1. 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

2. 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

3. 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

4. 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.

5. transversely coherent
XPCS using ‘Sequential’ Mode
Milliseconds to seconds time resolution
Uses high average brilliance t1 t2 t3
sample
transversely coherent
X-ray beam
monochromator
“movie” of speckle
recorded by CCD 1

6. XPCS at LCLS using ‘Split Pulse’ Mode
sample
XPCS at LCLS using ‘Split Pulse’ Mode
Femtoseconds to nanoseconds time resolution
Uses high peak brilliance
sum of speckle patterns
from prompt and delayed pulses
recorded on CCD
splitter
variable delay
Contrast
Analyze contrast
as f(delay time)
transversely coherent
X-ray pulse from FEL

7. XPCS of Non-Equilibrium Dynamics using ‘Pumped’ Mode
Femtoseconds to seconds time resolution
Uses high peak brilliance
before
sample
transversely coherent
X-ray beam
t after pump
monochromator
Pump sample e.g. with laser, electric, magnetic pulse
Correlate a speckle pattern from before pump to one at some t after pump

8. transversely coherent
‘Split Pulse - Sequential’ Mode: Crossed Beams
Femtoseconds to nanoseconds time resolution
Uses high peak brilliance
sample
splitter
transversely coherent
X-ray pulse from FEL
variable delay
Crossed beams at sample allows recording of separate speckle patterns from prompt and delayed pulses (SAXS from 2-D samples) 1

9. 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)

10. 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:
Minimum required photons per pulse to give sufficient signal:
Maximum tolerable photons per pulse due to temperature rise:
See analysis in LCLS: The First Experiments

11. Heating and XPCS Signal from Single Pulse
Criterion for heating is more restrictive than standard damage limit
“Henderson Limit” for soft materials (1.e7 Gray)
Shaded areas show feasibility regions e.g. for liquid or glass (green) or nanoscale cluster (yellow)
See analysis in LCLS: The First Experiments

12. Detector Specifications
Optimum pixel size: ~1 ‘speckles’
Detector Specifications
Pixel Size, Noise Level,
Number of Pixels, Efficiency
Speckle: negative binomial distrib.
Mean counts per pixel
Inverse contrast M
Probability of k counts:
Required signal/noise: determine P2 to a few %;
need N2 ~ Ntot k2 > 1000
Low count rate limit
Required Ntot (number of pixels at “same” Q): 106 to 108

13. 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

14. Beam Size at Sample
Larger gives less heating per total signal, but size limited by ability to resolve speckle pattern in reasonable sample-to-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

15. 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

16. 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

17. Far exp. hall Conceptual Design: Beamline Layout Hutch Sample 10 m
Defining
apertures
Detectors
Pulse
Splitter
Focusing
Optics
Horiz. offset
monochromator
Transmitted Beam
15-20 m
Sample
~100 m

18. 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

19. 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)

20. Multilayer Laue Lenses: A Path Towards One-Nanometer Focusing of Hard X-rays
Deposition of thick, graded multilayer at APS; sectioning and microscopy at MSD/EMC/CNM.
WSi2/Si, 728 layers
12.4 mm thick
Dr~58 nm
Dr~10 nm
Electron microscopy shows accuracy of layer spacings
Theory
An ideal Multilayer Laue Lens should focus X-rays to 1 nm with high efficiency.
Nearly diffraction-limited performance of test structures
30 nm FWHM, 44% efficiency, 0.06 nm wavelength
H.C. Kang et al, Phys. Rev. Lett. 96, (2006)
Experiments
We have fabricated partial MLLs and measured their performance. The results support the predictions of theory.
H. C. Kang, G. B. Stephenson, J. Maser, C. Liu, R. Conley, S. Vogt, A. T. Macrander (ANL)

21. Sub-20 nm Hard X-ray Focus
Section depth = mm, Drmin=5nm, f=2.6 mm @APS 12BM
FWHM ~ 19.3 nm
E = 19.5 keV
h ~ 33 %