Electron–electron correlation in strong laser fields

Abstract

In the context of strong field–matter interaction, an increasing number of phenomena has been found to be not understood within the single-active-electron approximation. For such phenomena, electron–electron correlation plays an important role in the underlying dynamics. In this review, we will provide a broad overview of electron–electron correlation and examine two distinct cases of its manifestation in strong field physics. In the first example, we examine nonsequential double and multiple ionization of atoms, discussing the experimental manifestation of the electron correlation and the theoretical models that have been developed to describe the effect. The second case examines the interaction of larger systems with intense laser fields, for which multielectron effects have to be invoked for an accurate description of the dynamics.

Keywords:

• strong field–matter interaction
• nonsequential double ionization
• electron–electron correlation
• multielectron effects

Acknowledgements

We would like to thank W. Becker for his collaboration over many years, which led to some of the publications discussed in this review. We are also grateful to the authors of several references, whose figures are partly reproduced in this article, for kindly agreeing to that and in many cases even providing the original files. This work has been funded by the UK Engineering and Physical Sciences Research Council (Advanced Research Fellowship, Grant No. EP/D07309X/1) and the National Natural Science Foundation of China (Grant No. 10925420).

Notes

Notes

1. In this regime, the Keldysh parameter , where I _p and U _p give the ionization potential and the ponderomotive energy, is smaller than unit. Physically, this means that a quasi-static picture can be adopted for the external field and one can describe the process of ionization as tunneling through an effective potential barrier.

2. Recently, however, it has been shown that there may be a recollision of the first electron with its parent ion, and hence NSDI, for highly elliptically (or even circularly) polarized fields. This recollision has been explained in 68,124 using classical models.

3. Kinematic constraints determined by SFA-based models suggest that should correspond to the most probable, but not the maximum electron momentum in NSDI electron-momentum distributions. In fact, depending on the intensity of the driving field, this momentum can go beyond 4U _p. This is in agreement with this recent outcome of TDSE computations. More detailed discussions on this constraint will be provided in Section 2.4.

4. One should note, however, that, due to the presence of the Coulomb potential the symmetries and over half a cycle are no longer present, so that there are distortions in the patterns encountered with regard to those found employing the SFA.

5. One should note, that, even though . is formally what one would obtain by including a contact-type interaction, the idea behind the present model is different, namely that a hard collision took place, and the energy is being redistributed without making further assumptions on the system dynamics apart from the time delay Δt.

6. Note, however, that multielectron effects do introduce quantitative changes in the high-order harmonic spectra of multielectron atoms; for a discussion of this issue see, e.g. 161.