Transcript No Slide Title

Mechanisms of
Photo Double Ionization of Helium
by 529 eV Photons
Alexandra Knapp
Group of R. Dörner and H. Schmidt-Böcking
University of Frankfurt, Germany
Energy
Double ionization
Energy
Single ionization
0
0
25 eV … 79 eV: only single ionization
79 eV and higher: single + double ionization
Shake off
Shake off
First electron absorbs photon
and removes from the nucleus
Shake off
Shake off
Change of the
effektiv nuclear charge
Shake off
Second electron is in its eigenstate
 Only single ionization occurs
Shake off
Second electron is NOT
in its eigenstate  Shake off
Electron-electron scattering (TS1)
Electron-electron scattering (TS1)
Electron-electron scattering (TS1)
Electron-electron scattering (TS1)
Electron-electron scattering (TS1)
Electron-electron scattering (TS1)
Electron-electron scattering (TS1)
Electron-electron scattering (TS1)
Electron-electron scattering (TS1)
90°
(e,2e) like collision
between the two electrons
Ratio of double to single ionization (theory)
Shake off + TS1
 
%


Shake off
TS1
Photon energy above the threshold [eV]
COLTRIMS
with electric field
COLTRIMS
Collecting electrons up to 60 eV
with 4  solid angle with a combination
of an electric and a magnetic field
with electric + magnetic field
Questions
• Is the assumption of a two-step model
valid?
• Energy sharing
• Asymmetry parameter
• Mechanisms of photo double ionization
• Angular distributions
Energy sharing
CCC-Calculation
A. Kheifets, I. Bray
Extreme asymmetric energy sharing
Asymmetry parameter
Polynomial fit
Fast electron absorbs photon energy
and its angular momentum
Asymmetry parameter
Polynomial fit
Two-step model is valid
Angular distributions
Very slow electrons: 2 eV
Faster electrons: 30 eV
Shake off
CCC-Calculation
TS1
CCC-Calculation
The fast electron (indicated by the red arrow) is fixed into the direction of the polarization
TDCS for Eslow = 2 eV and 30 eV
fast electron (448 eV)
q
slower electron (30 eV)
q
slower electron (2 eV)
q
q
fast electron (420 eV)
Shake off and TS1 can be seen for all angles
fast electron (448 eV)
slower electron (2 eV)
q
slower electron (30 eV)
q
fast- slow =180
q
fast- slow =90
q
fast electron (420 eV)
Comparison between experiment and theory
fast electron (448 eV)
q
slower electron (30 eV)
q
slower electron (2 eV)
q
q
fast electron (420 eV)
Conclusion
• TDCS of the DPI of Helium were measured at
450 eV above the threshold
• electrons are distinguishable because of the
asymmetric energy sharing
• =2 for very fast and =0 for very slow
electrons
• very slow ( 2 eV) electrons: Shake off
• slightly faster ( 30 eV) electrons: TS1
University Frankfurt: Reinhard Dörner
Horst Schmidt-Böcking
Alexandra Knapp
Thorsten Weber
Sven Schößler
Till Jahnke
Jürgen Nickles
Susanne Kammer
Ottmar Jagutzki
Lothar Schmidt
Kansas State University: C. Lewis Cocke
Timur Osipov
LBNL: Michael H. Prior
Jürgen Rösch
Western Michigan University: Allen Landers
Australian National University Canberra: Anatoli Kheifets
Murdock University Perth: Igor Bray
Supported by BMBF, DFG and DOE