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Laser-Assisted Electron Capture and Emission in Slow Proton-Hydrogen Collisions

Laser-Assisted Electron Capture and Emission in Slow Proton-Hydrogen Collisions. Thomas Niederhausen 1) , Bernold Feuerstein 2) and Uwe Thumm 1). 2) Max-Planck Institut für Kernphysik Saupfercheckweg 1 69117 Heidelberg, Germany. 1) J. R. Macdonald Laboratory, Department of Physics,

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Laser-Assisted Electron Capture and Emission in Slow Proton-Hydrogen Collisions

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  1. Laser-Assisted Electron Capture and Emission in Slow Proton-Hydrogen Collisions Thomas Niederhausen1), Bernold Feuerstein2) and Uwe Thumm1) 2)Max-Planck Institut für Kernphysik Saupfercheckweg 169117 Heidelberg, Germany 1)J. R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, KS 66506 United States of America Kansas State University James R. Macdonald Laboratory

  2. Abstract We investigate the effects of a strong laser field on the dynamics of ion-atom collisions by solving the time-dependent Schrödinger equation on a numerical grid for a 2D (reduced dimensionality) model of the scattering system. In the 2D model the electron system is confined to the two dimensions of the scattering plane, which also includes the laser electric field vector. This allows us to study the influence of the laser intensity and polarization (linear, circular, elliptic) on the capture and ionization probabilities for a large number of collision and laser parameters. After integrating over impact parameters of the classical projectile trajectory and after averaging over the relative phase between the laser electric field and the collision, we find for intensities above 1013 W/cm2 noticeable laser electric field effects and circular dichroism on the capture probability.

  3. Motivation • Why laser-assisted collisions? • Well-defined laser parameters • So far only few experiments for heavy particle impact • Why ion-atom? • Classical trajectory approach • Two channels (capture, ionization) • Why slow collisions? • Collision time ~ oscillation period of near-IR lasers • Capture process dominated by transition into ground state, thus giving a simple energetic picture

  4. Scenario without Laser Possible reaction channels: p+H + hn p+H  p+H*  H+p  H*+p  p+p+e-

  5. Scenario with Laser

  6. Target: Projectile: *)Softening parameter a = 0.641, adjusted to E0=0.5a.u. 2D Soft-Core Coulomb Potential

  7. Laser: Laser Potential Electronic Potential

  8. Electron Dynamics Hamiltonian: Propagation: Method: Direct numerical solution of the Schrödinger equation (spilt-operator Crank-Nicholson wave packet propagation)

  9. Comparision p + H g H + p Ekin = 2 keV experiment (3D) by Gealy and Van Zyl (PRA 36 – 3091) Lein and Rost, field free, 2D model (PRL 91 – 243901)

  10. Current Parameters Laser: • l =1064 nm, near IR (1.16 eV) • I = 1·1012 - 1·1014 W/cm2 • Pulse length ≈ 30 fs • right / left circular polarized Projectile: • Proton (charge = 1) • Ekin = 1.21 keV (v=0.22 a.u.) • Impact parameter = 0 – 20 a.u.

  11. Time Scales • Electron ~ 10-17 s • Laser cycle ~ 10-15 s • Interaction ~ 10-14 s • Laser pulse ≤ 10-13 s • Measurement ~ 10-9 s electronics

  12. Dichroism laser helicity anti-parallel to projectile ang. momentum laser helicity parallel to projectile ang. momentum Typical scenario with b=±4 a.u. and I=5·1013 W/cm2

  13. Capture Probability • enhanced at b=±2 and b=±4 and laser phases of 90° and 270°, when both projectile and target have the same absolute energy levels at distance of closest approach. • Slightly stronger at at distance of closest approach. 270°, when

  14. CREI Process

  15. Ionization Probability • b–b approximate invariance. Little di-chroism for ionization. • Enhanced at j=90°, when at point of closest approach. • Enhanced at j=180° due to CREI mechanism, when at point of closest approach.

  16. Electron Loss Probability • Symmetric be-havior with res-pect to laser phases at the distance of clo-sest approach for which or

  17. Static Electric Field An unphysical static electric field shows same dependence on laser phase

  18. Weighted Capture Probability • Strong dichroism for capture bet-ween co- and counter - rotating scenario at laser intensities of 1013 W/cm2 and above, up to 1014 W/cm2.

  19. Laser Intensity Dependence • Up to 25% different capture probabilities for co- versus counter - rotating collisions at intensities of 5·1013 W/cm2 . • Rapid decrease of capture proba-bility above 7·1013 W/cm2. • Noticeable di-chroism above 5·1012 W/cm2.

  20. Outlook • Projectile velocity dependence • Laser frequency dependence and transition resonant laser • Ellipticity effect of the laser radiation • Different projectile/target system (a-particle on He+, etc.) • High-Harmonics and Ultra-High-Harmonics Generation • Full 3-dimensional calculations

  21. References • T. Niederhausen, B. Feuerstein, and U. Thumm,Phys. Rev. A 70 – 023408 (2004) • T. Zuo, and A. D. BandraukPhys. Rev. A 52 – R2511 (1995) • B. Voitkiv, and J. Ullrich, J. Phys. B 34 – 1673 (2001) • L. B. Madsen, and L. Kocbach, Phys. Rev. Lett. 89 – 093202 (2002) • T. Kirchner, Phys. Rev. Lett. 89 – 093203 (2002) • M. S. Pindzola, T. Minami, and M. Schultz, Phys. Rev. A 68 – 013404 (2003) • M. Lein, and M. Rost, Phys. Rev. Lett. 91 – 243901 (2003) This work is supported by the Division of Chemical Sciences, Office of Basic Energy Sciences, Office of Energy Research, US DoE

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