Absolute triply differential cross sections for double photoionization of helium at 10, 20, and 52.9 eV above threshold

We have calculated the coplanar triply differential cross section (TDCS) for double ionization of helium by one photon at total energies of 10, 20, and 52.9 eV above threshold. Our results agree very well with recently measured and calculated angular distributions [O. Schwarzkopf, B. Krässig, J. Elmiger, and V. Schmidt, Phys. Rev. Lett. 70, 3008 (1993); O. Schwarzkopf, B. Krässig, V. Schmidt, F. Maulbetsch, and J. S. Briggs, J. Phys. B 27, L347 (1994); F. Maulbetsch and J. S. Briggs, ibid. 26, L647 (1993)] for the cases of equal energy sharing (photoelectron energies ${\mathit{E}}_1$ and ${\mathit{E}}_2$, such that ${\mathit{E}}_1$=${\mathit{E}}_2$=5 eV and ${\mathit{E}}_1$=${\mathit{E}}_2$=10 eV) and unequal energy sharing (${\mathit{E}}_1$=5 eV, ${\mathit{E}}_2$=47.9 eV). In contrast to previous calculations of the TDCS, our calculation is based on a basis-set method that is, in principle, exact, and we obtain absolute values of the TDCS that are fairly well converged with respect to the basis size.