Transcript Document

Attosecond Physics
Ultrafast Physics at a new Frontier
Dawn Fraser
University of Ottawa, Dec 2005
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
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:
15)s
< Femtosecond (10^-
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
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”
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
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 <250as !!
How is this being applied?
Well… maybe don’t 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
• Interpretation of data
• Optical tools
• Wavelength barrier?
The Future
Free Electron Laser:
• Electrons in HHG have attosecond duration
•
Consecutive ‘snapshots’ can be taken - <1fs timescale
• Application of HHG to molecules can provide spatial
information about electrons in the valence orbital!!
What might be next?
• Septosecond physics??
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, 306:1313, 2004
Lewenstein M, Resolving Physical Processes on the Attosecond Time
Scale, Science, 297:1131, 2002
Silberberg Y, Physics at the Attosecond Frontier, Nature, 414: 494-495,
2001