Strong field double ionization: Insight from non-linear dynamics

F. Mauger1, C. Chandre1 , T. Uzer2

1Centre de Physique Théorique, CNRS, Aix-Marseille Université2School of Physics, Georgia Institute of Technology – Atlanta

Financial support:

PICS

Double ionization: the puzzling knee-shape

Double IonizationSDI

NSDI

Linear polarization (LP)λ = 780 nmT = 100 fs (10-13 s)

Experimental dataWalker et al (1994)

May 11, 2011 2Strong field double ionization

ion detector

electron detector

gain all information about the orbital

position of a molecule's atoms

observe attosecond dynamics

http://hsb.uni-frankfurt.de/web/research/atomic/strongfields/press/

Web of science, topics:“nonsequential double ionization”

COLTRIMS setup

May 11, 2011 3Strong field double ionization

Motivations

Classical mechanics: a knee

He2+

NS

May 11, 2011 4Strong field double ionization

Dynamics without the field

5

Chaotic motion organized by hyperbolic periodic orbits

At any time it defines an inner and an outer electronMay 11, 2011

Strong field double ionization

Reduced models for inner and outer electrons

Outer electron Effective Hamiltonian

Maximum return energy

3 step model (Corkum 1993)1. ionization2. return to the core3. collision with the core electron

Inner electron Effective Hamiltonian

Laminar plot

May 11, 2011 6Strong field double ionization

Double ionization: What is under the knee ?

Double ionization: separate NSDI and SDI components.

Complete SDI

Maximum NSDIEqual sharing

relation

May 11, 2011 7Strong field double ionization

Linear polarization vs. circular polarization: “standard wisdom”

“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)

“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)May 11, 2011

Linear polarization

Circular polarization

8Strong field double ionization

Circular polarization: no knee ?

Experimental results (CP)

Gillen et al (2001)Fittinghoff et al (1994)

contradiction?

May 11, 2011 9Strong field double ionization

Observation of a knee for Mg no knee for He significant amount of recollision

for Mg. for He, recollision suppressed

because of initial conditions.

Mg2+

He2+

Numerical simulations (CP)

May 11, 2011 10Strong field double ionization

NSDI with circular polarization

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

May 11, 2011 11Strong field double ionization

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

May 11, 2011 12Strong field double ionization

Physical Review Letters 105,083002 (2010)

Actualités de l’INP-CNRS: http://www.cnrs.fr/inp/spip.php?article377

Conclusions/Perspectives