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 $({\phi }_{12}\approx 110°–200°)$ is determined from the experimental data for both $R=5\mathrm{}$ 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.