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Robert W. Schoenlein
Materials Sciences DivisionLawrence Berkeley National Laboratory
Ultrafast X-ray Science:A New Frontier for Next Generation Light Sources
SRI 2001 Workshop:Energy Recovery Linac Sources of Synchrotron Radiation
• Developing Research Program in Ultrafast X-ray Science
• Femtosecond x-ray beamline(s) at the Advanced Light Source
C. BresslerM. CherguiU. Lausanne
R. AbelaSwiss Light Source - PSI
R.W. FalconeS. Johnson
A. LindenbergU.C. Berkeley
T. E. GloverP.A. HeimannH.A. Padmore
ALS Berkeley Lab
R.W. SchoenleinA. Cavalleri
H.H.W. ChongC.V. Shank
Materials Sciences Div. LBNL
A.A. ZholentsM.S. Zolotorev
Accelerator and FusionResearch Div. LBNL
A. BelkacemM. Hertlein
M. PriorChemical Sciences Div. LBNL
J. LarssonLund
Scientific Motivation for Ultrafast X-ray Research
Existing third generation synchrotron sources:
Current state of the art from infrared through EUV:modelocked femtosecond lasers and amplifiers
• <10 femtosecond resolution (10-4 tsynch)
• powerful x-ray probes of ‘static’ structure of matter
• optical properties/valence electrons
• indirect probe of structural dynamics
Is there a scientific reason to measure structural changes with femtosecond resolution?
• high flux, high brightness, spectral range (10 eV-100 keV)
• temporal resolution ~100 ps
time-resolved EXAFS, NEXAFS, surface EXAFS
delay
���������
�� �������
diffraction angle
��������
time delay
���������
�� �����
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ordered crystals - phase transitions, coherent phonons
r
energy
���
Kedge
detector
time-resolved x-ray diffraction
� �������
f(r)
complex/disordered materials - chemical reactions
bonding geometrysurface dynamics
fundamental time scale for atomic motionvibrational period: 1/νvib ~ 100 fs
Structural Dynamics in Condensed Matter
• ultrafast chemical reactions
• ultrafast phase transitions
• surface dynamics
• ultrafast biological processes
Rapidly emerging filed of researchPhysics, Chemistry and Biology
Femtosecond X-ray Science
Ultrafast Structural Dynamics in Solids
• solid-solid phase transitions
• order/disorder transitions (melting)
Ultrafast Molecular Dynamics
• structural dynamics of the transition state
• solvent/solute interactions (solvent structure)
Ultrafast Processes in Biology
structural dynamics/reactions at surfaces
magnetization and spin dynamics
Outline
Solid/Liquid Phase Transitions on the Femtosecond Time Scale
Atomic disordering on a time scale of a vibrational period ?
• electron temperature >> lattice temperature
• no equilibration of vibrational modes (vibrational coherence)
• Lattice Instabilities - high density electron-hole plasma
Nonequilibrium conditions
Phase Transition
(femtosecond optical excitation)
temperature?
vibrational motion~105 cm/sec~1 Å in 100 fs
• heating at constant volume – Warm Dense Matter
e-e scattering e-phonon scattering phonon-phonon scattering
100 fs 1 ps 10 ps 100 ps10 fs1 fs
• “non-thermal” melting
laser (visible photons)
electron-hole plasma
lattice (electron-phonon coupling)
Conventional Laser Melting
P. Stampfli and K.H. Bennemann, Phys. Rev. B 49, 7299 (1994).
thermal melting non-thermal melting
Diamond/zinc-blende structure unstable to shear forces (TA phonons)
Eb – cohesive energy per atom
ξo – electron-hole plasma density
Non-Thermal melting: Lattice Instability
Laser Heated InSb Data
-40 -20 0 20 40 60
1.6
1.7
1.8
1.9
2.0
2.1
2.2
time delay (ps)
��������������������� �������
-40 -20 0 20 40 60 80
-60
-40
-20
0
20
time delay (ps)
���������� ��������
~ 10 ps delay
lattice expansion propagating at the sound speed
(300 fs, 30 keV probe)
electronbeam
90 µm
femtosecond x-ray pulses
∆θ
femtosecondlaser pulse
Thomson Scattering Source
Leemans et al., Phys. Rev. Lett., 1996.Schoenlein et al., Science, 1996.
Chin et al., Phys. Rev. Lett., 1999.
Indication of Ultrafast Disordering• ~6 % reduction in integrated diffracted photons for τdelay<1 ps
• sub-picosecond formation of ~ 30 Å melt depth
• higher sensitivity to the surface7.5 keV photons from Thomson source (25 MeV e-beam)
InSb 12.8 degrees off (111)
7 7.2 7.4 7.60
50
100
150
200
250
x-ray photon energy (keV)
Gaussian fits-10 ps+1 ps+10 ps
-10 -5 0 5 10
0.90
0.95
1.00
1.05
time delay (ps)
������� �������������
�����
Chin et al., Phys. Rev. Lett., 1999.
Ultrafast Structural Dynamics in Crystalline Solids
beyond Bragg studies of order disorder transitions
Femtosecond X-ray Spectroscopy (EXAFS and XANES)
• amorphous/polycrystalline materials
• surface sensitivity
• short-range order dynamics, coordination and bonding
• semiconductors - structural dynamics of semiconductor/metal transition
• graphite (diamond) - liquid carbon, diamond graphitization
Structural Dyanamics of Nanocrystal Materials
• reversible solid/solid phase transitions
Systems of interest
WZRS WZ
RSRS WZ
pressure (GPa)
70
90
110
130
0 2.0 4.0 6.0 8.0
����������������!��
EA
PT
0 1 2 3 4 50
0.2
0.4
0.6
0.8
1
r (Å)
4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8-0.03
-0.02
-0.01
0
0.01
0.02
0.03
E (keV)
wurzite rocksalt
����
CdSe EXAFS
CdSe Nanocrystals: Solid-Solid Phase Transformation
A.P. Alivisatos et al. - U.C. Berkeley
Ultrafast Chemical Reactions
Structural Dynamics of the Transition State
• intramolecular vibrational relaxation (IVR)
• internal conversion - IC
reaction coordinate������
hν
reactant
photo-product
τIC < τIVR
reaction coordinate
������
hν
reactant
photo-product
τIVR < τIC
hνhigh-spin state
charge-transfer state
low-spin state
τ~700 fs
Fe
L
Fe
L
hν
• ~10-15% increase in metal-ligand bond distances
• structural dynamics concomitant with changes in optical and magnetic properties
• structural dynamics - spin crossover and electron transfer
• mechanistic role in biochemical processes (cytochrome P450)
• magnetic and optical storage material
0 1 2 3 4 5
0.2
0.4
0.6
0.8
r (Å)0
7.2 7.25 7.3 7.35 7.4 7.45 7.5 7.55 7.6
-0.04
-0.02
0
0.02
0.04
E (keV)
low-spin (ground state) high-spin (photoexcited)
FeII EXAFS
����
FeII Spin-Crossover Molecules
Ultrafast Chemical Reactions - Solvent Dependence
Ru – charge-transfer complex [Ru(bpy)3]2+
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$%�$& *+ � � ,,-,
$%�$%)$& ��� ��� ��� ./-0
$%�$%)$%)$& �.� ��� ��� �,)1
Femtosecond Anisotropy Measurements (optical)
Yeh, Shank, and McCusker, Science, 289 (2000)
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C. Bressler, M. Chergui et al. - U. LausanneA. Filipponi et al. - ESRF
Solvent-Solute Structural Dynamics
X- + hν →→→→ Xneutral + esol
Structural Dynamics of Ultrafast Biological Processes
Role of protein environment in chemical reaction?
structure ⇔ dynamics ⇔ function
• large (and small) scale conformational changes → function
pump-probe techniques with laser and x-ray pulses
• light-induced reactions in bio-molecules
• transient changes in temperature, pressure, ph etc.
• proteins exist on a multidimensional energy surface
• dynamic measurements in structural biology (msec to femtosecond scale)
Rhodopsin - photoreceptor for vision• cis-trans isomerization complete in 200 fs
Structural Dynamics of Ultrafast Biological Processes
• vibrationally coherent
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Schoenlein et al. Science (1991)Wang et al. Science (1994)
Measured ‘static’ Structure of Bacteriorhodopsin (M-state intermediate)
(2 Å resolution)
H. Luecke et al, Science, 286, 255, (1999) ALS Beamline 5.0.2
Heme Protein Dynamics
• vibrationally coherent photodissociation - ultrafast optical spectroscopy
Zhu, Sage, and Champion, Science, 266 (1994)
• structural changes associated with ligand binding and dissociation?
• static EXAFS measurements of Fe-N distances in hemoglobinP. Eisenberger et al., Nature, 274 (1978)
Time-resolved Crystallography of CO-Mb Photolysis
Srajer et al., Science, 274, (1996) ESRF beamline ID9
photolysis τ<75 fsFe-His compression Tvib~150 fsHeme doming Tvib~430 fs
nanosecond resolution -> 100 ps
flux ~ 108 ph/pulse/0.1% BW
N
N
Fe
O
(1.8 Å resolution)
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 - 20 keV
(4) rep. rate: 100 Hz - 10 kHz
• high average brightness <1 mrad source divergence
X-rays for Ultrafast Structural Dynamics
• pulse duration
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bendmagnet
mirror����� x-rays
7�����
femtosecondelectron bunch
bend magnet beamline
30 ps electronbunch
femtosecondlaser pulse
spatial separationdispersive bend
�;
electron-photon interaction in wiggler
femtosecond x-rays
e-beam
Generation of Femtosecond X-rays from the ALS
Zholents and Zolotorev, Phys. Rev. Lett., 76, 916,1996.
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
80
100
120
140
160
180
200
220
240
260
delay (fs)-1000 -500 0 500 1000
1800
1900
2000
2100
2200
2300
2400
2500
2600
�����
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)
�#��
Schoenlein et al., Science, 287,2000
Femtosecond Pulses of Synchrotron Radiation
Femtosecond X-ray Flux and Brightness
103 10
4
105
106
107
108
109
1010
1011
1012
photon energy (eV)
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105
106
107
108
109
1010
1011
1012
Thomson Source: flux: 2x103 ph/s/0.1% BW brightness: 3x103 ph/s/mm2/mrad2/0.1% BW
undulator brightness (200 fs, 40 kHz)
bend magnet brightness (100 fs, 5 kHz)
(20 mm period, 1.0 T, 1 m length)
undulator flux (200 fs, 40 kHz)
bend magnet flux (100 fs, 5 kHz)
(20 mm period, 1.0 T, 1 m length)
ALS beamlines for ultrafast x-ray spectroscopy• BEND: 105 ph/s/0.1% BW, ~100 fs, 0.3-12 keV
• UNDULATOR: 108 ph/s/0.1% BW, ~200 fs, 0.5-10 keV
Time-resolved Measurements of Structural Dynamics in Condensed Matter
Scientific Applications for Femtosecond X-ray Pulses
fundamental time scale for atomic motion - vibrational period ~100 fs
Solid-State Physics• ultrafast phase transitions (solid/liquid and solid solid)
Chemistry• structural dynamics of transition state - kinetic pathway of reaction
Biology• structural dynamics - biological function and efficiency
• reaction dynamics in solution (dilute) Hb EXAFS >1012 photons (∆t, ∆E)
• structural dynamics of complex molecules and biomolecules LAUE >108 ph/pulse
Dedicated X-ray facility for studies of Structural Dynamics