## Atomic dynamics in single and multi-photon double ionization: An experimental comparison

Optics Express, Vol. 8, Issue 7, pp. 368-376 (2001)

http://dx.doi.org/10.1364/OE.8.000368

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### Abstract

We have used a multi-particle imaging technique (COLTRIMS) to observe the double ionization of rare gas atoms by multi-photon absorption of 800 nm (1.5 eV) femto-second laser pulses and by single photon absorption (synchrotron radiation). Both processes are mediated by electron correlation. We discuss similarities and differences in the three-body final state momentum distributions.

© Optical Society of America

## 1 Introduction

## 2 Experiment

2. R. Dörner, V. Mergel, O. Jagutzki, L. Spielberger, J. Ullrich, R. Moshammer, and H. Schmidt-Böcking, “Cold Target Recoil Ion Momentum Spectroscopy: A ‘momentum microscope’ to view atomic collision dynamics,” Physics Reports **330**, 96–192 (2000). [CrossRef]

4. H.P Bräuning, R. Dörner, C.L. Cocke, M.H. Prior, B. Krässig, A. Kheifets, I. Bray, A. Bräuning-Demian, K. Carnes, S. Dreuil, V. Mergel, P. Richard, J. Ullrich, and H. Schmidt-Böcking, “Absolute triple differential cross sections for photo-double ionization of helium - experiment and theory,” J. Phys. **B31**, 5149 (1998).

5. R. Dörner, J. Feagin, C.L. Cocke, H. Bräuning, O. Jagutzki, M. Jung, E.P. Kanter, H. Khemliche, S. Kravis, V. Mergel, M.H. Prior, H. Schmidt-Böcking, L. Spielberger, J. Ullrich, M. Unverzagt, and T. Vogt, “Fully Differential Cross Sections for Double Photoionization of He Measured by Recoil Ion Momentum Spectroscopy,” Phys. Rev. Lett. **77**, 1024 (1996). [CrossRef] [PubMed]

6. R. Dörner, H. Bräuning, J.M. Feagin, V. Mergel, O. Jagutzki, L. Spielberger, T. Vogt, H. Khemliche, M.H. Prior, J. Ullrich, C.L. Cocke, and H. Schmidt-Böcking, “Photo-double-ionization of He: Fully differential and absolute electronic and ionic momentum distributions,” Phys. Rev. **A57**, 1074 (1998).

## 3 Single Ionization

*He*

^{+}ions created by 85 eV linear polarized photons and by 1.5 eV (800 nm), 220 fsec, 1.4×10

^{15}W/cm

^{2}laser light are shown in figure 2. In both cases the photon momentum is negligible on the scale of the figure (an 85eV photon has 0.02 a.u. momentum). Therefore, due to momentum conservation, the ion and electron are emitted with almost equal and opposite momentum. The ion momentum distribution is just a mirror image of the electron distribution. The outer ring in figure 1a corresponds to ions in the ground state, the inner rings to the excited states of the

*He*

^{+}ion. For the single photon case the electron energy is determined by the photon energy, leading to discrete rings. In the multi-photon case no ATI structure (isolated peaks in the energy distribution) is observed. In the present experiment this might be due to our resolution, however even for high resolution electron spectroscopy no ATI structure is found for He at this intensity. A very different angular distribution is observed in the two cases. For the single-photon case the ground state (main) line shows a dipole distribution. In the multi-photon case, however, at least 17 photons must be absorbed to overcome the binding energy. Therefore high angular momentum states can in principle be populated allowing for a highly directed breakup of the atom along the polarization vector. In a simple two step picture one can assume the electron to tunnel throught the barrier of the joint optical and atomic potential. Once set free the electron and the ion are accelerated by the laser field. The net momentum transfered from the field depends only on the phase at the instant of ionization with momentum zero corresponding to the field maximum.

## 4 Double Ionization

^{14}W/cm

^{2}. The momentum distributions of the doubly charged ions parallel to the polarization, however, show surprising similarities (figure 3). In both cases a double peak structure with a minimum at momentum zero is found. For single-photon absorption this minimum holds for all photon energies investigated so far [3, 5

5. R. Dörner, J. Feagin, C.L. Cocke, H. Bräuning, O. Jagutzki, M. Jung, E.P. Kanter, H. Khemliche, S. Kravis, V. Mergel, M.H. Prior, H. Schmidt-Böcking, L. Spielberger, J. Ullrich, M. Unverzagt, and T. Vogt, “Fully Differential Cross Sections for Double Photoionization of He Measured by Recoil Ion Momentum Spectroscopy,” Phys. Rev. Lett. **77**, 1024 (1996). [CrossRef] [PubMed]

6. R. Dörner, H. Bräuning, J.M. Feagin, V. Mergel, O. Jagutzki, L. Spielberger, T. Vogt, H. Khemliche, M.H. Prior, J. Ullrich, C.L. Cocke, and H. Schmidt-Böcking, “Photo-double-ionization of He: Fully differential and absolute electronic and ionic momentum distributions,” Phys. Rev. **A57**, 1074 (1998).

7. R. Wehlitz, F. Heiser, O. Hemmers, B. Langer, A. Menzel, and U. Becker, “Electron-energy and -angular distributions in the double photoionization of helium,” Phys. Rev. Lett. **67**, 3764 (1991). [CrossRef] [PubMed]

8. 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 (2000). [CrossRef] [PubMed]

9. Th. Weber, M. Weckenbrock, A. Staudte, L. Spielberger, O. Jagutzki, V. Mergel, G. Urbasch, M. Vollmer, H. Giessen, and R. Dörner, “Recoil-Ion Momentum Distributions for Single and Double Ionization of Helium in Strong Laser Fields,” Phys. Rev. Lett. **84**, 443 (2000). [CrossRef] [PubMed]

10. R. Moshammer, B. Feuerstein, W. Schmitt, A. Dorn, C.T. Schöter, J. Ullrich, H. Rottke, C. Trump, M. Wittmann, G. Korn, K. Hoffmann, and W. Sandner, “Momentum Distributions of N^{n+} Ions Created by an Intense Ultrashort Laser Pulse,” Phys. Rev. Lett. **84**, 447 (2000). [CrossRef] [PubMed]

14. M. Lein, E.K.U. Gross, and V. Engel “Intense-Field Double Ionization of Helium: Identifying the Mechanism,” Phys. Rev. Lett. **85**, 4707 (2000). [CrossRef] [PubMed]

15. R. Kopold, W. Becker, H. Rottke, and W. Sandner, “Routes to Nonsequential Double Ionization,” Phys. Rev. Lett. **85**, 3781 (2000). [CrossRef] [PubMed]

^{+}the first excited states are around 16–17 eV. In order to have this return energy at the 3.8.10

^{14}W/cm

^{2}the primary electron has to return at a phase of about 35 deg off the field maximum. The electron will then be stopped by the excitation, the second electron will be field ionized and hence both electrons start with almost zero momentum in the laser field. Finally the starting phase of 35 deg will lead to a drift momentum of 1 a.u. for both electrons to the same side. This acceleration by the laser field drives the electron distribution into the first and third quadrant of figure 4c. Electron repulsion on the contrary tends to drive the electrons to opposite sides and hence into the second and fourth quadrant. Obviously the effect of the driving field wins over electron repulsion. the observed emission of the electrons to the same side This confirms a recent prediction of Taylor and coworkers [17]. They have solved the time-dependent Schrödinger equation for two electrons in an optical field in three dimensions and found that most of the double ionization probability flux emerges to the same side. Similar conclusions have been drawn from one-dimensional model calculations [18

18. M. Lein, E.K.U. Gross, and V. Engel, “On the mechnism of strong-field double photoionisation in the helium atom,” J. Phys B **33**, 433–442 (2000) [CrossRef]

^{1}

*P*

*symmetry. This results in selection rules leading to several nodes in the three-body momentum distribution (see [19]). The two most important ones are:*

^{o}*ϑ*

_{1}with respect to the polarization axis, there is a cone shaped node for the second electron at a polar angle

*ϑ*

_{2}=180-ϑ

_{1}.

20. I.E. McCarthy and E. Weigold, “Electron momentum spectroscopy of atoms and molecules,” Rep. Prog. Phys. **54**, 789 (1991). [CrossRef]

## 5 Conclusions

25. S. Bhattacharyya and S. Mitra, “Double photoionization of He by circularly polarized light: A QED approach,” Phys. Rev. **62**, 032709 (2000). [CrossRef]

## 6 Acknowledgements

## References and links

1. | J. Briggs and V. Schmidt, “Differential cross sections for photo-double-ionization of the helium atom,” J. Phys. |

2. | R. Dörner, V. Mergel, O. Jagutzki, L. Spielberger, J. Ullrich, R. Moshammer, and H. Schmidt-Böcking, “Cold Target Recoil Ion Momentum Spectroscopy: A ‘momentum microscope’ to view atomic collision dynamics,” Physics Reports |

3. | H.P Bräuning, R. Dörner, C.L. Cocke, M.H. Prior, B. Krässig, A. Bräuning-Demian, K. Carnes, S. Dreuil, V. Mergel, P. Richard, J. Ullrich, and H. Schmidt-Böcking, “Recoil ion and electronic angular asymmetry parameters for photo double ionization of helium at 99 eV,” J. Phys. |

4. | H.P Bräuning, R. Dörner, C.L. Cocke, M.H. Prior, B. Krässig, A. Kheifets, I. Bray, A. Bräuning-Demian, K. Carnes, S. Dreuil, V. Mergel, P. Richard, J. Ullrich, and H. Schmidt-Böcking, “Absolute triple differential cross sections for photo-double ionization of helium - experiment and theory,” J. Phys. |

5. | R. Dörner, J. Feagin, C.L. Cocke, H. Bräuning, O. Jagutzki, M. Jung, E.P. Kanter, H. Khemliche, S. Kravis, V. Mergel, M.H. Prior, H. Schmidt-Böcking, L. Spielberger, J. Ullrich, M. Unverzagt, and T. Vogt, “Fully Differential Cross Sections for Double Photoionization of He Measured by Recoil Ion Momentum Spectroscopy,” Phys. Rev. Lett. |

6. | R. Dörner, H. Bräuning, J.M. Feagin, V. Mergel, O. Jagutzki, L. Spielberger, T. Vogt, H. Khemliche, M.H. Prior, J. Ullrich, C.L. Cocke, and H. Schmidt-Böcking, “Photo-double-ionization of He: Fully differential and absolute electronic and ionic momentum distributions,” Phys. Rev. |

7. | R. Wehlitz, F. Heiser, O. Hemmers, B. Langer, A. Menzel, and U. Becker, “Electron-energy and -angular distributions in the double photoionization of helium,” Phys. Rev. Lett. |

8. | A. Becker and F.H.M. Faisal, “Interpretation of Momentum Distribution of Recoil Ions from Laser Induced Nonsequential Double Ionization,” Phys. Rev. Lett. |

9. | Th. Weber, M. Weckenbrock, A. Staudte, L. Spielberger, O. Jagutzki, V. Mergel, G. Urbasch, M. Vollmer, H. Giessen, and R. Dörner, “Recoil-Ion Momentum Distributions for Single and Double Ionization of Helium in Strong Laser Fields,” Phys. Rev. Lett. |

10. | R. Moshammer, B. Feuerstein, W. Schmitt, A. Dorn, C.T. Schöter, J. Ullrich, H. Rottke, C. Trump, M. Wittmann, G. Korn, K. Hoffmann, and W. Sandner, “Momentum Distributions of N |

11. | R. Moshammer, B. Feuerstein, and J. Ullrich, “Nonsequential multiple ionization in intense laser pulses: interpretation of ion momentum distributions within the classical ‘rescattering’ model,” J. Phys |

12. | K. Sacha and B. Eckhardt, “Pathways to double ionization of atoms in strong fields,” Phys. Rev. A:accepted for publication 2001, (2001). |

13. | L.B. Fu J. Chen, J. Liu, and W. M. Zheng, “Interpretation of momentum distribution of recoil ions from laser-induced nonsequential double ionization by semiclassical rescattering model,” Phys. Rev. |

14. | M. Lein, E.K.U. Gross, and V. Engel “Intense-Field Double Ionization of Helium: Identifying the Mechanism,” Phys. Rev. Lett. |

15. | R. Kopold, W. Becker, H. Rottke, and W. Sandner, “Routes to Nonsequential Double Ionization,” Phys. Rev. Lett. |

16. | Th. Weber, H. Giessen, M. Weckenbrock, A. Staudte, L. Spielberger, O. Jagutzki, V. Mergel, G. Urbasch, M. Vollmer, and R. Dörner, “Correlated electron emission in multiphoton double ionization,” Nature |

17. | K.T. Taylor, J.S. Parker, D. Dundas, E. Smyth, and S. Vitirito, “Laser Driven Helium in Full- Dimensionality,” Laser Physics |

18. | M. Lein, E.K.U. Gross, and V. Engel, “On the mechnism of strong-field double photoionisation in the helium atom,” J. Phys B |

19. | F. Maulbetsch and J.S. Briggs, “Selection rules for transitions to two-electron continuum states,” J. Phys. |

20. | I.E. McCarthy and E. Weigold, “Electron momentum spectroscopy of atoms and molecules,” Rep. Prog. Phys. |

21. | A. Becker and F.H.M. Faisal, “Correlated Keldysh-Faisal-Reiss theory of above-threshold double ionization of He in intense laser fields,”, Phys. Rev. |

22. | J.H. McGuire, N. Berrah, R.J. Bartlett, J.A.R. Samson, J.A. Tanis, C.L. Cocke, and A.S. Schlachter, “The ratio of cross sections for double to single ionization of helium by high energy photons and charged particles,” J. Phys. |

23. | S. Keller, “Perturbation theory for (γ,2e) on helium,” J. Phys. |

24. | Ken-ichi Hino, T. Ishihara, F. Shimizu, N. Toshima, and J.H. McGuire, “Double photoionization of helium using many-body perturbation theory,” Phys. Rev. |

25. | S. Bhattacharyya and S. Mitra, “Double photoionization of He by circularly polarized light: A QED approach,” Phys. Rev. |

26. | A. Becker and F. H. M. Faisal, “Mechanism of laser-induced double ionization of helium,” J. Phys. |

27. | A. Becker and F.H.M. Faisal, “Interplay of electron correlation and intense field dynamics in the double ionization of helium,” Phys. Rev. |

**OCIS Codes**

(020.0020) Atomic and molecular physics : Atomic and molecular physics

(020.4180) Atomic and molecular physics : Multiphoton processes

**ToC Category:**

Focus Issue: Laser-induced multiple ionization

**History**

Original Manuscript: February 5, 2001

Published: March 26, 2001

**Citation**

Th. Weber, M. Weckenbrock, A. Staudte, M. Hattass, L. Spielberger, O. Jagutzki, V. Mergel, H. Bocking, G. Urbasch, Harald Giessen, H. Brauning, C. Cocke, M. Prior, and Reinhard Doerner, "Atomic dynamics in single and multi-photon double ionization: An experimental comparison," Opt. Express **8**, 368-376 (2001)

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-8-7-368

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### References

- J. Briggs and V. Schmidt, "Differential cross sections for photo-double-ionization of the helium atom," J. Phys. 33, R1 (2000).
- R. Doerner, V. Mergel, O. Jagutzki, L. Spielberger, J. Ullrich, R. Moshammer, and H. Schmidt-Boecking, "Cold Target Recoil Ion Momentum Spectroscopy: A 'momentum microscope' to view atomic collision dynamics," Physics Reports 330, 96--192 (2000). [CrossRef]
- H.P. Brauning, R. Doerner, C.L. Cocke, M.H. Prior, B. Krassig, A.Brauning-Demian, K.Carnes, S.Dreuil, V.Mergel, P.Richard, J.Ullrich, and H. Schmidt-Boecking, "Recoil ion and electronic angular asymmetry parameters for photo double ionization of helium at 99 eV," J. Phys. B 30, L649 (1997).
- H.P Brauning, R. Doerner, C.L. Cocke, M.H. Prior, B. Krassig, A. Kheifets, I. Bray, A. Brauning-Demian, K. Carnes, S. Dreuil, V. Mergel, P. Richard, J. Ullrich, and H. Schmidt-Boecking, "Absolute triple differential cross sections for photo-double ionization of helium - experiment and theory," J. Phys. B31, 5149 (1998).
- R. Doerner, J. Feagin, C.L. Cocke, H. Brauning, O. Jagutzki, M. Jung, E.P. Kanter, H. Khemliche, S. Kravis, V. Mergel, M.H. Prior, H. Schmidt-Boecking, L. Spielberger, J. Ullrich, M. Unverzagt, and T. Vogt, "Fully Differential Cross Sections for Double Photoionization of He Measured by Recoil Ion Momentum Spectroscopy," Phys. Rev. Lett. 77, 1024 (1996). [CrossRef] [PubMed]
- R. Doerner, H. Brauning, J.M. Feagin, V. Mergel, O. Jagutzki, L.Spielberger, T. Vogt, H. Khemliche, M.H. Prior, J. Ullrich, C.L. Cocke, and H. Schmidt-Boecking, "Photo-double-ionization of He: Fully differential and absolute electronic and ionic momentum distributions," Phys. Rev. A 57, 1074 (1998).
- R. Wehlitz, F. Heiser, O. Hemmers, B. Langer, A. Menzel, and U. Becker, "Electron-energy and -angular distributions in the double photoionization of helium," Phys. Rev. Lett. 67, 3764 (1991). [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 (2000). [CrossRef] [PubMed]
- Th. Weber, M. Weckenbrock, A. Staudte, L. Spielberger, O. Jagutzki, V. Mergel, G. Urbasch, M. Vollmer, H. Giessen, and R. Doerner, "Recoil-Ion Momentum Distributions for Single and Double Ionization of Helium in Strong Laser Fields," Phys. Rev. Lett. 84, 443 (2000). [CrossRef] [PubMed]
- R. Moshammer, B. Feuerstein, W. Schmitt, A. Dorn, C.T. Schoeter, J. Ullrich, H. Rottke, C. rump, M. Wittmann, G. Korn, K. Hoffmann, and W.Sandner, "Momentum Distributions of N^n+ Ions Created by an Intense Ultrashort Laser Pulse," Phys. Rev. Lett. 84, 447 (2000). [CrossRef] [PubMed]
- R. Moshammer B. Feuerstein and J. Ullrich, "Nonsequential multiple ionization in intense laser pulses: interpretation of ion momentum distributions within the classical 'rescattering' model," J. Phys B 33, L823 (1992).
- K. Sacha and B. Eckhardt, "Pathways to double ionization of atoms in strong Fields," Phys. Rev. A: accepted for publication 2001, (2001).
- L.B. Fu J. Chen, J. Liu and W. M. Zheng, "Interpretation of momentum distribution of recoil ions from laser-induced nonsequential double ionization by semiclassical rescattering model," Phys. Rev. A 63, 011404R (2000).
- M. Lein, E.K.U. Gross, and V. Engel "Intense-Field Double Ionization of Helium: Identifying the Mechanism," Phys. Rev. Lett. 85, 4707 (2000). [CrossRef] [PubMed]
- R. Kopold, W. Becker, H. Rottke, and W. Sandner, "Routes to Nonsequential Double Ionization," Phys. Rev. Lett. 85, 3781 (2000). [CrossRef] [PubMed]
- Th. Weber, H. Giessen, M. Weckenbrock, A. Staudte, L. Spielberger, O. Jagutzki, V. Mergel, G. Urbasch, M. Vollmer, and R. Doerner, "Correlated electron emission in multiphoton double ionization," Nature 404, 608 (2000).
- K.T. Taylor, J.S. Parker, D. Dundas, E. Smyth and S. Vitirito, "Laser Driven Helium in Full-Dimensionality," Laser Physics 9, 98-116 (1999)
- M. Lein, E.K.U. Gross, and V. Engel, "On the mechnism of strong-field double photoionisation in the helium atom," J. Phys. B 33, 433-442 (2000) [CrossRef]
- F. Maulbetsch and J.S. Briggs, "Selection rules for transitions to two-electron continuum states," J. Phys. B 28, 551 (1995).
- I.E. McCarthy and E. Weigold, "Electron momentum spectroscopy of atoms and molecules," Rep. Prog. Phys. 54, 789 (1991). [CrossRef]
- A. Becker and F.H.M. Faisal, "Correlated Keldysh-Faisal-Reiss theory of above-threshold double ionization of He in intense laser fields," Phys. Rev. A 50, 3256 (1994).
- J.H. McGuire, N. Berrah, R.J. Bartlett, J.A.R. Samson, J.A. Tanis, C.L. Cocke, and A.S. Schlachter, "The ratio of cross sections for double to single ionization of helium by high energy photons and charged particles," J. Phys. B2 8, 913 (1995).
- S. Keller, "Perturbation theory for (gamma,2e) on helium," J. Phys. B 33, L513 (2000).
- Ken-ichi Hino, T. Ishihara, F. Shimizu, N. Toshima, and J.H. McGuire, "Double photoionization of helium using many-body perturbation theory," Phys. Rev. A 48, 1271 (1993).
- S. Bhattacharyya and S. Mitra, "Double photoionization of He by circularly polarized light: A QED approach," Phys. Rev. 62, 032709 (2000). [CrossRef]
- A. Becker and F. H. M. Faisal, "Mechanism of laser-induced double ionization of helium," J. Phys. B 29, L197 (1996).
- A. Becker and F.H.M. Faisal, "Interplay of electron correlation and intense field dynamics in the double ionization of helium," Phys. Rev. A 59, R1742 (1999).

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