∆Ε ∼ σEthen the required laser pulse energy
scales as: AL ~ Eo4
∆E ≅ 17 MeV9σE(72 fs)
(780 µJ)
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Dynamics of Modulated Electron Beam
x,E ~100 fs laser pulse~70 ps electron bunch
z,t
x,E
z,t
x,E
z,t
Torbit = 656 ns
tdamp = 6 ms
x,E
z,t
300 fs (BL6.3.2)100 fs (BL5.3.1)
tx-ray
ALS Storage Ring Dispersion
σσσσdispersion ~ 85 fs per full arc(200 fs FWHM)
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Laser Synchrotron Beam Slicing - Layout
WIGGLER (W11)
BACK TANGENT PORT
BEAMLINE 5.3..1
LASER SYSTEM
BL 5.3.1X-RAY HUTCH
LASER TRANSPORT TUBE
SR05 SR04
SR06
PHOTON STOP
ALIGNMENT AND TIMING DIAGNOSTICS
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Laser Gain through Wiggler (FEL Gain)
)()()( field optical total ωωω εε slasertotal e+=)()(2)()()( 222 ωωωωω εεε slaserslasertotal ee ++=
⋅⋅⋅⋅+∆∂
∂+= ωωωωω )()()( ososs
eee
22γλ
λ wigglerradiated = EEdd
r
r
r
r ∆==− 2ωω
λλ
laserε∝∆Ε
( ) ηπγπ ���
�
��
�
= 222 )(sin
22
xx
dxd
I
IMgain
A
peak
o
oMx ωωωπ )( −=
gain
I(t)
time
I(ω)
ω−ωο
laserosss
lasertotal eee εεε ωωξω
ωω
)(2)(2)(
21 22 ++���
���
�
���
�
���
�
Ε∂∂+=2
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Measurement of Laser Gain through Wigglerga
in
λλο λ1λ2
laser spectrumgain function
wiggler
laser
e-beam
IF λ1
IF λ2 +-
( ) laserWradiated K λγλλ =+= 2/12
22
λW
-60 -40 -20 0 20 40 60 80
0
1
2
3
4
5
gain
(x10
-3)
delay (ps)
electron bunch laser pulse
σ = 16.6 ps
720 760 800 840 880
-0.5-0.4-0.3-0.2-0.1
00.10.20.30.40.5
central wiggler emission λe (nm)
gain
(%
)
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CalculatedElectron Density
Distribution
-3σx to +3σx +3σx to +8σx +4σx to +8σx
-1200-1000 -800 -600 -400 -200 0 200
60
80
100
120
140
160
delay (fs)-1200 -1000 -800 -600 -400 -200 0 200
80100120140160180200220240260
delay (fs)-1000 -500 0 500 1000
18001900200021002200
2300240025002600
coun
ts
delay (fs)
-1000 -500 0 500 1000 0
.2
.4
.6
.8
1.0
0
1
2
3
4
-4
-3
-2
-1
time (fs)
x/σσ σσ x
Schoenlein et al., Science, 287, 2237 (2000)
Femtosecond Pulses of Synchrotron Radiation
wiggler
bendmagnet
mirrorbeamline
e-beam
modulated electron bunch
visible synchrotron radiation
Laser System
BBO
�
ωωωω2 = ~2 eV
�
ωωωω1 = 1.55 eV �
ωωωω1+
�
ωωωω2
delay
slit
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CalculatedElectron Density
Distribution
-1000 -500 0 500 1000 0
.2
.4
.6
.8
1.0
0
1
2
3
4
-4
-3
-2
-1
time (fs)
x/σσ σσ x
Femtosecond Pulses of Synchrotron Radiation
195 fs(FWHM)
delay (fs)-800 -600 -400 -200 0 200 400 600 800
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
wigglerbend
magnet mirror
beamlinee-beam
modulated electron bunch
visible synchrotron radiation
Laser System
BBO
�
ωωωω2 = ~2 eV
�
ωωωω1 = 1.55 eV �
ωωωω1+
�
ωωωω2
delay
slit
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Coherent Infrared Radiation from Modulated Electron Bunch
( )2/sin2 θρ=photonAB
ρθ=eAB
24
3θρλ ≈=− Rphotone ABAB
R
oRformation ZL λ
πωρθ2
=≅=
• longitudinal modulation of electron density ~λIR• vacuum chamber aperture must accommodate source divergence (formation length)
2/30
2/1 ωρλ −≤R θ
A B
ωo
ρ
zo zo+λIR
θ
Coherent Synchrotron Radiation
λR ≤ 1.4 mm (ρ = 4 m, ωo = 2 cm)
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Coherent Infrared – Measurement Schematic
bolometer
vacuum windowfused silica
silicon
FTIRSpectrometer
BL5.3.1
e-
J. Byrd, Z. Hao, M. Martin, D. Robin, F. Sannibale, R. Schoenlein, A. Zholents, M. Zolotorev, PRL, 96, 2006
dP/d
ω(µ
W c
m) c
alc.
freq. (cm-1)
Coherent Synchrotron Radiation
-1000 -500 0 500 1000
elec
tric
field
time (fs)
0
-1000 -500 0 500 1000 0
.2
.4
.6
.8
1.0
01234
-4-3-2-1
time (fs)
x/σσ σσ x
e-
~ 1.5 m ~ 3 m
1 cm
∆L ~ 12 µm∆ν ~ 11 cm-1
vacuum window
Coherent IR Detection
Waveguide Effects
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bend magnetsource
1:1 focusing toroid
crystalmonochromator
1000 Åcarbon foil slits
selection offs x-ray pulse
hutch0 m 12 m 24 m
visible light (to hutch)for diagnostics
differential pumping
chopperangular slitse-beam
Femtosecond x-ray Beamline 5.3.1
• 1:1 image of bend magnet source250 µm (H) x 50 µm (V)
• white beam, 0.1-12 keV(possibility for Laue diffraction)
• flux ~1013 ph/sec/0.1% BW (30 ps pulse duration)
flux ~105 ph/sec/0.1% BWbrightness ~108 ph/s/mm2/mrad2/0.1% BW
100 fs pulse duration(5 kHz repetition rate)
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Separation of Femtosecond X-rays
• laser modulation of e-beam energy (∆E)laser power, wiggler matching
• storage ring dispersion (∆E→∆x)emittance and lifetime degradation
• beamline image qualitymirror scattering (non-specular)depth of source effects
Sig (fsec)background > 1
Requirement – gated detectors for isolating individual bunchesavalanche photodiodesgated microchannel plates
laser wiggler
femtosecond electron bunch femtosecond x-rays
e-beam slits
∆E ∆x
L
2 nsec
e-bunch pattern
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2 4 6 8 10 12 140
0.5
1
1.5
2
2.5
3x 10
-4
∆E/σEdN
x/σE
x 10
-4
∆ρ(E) = ρ(E)laser on - ρ(E)laser offModulation: 3σE to 10σE τlaser/τe = 10-3
-10 -5 0 5 10
-10
-8
-6
-4
-2
0
2
4
∆E/σE
dNx/σ
Ex
10-4
Calculated Electron Density Distribution
-1000
01234
-4-3-2-1
-500 0 500 1000 0
.2
.4
.6
.8
1.0
time (fs)
x/σ x
Differential Beam Profiles
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5 mrad
∆x
-0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.510-4
10-3
10-2
10-1
100
∆x (mm)
coun
ts (n
orm
.)
σx = 100 µmλ = 1.2 Å
APD
Si(111)
- fraction of e-beam that is modulated = 75 fs × 0.1 /75 psec = 10-4
σE/∆E=1/10
Beam Profile Measurements – BL5.3.1 Camshaft Bunch
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Femtosecond X-ray Profile Measurements – BL5.3.1
0
20
40
60
80
100
120
140
-1000 -500 0 500 1000∆x (µm)
diffe
renc
e co
unts
−∆Emax=6σE (11.4 MeV)−∆Emax=7σE (13.3 MeV)−∆Emax=8σE (15.2 MeV)
Calculated Electron Density Distribution
-1000
01234
-4-3-2-1
-500 0 500 1000 0
.2
.4
.6
.8
1.0
time (fs)
x/σ x
Peak Laser Power ~ 10 GW(0.8 mJ, 75 fs)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
-1000 -500 0 500 1000∆x (µm)
Sig
nal/b
kg r
atio
Differential Beam Profile (Laser On-Laser Off) Femtosecond Flux / Background
σx = 100 µm
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• mÅ charge displacement – THz phonon-polariton mode in LiTaO3A.Cavalleri et al., Phys. Rev. Lett., 95, 067405, (2005).
• Ultrafast insulator-metal transition in VO2 - XANESA.Cavalleri et al., Phys. Rev. Lett., 95, 067405, (2005).
• Time-resolved EXAFS - spin-crossover transition in Fe[tren(py)3]2+M. Khalil et al., J. Phys. Chem. (in press)
• Bonding Properties of Liquid Silicon and Liquid CarbonS. L. Johnson et al., Phys. Rev. Lett., 94, 057407 (2005)S. L. Johnson et al., Phys. Rev. Lett. 91, 157403 (2003)
• X-ray/laser ionization dynamics in atomic systemsM. Hertlein, A. Belkacem et al.
Science at time-resolved x-ray science beamline (ALS BL5.3.1)
Fe
N
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N
NN
N
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• pulse duration η2 = τlaser / τsynchrotron = 10-3 (τx-ray ≈ 170 fs)(70 fs) (70 ps)
• repetition rate η3 = flaser / fsynchrotron = 2x10-6(1 kHz) (500 MHz)
• flux ~1013 ph/sec/0.1% BW• brightness ~1016 ph/sec/0.1% BW
• flux ~1015 ph/sec/0.1% BW• brightness ~1019 ph/sec/0.1% BW
Bend Magnet Undulator
Femtosecond X-ray Facility – Scaling the X-ray Flux
flaser / fsynchrotron flimit ≈ 3× =150 kHz(40 kHz) (500 MHz)
number of bunchesτdamping
Average Femtosecond X-ray Flux ~ Average Femtosecond Laser Power
• phase factor η1 = 0.1 (fraction of electrons in optimum phase)
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Femtosecond Undulator Beamline – Overview
I. Insertion Device
• small-gap undulator/wiggler (1.5 T, 50 x 3cm period)
III. Laser: average power/repetition rate• 30 W (1.5 mJ per pulse, 20 kHz)
sector 6 - proximity to existing wiggler 200 fs x-rays
x102 increase in flux, x103 increase in brightness
x10 increase in flux
• highest possible flux and brightness 0.2-10 keV
II. Beamlines for Femtosecond X-ray Science
IV. Storage Ring Modifications• local vertical dispersion bump – sector 6 and/or 5
• isolation of femtosecond x-ray, 0.2-2 keV, 2-10 keV
wiggler
mirror
beamline
femtosecondx-rayse-beam
undulator
laser
monochroma
torspectro
graph
bend magnet
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magnetic structurevacuum chamber
In-Vacuum Undulator/Wiggler
SpecificationsMagnetic gap 5.5 mmPeriod 30 mmNo. periods 50Vacuum gap >5 mmBo 1.45 T
S. Marks et al.
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ALS Femtosecond Undulator Beamline 6.0 Layout
soft x-ray branchline(250 eV – 2 keV)
hard x-ray branchline(2-10 keV)
soft x-ray spectrograph
hard x-ray hutchSeparate M1 mirrors for hard and soft x-rays
sample chamber(dispersive soft x-ray)
slits(intermediate focus)
20 kHz choppers
crystal monochromator20 kHz femtosecond
laser system 2x – 30 W
P. Heimann, D. Plate, H. Padmore, R. Duarte, D. Cambie et al.
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ALS Femtosecond Undulator BranchlinesP. Heimann, D. Plate, H. Padmore, R. Duarte, D. Cambie et al.
soft x-ray branch (0.2-2 keV)
Focus: 710 µm (H), 72 µm (V)Focus: 60 µm (H), 37 µm (V)
∆E3000
commissionFall 2006
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X-ray Chopper
• Absorbed x-ray power: ~500 W • Slot dimensions: 3 mm horizontal x 300 mm vertical• Rotating disk, water-cooled, in vacuum – ferro-fluidic feedthroughs• Frequency: 20 kHz matched to laser repetition rate (100 slots at >12,000 RPM)• Synchronization to the laser frequency: allowable phase error 250 ns• LBNL/Rigaku design
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M203
Gratingmono
SampleChamberand slits
M201(behind wall)
First Light10/4/05
Femtosecond Soft X-ray Beamline 6.0.1.2
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Femtosecond Laser System
Electron beam interaction requirements:~1.5 mJ pulse energy, 60 fs FWHM, at ~800 nm20 kHz repetition rate, 30 W average powerdiffraction limited focusing, beam parameter: M2 �1.1
Excitation pump pulses for time-resolved experiments:~1 mJ pulse energy at 800 nm (OPA)60 fs pulse duration, 20 kHz repetition rate~500 ns relative delay
60 fs1.5 mJ
Oscillator Stretcher
Compressor2-Pass Amplifier 0.5 ns
2 mJ 0.5 ns300 µµµµJ
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Femtosecond Laser System
Electron beam interaction requirements:~1.5 mJ pulse energy, 60 fs FWHM, at ~800 nm20 kHz repetition rate, 30 W average powerdiffraction limited focusing, beam parameter: M2 �1.1
Excitation pump pulses for time-resolved experiments:~1 mJ pulse energy at 800 nm (OPA)60 fs pulse duration, 20 kHz repetition rate~500 ns relative delay
Ti:SAPPHIRE RODFARADAY
ROTATOR
Ti:SAPPHIRE ROD
OUTPUT BEAM
INPUT BEAM
HIGH REFLECTOR
PUMP BEAMNd:YLF (2ωωωω)
~90 W, 10 kHz
PUMP BEAMNd:YLF (2ωωωω)
~90 W, 10 kHz
PUMP BEAMNd:YLF (2ωωωω)
~90 W, 10 kHz
PUMP BEAMNd:YLF (2ωωωω)
~90 W, 10 kHz
λλλλ/2 wave plate 77 K
77 K
cryogenic power amplifier
R. Wilcox, R. Schoenlein
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Femtosecond Pulse Compression
Diffraction Grating Compressor Transmission Grating Compressor
Power Densities: 10-100 W/cm2
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Femtosecond X-ray Flux
HHG flux from F. Krausz, laser: 10 fs, 3 mJ/pulse, 30 W
Plasma source flux in mrad2 laser: 40 fs, 1 mJ/pulse, 30 W (continuum includes projected 105 improvement)
103 104
104
105
106
107
108
photon energy (eV)
flux
(ph/
s/0.
1% B
W)
bend magnet flux (150 fs, 1 kHz)
undulator flux (200 fs, 20 kHz)(3 cm period, 1.5 m length, Bmax= 1.5 T)
HHG
plasma Kα
fs plasma continuum
ALS typical average x-ray fluxundulator ~1015 ph/s/0.1% BWbend-magnet ~1013 ph/s/0.1% BW
Cu Kα - 1010 ph/s/4π (proj. 1012 with Hg target)cont. 6x107 ph/s/4π (integ. from 7-8 keV)
300
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Ultrafast X-ray Facilities
• Femtosecond soft x-ray ‘slicing’ beamline – BESSY (operational)
• Femtosecond hard x-ray ‘slicing’ beamline – Swiss Light Source (commissioning)
• Femtosecond x-ray beamline – SOLEIL (planning)
• VUV free electron laser – DESSY (operational)
• X-ray free-electron laser – LCSL SLAC (under construction)
• X-ray free-electron laser – EURO X-FEL Hamburg (planning)
• FERMI@ELETTRA soft x-ray FEL – Trieste (design/construction)
• Soft x-ray FEL – BESSY (planning)
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A. Cavalleri – VO2M. Rini
M. Khalil – Fe(II) Materials Sciences Division
LBNL
P.A. HeimannT.E. GloverH. Padmore
ALS - Experimental Systems GroupLBNL
A. PatersonM. Howells
Z. HaoAdvanced Light Source
LBNL
A. ZholentsM. Zolotorev
Accel. and Fusion Res. DivisionLBNL
R.W. FalconeU.C. Berkeley
C. Steier W. Wittmer
W. WanH. Nishimura
D. RobinALS – Accel. Physics Group
LBNL
D. PlateS. MarksR. Wilcox
R. SchlueterR. DuarteD. Cambie
Engineering DivisionLBNL
Femtosecond Undulator Beamline Development
Acknowledgements