The role of correlation in non-sequential double ionization

We present the results of recent numerical studies of double ionization and correlation in a two-electron model atom. We briefly review basic features of our model and describe the invariant measure of correlation that we find convenient. Our results help to illuminate the dynamics of the double-ionization process. We focus on the well-known "knee" zone. We show that the spatial probability distribution of the two-electron system exhibits jets of double ionization which occur each half cycle. We note a competing process of rapid sequential ionisation. We also examine the dependence of these processes on the strength of the electron-electron repulsion, and we find that the size of the jets is particularly sensitive to it in the vicinity of the knee.