F. Mauger1, C. Chandre1 , T. Uzer2
1Centre
de Physique Théorique, CNRS, Aix-Marseille Université
2School of Physics, Georgia Institute of Technology – Atlanta
Financial support:
PICS
Double ionization: the puzzling knee-shape
Linear polarization (LP)
λ = 780 nm
T = 100 fs (10-13 s)
 Double Ionization
 SDI
 NSDI
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Motivations
 gain all information about the
orbital
Web of science, topics:
“nonsequential double ionization”
 position of a molecule's atoms
 observe attosecond dynamics
COLTRIMS setup
ion
detector
electron
detector
http://hsb.uni-frankfurt.de/web/research/atomic/strongfields/press/
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Classical mechanics: a knee
He2+
NS
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Dynamics without the field
 Chaotic motion organized by hyperbolic periodic orbits
 At any time it defines an inner and an outer electron
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Reduced models for inner and outer electrons
 Outer electron
 Effective Hamiltonian
 Maximum return energy
 3 step model (Corkum 1993)
1.
ionization
2.
return to the core
3.
collision with the core electron
 Inner electron
 Effective Hamiltonian
 Laminar plot
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Double ionization: What is under the knee ?
Double ionization: separate
NSDI and SDI components.
Complete SDI
Maximum NSDI
Equal sharing relation
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Linear polarization vs. circular polarization:
“standard wisdom”
 Linear
polarization
“only a slight ellipticity of the laser polarization will ensure that the
electron never returns to the environment of the ion”
P. B. Corkum, PRL 71, 1994 (1993)
“circular polarization suppresses the enhancement.”
D.N. Fittinghoff et al., PRA 49, 2174 (1994)
“enhanced double ionization for circular polarization contradicts
simple rescattering theories”
G. D. Gillen et al., PRA 64, 043413 (2001)
 Circular
polarization
“For a laser field with circular polarization and already a field with
significant elliptical polarization (…) the recollision mechanism will
lose its significance.”
W. Becker and H. Rottke, Cont. Phys. 49, 199-223 (2008)
“If the polarization is circular, then as soon as any portion of the
wavepacket emerges from the atom (…) the motion ensures that the
wavepacket never returns to the ion of its birth”
P.B. Corkum, Physics Today (March 2011)
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Circular polarization: no knee ?
Experimental results (CP)
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NSDI with circular polarization
 Numerical simulations (CP)
Observation of a knee for Mg
no knee for He
 significant amount of recollision for
Mg.
 for He, recollision suppressed because
of initial conditions.
He2+
Mg2+
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Circular polarization:
insight from nonlinear dynamics
 We observe a knee shape
with Mg
 Even with CP we get a
significant amount of
recollisions
 Canonical transformation
into a rotating frame
 Time independent laser
field
 Saddle point which
controls both ionization
and recollision
 Zero velocity surface
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Conclusions/Perspectives
LP
 inner/outer electrons
 reduced models
 predictions on the knee
 symplectic map for recollision
dynamics
CP
 conditions for knee in CP
 agreement with experiments
 modified recollision scenario
Physical Review Letters 105,083002 (2010)
Actualités de l’INP-CNRS:
http://www.cnrs.fr/inp/spip.php?article377
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