Attosecond Physics

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Attosecond Physics
Ultrafast Physics at a new Frontier
Dawn Fraser University of Ottawa, Dec 2005
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Flash Photography and Film
Application on molecular and atomic scale ??
Can we take pictures of electrons or make movies
of molecular vibration?

• For a camera to freeze the motion of an object
  
• the wavelength of the light must be shorter
  than the
  extension of the
  subject
• the duration of the light flash must be short
  relative to the speed of the subject

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Just how fast is ultrafast?
A classical electron makes one Bohr orbit in 150
attoseconds.
To make movies of molecular and atomic processes
we need pulses with Spatial resolution
Angstrom (10-10)m Temporal resolution
lt Femtosecond (10-15)s

• Right now
• Spatial needs met by electron microscopes,
  Synchroton X-ray sources
• Temporal needs met by lasers
• No one source can yet meet both needs

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The Femtosecond Barrier
Historical progress of ultra-short laser
technology shows evidence of a femtosecond barrier
Natural limit due to pulse limitations in the
visible range Lead to the introduction of
High-Order Harmonics
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High-Order Harmonic Generation
Produces pulses in the extreme ultra-violet
regime (XUV)
Three step recombination model (1) Laser
driver induced tunneling (2) Electron
trajectory under EM field (3) Recombination with
parent ion
Generates a train of attosecond pulses
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The Trouble was
In order to meet the goals of attosecond physics,
they needed to isolate a single attosecond pulse!

• Short driver pulse
• Control of the carrier-envelope phase

Advances resulted in a single neat XUV pulse
Streak Camera determined that single pulses had
been localized to a time scale of lt250as !!
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How is this being applied?
Well maybe dont grab the popcorn just yet.
Attosecond pulses first used to probe Auger decay
in krypton gas

• Electrons emitted at different times will
  receive different energies
• Time differences can be inferred

• Limitations
• Laser intensity
• Optical tools

• Interpretation of data
• Wavelength barrier?

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The Future
Free Electron Laser

• Electrons in HHG have attosecond duration
• Consecutive snapshots can be taken - lt1fs
  timescale
• Application of HHG to molecules can provide
  spatial information about electrons in the
  valence orbital!!

• What might be next?
• Septosecond physics??

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References
Agostini P and L. F. DiMauro, The Physics of
Attosecond Light Pulses, Rep. Prog. Phys. 67
813-855, 2004 Brabec T, New Science at the
Ultrafast Frontier, Physics World, 2004 Hellemans
A, In the Blink of an Eye, Science, 3061313,
2004 Lewenstein M, Resolving Physical Processes
on the Attosecond Time Scale, Science, 2971131,
2002 Silberberg Y, Physics at the Attosecond
Frontier, Nature, 414 494-495, 2001