We consider two-photon double ionization of helium by two xuv photons in the region around the sequential ionization threshold. We show that, on the attosecond timescale, the mechanism for double ionization is dominated by the absorption of one photon by each electron in the fundamental state He(1s~(2)). We examine the dynamics of two-photon double ionization of helium for an averaged photon energy omega velence50 eV, with a pulse duration of two optical cycles. The double ionization rate, energy and angular distributions are calculated by solving the time-dependent Schrodinger equation. Results are discussed on the basis of a model.
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