Fully Differential Cross Sections for Double Photoionization of He Measured by Recoil Ion Momentum Spectroscopy

Recoil momentum spectroscopy has been used to measure fully differential cross sections for double photoionization of He at energies of 1--80 eV above threshold. The measurement technique allows the determination of the vector momenta of all three escaping particles, and samples the entire final momentum space. When presented in terms of the momentum vector of the center of mass of the electron pair and the relative momentum of the two electrons, the data reveal simple features of the correlated motion. The resulting patterns near threshold are found to be in agreement with a Wannier description of the process.