LUSI XPCS Status

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

6. XPCS at LCLS using ‘Split Pulse’ Mode Femtoseconds to nanoseconds time resolution Uses high peak brilliance sample variable delay sum of speckle patterns from prompt and delayed pulses recorded on CCD Analyze contrast as f(delay time) Contrast splitter 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. splitter ‘Split Pulse - Sequential’ Mode: Crossed Beams Femtoseconds to nanoseconds time resolution Uses high peak brilliance sample 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 Shaded areas show feasibility regions e.g. for liquid or glass (green) or nanoscale cluster (yellow) See analysis in LCLS: The First Experiments

12. 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 to108

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. Conceptual Design: Beamline Layout Far exp. hall Hutch 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 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, 127401 (2006) Multilayer Laue Lens Deposition of thick, graded multilayer at APS; sectioning and microscopy at MSD/EMC/CNM. WSi2/Si, 728 layers 12.4 mm thick Dr~10 nm Dr~58 nm Electron microscopy shows accuracy of layer spacings Theory An ideal Multilayer Laue Lens should focus X-rays to 1 nm with high efficiency. 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 = 13.05 mm, Drmin=5nm, f=2.6 mm @APS 12BM FWHM ~ 19.3 nm E = 19.5 keV h ~ 33 %