Attosecond PhysicsAttosecond Physics

Dawn Fraser

University of Ottawa, Dec 2005

Dawn Fraser

University of Ottawa, Dec 2005

Ultrafast Physics at a new Frontier

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

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

Application on molecular and atomic scale ??Application on molecular and atomic scale ??

Flash Photography and FilmFlash Photography and Film

Can we take pictures of electrons or make movies of molecular vibration?Can we take pictures of electrons or make movies of molecular vibration?

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

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

To make movies of molecular and atomic processes we need pulses with:

Spatial resolution: Angstrom (10^-10)m

Temporal resolution: < Femtosecond (10^-15)s

To make movies of molecular and atomic processes we need pulses with:

Spatial resolution: Angstrom (10^-10)m

Temporal resolution: < Femtosecond (10^-15)s

Just how fast is ultrafast?Just how fast is ultrafast?

A classical electron makes one Bohr orbit in ~150 attoseconds.A classical electron makes one Bohr orbit in ~150 attoseconds.

Natural limit due to pulse limitations in the visible range

Lead to the introduction of ‘High-Order Harmonics”

Natural limit due to pulse limitations in the visible range

Lead to the introduction of ‘High-Order Harmonics”

Historical progress of ultra-short laser technology shows evidence of a femtosecond barrier

Historical progress of ultra-short laser technology shows evidence of a femtosecond barrier

The Femtosecond BarrierThe Femtosecond Barrier

Three step recombination model

(1) Laser “driver” induced tunneling

(2) Electron trajectory under EM field

(3) Recombination with parent ion

Three step recombination model

(1) Laser “driver” induced tunneling

(2) Electron trajectory under EM field

(3) Recombination with parent ion

Produces pulses in the extreme ultra-violet regime (XUV)Produces pulses in the extreme ultra-violet regime (XUV)

High-Order Harmonic GenerationHigh-Order Harmonic Generation

Generates a train of attosecond pulsesGenerates a train of attosecond pulses

In order to meet the goals of attosecond physics, they needed to isolate a single attosecond pulse!

In order to meet the goals of attosecond physics, they needed to isolate a single attosecond pulse!

The Trouble was… The Trouble was…

• Short driver pulse

• Control of the carrier-envelope phase

• Short driver pulse

• Control of the carrier-envelope phase

Advances resulted in a single neat XUV pulseAdvances resulted in a single neat XUV pulse

“Streak Camera” determined that single pulses had been localized to a time scale of <250as !!

“Streak Camera” determined that single pulses had been localized to a time scale of <250as !!

Well… maybe don’t grab the popcorn just yet.Well… maybe don’t grab the popcorn just yet.

How is this being applied? How is this being applied?

Attosecond pulses first used to probe Auger decay in krypton gasAttosecond pulses first used to probe Auger decay in krypton gas

• Electrons emitted at different times will receive different energies

• Time differences can be inferred

• Electrons emitted at different times will receive different energies

• Time differences can be inferred

Limitations:

• Laser intensity

• Optical tools

Limitations:

• Laser intensity

• Optical tools

• Interpretation of data

• Wavelength barrier?

• Interpretation of data

• Wavelength barrier?

Free Electron Laser:Free Electron Laser:

The Future The Future

• 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!!

• 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??

What might be next?

• Septosecond physics??

References 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

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