Reinhard Kienberger

Technische Universität MünchenMax-Planck Institut für Quantenoptik, Garching

X-Ray Science in the 21st CenturyKITP

06/Aug/2010

Attosecond spectroscopy on solids

Overview

• Needs for generating isolated attosecond x-ray pulses via HHG:

Phase-stable few-cycle driver pulses at long wavelengths• attosecond measurement technique:

streaking• What to do with attosecond pulses?• Pulse duration measurement at LCLS

Ti:Sapphire Oscillator

sub-10 fs pulse duration4.6 nJ energy82 MHz repetition rate

CPA Amplifier

20 fs pulse duration1.3 mJ energy3 kHz repetition rate

Hollow Fiber/Chirped MirrorPulse Compressor

<3.5 fs pulse duration400 µJ energy

Experiment

The Laser System

Booster: 4 kHz, 4 mJ, 28 fs

104104

102102

100100

400400 700700 10001000

spectrum

λ [nm]λ [nm]in

tens

ityin

tens

ity

key tools of attosecond technology: synthesized few-cycle wave & synchronized sub-fs xuv pulsesynthesized few-cycle wavesynthesized few-cycle wave

hollow fiber

neon gas

A. L. Cavalieri et al, New J. Phys. 9, 242 (2007); E. Goulielmakis et al, Science 317, 769 (2007) -15-15 -10-10 -5-5 00 55 1010 1515

delay [fs]delay [fs]-20-20 2020

88

77

66

norm

aliz

edin

tens

ityno

rmal

ized

inte

nsity

55

44

33

22

11

00

pulse duration< 3.5 fs

pulse energy> 0.4 mJ

< 1.5 cycles > 0.1 TW

T0 /4 ≈ 625 as (@ λ0 ≈ 0.75 µm)T0 = λ0/c ≈ 2.5 fs

Few-Cycle Laser PulsesControl of the Waveform

Sine waveformφ = π/2

Requires measurement & control of φ

Cosine waveformφ = 0E(t) = Ea(t)cos(ωLt + φ)

Phase change byglass wedges

slit

Electron detection:

MCP

MCP

Ionized gas:

Xenon

Trigger:PD

Laser beam

Shielded drift tube

Left-right ATI spectra

Previous results: average of

10000 shots

Detection of the absolute phase

Paulus et al. Nature, 414 182 (200

consecutive time-of-flight ATI spectra of rescattered electrons (laser rep. rate = 3kHz)

shot-to-shot evolution of the CEP

Stdsingle shot = 278mrad

phase distribution of CEP-stabilized shots (4500 shots; 3kHz)

CEP of consecutive phase-stabilized pulses

Parametric (Lissajous-like) representation

phase scan- limited by fluctuations

asymm. 2

asymm. 1

asym

m2

asymm 1

Non-phase-stabilized singleshots- random distribution

2π

π/6 π/3

π/2

2π/3

5π/6

π

7π/6

4π/3

3π/2

5π/3

11π/6

No phaseambiguit

y

High precisionstd

mean

Left-RightLeft+Righ

t

Left-RightLeft+Righ

t

Left-RightLeft-RightLeft+Righ

t

Left-Right

CEP=0 CEP=πsingle shot left-right TOF spectra

Wittmann et al. Nature Physics 4 (200

Non-phase-stabilized laser shots as they’re arriving…

non-stabilized shots has random phase distribution

first principle calibration:phase difference between shots is immediately given

real CEP retrieved by TDSE

Wittmann et al. Nature Physics 4 (200

Phase-scan with a stabilized laser

Wittmann et al. Nature Physics 4 (200

E (t)L

e-

Optical field ionization

Step 1

E (t)L

Step 2

e-

e Acceleration-

Spec

tral

Inte

nsity

E (t)L

Step 3

XUV emission on recollision

e-

High-order Harmonic Generation in the gas phase

P.B. Corkum, PRL 71 (1993)

Extending the cutoff

using an IR driving field

Comparison VIS / IR driver

V. Tosa and V. Yakovlev

0.9 mJ, 15 fs

12 mJ

2.1 μm few-cycle OPCPA system

New pump laserDisc regen

3 kHz / 1.5 ps / 27 mJ

> 2mJ… .??

IR – driven HHG

Cut-off ~1.6 keV

Recombination Emission from Strongly-Driven Atoms

21 51 81 111

25 nm 12.5 nm 7.5 nm

1

0.1

Cut-off harmonics: train of attosecond bursts

Multi-cycle driver pulse : τp » To

High-order odd harmonics of the driver laser

L’Huillier, Balcou, 1993, PRL 70, 774Macklin et al, 1993, PRL 70, 766

Paul et al, Science 292, 1689 (2001)Tsakiris, Charalambidis et al, 2003

Harmonic order

Spe

ctra

lin

ten

sity

xuv-filterxuv-filter

6060 7070 8080 9090 100100 11011000

10001000

inte

nsity

[a.u

.]in

tens

ity[a

.u.]

photon energy [eV] photon energy [eV] 5050

cosine wavecosine wave

A. Baltuska et al, Nature 421, 611 (2003)

electron trajectorieselectron trajectories

ħωx

EELL((tt))

EELL((tt)) EELL((tt))

EELL((tt))

EL(t)EL(t)

EELL((tt))

steering bound electrons with controlled light fields: the birth of an attosecond pulse

6060 7070 8080 9090 100100 11011000

10001000

inte

nsity

[cou

nts]

inte

nsity

[cou

nts]

photon energy [eV] photon energy [eV]

sine wavesine wave

attosecond xuv/x-ray pulse generation

A. Baltuska et al., Nature 421, 611 (2003)

6060 7070 8080 9090 100100 11011000

10001000

inte

nsi

ty[a

.u.]

inte

nsi

ty[a

.u.]

5050

and measurement

Ne gasNe gasNe gas

few-femtosecond,few-cyclelaser pulseλL ≈ 750 nmτL = 3.5 - 5 fsWL = 0.3 - 0.5 mJ

fewfew--femtosecondfemtosecond,,fewfew--cyclecyclelaserlaser pulsepulseλλLL ≈≈ 750 nm750 nmττLL = 3.5 = 3.5 -- 5 5 fsfsWWL L = 0.3 = 0.3 -- 0.5 mJ0.5 mJ

time-of-lightelectronspectrometer

timetime--ofof--lightlightelectronelectronspectrometerspectrometer

atomicgas

atomicatomicgasgas

near- diffraction-limitedxuv/soft-x-ray beam

nearnear-- diffractiondiffraction--limitedlimitedxuvxuv//softsoft--xx--rayray beambeam

xuv pulseknocks electrons

free in thepresence of thefew-cycle laser

field

xuvxuv pulsepulseknocksknocks electronselectrons

freefree in in thethepresencepresence of of thethefewfew--cyclecycle laserlaser

fieldfield

Drescher et al, Science 291, 1923 (2001)

Hentschel et al, Nature 414, 509 (2001)

Kienberger et al, Science 297, 1144 (2002)

attosecond pulse generation

XUV spotXUV spot

Ionization with an Isolated Attosecond Pulse

Mo-Si multilayer mirror

Time-of-flightspectrometer

Nozzle

Ne

( )∫∞

′′=rt

L tdtEep t( )rΔ

pi

Δp

pf

XUV cut-off energy: ~100 eVMirror reflectivity bandwidthup to: 30 eV (FWHM)

Detection as in:Kienberger et al., Science 297, 1144 (2002)

delay possible

Ionization at different instants of time

-Δpmax--ΔΔppmaxmax

+Δpmax++ΔΔppmaxmax

000

final momentum of photoelectronsdepending on the release time

final momentumof the electron

time

Incident X-rayintensity

Mapping Time to Energy

ħωx

instant ofelectronrelease

ΔW(t7)

ΔW(t3)

ΔW(t2)

ΔW(t1)

ΔW(t4)

ΔW(t6)

ΔW(t5)

Change in electronenergy

-500 as 0 500 as

Laser electric field

t7t1 t2 t3 t4 t5 t6

Optical Streak Camera, 1834

sampling field oscillations

ħωx

+10 +10 eVeV

--10 10 eVeV

00

ΔW

tD

R. Kienberger et al, Nature 294 (2004)

656565

757575

858585

a streaking traceel

ectr

onki

net

icen

ergy

[eV

][[ e

VeV]]

elec

tron

elec

tron

kin

etic

kin

etic

ener

gy

ener

gy

delay [fs]delaydelay [[fsfs]] 000 444-4--44 888

E. Goulielmakis et al, Science 305, 1267 (2004

isolated sub-100-as pulses

Goulielmakis et al, Science 320, 1614 (2008)

AS beamline

core-levelphoto-

emission

+1

corecore--levellevelphotophoto--

emissionemission

+1+1

Augerdecay

+2

AugerAugerdecaydecay

+2+2

photo-emission

&shake up

+1

photophoto--emissionemission

&&shakeshake upup

+1+1

Augerdecay

&shake up

+2

AugerAugerdecaydecay

&&shakeshake upup

+2+2

kin

etic

ener

gyki

net

icki

net

icen

ergy

ener

gy

00

coreorbitalcorecoreorbitalorbital

occupiedvalenceoccupiedoccupiedvalencevalence

unocc.valenceunoccunocc..valencevalence

valencephoto-

emission

+1

valencevalencephotophoto--

emissionemission

+1+1final

charge statefinalfinal

chargecharge statestate

bin

din

gen

erg

ybi

ndi

ng

ener

gy

real-time observation of multi-electron dynamics(excitation, relaxation, correlation) in atoms, molecules & solids?

by means of strong-field-induced free-free transitions: streakingby means of strong-field-induced free-free transitions: streaking

Ionization of electrons in a solid sample

( )lA t ( ')lA tXUV

sample system

TOF

( )lA tXUV

NIRNIR

EX (t)

EL(t)

400400

800800

4040 60602020 8080 120120 14014010010000

1.51.5

3.03.0

4.54.5

-1.5-1.54040 60602020 8080 120120 140140

photoelectron energy [eV]photoelectron energy [eV]100100

00

00

5.05.0

electrons from4f band Fermi edge

τx = 300 asħωx = 95 eVτL = 5 fs

λL = 750 nm

dela

y [

fs]

dela

y [

fs]

proof of principle: attosecond streaking of core-level (4f) & conduction-band (Fermi-edge) electrons in tungsten

Augerdecay

+2

Augerdecay

+2

photo-emission

&shake up

+1

photo-emission

&shake up

+1

Augerdecay

&shake up

+2

Augerdecay

&shake up

+2

attosecond spectroscopy in solids?

A. L. Cavalieri et al., Nature 449, 1029 (2007)A. L. Cavalieri et al., Nature 449, 1029 (2007)

delay

5959

6363

-2-2 00-4-4 22 44-6-6delay [fs]delay [fs]

5555

6161

5757

6565

8787

9191

8383

8989

8585

valencephoto-

emission

+1

valencevalencephotophoto--

emissionemission

+1+1

core-levelphoto-

emission

+1

corecore--levellevelphotophoto--

emissionemission

+1+1

ener

gyen

ergy

00

-2-2 00-4-4 22 44-6-6delay [fs]delay [fs]

00

-0.5-0.5

0.50.5

11

-1-1

ener

gy s

hif

t [e

V]

ener

gy s

hif

t [e

V]

Δτ = 110 ± 70 as

Fermiedge

4f band

electrons from the 4f band reach the surface~ 110 as later than those from the Fermi-edge

electrons from the 4f band reach the surface~ 110 as later than those from the Fermi-edge

CB

4f

Δt

Re (0001)

Delay of 4f core levels relative to CB:64 ± 10 as

Spectrogram analysis:retrieval algorithm based on analytical solution of TDSE

Samples:Re(0001) and W(110)

Photon energies: 90, 120, 130 eV

Core level electrons delayed by 55 – 90 as.

as spectroscopy of clean metal surface

Origin of delay?

Propagation effect

Assumption:streaking acts outside solid

• Different inelastic mean free path different depth profile • Different group velocity

(final-state effect?)

4f emitted after CB

Theory:A. Kazansky et al., PRL 102, 177401 (2009).C. Lemell et al., PRA 79, 62901 (2009).C.-H. Zhang et al., PRL 102, 123601 (2009).J.C. Baggesen et al., PRA 78, 32905 (2008).

,

,

16vac

solid

EE

⊥

⊥

≈

Current Effort: Absolute Emission Time

…..blow gas on the sample…..

geometric effects….

0011

4040

6060

2020

8080

100100

phot

oele

ctro

n en

ergy

[eV]

phot

oele

ctro

n en

ergy

[eV]

intensity [arb. units]intensity [arb. units]

2s2s

2p2p

M. Schultze et al, Science 328, 1658 (2010).M. M. SchultzeSchultze et al, et al, ScienceScience 328328, 1658 (2010)., 1658 (2010).

What about the reference? Ne 2s / 2p gas phase

delay

emission of low-energy photoelectron is delayed by about 20 asemission of low-energy photoelectron is delayed by about 20 as

kine

tic e

nerg

yki

netic

ene

rgy

00

bind

ing

ener

gybi

ndin

g en

ergy

00-5.5-5.5delay [fs]delay [fs]

5.55.5

4040

6060

2020

8080

100100

phot

oele

ctro

n en

ergy

[eV]

phot

oele

ctro

n en

ergy

[eV]

1.01.0

0.50.5

0.00.0-300-300 30030000

EX(t)

2s2s

2p2p

Duration of photoemission?

Idea:

Introduce electronic reference state localized at the surface

time zero marker

Baggesen et al., PRA 78, 32905 (2008).

Re CB

Re 4f

Xe 4d

Xe 5p

Xe monolayer on Re

46 as

Order of appearanceTime delay

65 as

6 as6 as

Xe 4d

Re 4f

Xe 5pRe CB

Xe 4d

Re 4f

Xe 5pRe CB

46 as

± 11 as

NIR intensity ~ 5.5 · 1011 W/cm2

Xe monolayer on Re

+22 ± 12 as

4d is first

–20 ± 3 as

5p is first

Comparison atomic vs. solid xenon

solid xenon

(50 layers)

atomic xenon

electronpropagation

effects

Electron transport through defined adlayers

substrate

and electron states

1 – 3 metallic layers

substrate

dielectricmultilayer

localizedand delocalizedelectron states

IRXUV

IR refractionand penetration

electron transport

Electron transport through defined adlayers

Outlook

• Generation of UV pulses for excitationof molecules: UV-pump/XUV-probe

• Charge-transfer in molecules and soldis

Goal: study excited state dynamics with as to few-fs time resolution

Requirements: few-cycle UV pump pulses (hν= 4-6 eV)synchronized withIsolated XUV probe pulse (hν= 80-130 eV)

Attosecond 2PPE

E

ΔE≈hν(UV)

TOF

variable Δt

Intense pulses in the deep ultraviolet

U. Graf et al., Optics Express 16,18956 (2008)

SD- FROG setup

Gas target, Ne 1 – 9 bar

Emission of UV light at different target pressures

Intense (>2 μJ) pulses in the deep ultraviolet

U. Graf et al., Optics Express 16,18956 (2008)

Autocorrelation trace on Kr ion yield

Graf et al. Opt. Exp. accepted

delay chamber

Collinear generation of UV and XUV

Neon ca 0.2-0.3 bar

Neon ca 3-5 bar

Argon ca 1 bar

60 70 80 90 100 1100

1000

Inte

nsity

[cou

nts]

Photon energy [eV]

Isolated XUV attosecond pulses

U. Graf et al., Optics Express 16, 18956 (2008)

NIR/VISτ < 4 fs400 μJ

XUV

τ ≥ 80 as

UVτ ≤ 4 fsE ≤ 1.5μJ

A. Baltuska et al., Nature 421, 611 (2003)

E. Goulielmakis et al., Science Vol. 320 (2008)

Intense sub-4 fs pulses in the deep UV

Time [fs] Wavelength [nm]

Inte

nsity

Pha

se

Pha

se

In

tens

ity

Neon ca 0.2-0.3 bar

Neon ca 3-5 barArgon ca 1 bar

NIR/VIS NIR/VIS +UV + XUV

Collinear generation of UV and XUV

Neon Neon 230 mbar

Collinear generation of UV and XUV

E. Bothschafter et al., Optics Express (2010)

up to 1 µJ up to 107 ph/pulse

Exciting an electron wavepacket in a molecule

First candidate:ozone

Sampling the evolutionwith XUV AS-pulses

Oriented molecules on a surface

or SAM

uv-

probing charge transfer/migration in complex (bio-)molecules?

8082

8486

8890

9294 0.5 0.75 1 1.25 1.5

photoelectronenergy [eV]

time delay[fs]

F. Remacle, R. D. Levine, PNAS 103, 6793 (2005)F. Remacle, R. D. Levine, PNAS 103, 6793 (2005)

Colleagues & CooperationsF. Krausz R. Ernstorfer M. Schultze Y. Deng A. Schiffrin

N. Karpowics E. Goulielmakis A. Cavalieri X. Gu G. Marcus

I. Grguras M. Fiess W. Helml T. Paasch M. Jobst

F. Reiter B. Horvath E. Magerl T. Metzger B. DennhardtM. Hassan T. Wittmann E. Bothschafter A. Schwarz

theory: J. Gagnon, V. YakovlevMPQ Garching, Germany

P. EcheniqueSan Sebastian, Spain

XUV optics & spectroscopy: M. Hofstetter, U. KleinebergLudwig Maximilians Univ. Munich, Germany

surface dynamics: S. Neppl, P. Feulner, J. Barth TU Munich, Germany

CEP measurement: G. G. PaulusUniv. Jena, Germany

X-rayPulse duration measurement

at LCLS

In collaboration with:DESY, CFEL, Ohio State U., Dublin U., SLAC

Electronenergy

Ix(t)

Wbinding

EL(t)hνL

hνx

τx>> T0/2

„long“ X-ray pulse

Laser-field dressed photoelectrons

0

Electronenergy

Ix(t)

Wbinding

Detector

EL(t)

hνx

τx< T0/2„short“ X-ray pulse

λIR = 2 μmT0/2 = 3.3 fs

Laser-field dressed photoelectrons

single-shot streaking measurement of τx-ray

ħωx

Maximum shift!

EEelel

ħν- Ip

+ΔE

time-jitter

- ΔEALaser

Retrieval of Amax

Maximum broadening!

Retrieval of τx-ray

taking into account: - photon energy jitters by 1 %- bandwidth jitters (7 eV + 3

eV)

spectra sorted acc. to phase cavity timer„long“ pulse, λLaser = 2 μm

photoelectron energy (TOF)

delayFEL IR

spectra sorted acc. to phase cavity timer„short“ pulse, λLaser = 2 μm

photoelectron energy (TOF)delay FEL IR

g{xXÇw