Abstract

The application of Fermi Molecular Dynamics (FMD) to the modeling of the photoionization of atoms by a short pulse of long wavelength laser radiation is examined in detail. Depression of the single ionization threshold to values of the electric field strength below the classical over-the-barrier threshold, a common occurrence in FMD, is shown to arise from the preexcitation of bound electrons into a continuum of unphysical low-lying excited states. A connection is made to analogous calculations performed with the quantum Hamilton-Jacobi equation, in which the time-dependent quantum potential (Q) plays a role similar to that played in FMD by the so-called Heisenberg potential (VH). Replacement of VH by Q in the FMD equations of motion results in a large reduction in the number of excitations to unphysical bound states, while producing no essential change in the photoionization probability.

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References

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  1. D. Fittinghoff, P. Bolton, B. Chang, and K. Kulander, "Observations of nonsequential double ionization of helium with optical tunneling," Phys. Rev. Lett. 69, 2642-2645 (1992).
    [CrossRef] [PubMed]
  2. K. Kondo, A. Sagisaka, T. Tamida, Y. Nabekawa, and S. Watanabe, "Wavelength dependence of nonsequential double ionization in He," Phys. Rev. A 48, R2531-R2533 (1993).
  3. B. Walker, E. Mevel, B. Yang, P. Berger, J. P. Chamberet, A. Antonetti, L. F. Dimauro, and P. Agostini, "Double ionization in the perturbative and tunneling regimes," Phys. Rev. A 48, R894-R897 (1993).
  4. S. Augst, A. Talebpour, S. L. Chin, Y. Beaudoin, and M. Chaker, "Nonsequential triple ionization of argon atoms in a high-intensity laser field," Phys. Rev. A52, R917-R919 (1995).
  5. P. Lambropoulos, "Mechanisms for multiple ionization of atoms by strong pulsed lasers," Phys. Rev. Lett. 55, 2141-2144 (1985).
    [CrossRef] [PubMed]
  6. P. Corkum, "Plasma perspective on strong-field multiphoton ionization," Phys. Rev. Lett. 71, 1994-1997 (1993).
    [CrossRef] [PubMed]
  7. T. Brabec, M. Ivanov, and P. Corkum, "Coulomb focusing in intense field atomic processes," Phys. Rev. A 54, R2551-R2554 (1996).
  8. K. J. LaGattuta and James S. Cohen, "Quasiclassical modeling of helium double photoionization," J. Phys. B 31, 5281-5291 (1998).
  9. A. Becker and F. H. M. Faisal, "Mechanism of laser-induced double ionization of helium," J. Phys. B 29, L197-L202 (1996).
  10. K. LaGattuta, "Multiple ionization of argon atoms by long-wavelength laser radiation: a fermion molecular dynamics simulation," J. Phys. B 33, 2489-2494 (2000).
  11. Th. Weber, M. Weckenbrock, A. Staudte, L. Spielberger, O. Jagutzki, V. Mergel, F. Afaneh, G. Urbasch, M. Vollmer, H. Giessen, and R. Dorner, "Recoil-ion momentum distributions for single and double ionization of helium in strong laser fields," Phys. Rev. Lett. 84, 443-446 (2000).
    [CrossRef] [PubMed]
  12. R. Moshammer, B. Feuerstein, W. Schmitt, A. Dorn, C. Schroter, J. Ullrich, H. Rottke, C. Trump, M. Wittmann, G. Korn, K. Hoffmann, and W. Sander, "Momentum distributions of Ne(n+) ions created by an intense ultrashort laser pulse," Phys. Rev. Lett. 84, 447-450 (2000).
    [CrossRef] [PubMed]
  13. A. Becker and F. H. M. Faisal, "Interpretation of momentum distribution of recoil ions from laser induced nonsequential double ionization," Phys. Rev. Lett. 84, 3546-3549 (2000).
    [CrossRef] [PubMed]
  14. K. LaGattuta, "Laser effects in photoionization: numerical solution of coupled equations for a three-dimensional Coulomb potential," J. Opt. Soc. Am. B 7, 639-646 (1990).
  15. D. Bohm, "A suggested interpretation of the quantum theory in terms of `hidden' variables. I," Phys. Rev. 85, 166-179 (1952).
    [CrossRef]
  16. C. Lopreore and R. Wyatt, "Quantum wave packet dynamics with trajectories," Phys. Rev. Lett. 82, 5190-5193 (1999).
    [CrossRef]
  17. D. Wasson and S. Koonin, "Molecular-dynamics simulations of atomic ionization by strong laser fields," Phys. Rev. A 39, 5676-5685 (1989).
  18. K. LaGattuta, "Laser effects in photoionization II. Numerical solution of coupled equations for atomic hydrogen," Phys. Rev. A 41, 5110-5116 (1990).

Other (18)

D. Fittinghoff, P. Bolton, B. Chang, and K. Kulander, "Observations of nonsequential double ionization of helium with optical tunneling," Phys. Rev. Lett. 69, 2642-2645 (1992).
[CrossRef] [PubMed]

K. Kondo, A. Sagisaka, T. Tamida, Y. Nabekawa, and S. Watanabe, "Wavelength dependence of nonsequential double ionization in He," Phys. Rev. A 48, R2531-R2533 (1993).

B. Walker, E. Mevel, B. Yang, P. Berger, J. P. Chamberet, A. Antonetti, L. F. Dimauro, and P. Agostini, "Double ionization in the perturbative and tunneling regimes," Phys. Rev. A 48, R894-R897 (1993).

S. Augst, A. Talebpour, S. L. Chin, Y. Beaudoin, and M. Chaker, "Nonsequential triple ionization of argon atoms in a high-intensity laser field," Phys. Rev. A52, R917-R919 (1995).

P. Lambropoulos, "Mechanisms for multiple ionization of atoms by strong pulsed lasers," Phys. Rev. Lett. 55, 2141-2144 (1985).
[CrossRef] [PubMed]

P. Corkum, "Plasma perspective on strong-field multiphoton ionization," Phys. Rev. Lett. 71, 1994-1997 (1993).
[CrossRef] [PubMed]

T. Brabec, M. Ivanov, and P. Corkum, "Coulomb focusing in intense field atomic processes," Phys. Rev. A 54, R2551-R2554 (1996).

K. J. LaGattuta and James S. Cohen, "Quasiclassical modeling of helium double photoionization," J. Phys. B 31, 5281-5291 (1998).

A. Becker and F. H. M. Faisal, "Mechanism of laser-induced double ionization of helium," J. Phys. B 29, L197-L202 (1996).

K. LaGattuta, "Multiple ionization of argon atoms by long-wavelength laser radiation: a fermion molecular dynamics simulation," J. Phys. B 33, 2489-2494 (2000).

Th. Weber, M. Weckenbrock, A. Staudte, L. Spielberger, O. Jagutzki, V. Mergel, F. Afaneh, G. Urbasch, M. Vollmer, H. Giessen, and R. Dorner, "Recoil-ion momentum distributions for single and double ionization of helium in strong laser fields," Phys. Rev. Lett. 84, 443-446 (2000).
[CrossRef] [PubMed]

R. Moshammer, B. Feuerstein, W. Schmitt, A. Dorn, C. Schroter, J. Ullrich, H. Rottke, C. Trump, M. Wittmann, G. Korn, K. Hoffmann, and W. Sander, "Momentum distributions of Ne(n+) ions created by an intense ultrashort laser pulse," Phys. Rev. Lett. 84, 447-450 (2000).
[CrossRef] [PubMed]

A. Becker and F. H. M. Faisal, "Interpretation of momentum distribution of recoil ions from laser induced nonsequential double ionization," Phys. Rev. Lett. 84, 3546-3549 (2000).
[CrossRef] [PubMed]

K. LaGattuta, "Laser effects in photoionization: numerical solution of coupled equations for a three-dimensional Coulomb potential," J. Opt. Soc. Am. B 7, 639-646 (1990).

D. Bohm, "A suggested interpretation of the quantum theory in terms of `hidden' variables. I," Phys. Rev. 85, 166-179 (1952).
[CrossRef]

C. Lopreore and R. Wyatt, "Quantum wave packet dynamics with trajectories," Phys. Rev. Lett. 82, 5190-5193 (1999).
[CrossRef]

D. Wasson and S. Koonin, "Molecular-dynamics simulations of atomic ionization by strong laser fields," Phys. Rev. A 39, 5676-5685 (1989).

K. LaGattuta, "Laser effects in photoionization II. Numerical solution of coupled equations for atomic hydrogen," Phys. Rev. A 41, 5110-5116 (1990).

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Figures (4)

Fig. 1.
Fig. 1.

Values of the quantum potential Q(x, t) are plotted along the verticle axis as a function of x and t; primarily positive values of Q appear.

Fig. 2.
Fig. 2.

Same as Fig. 1, but the surface has been inverted; now primarily negative values of Q(x, t) appear.

Fig. 3.
Fig. 3.

Values of vx =dS/dx, from the quantum HJ equation, are plotted along the verticle axis as a function of x and t.

Fig. 4.
Fig. 4.

A spectrum of values of the final electron total energy ∊ (a.u.) is plotted, as computed with FMD: for the case in which the FMD Heisenberg potential VH has been invoked (solid curve); for the case in which VH has been replaced by Q (chain curve).

Equations (21)

Equations on this page are rendered with MathJax. Learn more.

H ( t ) Ψ real = Ψ imag t
H ( t ) Ψ imag = Ψ real t
H ( t ) = 1 2 r 2 1 r r . E ( t )
E ( t ) = x ̂ E pulse ( t ) sin ( ω t + ϕ )
Ψ = R exp ( i S )
ρ t + r . ( ρ r S ) = 0
S / t = 1 2 ( r S ) 2 + Q 1 / r r . E ( t )
Q = 1 2 R r 2 R
d υ / d t = r ( Q 1 / r r . E ( t ) )
υ r S
d / d t / t + υ . r
Q 1 2 + 1 / r
d υ / d t = r ( Q 1 / r ) = 0
r S = 0
H ( t ) = p 2 / 2 1 / r r . E ( t ) + V H ( r , p )
V H ( r , p ) A H r 2 exp ( B H r 4 p 4 )
d r / d t = p H ( t )
d p / d t = r H ( t )
d p / d t = r ( V H 1 / r r . E ( t ) )
d p / d t = r ( V H 1 / r ) = 0
υ = p + p V H ( r , p ) = 0

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