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Time-Dependent Calculations of Strong Field Ionization and High Harmonics Generation

Igor Bray. Centre for Antimatter-Matter Studies. Time-Dependent Calculations of Strong Field Ionization and High Harmonics Generation. Interplay between strong field effects. and many-electron correlations. Anatoli Kheifets and Igor Ivanov. Motivation. Strong Field Ionization

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Time-Dependent Calculations of Strong Field Ionization and High Harmonics Generation

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  1. Igor Bray Centre for Antimatter-Matter Studies Time-Dependent Calculations of Strong Field Ionization and High Harmonics Generation Interplay between strong field effects and many-electron correlations Anatoli Kheifets and Igor Ivanov

  2. Motivation • Strong Field Ionization • New XUV sources • FEL’s (FLASH, SCSS, LCLS etc) • High harmonic generation • Fundamental importance • Interplay of correlations and strong field • High harmonic generation • Race for the “table-top synchrotron” • Coherent, compact, intense, tunable, source of XUV radiation • Neutral gases or ionized plasmas of noble gas atoms • Attosecond control • Steering of coherent wave packets. • Time-resolved atomic physics

  3. Time-Independent Photoionization (g,2e), (2g,2e) HHG (Ng, g’) FEL HG, photoionziation (ng, g’), (ng, e) Time-Dependent Photoionization (g,2e), (2g,2e) Lasers XUV bursts Coherent control Time-dependent theory road map Number of cycles ∞ 100 10 1 Target complexity Two-electron Targets He, H─ Many-electron Targets Ne, Ar, Xe One-electron targets Li, K, Rb

  4. Outline • Theoretical model • Time-dependent Schrödinger equation • Basis based integration vs coordinate space integration • Field-free atomic states • One-electron HF states • Two-electron CCC states • Discretization of continuum • Pseudostates vs continuum states

  5. Outline • Applications • Two-photon double ionization of He • Total ionization cross-section • DC field assisted double ionization of He and H- • Field stabilization • DC tunneling ionization • Four-photon ionization of Li • MOT based experiment • Photoelectron momentum distribution • Harmonics generation from Li/Li*, K Rb • Ground state vs excited state • Resonant enhancement of HG

  6. Theoretical Model Field on:

  7. CCC expansion for two-electron continuum Coulomb wave Pseudostate Theoretical Model Field off:

  8. Theoretical Model Harmonics Generation:

  9. 3.5 x 1014 W/cm2 Integrated TPDI Cross-section of He 2 orders

  10. Integrated TPDI Cross-section of He Theory vs. experiment:

  11. He F=0 F=0.01au F=0.02au ω=90eV F=0.03au ω=85eV DC field assisted double ionization of He

  12. DC tunneling ω=15 eV H- DC field assisted double ionization of H-

  13. MOT-transition Four-photon ionization of Li 25fs @795nm MOT experiment 4-photon ionization from 2s3-photon ionization from 2p Jochen Steinmann, Max-Planck-Institut für Kernphysik, Heidelberg, ISIAC 2007

  14. Over-the-barrier-ionization • - highest intensities • complete suppression of • the Coulomb-barrier of bound • state • Atomic system dominated by • external field • Multiphoton-ionization • low intensity, • E-field of laser weak • compared to atomic field • - perturbative regime • Tunneling-ionization • - high intensity • classical field picture • field ionization in • quasistatic laser field Vs=Ub Regimes of strong field ionization Adiabaticity parameter (Keldysh 1964)

  15. Lithium atom in intense laser field Jochen Steinmann, Max-Planck-Institut für Kernphysik, Heidelberg, ISIAC 2007

  16. Experiment:Li(2s), 30 fs, 775 nm, 150mW Calculation:Li(2s), 25 fs, 800 nm, 3x1011 W/cm2 Photoelectron momentum distribution Momentum space multi-photon rings:Px2+Pz2=Nw ─ IP, N≥4 for Li 2s

  17. 0.78 mm 100 W/cm2 3.5 mm 0.5 TW/cm2 From noble gases in NIR To alkaline metals in MIR Resonant Enhancement of Harmonics Generation

  18. 2p@2x1011W/cm2 Ncut-off ≈ 12 2s@8x1011W/cm2 Ncut-off ≈ 24 Harmonic spectrum of Li @ 330 fs, 3500 nm

  19. Harmonic spectrum of Li @ 330 fs, 3500 nm

  20. 3d 7th 5th 5-photon 4s-4f transition (0.7 eV) 9th Harmonic spectrum of K @ 150 fs, 1750 nm

  21. 3d 7th 5th 4-photon 5s-4d transition (0.6 eV) 9th Harmonic spectrum of Rb @ 200 fs, 2000 nm

  22. Conclusion • Basis-based solution of TDSE applied to • Photoionization • (2g,2e) on He • (g DC,2e) on He and H ─ • (4g,e) on Li • HHG • Li/Li* K. Rb Ncut-off ≈10 (optical regime) • Future plans • Very High Harmonics Generation • Ncut-off≈100 XUV regime • Laser cooled He* and Ne* • Uttosecond Pulse Generation / Attosecond control • Two-color / Pump-Probe

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