Double photoionization of helium at an excess energy of 60 eV using left- and right-elliptically-polarized light

Helium double photoionization (gamma,2e) triple differential cross sections (TDCSs) were measured at an excess energy of 60 eV using a dual toroidal spectrometer and synchrotron radiation from a helical undulator (BL-28A, Photon Factory, Japan). Energy-sharing ratios (R=E-2/E-1) for the two ejected electrons of 5 and 11 are studied with both right- and left-handed elliptically polarized light. The TDCSs are found to be in good agreement with those obtained using the hyperspherical R matrix with semiclassical outgoing waves theory. The circular dichroism for a limited mutual angular range (phi(12)approximate to110degrees-200degrees) is determined from the experimental data for both R=5 and 11, and compared to theoretical calculations performed over the complete range of mutual angles. No dynamic nodes are found in either the experimental (within the explored phi(12) range) or theoretical circular dichroism for these R values at this excess energy.