Strong field double ionization: Insight from non-linear dynamics

1. Strong field double ionization: Insight from non-linear dynamics 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

2. Double ionization: the puzzling knee-shape Experimental data Walker et al (1994) • Double Ionization • SDI • NSDI • Linear polarization (LP) • λ = 780 nm • T = 100 fs (10-13 s) Strong field double ionization

3. Motivations Web of science, topics: “nonsequential double ionization” • gain all information about the orbital • 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/ Strong field double ionization

4. Classical mechanics: a knee He2+ NS Strong field double ionization

5. Dynamics without the field • Chaotic motion organized by hyperbolic periodic orbits • At any time it defines an inner and an outer electron Strong field double ionization

6. Reduced models for inner and outer electrons • Outer electron • Effective Hamiltonian • Maximum return energy • 3 step model (Corkum 1993) • ionization • return to the core • collision with the core electron • Inner electron • Effective Hamiltonian • Laminar plot Strong field double ionization

7. Double ionization: What is under the knee ? Double ionization: separate NSDI and SDI components. • Complete SDI • Maximum NSDI • Equal sharing relation Strong field double ionization

8. Linear polarization vs. circular polarization: “standard wisdom” • Linear polarization • Circular 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) “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) Strong field double ionization

9. Circular polarization: no knee ? Experimental results (CP) Fittinghoffet al (1994) Gillen et al (2001) contradiction? Strong field double ionization

10. NSDI with circular polarization Observation of a knee for Mg no knee for He • significant amount of recollision for Mg. • for He, recollision suppressed because of initial conditions. • Numerical simulations (CP) He2+ Mg2+ Strong field double ionization

11. 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 Strong field double ionization

12. Conclusions/Perspectives • CP • conditions for knee in CP • agreement with experiments • modified recollision scenario • LP • inner/outer electrons • reduced models  predictions on the knee • symplectic map for recollision dynamics Physical Review Letters 105,083002 (2010) Actualités de l’INP-CNRS: http://www.cnrs.fr/inp/spip.php?article377 Strongfield double ionization