Photon Applications

of Accelerators

Elaine A. Seddon

16th February 2015

Courtesy W. Eberhardt

• FELs

– examples

– photon output characteristics

• Photon science opportunities

– atoms in intense fields

– mass selected clusters

– reaction dynamics

– nano-crystallography

– single molecule diffraction

Overview

Overview

The first X-ray FEL LCLS at SLAC

Golden Gate bridge

San Francisco Bay

Pacific Ocean

San Francisco

San Jose

SLAC

Status

• April 10th 2009 first lasing at 1.5 Å

• April 14th achieved saturation

• October 1st 2009 LCLS became

the world’s first operational

multi-user X-ray free electron

laser

From:

E Trakhtenberg

G Weimerslage

Beam quality sufficient to lase at 1.5 Å

0.75-2 keV X-rays 5-30 mins to change

Pulses 60-300 fs

10 fs pulses possible takes 1-3 hrs to set up

- many parameters to adjust

Courtesy H. Braun, PSI

Worldwide two hard X-ray FELs in operation

RIKEN-JASRI Joint-Project for SPring-8 XFEL

Emax 8 GeV

≤ 0.1 nm

3.5mm fixed gap

Period 15 mm

fs pulse widths

Peak brilliance

~1033

SACLA & SCSS

SPring-8

8GeV XFEL

Funding April 2006

FEL Prototype Machine,

Succeeded in lasing,

June 2006

Status

•building construction

completed March

2009

• first lasing June 2011

LCLS

SACLA

FLASH I & II

FERMI@Elettra

Operational short wavelength FELs:

Other examples, under construction or proposed

e.g. European XFEL – first light 2017

SwissFEL – first light 2019

PAL XFEL – Korea, first light 2016

LCLS II – development at SLAC

test facilities (e.g. SCSS)

Many examples of long wavelength FELS not included here

Photons …

Radiation Sources

Bending magnet, broad band

NW x bending magnet

NU2 x bending

magnet

NU2 x Ne x bending magnet

NU , NW = # magnetic periods

Ne = # electrons in a bunch

Synchrotron radiation vs. FEL radiation

The difference is in the electron beam quality

Conventional synchrotron radiation

Electron brightness << diffraction limit of emitted radiation

Electromagnetic field effects on the electrons are not

significant

Each electron radiates independently, not coherently with

others

Free Electron Laser radiation

Electron brightness ~ diffraction limit of radiation

EM field can cause microbunching of electrons, on scale of

radiation wavelength

Electrons radiate collectively, coherently

Courtesy John Arthur SSRL/SLAC

Intense pulses

• Extremely high brightness

>1030 ph/(s mm2 mrad2 0.1% B.P.)

9 orders of magnitude

• High peak powers

GWs. High average powers – 10kW at JLAB

• Broad wavelength range accessible (THz through to x-ray) and easily tuneable by varying electron energy or undulator parameters.

1013

Photonen

109

Photonen

FEL

Undulator (x 10 )

6

100 ps

100 fs

Photons

Photons

time

Sub 100 fs

Spontaneous radiation

t (fs) Dw/w (%)

The SASE radiation is powerful, but noisy!

SASE FEL amplifies random e density modulations

Problem with SASE FELs

– start up from noise means each shot is

different

Sometimes you can use this to scan over a range of arrival times

0 1 2 3 4 5 6 7

0.00

0.05

0.10

0.15

SASE (no seed) x10

Seeding

Insta

nta

ne

ou

s P

ow

er

(GW

)

Time (psec)

Nature Photonics, 2008

Seeding at 160 nm: HHG with a conventional laser

Pulses transversely coherent without seeding

Pulses transversely and longitudinally coherent with seeding

-4

-3

-2

-1

0

1

2

3

4

corrected diffraction pattern

Slits 0.5 mm apart

FLASH

COHERENCE

In summary, SR to FEL …

More than a million-fold

increase in peak brightness

thousand fold reduction

in pulse lengths

coherence

ph/(s mm2 mrad2 0.1% B.P.)

Science Opportunities

Probing the ultra-small

• Single molecule diffraction

• Imaging nano-crystals

• Imaging live cells

• Sub-cellular imaging

Capturing the ultra-fast

• Structural dynamics

• Electron dynamics

Exploring the extremes

• Dilute systems

• Non-linear processes Atoms, molecules, clusters &

solids in intense fields

Care!

Science matched

to the source

characteristics

Atoms in intense X-ray fields: non-linear XPS

Optical regime: many photons required for photoemission

X-ray regime: each photon may carry sufficient energy for ionisation

• Target changes throughout the pulse duration

• Very different from lab- or SR-based XPS

Removal and rearrangement of electrons on fs timescale within

a single X-ray pulse

• fundamental physics

• fs structural determinations

Ne LCLS ~1018 W cm-2

hʋ < 870 eV: valence electrons stripped

hʋ > 870 eV: inner shell electrons preferentially ejected

hʋ > 993 eV: ‘hollow’ neon formed (i.e. no 1s es) if PI rate > Auger decay

Ne

X-ray Transparency

At 2000 eV photoabsorption decreases if pulse length is reduced

from 230 fs to 80 fs

Qualitatively: 1s photoionisation dominant

When both emitted cross-section drops until

they’re replaced by valence electrons.

But

Auger decay very fast, 2.4 fs, why do we see

anything?

Cause: Auger refilling time increases dramatically

with charge state.

Non Linear effects at short

wavelengths: Xe

Photon

Wavelength 13.3 nm

Energy 93 eV

Focus 3 μm diameter Irradiance level

Non Linear effects at short wavelengths: Xe

TOF mass spectra

Starting from neutral Xe, Xe21+ requires at least 5 keV

Implies >57 93 eV photons absorbed in 10 fs

Theory still being developed

Photons

Wavelength 13.3 nm

Energy 93 eV

Focus 3 μm diameter

Irradiance level

7.8x1015 W cm-2

Richter, et al.

App. Phys. Lett.,

92 (2008) 473

MPI Xe: LCLS

Rudek, et al.

Nature Photonics (2012) 858

result of resonantly

enhanced absorption

Ultra Dilute Systems

FLASH: 1013 photons per pulse

i.e. in 100 fs it delivers the same as a 3rd generation SR source does in 1 s.

Experiments in the soft x-ray regime on ultra dilute targets (typically with only a few

particles in the interaction volume) become possible for the first time.

e.g. Mass-selected

clusters

Highly

charged ions

Molecular Ions

MASS SELECTED CLUSTERS

32.8 nm ~38 eV

27 pulses of approx 20 fs each

Separated by 10 μs at 5Hz rep rate

MASS SELECTED CLUSTERS PE counts red - with clusters

blue - background

V. Senz and coworkers,

Phys. Rev. Letters, 102 (2009) 138303

MASS SELECTED CLUSTERS

FEL

laser

Variable time delay

Laser-laser pump-probe

Single beam split get excellent

synchronisation

Limited in probe wavelength

Laser-FEL pump-probe

Synchronisation challenging

Short pulses

X-rays

• Reaction dynamics

• Structural dynamics

Time resolved studies

Not just interested in static information

Reaction dynamics: OPXP Optical Pump X-ray Probe

Optical pulse initiates reaction, X-ray probe monitors change

by TR X-ray-induced X-ray photoionisation and fragmentation

Ion fragmentation patterns encode info on instantaneous molecular

geometry and motion

1,3 cyclohexadiene

CHD

• uv pulse initiates ring opening

• Delayed X-ray pulse starts to fragment the molecule

1,3,5-hexatriene

HT

insight into the isomerisation

Relevant to vitamin D biosynthesis Petrovic et al. PRL 108 (2012 ) 253006

Advantages of X-rays:

• Very short X-ray pulses (<5 fs)

• Initial interaction with core electrons

structural probe that doesn’t

perturb valence electrons

• Atom specific

Ring opens

<200 fs

850 eV

X-ray pulse

Temporal evolution to HT – over 1 ps

X-ray probe: 850 eV, <70 fs, variable

delay

uv pump: 4.7 eV

Core ionisation,

Fragmentation

500 FEL shots/delay point

Pulse energy 0.95-1.10 mJ/pulse

Petrovic et al. PRL 108 (2012 ) 253006

KER and no. of H+ ion fragments per molecule evolve over 1 ps

When electrons removed faster than the timescale for nuclear

motion the Kinetic Energy Release (KER) is a measure of the

distance between the +ve charges before they start flying apart

(Coulomb explosion)

- Reconstruct molecular geometry

Petrovic et al. PRL 108 (2012 ) 253006

Molecular structure

Data obtained on the Diamond Light Source

Protein Structures using SR: Cysteine Protease

Ribbon diagram:

Helices

Beta sheets

Bradshaw et al. Acta Cryst. D70-7, (2014) 983.

Twelve data sets

collected from

four crystals

SR structural

determinations

crystal size mm

down to 10s

microns

X-rays scatter from the ordered protein molecules, diffraction pattern

encodes the atomic positions.

Pioneering work on Structural Dynamics

Michael Wulff and coworkers, Science 2003

Global structural

changes have already

occurred on the 100ps

timescale

ESRF experimental results

Why is a FEL needed?

Have the wavelength required

- but not the intensity at the

required time resolution

Electron densities of CO-myoglobin

before and after photolysis

Understanding of how a protein

functions at a mechanistic level

Need, in real time, information on

the motions that accompany that

function

Measured diffraction pattern of a

Lysozyme single crystal irradiated

with SR

Calculated diffraction image

of a Lysozyme molecule

J.Hajdu et al.

Single Molecule Diffraction

2007

More than ~45,000 structures determined but only ~450 of them membrane proteins

Why? Very hard to purify and crystallise

Source: Protein Data Bank, July ‘07

To escape ‘the tyrany of the crystal’

especially for membrane proteins Why try to do it?

Ideally

< 10 fs pulses

> 1011 photons/pulse

Single molecule diffraction Hydrated protein

X-ray pulse

Challenges

• Molecule and X-ray pulse temporal

and spatial overlap

• Very few photons per ‘successful

shot’ at detector

• Obtain data before the molecule

starts to fly apart

Reconstitute 3D intensity distribution

from 2D snapshots from randomly

oriented molecules.

Example:

Lysozyme

white: H

grey: C

blue: N

red: O

yellow: S

e

Problems if pulse is too long!

R. Neutze et al. Nature, August 2000

Approaches:

After classification ~8 months of beamtime needed for experiment

Capture diffraction snapshots from a train of identical objects of random orientation

Isosurfaces of electron density of the protein

chignolin, recovered from 72,000 noisy

diffraction patterns of unknown orientation.

C bonds yellow

N bonds blue

O bonds red.

Chignolin 10 residue peptide

Russell Fung, Valentin Shneerson, Dilano K.

Saldin and Abbas Ourmazd*,

Nature Physics, 5 (2009) 64

Single Shot diffraction

http://lcls.slac.stanford.edu/AnimationViewCXIScience.aspx

Single Shot diffraction: FLASH

Henry Chapman et al. Nature Physics 2 (2006) 839

1 m

25fs, 4x1013 W cm-2, 1012 photons, 32nm

diffraction pattern

SEM of test object Image reconstructed

from A

Single FEL pulse

diffraction pattern

Diffraction pattern

from hole created

by first pulse

Sample damage

Average of 250

independent

reconstructions

Results from FLASH & LCLS: Imaging the Mimivirus

Results from August 2009 & 2011

collaboration led by Hajdu and Chapman

Serial femtosecond crystallography

Bogan, Anal. Chem., 85 (2013) 3464

Micro- or

nano-crystals

Patterns captured one at a time before X-ray damage manifests itself

Process repeated thousands to millions of times to get complete data

set.

Bacillus Thuringiensis Toxin

crystal

spore

fs crystallography: first example of in vivo diffraction

http://www.pnas.org/content/111/35/12769.full

2.9 Å resolution structure

Sawaya et al. PNAS 2014

Map obtained from 15,000 patterns

Photosystem I: LCLS Data Chapman et al. Nature 2011

Reconstruction from b) Conventional SR diffraction result

Single Molecule diffraction: proof of principle I atoms strong

X-ray scatterers

Laser aligned

molecular beam

100 fs

pulses;

2 keV

(620 pm) Kuepper et al. PRL (2014) 083002

I to I separation in DIBN is 8Å

• Iodine to iodine separation is 8Å

• X-ray diffractive imaging of aligned gas-phase

molecules is feasible

• High frequency X-rays far from resonances are appropriate

• Spatially resolved single X-ray photon counting is possible

• Radiation damage avoidable by using shorter pulses with

lower fluences at higher repetition rates

• Averaging over many shots works well

What has been shown?

To finish…

Not covered huge areas of the

science or all of the projects

Flavour of the excitement

generated by FELs

References

• Status of FEL projects: http://www.fel2014.ch/prepress/FEL2014/

• Ribik and Margaritondo, J. Phys. D: Appl. Phys., 45 (2012) 213001

• Bostedt et al., J. Phys. B: Mol. Opt. Phys., 46 (2013) 164003

• Feldhaus et al., J. Phys. B: Mol. Opt. Phys., 46 (2013) 164002

With special thanks to:

Wilfried Wurth, Annette

Pietzsch, Volkmar Senz,

Abbas Ourmazd, Mike Poole,

Jon Marangos, David

Dunning, Siegfried Schreiber,

Josef Feldhaus, Thomas

Tschentscher, Fulvio

Parmigiani, Roger Falcone,

John Corlett, Sven Reiche,

Dave Fritz, Tetsuya Ishikawa

…

How does an FEL work?

• Basic components

N S S N S

N S N S N

B field Electron path E field

B

E

z

v

x

y

vx

r

e-

u

2nd Harmonic

3rd Harmonic

Harmonics of the

fundamental are

also phase-

matched.

Resonant wavelength, slippage and

harmonics

2

RMS

u uu

e Ba

mc

2

2

0

1

2

ur u

a

Feldhaus, Arthur and Hastings, J. Phys., B, 38 (2005) S799

Electric field vector of the radiation couples to

transverse velocity component of electron

Purple: e experiences –ve force

Green: e experiences +ve force

Some electrons gain energy and some lose energy

GENESIS, S. Reiche

SASE FEL simulation

Paul Scherrer Institut: Sven.Reiche@psi.ch

http://pbpl.physics.ucla.edu/~reiche/aboutgenesis.html

optical pulse

Electrons bunching:

coherence growing

Random electron phase

incoherent emission

Electrons bunched at

radiation wavelength:

coherent emission and

saturation

High Gain Amplifier FEL

Amplifier FELs

e-

~100 fs

• Very long 10s to >100m

• No optics

• Needed for short

wavelengths

• SASE (self amplified

spontaneous emission)

or seeded

Emission from bunches

0.2; 0.5; 1 s

t

FEL bunch trains

up to 800 bunches of 1 nC

0.2; 0.5; 1

s

Dt 1 µs

t

≤ 800 s

t

10-50 fs

• Pulse train repetition: 1, 2, 5, (10) Hz

• Bunch separation: 1, 4, 10 µs

• Number of bunches: 1 – Nmax (≤800 µs)

FLASH time structure