Istituto di Struttura della Materia del CNRvia del Fosso del Cavaliere 100, 001��33 ROMA

P. PerfettiTrieste, 05-12-01

OUTLINE

• FEL/SASE CHARACTERISTICS

• PERSPECTIVES IN THE SOFT X-RAY

• PERSPECTIVES IN THE HARD X-RAY

SCIENTIFIC OPPORTUNITIESWITH AN ULTRABRIGHTPULSED LASER SOURCE

EXPERIMENTS ON IVGENERATION SR SOURCES MUST

BE TAILORED ON THE MAINCHARACTERISTICS OF THESE

SOURCES

• BRILLIANCE (10 orders ofmagnitude higher than 3rd

generation SR sources)

• COMPLETE TRANSVERSECOHERENCE

• PULSE TIME STRUCTURE<100fs

POSSIBLE APPLICATIONS IN THESOFT X-RAY

ATOMIC AND MOLECULARPHYSICS

• The interaction of a highintensity photon beam withisolated atoms and clusters is afirst step in:

• Understanding the interactionwith condensed matter

• To tailor new experiments• To choose the right materials for

the optical elements (mirrors,monochromators, slits, …....)

• The interaction of the FEL photons with theatomic beam produces ions, electrons andfluorescence photons

• The simultaneous detection of the differentoutgoing species will give detailed informationon the Auger and fluorescence cascaderesulting in highly charged final ions

set-up for experiments on isolatedatoms

FELhν

BeamMonitor

Pulsed Atomic beam

electrons

ions

Time of flightspectrometer

AreaDetector

FluorescenceSpectrometer

Grating

hν

MULTIPLE CORE-HOLE FORMATION

• ELECTRON CORRELATIONIS RESPONSIBLE OF MULTIPLECORE-HOLE FORMATION

• FOR DEEP CORE- LEVELS THIS IS ALOW CROSS SECTION PROCESS

• NEED FOR THE SHORT AND INTENSE FELPULSE RADIATION TO CREATE ASUFFICENTLY LARGE NUMBER OFPROCESSES TO BE DETECTED

•NEED FOR AN X-FEL

•NONLINEAR PHOTON-ATOM INTERACTIONS

•FOR INNER SHELLS:THE TWO PHOTONPHOTOIONIZATIONCROSS SECTIONS AREEXCEEDINGLY SMALL

2-2-photon double ionizationphoton double ionization

hν + He → He2+ + 2e

correlated electron-electron dynamics

[Review : Briggs and Schmidt J. Phys.B33 (2000)R1;King and Avaldi J. Phys.B33 (2000)R215]

nhν’ + He → He2+ + 2e

correlated emission /sequential process ??

[Frankfurt+Marburg PRL 84 (2000)443; Freiburg+BerlinPRL 84 (2000)447]

Ti-Ti-sapphiresapphire laserlaser λλ=800=800 nmnm, E=1.54 eV, E=1.54 eV

∆∆tt=220=220 →→3030 fsfs

I= 10-100I= 10-100 TwattTwatt/cm/cm22

a mechanism : rescattering

XX--FEL :FEL :

2-photon process

non-perturbative regime ( Ep∝I/ω2)

Mechanism:rescattering

virtual state τ≅10-14 s

hν

22 photon innerphoton inner--shellshellionization and Auger decayionization and Auger decay

• What about the Auger decay ?

• What about the interaction between the

Auger electron and the photoelectron ?

[ Rioual et al. PRA 61 (2000)044702, PRL 86 (2001) tobe published]

• Is it possible to observe laser assisted Auger

processes ?

Γ ≅ 100 meV

τAuger≅10-14 s

hν

CLUSTER PHYSICS

• PHOTON-CLUSTER INTERACTIONCAN CAUSE:

• PHOTO-FRAGMENTATION• HIGHLY CHARGED IONS• COULOMB EXPLOSION

• DIRECT STUDIES OF FEL-CLUSTERINTERACTION

• PUMP-PROBE EXPERIMENTS USINGAN EXTERNAL fs-LASER

• FOR A FOCUSED BEAM, DEPENDING ONTHE ATOMIC SPECIES CROSS SECTIONS,ALL THE ATOMS IN THE CLUSTERCOULD BE IONIZED CREATING A BALLOF CHARGE GIVING RISE TO A

COULOMB EXPLOSION(C.E.)• C.E. ENERGIES AND CHARGE STATESARE MEASURED BY OBSERVING THEEXPLODING FRAGMENTS

• THESE EFFECTS WILL GIVE INSIGHTINTO MATERIAL DAMMAGE INDUCEDBY THE FEL RADIATION

• ELECTRONIC STRUCTURE OFOCCUPIED AND UNOCCUPIED LEVELS:

•PHOTOELECTRON SPECTROSCOPY(UPS,XPS)•ABSORPTION SPECTROSCOPY(NEXAFS)

• GEOMETRICAL STRUCTURE:•(XANES, EXAFS)

• DYNAMICS:•VIBRATION•DISSOCIATION•COULOMB EXPLOSION•PUMP-PROBE EXPERIMENTS

• CHEMICAL, ELECTRONIC ANDDYNAMIC PROPERTIES

•CLUSTER ON SURFACES•CLUSTER MATTER

CHEMISTRY

• THE MOST EXCITING EXPERIMENTSARE THOSE BASED ON THE TIMESTRUCTURE OF THE FEL PULSE(<100 fs) AND WE ENTER IN THEDOMAIN OF FEMTOCHEMISTRY

• DYNAMICS OF CHEMICAL REACTION•MOLECULAR BOND LENGTH•ELECTRONIC STRUCTURE•MOLECULAR VIBRATION•POSITION IN SPACE

• A TYPICAL EXPERIMENT IN THISFIELD IS A PUMP-PROBE EXPERIMENT

• PUMP: A SHORT LASER PULSE (OR THEFEL/SPONTANEOUS EMISSION) DRIVETHE EXCITATION MECHANISM

• THE RETARDED FEL-PULSE ALLOW THEDEFINITION OF THE TIME-EVOLUTIONOF THE SYSTEM

• THE TIME SCALE OF A CHEMICALREACTIONS ARE OFTEN IN THE fsSCALE

• E.g. THE UV PHOTODISSOCIATION OFA H2O MOLECULE IN H+OH OCCURSIN ≅ 10 fs

• THE BEST SYNCHROTRON SOURCESALLOW STUDIES IN A FEW TENSOF PICOSECONDS

• 1999: NOBEL PRIZE IN CHEMISTRY TOAHMED ZEWAIL IN THE AREA OFULTRAFAST SPECTROSCOPY

• THE SOFT-X-RAY FEL WILL EXTENDTHESE STUDIES TO HIGH ENERGIESAND AND CAN USE EXPERIMENTALMETHODS TO INVESTIGATE THETHE STRUCTURAL PROPERTIES (TIMEDEPENTENT XANES/ EXAFS)

EXAMPLE OF DIATOMICPHOTODISSOCIATION:

THE RED WAVE PACKET IS EXCITED TOA REPULSIVE STATE . THE WAVEFUNCTIONOFTEN REMAIN LOCALIZED AND THE BESTWAY TO KNOW THE BOND LENGTH IS TOMEASURE IT DIRECTLY

TIME DEPENDENTXANES, EXAFS, RAMAN XAS

O. Bjorneholm et al. Phys. Rev. Lett. 84,2826 (2000)

O2 +hν = (O2 )*=O*O+OO*

O2++ e- O++ e-

τ Auger = 3fs τ diss. = 7fs

O O

photo-absorpt..selectivity

Intermolecular-direction

parallel topolarization vector e

doppler shift iszero for

p ⊥ eAnd

Opposite forp || e

Ultrafast Time-Resolved Photoelectron Spectroscopyof Dissociating Br2

Lora Nugent-Glandorf et al. Phys.Rev.Lett.87, 103002-1 (2001)

Probe: table-top x-ray sourcehν = 26.4 eV, 250 fs

3x106 phs/pulse

Pump: hν = 3 eV, 80 fs

A, B, X final stateswith hν = 26.4 eV

with a pump-probedelay of 500 fs

a clear signal from atomicspecies is present

40 fs is the calculateddissociation time

From cross-correlationanalysis

HETEROGENEOUS CATALYSIS

• PHOTOELECTRON SPECTROSCOPY ISONE OF THE MOST FREQUENTLY USEDTECHNIQUES TO STUDY H.C.

• IT PROVIDES INFORMATION ABOUTTHE CHEMICAL PROPERTIES OF THENEAR-SURFACE REGION

• IDENTIFICATION OF THE DIFFERENTREACTION PRODUCTS AND THEIRTIME EVOLUTION

• LIMITATION OF PRESENT S.R. SOURCES:LONG DATA ACQUISITION TIME DUE TOLOW PHOTON FLUX

• FEL RADIATION WILL PERMIT XPS DATAACQUISITION WITH UNPRECEDENTEDSPEED

• (POSSIBILITY FOR TIME-RESOLVEDAND LATERALLY RESOLVED XPSMAPPING)

MICROSCOPY ANDSPECTROMICROSCOPY

• CONTRAST IN THE SOFT-X-RAY AREMAINLY DETERMINED BY:

• PHOTOELECTRIC ABSORPTION• PHASE SHIFT

• THE BEST SPATIAL RESOLUTIONOBTAINED UP TO NOW IS ≅ 30 nm(ZONE PLATE, PEEM)

• CONTRIBUTION TO THIS LIMIT COMESFROM ABERRATIONS OF THE OPTICALELEMENTS SCALING WITH THEIRDIMENSIONS

• THE HIGH BRILLIANCE OF THE FELALLOWS THE REDUCTION OF THEDIMENSIONS AND A BETTER LATERALRESOLUTION

• OF EXTREME INTEREST FOR BIOLOGYIS THE WATER WINDOW (280-530 eV)

• IN A RECENT REVIEW (J. KIRZ ET AL. 1995)MANY APPLICATIONS ARE SUMMARIZED:

• CHROMOSOMES

• MALARIA INFECTED ERYTROCYTES

• CALCIFIED TISSUES

• MUSCLES

• LIPID MEMBRANES

• POLYMERS

• ETC.

Coherence-Enhanced Radiography:Refraction vs

Diffraction Mechanisms

"Refraction"radiograph

"Diffraction"radiographs

(Y. Hwu et al., data taken at the Pohang source)

SOLID STATEHIGH RESOLUTION PHOTOELECTRON

SPECTROSCOPY

• THE ACTUAL LIMIT IN ENERGYRESOLUTION OF PRESENTSPECTROMETERS IS ∆E ≅ 10 meV

• INCREASING RESOLUTIONDECREASING PHOTON FLUXAND COUNTS RATE

• THE HIGH FEL PHOTON FLUXALLOWS TO REDUCE ∆E DOWNTO ≅ 1 meV

• SPECTROSCOPY AT AND CLOSETO THE FERMI SURFACE, TOUNDERSTAND TRANSPORT,MAGNETIC PHENOMENA,SUPERCONDUCTIVITY,HIGHLY CORRELATED MATERIALS

• DILUITE CONCENTRATIONS OFATOMS IN SOLIDS, SURFACES,INTERFACES

• Spin-Resolved photoelectron Spectroscopy onMagnetic surfaces

• Pump: laser beam for heating the samplefor T>Tc the spin alignment is destroyed

• on what time-scale the rise in latticetemperature (phonon population) destroythe spin alignment

• Dynamics: spin-lattice relaxation (nsecfsec ?)

• Important for magneto-optical recording• Probe: FEL radiation spin-

polarized photo-, Auger-electrons

FELhν

PumpLaser

Magneto-OpticalMicroscopy

Spinpolarized

Photo-Auger-Secondary-

Electrons

SampleScanningMicroscopy

FluorescentRadiation

hω2 (t + ∆t) probe(MXCD)

hω1 (t) pump

H (t)

I

Probe Charge and Spin Dynamics (fs < ∆t < ps)

Magnetic Microscopy (XMCD)F. Nolting et al., Nature 405, 767 (2000)

NANOLITOGRAPHYDRAM (Dynamic Random Access Memory) in bits/chipand Logic (transistors/cm2) according with the NationalTechn. Roadmap of the Semiconductor Industry Assoc.April 1999.

0 50 100 150 200 2500.1

1

10

100

1000

DRAMGbits

Dense line width δ (nm)

Logic(M-trans./cm2)

1999

2002

2005

2008

2011

1997

Candidate technologies for sub-100 nm lithography:

- Optical-L: by using the F2 laser at λ=157 nm- X-ray-L: proximity lithography @ hν~ 1.2 keV- EUV-L: projection lithography @ hν~ 90 eV- EPL: Electron Projection Lithography @ e--beam- IONS-L: projection lithography @ ions-beam

Dense line width "Lw" (solid) and Depth Of Focus"DOF" (dashed) vs radiation wavelength "λ".

Lw = k1.λ/NA k1~ 0.6 NA=numerical apertureDOF= k2. λ/NA2 k2~ 0.5

0 50 100 150 200 2500

100

200

300

400

500

Lw

Radiation wavelength (nm)

LwDOF

DOF

NA=0.14

NA=0.7

Lw &DOF

(nm)

KrFArFF2

EUV

Power requirements (T. Silvfast, J. Q. Elect, Vol 35, 1999) :

On the 300 mm wafer: 120 mW (for 60 Wafer*layer/hour)From mercury lamp (λ=248 nm): 1 kWFrom excimer lasers (ArF, KrF): few WattsFrom F2 laser (λ=157 nm): few WattsFrom EUV source: 3 W (on the condenser mirror in

2.5% refl. band-width @ 13 nm)

HARD X-RAY

• X-FEL CAN BE USED TOPRODUCE AND/OR TO STUDY WARMDENSE PLASMA• IMPORTANT STUDIES FOR

FUSION PROCESSES• WARM DENSE MATTER REFERS TOTHAT PART OF THE DENSITY-TEMPERATURE PHASE DISGRAMWHERE STANDARD THEORIES OFCONDENSED MATTER PHYSICS ANDPLASMA STATISTICS PHYSICS ARENOT VALID. THE WARM DENSEMATTER IS A STATE INTERMEDIATEBETWEEN THE SOLID STATE ANDTHE PLASMA; A POSSIBLE STATE OF:PLANETS INTERIOR, COLD DENSESTARS, PLASMA DIRECTLY CREATEDFROM CONDENSED MATTER (LASERABLATION, INERTIAL FUSIONPROCESSES)

• PUMP-PROBE EXPERIMENTS

• PUMP: SPONTANEOUS EMISSION

• PROBE: X-FEL EMISSION

• THOMSON SCATTERING GIVEINFORMATION ON THE IONIZATIONSTATE, DENSITY, TEMPERATUREAND MICROSCOPIC PROPERTIESOF PLASMA

WITH AN X-FEL OF 1.5 Å WAVELENGTH

IT IS POSSIBLE TO ANALYSE PLASMA

WITH DENSITY > 1023 cm-3

THOMSON SCATTERING

• Coherent unshifted peak: intensity proportionalto tightly bounded electrons (ztb

2/atom)• Incoherent Compton peak: intensity

proportional to weakly bounded electrons(zwb/atom)

• Thomson scattering: spectral integratedintensity is proportional to free electrons(zf / atom)

BIOLOGY: STRUCTURALSTUDIES

• STRUCTURES AVILABLE (END 2000)X-RAY 10143NMR 2128

• PROTEIN CODED IN THE HUMANGENOME 100.000-140.000

• THE BOTTLENECK IS THENEED FOR CRYSTALS

• MANY BIOLOGICAL COMPLEXESCANNOT BE CRYSTALLISED

• AN X-FEL SOURCE CAN CHANGE THESCENARIO COMPLETELY: THE GOALIS TO BE ABLE TO PERFORMDIFFRACTION STUDIES ON SINGLEMACROMOLECULES, VIRUS,NANOCRYSTALS, …..

• SINGLE-SHOT EXPERIMENTS

• X-RAY HOLOGRAPHY

• X-RAY TOMOGRAPHY

• THE BOTTLENECK FOR MANY OFTHIS KIND OF EXPERIMENTS ISRADIATION DAMAGE

• THE X-FEL ADVANTAGE IS THESHORT PULSE LENGTH <200 fs

• MODELLIZATION OF RADIATIONDAMAGE ON THE BASIS OF THE :PHOTOELECTRIC EFFECT (95%) ANDOF ANELASTIC (COMPTON/RAMAN)EFFECTS SHOWS THAT IN THEMOLECULE A LARGE NUMBER OFPOSITIVE CHARGES ARE FORMEDGIVING RISE TO A COULOMBEXPLOSION

• NEED FOR SINGLE-SHOT EXPERIMENTS• THE DEGREE OF CONVERSION OF

POTENTIAL ENERGY INTO KINETICENERGY DURING THE X-RAY EXPOSUREIS INERTIA LIMITED AND STRONGLYDEPENDS ON THE PULSE DURATION

• THE MODEL SHOWS THAT A SERIOUSDAMAGE OCCURS AFTER 100 fs

R.Neutze, R.Wouts, D. van der Spoul,,E. Weckert, J. Hajdu; Nature 406, 752, (2000)

DINAMICAL PROCESSES INCONDENSED MATTER

• THE EXPERIMENTAL CHALLENGEIS TO MEASURE THE DYNAMICSTRUCTURE FACTOR S(Q, ω), ORTHE CORRESPONDING RESPONSEFUNCTION S(Q, t) IN THE APPROPRIATEREGION OF THE (ω - Q) SPACE

• THE X-FEL ALLOWS TO COVERREGIONS OF THE (ω - Q) SPACEINACCESSIBLE BY OTHERRADIATION SOURCES

• POSSIBLE EXPERIMENTS:• POLYMERS• CHARGE DENSITY WAVES• QUASICRYSTALS• SURFACES• DEFECTS IN CRYSTALS• FERROELECTRICS• MAGNETIC MATERIALS• ……….

CONCLUSIONS

• BRILLIANCE

• COHERENCE

• PULSE TIME STRUCTURE < 100fs

THE EXTRAORDINARYCHARACTERISTICS OF THE

X-FEL

MAKE THE NEW SOURCESCOMPLEMENTARY

RATHER THAN COMPETITIVETO 3RD

GENERATION (SR) FACILITIES