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Laser Assisted Charge transfer in He ++ + H Collisions

Laser Assisted Charge transfer in He ++ + H Collisions. Presented by Fatima Anis Dr. Brett D. Esry V. Roudnev & R. Cabrera-Trujillo. Dr. Ben-Itzhak Dr. Cocke. Introduction. Does presence of a Laser Field affect charge transfer? n h ν + α + H  He + + p How much does it affect?

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Laser Assisted Charge transfer in He ++ + H Collisions

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  1. Laser Assisted Charge transferin He++ + H Collisions Presented by Fatima Anis Dr. Brett D. Esry V. Roudnev & R. Cabrera-Trujillo Dr. Ben-Itzhak Dr. Cocke

  2. Introduction • Does presence of a Laser Field affect charge transfer? nhν + α + H  He+ + p • How much does it affect? • Can we control charge transfer during collision through CE phase? • Possibility for doing such an experiment

  3. Remi did some preliminary calculations using END 1- p + H2 H + H2+ 2- He+ + He  He + He+ 3- Li++ + He  Li+ + He+ 4- Li++ + Li  Li+ + Li+ FWHM = 10fs λ = 790nm I = 3.5x1012 W/cm2 Reference: T.Kirchner, PRL 89, 093203 (2002) Thomas did 3D grid calculations for same alpha on Hydrogen using circular polarized light. What has been done?

  4. Theory Collision Geometry Method: • What are we solving? • How are we solving? • Calculations Parameters • Calculation of charge transferprobability

  5. Projectile with Zp=1 moving with velocity vz EII E┴ And Laser Field is given as Target with ZT= 2 at origin Collision scheme • Collision Energy = 1keV/amu • Laser parameters: • Intensity = 3.5x1012W/cm2 • FWHM ≈ 6.0fs • λ = 800nm • φ is CEP ! Capture is possible for almost 1-2 optical cycles

  6. Dipole moment Electric Field What are we solving? We are solving 3D Time Dependent Schrödinger Equation with &

  7. Operator- Splitting for Time Evolution • Unitary operators of Cayley-Hamilton form is used for operator exponentials How are we solving? Crank-Nicholson method • Relaxation Method to get the ground state of Hydrogen • Our lattice solution utilizes a uniform grid and three-point finite-difference method

  8. Box size in our calculations [-4, 15]x x [-4, 4]yx [-25, 25]z a.u. Grid spacing = 0.2 a.u. supports EH = - 0.49 a.u. EHe+= - 1.90 a.u. Calculation parameters Time Step = 0.06 a.u. Time Range: ti = - 200.0 a.u. to tf = 200.0 a.u. Projectile Velocity = 0.1 a.u. xinitial(b,0,-20.0) → xfinal(b,0,20.0)

  9. Fig. A typical He++ + H final state density function Calculating Charge Transfer Probability We estimate the reaction probability by integrating the electron density function around a box ΩT surrounding the target at tf Where, We define ΩT as ΩT = [-4, 15]xx [-4, 4]y x [-25, 10]z a.u.

  10. Testing • The time step of 0.06 a.u. ensures energy conservation within 0.7% of its initial value • No Soft Core by making sure our vector lies exactly between the two grid points & • Comparison with other results • END • Kirchner’s

  11. Testing • No Laser Field • Collision Energy = 2keV/amu Reference: T.Kirchner, PRL 89, 093203 (2002) T. Kirchner, PRA 69, 063412 (2004) Fig. He++ + H charge transfer probability as a function of b with no Laser Field for projectile energy of 2keV/amu.

  12. Testing Fig. He+++H weighted transfer probabilityas a function of b for Eo = 0.0 a.u. and collision energy 1 keV/amu

  13. Projectile with Zp=1 moving with velocity vz EII E┴ Target with ZT= 2 at origin Results Collision scheme • Parallel Polarization Result & • Perpendicular polarization

  14. Parallel PolarizationComparison of END & Grid Calculation Fig. He+++H weighted Laser induced charge transfer probability as a function b for collision energy 1keV/amu, E0 = 0.01a.u. and CEP = - π/2

  15. Parallel Polarization σ(a.u.2) Field Free 0.95 E0 = 0.01a.u. CEP=π 5.83 CEP=3π/2 4.58 CEP Averaged 5.28 Fig. He++ + H weighted charge transfer probability as a function of b for collision energy of 1keV/amu

  16. Parallel Polarization Fig. Charge transfer total cross section as a function of CEP for a collision energy 1keV/amu

  17. Perpendicular Polarization σ(a.u.2) Field Free 0.95 E0 = 0.01a.u. α = 0.0 8.35 α = π/5 5.61 α = 2π/5 1.83 Total 4.66 Fig. CEP-Averaged weighted charge transfer probability as a function of b for different orientation of the laser field and collision plane

  18. Perpendicular Polarization Fig. CEP-Averaged cross section as a function the relative angle α

  19. Perpendicular Polarization Fig. Capture cross section as a function of CEP for different orientations of the laser field and the collision plane

  20. Without Field

  21. With Laser Field

  22. Conclusion • 4-5 fold enhancement in capture cross section in case of both parallel and perpendicular Laser polarization • Enhancement is CEP dependent for parallel and perpendicular Laser polarizations • For Parallel polarization capture cross section is enhanced significantly independent of CEP • For perpendicular polarization effect of CEP and relative angle α are related to each other.

  23. Thank You

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