Attosecond Physics:

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Attosecond Physics the Frontier in
Time-Microscopy (and what computations can do for
it)
Jeremie Caillat, Dmytro Luzhbin, Olga Smirnova,
Vladislav Yakovlev and Armin Scrinzi
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Preface Time-microscopy
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How to observe a fast process ?
Slow motion movie take snapshots at well-known
time intervals (Eadweard Muybridge 1878)

• Need
• - Fast shutter (or flashlight), faster than what
  we want to observe
• Precise control over the time intervals between
  exposures
• - A medium to record the images (e.g.
  photographic film)

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Very slow motion movies
The fastest flashlight - attosecond XUV
pulses Most precise timing - femtosecond
laser pulses Recording medium - electron
energy distributions How exactly do electrons do
their quantum leaps ?
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SFB ADLIS Advanced Light Sources
Inst. f. Photonik (TU Wien) - Inst. f.
Festkörperelektronik (TU) - Inst. f.
Theoretische Physik (TU Wien) -
Mikrostrukturzentrum (TU Wien) Uni Würzburg -
Inst. f. Theoretische Chemie (Uni Wien) Uni
Bielefeld
Short pulses in a wide frequency spectrum
Lasers
Terahertz radiation
High harmonics
Electron dynamics in quantum wells and -dots
Control and accelerate electrons
Electron dynamics in atoms and molecules
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I Pulses and time scales
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Short powerful light pulses

• Full control over the laser electric field

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Short the time scales
Ghz Electronics
Femtochemistry
Attophysics
nanosec
picosec
femtosec
attosec
10-9
10-12
10-15
10-18
?
Laser pulses
XUV pulses
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Short laser pulse its measured image
Measurement of the electric field of a
femtosecond laser pulse Stroboscopic image using
attosecond XUV pulses Recorded in electron energy
distributions
2 femtosceconds
Laser electric potential
Electron energy
Time
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Powerful pulse what it does to an atom
The hydrogen electron density in a strong field
Time (femtoseconds) -2.6 -1.3 0 1.3 2.6
4 x 1014 W/cm2 5 fs FWHM (simulation) Total
explosion during a few femtoseconds
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Full control pulse shape and electric
oscillations
Electric field of a 7 femtosecond laser pulse
We can Control the overall shape Choose the
phase (red or blue curve, or anything between)
Electric field strength
Blue-red phase shifted by 90o
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II High powers Electron accelerator
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A laser pulse plows through a plasma
Plasma-wave behind the pulse (like the water wave
behind a fast boat) Electrons accelerate on
plasma wave (like a surfer on an ocean wave)
Simulation by Pukhov Meyer-ter-Vehn
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Accelerate electrons to MeV energies
Focus very high power laser pulse into a thin
plasma
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Maxwells equations with movable charges
Self consistent solution of Maxwells equations
plus relativistic equation of motion of particles
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III Generation of attosecond pulses
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Not just destruction high frequency radiation
is generated
Measurement and simulations
When a strong pulse hits an atom during the
destruction process high frequency (XUV)
radiation is generated
Intensity
Frequency (multiples of laser frequency)
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Time-structure in high frequency radiation
Time-frequency analysis of the emitted
radiation (hydrogen, laser _at_ 800 nm, peak
intensity 4 x 1014 W/cm2)

Very short (attosecond) time structures
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Attosecond pulses - isolated bursts of high
frequency radiation
Extract highest frequencies, propagate through
gas volume
A clean, single pulse
Numerical simulation of a pulse generated in a
3-d volume
apresentation by Vlad Yakovlev
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IV Attosecond measurements
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• Attosecond measurements
• the streak camera principle

How to convert time distributions into electron
velocity distributions ?
Xuv ionization in a laser field Initial electron
velocity
Acceleration in the field E(t)
The laser maps time into velocity distribution
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An experimental streaking image
The first attosecond streaking image
Xuv pulse duration 650 as
M. Hentschel et al., 2001,Nature, 414, 509.
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and a much clearer image
Measurement of the electric field of a
femtosecond laser pulse
2 femtosceconds
Laser electric potential
Electron energy
Time
Kienberger et al., submitted to Nature
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V Time-resolved atomic physics
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Time-resolved Auger measurement
A quantum leap in an atom
Electron energy
Quantum states
Binding pot of the atom
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Auger streaking image measured data
Drescher et al., Nature, October 2002
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Lots of excitement !
In the community More than 220 citations of 3
articles since November 2001
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VI Challenges for Theory and Computations
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Tasks for theory
I) Control and measure XUV pulse parameters -
help to improve the new experimental
tools Influence of laser parameters
(time-structure, intensity etc.) ? Alternative
diagnostic methods other than streaking ?
II) Electron wave-packet dynamics and
acceleration - X-ray lasers and compact electron
accelerators Control excitations of matter by
laser generated electron packets ? Momenta and
time-structure of laser-accelerated electrons ?
III) Time-dependent atomic physics - what will
we see inside the atom ? Time-domain vs.
traditional spectroscopy what is new ? Develop
time-dependent analytical and numerical methods.
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Computations I Non-linear wave propagation
Solve simultaneously Laser pulse - propagation
with strong ionization
Free electron generation and energy loss due to
ionization
Harmonic pulse - linear propagtion equation with
source term
Absorption and atomic dipole source term
talk by Vlad Yakovlev
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Computations II PIC Particle-In-Cell code
Solve Maxwells equation in a (thin) plasma 3-d
lowest order finite difference method on a
rectangular grid Solution on a large parallel
computer
1 field cell
1 macro particle

• Could there be a substantial gain by higher
  order methods ?
• Optimal algorithms for load-balancing
• Minimize communication

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Compuations III MCTDHF
Multi-Configuration Time-Dependent Hartree-Fock
Describe the motion and interaction of several (4
8) electrons (Which quantum leaps
should we expect ?)
Why is it hard ?
High-dimensional problem 4 8 times 3
dimensional space Suppose each direction is
represented by only 10 points 1012 1024
floating numbers to represent the system !!!
! IMPOSSIBLE ! (not just hard)

• Make the MCTDHF approximation
• 3-dimensional, but more complicated system of
  equations
• FEASIBLE (still not
  easy)

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The equations of motion

• Problem size
• For each time step
• n4 (n 10) integrations in 3-dimensional space
• vector length for j(x) 1000 100 000
• Time steps 10 000 for one simulation

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Numerics and computations

• Numerical tasks
• General properties of the ansatz (convergence,
  stability)
• Discretization of 3-dimensional space
• Integration in time

• Computational tasks
• Parallelization strategies
• Visualization
• Real time code timing / performance prediction

Talks by Othmar Koch and Wolfgang Kreuzer
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The Photonics Institute Theory Group (nice photo,
slightly outdated)

Ulrich and Christian have left Jeremie Caillat
and Dmytro Luzhbin have joined us in fall 2003
Thank you for your attention !