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.

transversely coherent X-ray beam

sample

XPCS using ‘Sequential’ Mode

• Milliseconds to seconds time resolution• Uses high average brilliance

t1

t2

t3

monochromator

“movie” of specklerecorded by CCD

g2 (t) I(t) I(t t)

I2

1

t

g2

1(Q) Rate(Q)

I(Q, t)

transversely coherent X-ray pulse from FEL

sample

XPCS at LCLS using ‘Split Pulse’ Mode

Femtoseconds to nanoseconds time resolutionUses high peak brilliance

sum of speckle patternsfrom prompt and delayed pulses

recorded on CCD

I(Q,t)

splitter

variable delay t

t

Con

tras

t

Analyze contrastas f(delay time)

10 ps 3mm

transversely coherent X-ray beam

sample

XPCS of Non-Equilibrium Dynamics using ‘Pumped’ Mode • Femtoseconds to seconds time resolution• Uses high peak brilliance

before

t after pumpmonochromator

Correlate a speckle pattern from before

pump to one at some t after pump

Pump sample e.g. with laser, electric, magnetic pulse

transversely coherent X-ray pulse from FEL

sample

‘Split Pulse - Sequential’ Mode: Crossed Beams

Femtoseconds to nanoseconds time resolutionUses high peak brilliance

Crossed beams at sample allows recording of separate speckle

patterns from prompt and delayed pulses (SAXS from 2-D samples)

I(Q, t2)

splitter

variable delay t

10 ps 3mm

g2(t) I(t1) I(t2)

I2

1

t

g2

1(Q) Rate(Q)

I(Q, t1)

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

Maximum tolerable photons per pulse due to temperature rise:

NMIN 2 A E2abs

h2c2 el Mcorr

NMINSPECKLE

NMAX 3kBA

Eabs

TMAX

Minimum required photons per pulse to give sufficient signal:

Is there enough signal from a single pulse?Is sample heating by x-ray beam a problem?

NAVAIL f (E,E, A)

Maximum available photons per pulse:

See analysis in LCLS: The First Experiments

Heating and XPCS Signal from Single Pulse

See analysis in LCLS: The First Experiments

Shaded areas show feasibility regions e.g. for liquid or glass (green) or nanoscale cluster (yellow)

Detector SpecificationsPixel Size, Noise Level,

Number of Pixels, Efficiency

Speckle: negative binomial distrib.

Mean counts per pixel

Inverse contrast M

Probability of k counts:

Pk (k M)

(M)(k 1)1

M

k

k

1k

M

M

k

Low count rate limit

k 0.01

P1 k

1/ M 2P2 /P12 1

Optimum pixel size: ~1 ‘speckles’

Required Ntot (number of pixels at “same” Q): 106 to 108

P2 M 1

2Mk

2

Required signal/noise: determine P2 to a few %;

need N2 ~ Ntot k2 > 1000

Current Detector Questions1) 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 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

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

Sample

Detectors

Hutch

FocusingOptics

Horiz. offsetmonochromator

PulseSplitter

Defining apertures

Transmitted Beam 15-20 m

Conceptual Design: Beamline Layout

Far exp. hall

~100 m

10 m

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

H. C. Kang, G. B. Stephenson, J. Maser, C. Liu, R. Conley, S. Vogt, A. T. Macrander (ANL)

Multilayer Laue Lens Deposition of thick, graded multilayer at APS; sectioning and microscopy at MSD/EMC/CNM.

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.

WSi2/Si, 728 layers

12.4 m thick

r~10 nmr~58 nm

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)

-150 -100 -50 0 50 100 150

0.0

0.2

0.4

0.6

0.8

1.0

Sample A Sample B Sample C Gaussian fit

Inte

nsity

(no

rmal

ized

)

X (nm)

Substrate

Graded-spacing Multilayer

Substrate

Graded-spacing Multilayer

Sub-20 nm Hard X-ray Focus

Section depth = 13.05 m, rmin=5nm, f=2.6 mm @APS 12BM

FWHM ~ 19.3 nm

E = 19.5 keV

~ 33 %