LUSI XPCS Status
Team Leader:
Brian Stephenson (Materials Science Div., Argonne)
Co-Leaders:
Karl Ludwig (Dept. of Physics, Boston Univ.),
Gerhard Gruebel (DESY)
Sean Brennan (SSRL)
Steven Dierker (Brookhaven)
Eric Dufresne (Advanced Photon Source, Argonne)
Paul Fuoss (Materials Science Div., Argonne)
Randall Headrick (Dept. of Physics, Univ. of Vermont)
Hyunjung Kim (Dept. of Physics, Sogang Univ.)
Laurence Lurio (Dept. of Physics, Northern Illinois Univ.)
Simon Mochrie (Dept. of Physics, Yale Univ.)
Larry Sorensen (Dept. of Physics, Univ. of Washington)
Mark Sutton (Dept. of Physics, McGill Univ.)
LCLS SAC Meeting June 7-8, 2006
Scientific Impact of X-ray Photon Correlation Spectroscopy
at LCLS
New Frontiers:
• Ultrafast
• Ultrasmall
Time domain
complementary to
energy domain
Both equilibrium and
non-equilibrium
dynamics
Unique Capabilities of LCLS for XPCS Studies
Higher average coherent flux will move the frontier
• smaller length scales
• greater variety of systems
Much higher peak coherent flux will open a new frontier
• picosecond to nanosecond time range
• complementary to inelastic scattering
Wide Scientific Impact of XPCS at LCLS
•Simple Liquids – Transition from the hydrodynamic to the kinetic regime.
•Complex Liquids – Effect of the local structure on the collective dynamics.
•Polymers – Entanglement and reptative dynamics.
•Proteins – Fluctuations between conformations, e.g folded and unfolded.
•Glasses – Vibrational and relaxational modes approaching the glass transition.
•Dynamic Critical Phenomena – Order fluctuations in alloys, liquid crystals, etc.
•Charge Density Waves – Direct observation of sliding dynamics.
•Quasicrystals – Nature of phason and phonon dynamics.
•Surfaces – Dynamics of adatoms, islands, and steps during growth and etching.
•Defects in Crystals – Diffusion, dislocation glide, domain dynamics.
•Soft Phonons – Order-disorder vs. displacive nature in ferroelectrics.
•Correlated Electron Systems – Novel collective modes in superconductors.
•Magnetic Films – Observation of magnetic relaxation times.
•Lubrication – Correlations between ordering and dynamics.
XPCS using ‘Sequential’ Mode
• Milliseconds to seconds time resolution
• Uses high average brilliance
transversely coherent
X-ray beam
g2 (t) 
t1
sample
monochromator
t2
I(t) I(t  t)
2
I
t3
g2
 1 (Q)  Rate(Q)

1
t
“movie” of speckle
recorded by CCD
I(Q,t)
XPCS at LCLS using ‘Split Pulse’ Mode
Femtoseconds to nanoseconds time resolution
Uses high peak brilliance
sample
splitter
transversely coherent
X-ray pulse from FEL
variable delay
t
Contrast
10 ps  3mm
Analyze contrast
as f(delay time)

t
sum of speckle patterns
from prompt and delayed pulses
recorded on CCD
I(Q,t)
XPCS of Non-Equilibrium Dynamics using
‘Pumped’ Mode
• Femtoseconds to seconds time resolution
• Uses high peak brilliance
transversely coherent
X-ray beam
monochromator
Pump sample e.g. with
laser, electric,
magnetic pulse
sample
before
t after
pump
Correlate a speckle
pattern from before
pump to one at some
t after pump
‘Split Pulse - Sequential’ Mode: Crossed Beams
I(Q,t2 )
Femtoseconds to nanoseconds time resolution
Uses high peak brilliance
sample
splitter
transversely coherent
X-ray pulse from FEL
variable delay
t
10 ps  3mm
g2 (t) 
I(t1) I(t 2 )
I
g2

2
I(Q,t1)
Crossed beams at sample allows
recording of separate speckle
patterns from prompt and delayed

pulses (SAXS from 2-D samples)
 1 (Q)  Rate(Q)

1
t

Design of Experiments
Driven by analysis of sample heating by beam
For these studies of dynamics, we must avoid
changing the behavior of the sample by the beam
(e.g. < 1K heating)
Sample Heating and Signal Level
Is there enough signal from a single pulse?
Is sample heating by x-ray beam a problem?
Maximum available photons per pulse:
N AVAIL  f (E,E, A)
Minimum required photons per pulse to give sufficient signal:
NMIN
2 A E 2  abs SPECKLE
 2 2
N MIN
h c  el Mcorr
Maximum tolerable photons per pulse due to temperature rise:
NMAX
3k B A

TMAX
E  abs
See analysis in LCLS: The First Experiments
Heating and XPCS Signal from Single Pulse
Shaded areas show feasibility regions e.g. for liquid or glass
(green) or nanoscale cluster (yellow)
See analysis in LCLS: The First Experiments
Detector Specifications
Optimum pixel size:
~1 ‘speckles’
Pixel Size, Noise Level,
Number of Pixels, Efficiency
Speckle: negative binomial distrib.
Mean counts per pixel
k
Inverse contrast M
Probability of k counts:
M


(k M)  M 
k
Pk 
1  1 
(M)(k  1)  k   M 
Low count rate limit
k
k  0.01
Required signal/noise:
determine P2 to a few %;
P1  k
need N2 ~ Ntot k2 > 1000
M 1 2
P2   k
2M
1/ M  2P2 /P12 1
Required Ntot (number of pixels at
“same” Q): 106 to 108
Current Detector Questions
1) In order to get large number of pixels, need to
understand trade-offs between number of pixels,
pixel size, noise level, efficiency, cost
Can an inexpensive commercial technology be
adapted?
2) For XPCS, pixels do not have to be contiguous.
Using a mask to separate pixels could be a flexible
way to produce small pixels, and reduce noise due
to charge sharing between pixels
Beam Size at Sample
Larger gives less heating per total signal, but size limited
by ability to resolve speckle pattern in reasonable sampleto-detector distance
Beam size = pixel size = speckle size = d = (L)1/2
For L = 5 m, get
d = 20 microns, 8 keV;
d = 12 microns, 24 keV
Unfocused beam size at 8 keV is ~400 microns
Can use large coherent beam to
- split beam spatially to produce time delay
- doing heterodyne detection using reference beam
- feed another experiment
Conceptual Design: Mono and Splitter
Si (220) or C (111) energy resolution typ., 6-24 keV
Pulse splitter - 3 concepts:
• Partially-transmissive reflection e.g. Laue
• Split energy spectrum
• Split spatially (should be ~100 m upstream to combine at
minimum angle)
For times longer than ~1 ns, should consider two pulses in linac
Mono upstream of splitter would remove heat load and avoid
any effect of first pulse on second
Conceptual Design: Beamline Layout
Hutch in far hall
10 m long by 10 m wide hutch, with slits upstream; for
SAXS region, 15 m long would be more flexible
Need very low background (mirror system in front end will
solve)
Concerned about stability of upstream optics (need 0.5
microradian)
Either no focusing or moderate (up to 1:1), compound
refractive lenses in upstream tunnel
Pumped mode experiments will require synchronized
lasers
Conceptual Design: Beamline Layout
Far exp. hall
Hutch
10 m
Defining
apertures
Pulse
Splitter
Horiz. offset
monochromator
Detectors
Focusing
Optics
Transmitted Beam
~100 m
15-20 m
Sample
Large Offset Monochromator
XPCS requires monochromator
Mono offset can be used to separate beams, eliminate 'flipper' mirrors
Transparent first crystal could allow simultaneous operation of other
station(s)
Goniometer and Sample Chambers
Plan 3 different chambers for different T regions
Flight paths and detector supports require thought
Summary of R&D Needs, Sub-Teams
• Detector and Algorithm (Lurio, Mochrie)
• Split/Delay (Gruebel, Stephenson)
• Beam Heating of Sample (Stephenson, Ludwig)
• Large Offset Mono (Stephenson, Gruebel)
• Goniometer and Sample Chamber (Ludwig, Sutton)
Multilayer Laue Lenses: A Path Towards
One-Nanometer Focusing of Hard X-rays
Multilayer Laue Lens
Graded-spacing
Multilayer
Substrate
Deposition of thick,
graded multilayer at
APS; sectioning and
microscopy at
r~10 nm MSD/EMC/CNM.
WSi2/Si, 728 layers
12.4 mm thick
r~58 nm
Electron microscopy shows
accuracy of layer spacings
Theory
Experiments
Intensity (normalized)
An ideal Multilayer Laue Lens
should focus X-rays to 1 nm with
high efficiency.
0.8
0.6
30 nm FWHM, 44% efficiency,
0.06 nm wavelength
0.4
0.2
0.0
-150
We have fabricated partial MLLs
and measured their performance.
The results support the
predictions of theory.
Nearly diffraction-limited
performance of test structures
Sample A
Sample B
Sample C
Gaussian fit
1.0
-100
-50
0
X (nm)
50
100
150
H.C. Kang et al, Phys. Rev. Lett.
96, 127401 (2006)
H. C. Kang, G. B. Stephenson, J. Maser, C. Liu,
R. Conley, S. Vogt, A. T. Macrander (ANL)
Sub-20 nm Hard X-ray Focus
Section depth = 13.05 mm, rmin=5nm, f=2.6 mm @APS 12BM
6000
Intensity (cts/sec)
5000
FWHM ~ 19.3 nm
4000
E = 19.5 keV
3000
h ~ 33 %
2000
1000
0
-100
-50
0
X (nm)
50
100