R. Falcone -Science With New X-ray Lasers

8/4/2019 R. Falcone -Science With New X-ray Lasers

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Science with new x-ray lasers

Roger Falcone- UC Berkeley- Lawrence Berkeley National Laboratory



“synchrotron” x-ray pulsesare produced by relativistic electron bunches from accelerators

when the electrons pass through periodic magnetic fields



absorption of x-rays



3-d x-ray tomography of microstructure of a cell

Larabell, et al



Unbiased Biased

no conduction conduction

- Graphene, a single layer of carbon, is the

building block of graphite, nanotubes, buckyballs.- A bilayer of graphene can be a switch <1 nmthick for high current densities (~108 A/cm2).

Photoemission from Graphene reveals band structure of anew material for high performance electronics

T. Ohta, A. Bostwick, Th. Seyller, K. Horn, E. Rotenberg,Science, 2006. 313: p. 951-954.



Combustion chemistry and chemical dynamicsof new fuels

Multiplexing anduniversal detection

C3H3 + C3H3 C6H6

Enol formation in flames

Isomer selectivitymass spectrometry

anthracene

Sandia National Lab, ALS



Synchrotron radiation provides 100 ps x-ray pulsesthat can be detected by streak camera detector

with < ps resolution

Transmission measurements yieldnear-edge x-ray absorption fine structure (NEXAFS)



Bonding changes as carbon taken to high temperature:captured in K-edge spectroscopy



Fast dynamics: Laser heating rapidly enhances x-rayabsorption below Cu L-edge, followed by slow decrease

L2

L3

WDMRoom temp

Difference

Evolution of XAS Δε =20 MJ/kg

hv

e -



bendmagnets

mirror x-rays

femtosecondelectron bunch

30 ps electronbunch

femtosecondlaser pulse

spatial separation

dispersive bend

electron-photon

interaction in wiggler

femtosecond

x-rays

e-beam

Ultrafast (100 fs) x-ray pulses can be produced bylaser modulation of electron bunches in a synchrotron

Available at ALS, SLS and BESSY



Ultrafast Dynamics – Liquid Water Structure

Collaborators: A. Lindenberg et al. (Stanford)

Femtosecond excitation – OH stretch (3,300 cm-1)

Future:

• early ‘non-thermal’ dynamics (sub-picosecond)

• OH mode softening – water structure

• inhomogeneous dist. OH stretch mode (high/low energy side)

X-ray absorption⇔ Hydrogen-bond network

SD DD

150 picoseconds

200 nanoseconds





“As one attempts

to extend maser

operation towards

very short

wavelengths, a

number of newaspects and

problems arise,

which require a

quantitative

reorientation of

theoreticaldiscussions and

considerable

modification of the

experimental

techniques used…”



“… power in the

spontaneous

emission varies

rapidly with

frequency (υ) …

υ4 or υ6

… supply of this much

power becomes very

difficult…”

• milliwatts in the

microwave

• watts in the

ultraviolet

“… (masers) cannotbe pushed to

wavelengths much

shorter unless some

radically new

approach is found…”



Intense Multicolor HHG soft x-ray beamline

Laser System

Split Filter on

translation stage

Split mirror

interferometer

Compressor

Gas CellSi Mirror Monochromator



Potential energy

surfaces of

ethylene.

From Ben-Nun et al., J. Phys. Chem. A 104, 5161 (2000)

Ethylene (C2H4) is a prototype molecule for internal conversion oflight energy, and a benchmark case for quantum chemistry theories

Conical Intersection between

excited state and ground state enablesultrafast non-radiative decay

Relaxes to electronic ground state in ~ 50 fs

- ground state is extremely vibrationally hot and

eventually dissociates into C2H2 and H2

- can also dissociate by eliminating H atoms.



5th harmonic (7.7 eV) autocorrelation (symmetric pump/probe)reveals ultrashort excited electronic state lifetime

τ = 23 ± 3 fs

τ’ = 23 ± 7 fs

Low Energy photons can only

ionize

from the excited electronic state



Slower Rearrangement and H2

Elimination ChannelFast Hydrogen Atom Elimination

Channel

Higher harmonics canionize hot ground stateand dissociated fragments



Micro-bunching introduces coherent emissionin a Free Electron Laser (FEL)



LCLS X-Ray Free Electron Laser at SLAC

Injector (35º)at 2-km point

1 km long Linac

Near Experiment Hall

Far Experiment

Hall

Undulator (130 m)

e− Transfer Line (340 m)

X-ray TransportLine (200 m)

Proposed by Pellegrini in 1992; lasing in 2009



•depth of field limit

•lens-limited

•direct

sample

Microscopy

light

lens

image

New types of photography are possible

with coherent x-rays

•No depth of field limit

•No lens-limited•Computer-limited

sampleDiffraction Microscopy

Coherent-light

CCDcamera image

Th f LCLS X R FEL bl



The case for LCLS: X-Ray FELs may enable

atomic-resolution imaging of biological macromolecules

Combine 105-107 measurements

Classification Averaging Orientation Reconstruction

Noisy diffraction pattern

10-fspulse

Particle injection

One pulse, onemeasurement

Imaging spatial resolution is limited by radiation



Dose-Resolution relationship for imaging of frozen samples at 10 keV

Empirical data compiled by Malcolm Howells, LBLJ. Electron. Spec. Rel. Phenom. (2009)

0.1 1 10

Resolution (nm)

F l u e n c e

( p h / m 2 )

1021

1011

1013

1015

1017

1019

Imaging spatial resolution is limited by radiationdamage

Fast pulses

X-ray microscopy

100

109

10

18

108

1010

1012

1014

1016

106

D o s e ( G y )

c o r r e c t e d

b y

R F

Multiple

oriented

images

C t f Hi h R titi R t S d d



Concept for a High-Repetition Rate, Seeded,VUV–Soft X-ray FEL Facility

Array of 10 configurable FEL beamlines, up to 20 X-ray beamlines100 kHz CW pulse rate, capability of one FEL having MHz rate

Independent control of wavelength, pulse duration, polarizationEach FEL configured for experimental requirements;

seeded, attosecond, ESASE, mode-locked, echo effect, etc

Beam transport andswitchingCW superconducting linac

2.5 GeV

Laser systems,timing & synchronization

Low-emittance,MHz bunch rate

photo-gun

≤ 1 nC≤1 mm-mrad

Injector

Laser

heater Bunchcompressor



ANL-08/39

BNL-81895-2008

LBNL-1090E-2009

SLAC-R-917

LCLS

LCLS

FLASH

FLASH

NGLS

Peak Brightness



ANL-08/39

BNL-81895-2008

LBNL-1090E-2009

SLAC-R-917

LCLS

LCLS

FLASH single bunch ~1016–1017

NGLS

Average Brightness



Science at a Next Generation Light Source

• Two-color, THz to x-ray pump / x-ray probe, as to fs timescales- molecular dynamics in diffuse systems

• Imaging of charge carrier dynamics in molecules using core electron excitation- ultrafast movies of charge migration

• Coherent imaging at the nanoscale- tomographic, diffractive, chemically-specific

• Inelastic x-ray scattering- using high average power source and high dispersion analyzers

• Photoemission- low energy per pulse at high rep rate

• Photon correlation spectroscopy- on relevant length and time scales

• Transient absorption- mode-locked, spectrally broadened pulses

• Multi-dimensional and wave-mixing spectroscopy



Understand ultrafast energy and information flowin molecular systems





Proposed (Phase I) NGLS Facility

High Repetition Rate

Electron Source

2.0 – 2.5 GeV

CW SC LINAC

Capability for

10/20 FEL beamlines

BL 1 BL 2 BL 3

Photon Energy: 0.25- 1.0 keV3rd & 5th harmonics at reduced intensity

Beamlines BL1 – 2 Color BL2 - Short-pulse /

narrow-bandwidth

BL3 – High

Power

Type Chicaned andseededradiators

Seeded, time-bandwidth-limited

SASE

Feature X-raypump/probe

with fsresolution

Pump/probe withadjustable delay

(THz - UV pump)

Potential forseeding

Pulse duration 250 as - 25 fs 250 as - 50 fs (30meV BW)

1 - 50 fs

Rep rate 10 - 100 kHz 10 - 100 kHz to 1 MHz

Peak Power 10 - 100 MW 1 GW 1 GW

R&D / Options EEHG R&DHHG option

EEHG R&DHGHG option

>>1 MHz

Science

BL1 BL2 BL3

multidimensionalspectroscopy

x-ray pump / x-ray probe

species-selectiveintramolecular

dynamics

ultrafastdynamics

inelasticscattering

inelastic andcoherentscattering

diffractiveimaging

species-

selectivetomography



Understanding Chemical Reactivity

-beyond simple adiabatic potential energy surfacesBorn-Oppenheimer approximation

-charge transfer, catalysis, photosynthesis (natural and artificial)

Understanding Correlated Materials – what will follow the silicon age?

- beyond single-electron band structure- charge correlation, nanoscale organization, charge/spin/lattice coupling

- superconductivity, colossal magnetoresistance, exotic properties

ψ total ≠ ψnuclear ψelectronic

How do the properties of matter emerge from the:correlated motion of electrons, and coupled atomic/electronic structure?

Imaging structure ⇒ imaging “function” in biological systems (macromolecules)

- structure ♦ dynamics ♦ function

- identify conformational states -pathways connecting conformational states

New Understanding ⇒ New Mechanisms for Control:-Purposeful design: efficient catalysts, light harvesting complexes (cheap/abundant materials)

materials with tailored properties (electrical, magnetic, thermal….)

-Exploit understanding of biological “function” for health, medicine, mimic Nature specific applications



• Can we visualize coherent charge migration?

• Coherent electronic wavepackets – superposition of correlated electronic states

• Motivation: fundamental understanding of charge transport in Nature– photochemistry, catalysis, light harvesting – photosynthesis- role of correlation and relaxation

- ab initio calculations indicate purely electronicultrafast charge transport via electron

correlation and relaxation-charge transport on a femtosecond timescale(no nuclear dynamics)

Coherent Ultrafast Charge Migration



Emergent Phenomena – Complex Materials

Coherent Charge-transfer Transition

P(t)time

time

Charge-transfer excitation - exciton

Element-specific probe:- Cu and Oxygen charge states- simultaneous with 2-color probe?- stimulated x-ray Raman

- multidimensional x-ray wave mixing

C u - c

h a r g e s t a t e - O

~3 fs

500 as

Can we directly observe the time-formation of a quasiparticle?

charge-transfer transitionLövenich et al., PRB , 2001

Sr2CuO2Cl2 lattice



Correlated electron material properties emerge through complex nanostructure, near-equilibrium dynamics

- phase separation (charge, spin, orbit, polarons …) and fluctuations - e.g. CMR, high-TC superconductivity

Resonant scattering - element specificity for heterogeneous materials

- spectral contrast to image charge, magnetic, spin, orbital order

at various points in phase diagram, and in response to tailored ultrafast excitation

Analyze speckle patterns in time domain and/or invert to real space images - correlations in space and time

“Imaging” Material Complexity at the NanoscaleMicroscopy, Holography, Scattering, X-ray Photon Correlation Spectroscopy (speckle)

Imaging of magnetic nanostructuresvia x-ray spectro-holography

W. Eberhardt J. Stöhr et al. Nature 2004

limitation of present sources: coherent x-ray flux, time resolution

Orbital domain dynamics - Manganite

S.D. Kevan et al., New J. Phys. (2008)

∆t



• Can we image biological objects together with their function, in three

dimensions, with chemical specificity, on multiple spatial scalesextending down to nanometer resolution? (SXR and many images)

• Can we resolve the flow of energy and charge in molecular systems,with attosecond time resolution and atomically specific resolution, and

use this information to improve energy systems? (ultrafast andsynchronous pump and probe)

• Can we understand and improve the performance of complex andcorrelated electron materials, by resolving the energy scales of low-

level excitations? (high average and low peak flux for inelastic x-rayscattering)

• Can we understand and improve the limits of material performance, insitu? (SXR for information on bonding)

NGLS: The world’s most powerful coherent x-ray facility

Critical accelerator design



APEX CW VHF photo-gun cavityMHz bunch rate

APEX injector design

Control over the microbunchinginstability

Ultra-precision timing &

synchronization systems

High-resolution modelingwith LBNL code IMPACT

Critical accelerator designand R&D

High-efficiency, lowemittance photocathodes

Seeded FEL design

E h ff f h i i



G. StupakovSLAC-PUB-13445 (2008) Strong micro-bunching

Z

λ laser

Echo effect for harmonic generation

∆ E

σ E

E h d h h



Model 98th harmonic @ 1.8 nm

Echo seeding technique may reach x-raywavelengths in single cascade

λ x−ray =1.8nm

R&D at 7th harmonicunderway at SLAC

Documents

R. Falcone -Science With New X-ray Lasers