Institut für Photonik Technische Universität Wien Wien, Austria Dept. f. Physik, Ludwig- Maximilians-Universität München, Germany Max-Planck-Institut für.

Institut für PhotonikTechnische Universität WienWien, Austria

Dept. f. Physik, Ludwig-Maximilians-Universität München, Germany

Max-Planck-Institut für QuantenoptikGarching, Germany

Ferenc [email protected]

FRISNO-8, French-Israeli Symposium on Nonlinear & Quantum Optics, Ein Bokek, Israel, February 21-25, 2005

Attosecond Physics: Control & Measurement at

the Atomic Timescale

Characteristic time scale

Bohr-orbit time in hydrogen:

152 attoseconds

Femtochemistry Controlling and tracing the motion of atoms in molecules

controlling & tracing chemical reactions

Characteristic time scale:vibrational oscillation period≥ 7 fs (H2)

AttophysicsControlling & tracing electrons inside atoms & molecules

Inner-shell electron dynamics in atoms & molecules

Observation in real time requires

Energetic ( ≥ 100 eV) and sudden ( << 1 fs)

excitation Measuring technique capable of capturing subsequent dynamics

with sub-femtosecond or attosecond resolution

Inner-shell electron dynamics in atoms & molecules

Femtosecond metrology: utilizes controlled variation of the (cycle-averaged) intensity of ultrashort laser

pulses

Attosecond metrology: requires controlled variation of a physical quantity within 1 femtosecond

= ε(t)cos(ωLt + φ)ε(t)

T0 /4 = 625 attoseconds@ L 0.75 µm

E(t)

= ε(t)cos(ωLt + φ) Cosine waveformφ = 0

E(t)

Sine waveformφ = /2

T0 /4 625 as (@ 0 0.75 µm)T0 2.5 fs

Requires measurement & control of φ

Attosecond metrology: requires controlled variation of a physical quantity within 1 femtosecond

Vienna-Munich, 2003: Baltuska et al, Nature 421, 611

First measurement of Δφ: Vienna, 1996

Stabilization of Δφ: Boulder, Munich-Vienna 2000

Lasers produce pulses with varying φ

φn+1 = φn + Δφ

Intense few-cycle laser pulses with stabilized φ

pulses

0.4-mJ1-kHz5-fs

phase-locked

Hollow-Fiber-Chirped-Mirror

PulseCompressor

Few-cycle light with controlled φ: light waveform control

Baltuska et al, Nature 421, 611 (2003)P. H. Bucksbaum, Nature 421, 593 (2003)

WLG WLG

MultipassTi:sa Amplifier

CW PumpLaser

f-to-2f

Iinterfero-meter

pump laser synchronization

f-to-2f

IIinterfero-meter

Divider80000/

Divider/4

PersonalComputer

AOM

Phase-Locking

Electronics

BS 50% BS 0.7%

×2 ×2

kHz Pump Laser

Ti:sa Oscillator

Phase detector CCDPhase

detector

p = 5 fs Ip = 0.1 TW

Exposing atoms to linearly-polarized few-cycle light:

giant atomic dipole oscillations

3D-Solution of the Schrödinger equation for hydrogen: Armin Scrinzi Animation: Barbara Ferus, Matthias Uiberacker

Few-cycle-driven high harmonic emission Semiclassical recollision model

ħωx

Cosine waveform

Emission ofhighest-energy photonTrajectory x(t) of the most energetic

recolliding wavepacket

Ionizationthreshold

EL(t)

M. Lewenstein et al., Phys. Rev. A 49, 2117 (1994)

Few-cycle-driven high harmonic emission

Sine waveform

Ionizationthreshold

ħωx

EL(t)

Laser field transfers momentum to electrons knocked free by xuv photons

Drescher et al., Science 291, 1923 (2001)

Kienberger et al., Science 297, 1144 (2002)

Momentum transfer depends on instant of electron release within the wave cycle

t

teAtdtEetp )()()( LL

Incident X-rayintensity

Mapping time to momentum

Δpi

instant ofelectronrelease

Δp(t7)

Δp(t6)

Δp(t5)

Δp(t3)

Δp(t2)

Δp(t1)

Δp(t4)

Momentumchange along the EL vector

-500 as 0 500 as

Laser electric field

t7t1 t2 t3 t4 t5 t6

Optical-field-driven streak camera J. Itatani et al., Phys. Rev. Lett. 88, 173903 (2002)M. Kitzler et al., Phys. Rev. Lett. 88, 173904 (2002)

Resolution: several 100 fs

Electron-optical streak camera

D. J. Bradley et al., Opt. Commun. 2, 391 (1971)M. Y. Schelev et al., Appl. Phys. Lett. 18, 354 (1971)

Optical-field-driven streak camera

Attosecond pump-probe apparatus Time-of-lightelectron spectrometer

atomicgas

Near-diffraction-limitedXUV/Soft-X-ray beam

XUV pulseknocks electrons

free in the presence of the few-cycle laser

field

M. Drescher et al., Science 291, 1923 (2001)

Ne gas

Few-femtosecond,few-cyclelaser pulse

λL 750 nmTp = 5 - 7 fsWp = 0.3 - 0.5 mJ

Photon energy [eV]

85 90 95 100 105

Mo

/Si

mir

ror

refl

ecti

vity

0.0

0.1

0.2

0.3

ħωx

+10 eV

-10 eV

0

ΔW

Mo/Si mirror

dN/dW

Optical-field-driven streak camera

Photon energy [eV]

85 90 95 100 105

Optical-field-driven streak camera records electron emission with sub-fs resolution

ħωx

+10 eV

-10 eV

0

ΔW

Mo

/Si

mir

ror

refl

ec

tiv

ity

0.0

0.1

0.2

0.3

X-r

ay

in

ten

sit

y [

a.u

.]

0.0

0.5

1.0

1

fs

x <

500

as

1 fs

Optical-field-driven streak camera records electron emission with sub-fs resolution

dN/dW

X = 250 attoseconds

R. Kienberger et al., Nature 427, 817 (2004)

Full characterization of a sub-fs, ~100-eV xuv pulse

Reconstructed temporal intensity profile and chirp of the xuv excitation pulse:

Time [fs]

Inte

nsi

ty [

arb

. u

.]

0

1

Inst

anta

neo

us

ener

gy

shif

t [e

V]

-3

-2

-1

0

1

2

-0.4 -0.2 0.0 0.2 -0.4

xuv = 250as

EL(t)

td = -T0/4

td = +T0/4

td = -T0/4

td = +T0/4

Field-freespectrum

ħωx

+10 eV

-10 eV

0

ΔW

tD

probes the vector potentialof the electric field of light

Energy shift of sub-fs electron wavepacket

dN/dW

-20

-10

0

10

20

Delay t [fs]

Ph

oto

elec

tro

n k

inet

ic e

ner

gy

[eV

]

Vec

tor

po

ten

tia

l, A

(t

) [f

s M

V/c

m]

L

2 4 8 10 14 18 200 6 12 16 22

50

60

70

80

90

Attosecond light field detector L

igh

t el

ectr

ic f

ield

, EL(t

) (1

07 V

/cm

)

Time t (fs)

Direct measurement of light waves

Directly measured

Calculated from spectrum

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

Optical-field-driven streak camera can probe both primary (photo) and secondary (Auger) electrons

W1

W2

Wh

Wbind

WkindNdW

0

Photo-emission x - duration of X-ray pulse

Auger-emission h - lifetime of core hole

Δt

Streak images

Simulated streak images of Auger electron emissionversus delay between pump XUV pulse (X = 0.5 fs) and

the probe laser pulse (T0 = 2.5 fs, L = 5 fs)

hh < < TToo/2/2 hh > > TToo/2/2

30

Ph

oto

elec

tro

n k

inet

ic e

ner

gy

[eV

]

30

30

-2 -1 0 1 2

-2 -1 0 1 2

50

40

h = 0.2 fsa

50

40

h = 0.5 fsb

50

40

-2 -1 0 1 2h = 1 fsc

Delay t [fs]

L

50

50

40

40

30

30-4

-4

-2

-2

0

0

2

2

4

4

6

6

8

8

10

10

12

12

14

14

h = 2 fs

h = 5 fs

d

e

Sampling by laser field

Resolution 100 as

Sampling by pulse envelope

Resolution 1 fs

Snapshots of Electron Emission from Kr Following Core-Hole Excitation by a Sub-fs X-Ray Pulse

M. Drescher et al., Nature 419, 803 (2002)

Tracing core-hole decay directly in time Lifetime of M-shell (3d) vacancy, h = 7.91 fs

Drescher et al.,Nature 419, 803 (2002)

Observing field ionization in real time ?

Attosecond XUV pulse probes

remaining ground-state

population by single-photon

ionization

Laser field depletes the

ground state of the

most-weakly bound electron

by tunnel ionization

EL(t)EL(t)

Ground state population

T. Uphues, M. Uiberacker et al., Garching

First experiment :

0 2 4 6 8 100,0

0,2

0,4

0,6

0,8

1,0

Yie

ld (

a.u

.)

Time (fs)

Bound state population

Integrated XUV electron yield

Ground state population

Theory :

M. Spammer, O. Smirnova, A. Scrinzi, Vienna

Laser field

Probing collisional excitation & relaxation processes

Ionizationthreshold

EL(t)

Sub-femtosecond collisionalexcitation up to keV energies

Subsequent electronicrearrangement can be probed

by a sub-fs X-ray pulse

available up to 1 keV photon energy J. Seres et al., Nature 433, 596 (2005)

From femtochemistry towards attophysics

Time1 fs

1 Å

Space

Molecules

Femtochemistry: controlling & tracing atomic motion on the length scale of chemical bonds

Attophysics: controlling & tracing electronic motion on a sub-atomic scale

Atoms

Theory: P. B. Corkum, M. Y. Ivanov, NRC Canada T. Brabec, Univ. Ottawa, Canada J. Burgdörfer, Ch. Lemell, A. Scrinzi, O. Smirnova, Vienna Univ. Techn., A XUV optics

U. Kleineberg, U. Heinzmann, Univ. Bielefeld, D

XUV spectroscopy:Th. Uphues, M. Drescher, Univ. Hamburg, DESY, D

Light phase control: Ch. Gole, R. Holzwarth, T. Udem, T. W. Hänsch

Univ. Munich, MPQ Garching, D& measurement:

G. Paulus, M. Schätzel, F. Lindner, H. Walther A&M Univ. Texas, USA, MPQ Garching, D

Electron and ion spectroscopy: K. O‘Keeffe, M. Lezius

Vienna Univ. Techn., Austria

COLTRIMS: H. Rottke, W. Sandner, MBI Berlin, D

A. Apolonski

A. Baltuska

P. Dombi

A. Fernandes

E. Goulielmakis

N. Ishii

R. Kienberger

S. Köhler

T. Metzger

S. Naumov

J. Rauschenberger

M. Schultze

J. Seres

C. Teisset

M. Uiberacker

A.-J. Verhoef

V. Yakovlev

Coworkers Collaborators

Photon Energy (keV)

HH

In

tern

sity

(a.

u.)

HH

In

tern

sity

(a.

u.)

Fil

ter

tran

smis

sio

n (

%)

Fil

ter

tran

smis

sio

n (

%)

3030

2525

2020

1515

1010

55

000 0.5 1 1.5 2 2.5 3 3.5 4

100100

9090

8080

7070

6060

5050

4040

3030

2020

100

1010

Kiloelectronvolt high harmonic emission from few-cycle-driven helium atoms

Offers the potential for time-resolved spectroscopy with atomic (~ 24 as) resolution

Field-freedistribution

td = -T0/4

td = +T0/4 td = -T0/4

pi

Field-freedistribution

Example: linearly-chirped sub-fs emission

td = +T0/4

EL(t) eAL(t)

Optical-field-driven streak camera projects ne(p,t) to σe(p)

“Tomographic images“ of the time-momentum distribution of atomic electron emission

Complete reconstruction of atomic Complete reconstruction of atomic excitation and relaxation processes excitation and relaxation processes on an attosecond time scale by on an attosecond time scale by probing primary (photo) probing primary (photo) or secondary (Auger) or secondary (Auger) electron emission, respectively.electron emission, respectively.

R. Kienberger et al., Nature 427, 817 (2004)

dttteApnp )),(()( Lee

Atomic transient recorderRelease time, t

Mo

men

tum

, p

Initial time-momentumdistribution of positive-

energy electronsFinal momentum

distributions

Snapshots of electron emission from Kr following core-hole excitation by a sub-fs xuv pulse

M. Drescher et al., Nature 419, 803 (2002)

Tracing core-hole decay directly in time Lifetime of M-shell (3d) vacancy, h = 7.91 fs

Interfering quantum paths in atomic decay

4f5p

5s

4d

superCoster-Kronig direct

80 100 120 140 160 180Photon energy [eV]

0

10

20

30

Cro

ss s

ecti

on

[M

b]

Beutler-FanoLine-profile

C. Dzionk et al., PRL. 62, 878 (1989)

Dy

M. Wickenhauser, J. Burgdörfer et al., submitted

Resolving power of the atomic transient recorder

max

L

W

ω

π

Tt

2

0min

100 80 60 40

ΔWmax ΔWmax

Energy [eV]

R. Kienberger et al., Nature 427, 817 (2004)

~ 100 as @ ~ 100 eVxω

- 625- 625 attoseconds + 625 + 625 0

Main IdeaThe core idea is to watch the sub-cycle dynamics of strong field

ionization by probing the non-ionized portion of the electronic wave packet with attosecond XUV pulses

Fie

ld

Time (units of laser cycle)

Laser Field

XUV pulse

2. Laser field depletes ground state

3. XUV ionizes remaining ground state population to high continuum states

1. Field free situation:electron sits in ground state

4. Vary the XUV timing to probe time-dependent depletion

One-electron model

)()(1

2

1222

2

txVtxVaxx

H XL

Hamiltonian:

)(sin2

sin)( 2LL

LLL t

ttV

)(sin2ln4exp)(2

XXX

XXX tt

tttV

Soft-core:

L = 1.5×1014 W/cm2

L = 790 nm

L = 5 fs

X = 1011 W/cm2

X = 80 eV

X = 250 as

a = 1.59 a.u.

Models the ionization potential of Xe Ip = 12.31 eV

Strong laser field: XUV:

Strong fieldXUV

Strong Field Ionization – Depletion of Bound States

• Ionization occurs in steps with large depletion of the bound states population appearing near the peaks of the strong field.

Consider projections on to bound states during the strong field:2

)()( tta gg 2

)()( tta nn

Fields–free ground state Field-free excited states

• Ground state populationshows dips arising from virtual excitation in the presence of the strong field: