Analyses of two mechanisms of double ionization of He in an intense femtosecond laser pulse are made within the $S$-matrix theory. Their contributions are compared with each other and with the recent data of coincidence measurements for two-electron energy distributions. It is found that the correlated energy-sharing mechanism reproduces the data remarkably well and also confirms the so-called “excessive production” of hot electrons in the process. In contrast, the shakeoff mechanism is found to fail completely to account for either the strength or the trend of the data and is therefore ruled out.

• Received 15 July 2002

DOI:https://doi.org/10.1103/PhysRevLett.89.193003