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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: