Experimental and theoretical study of linear and circular dichroism in helium double photoionization

The fully resolved triply differential cross section (TDCS) of helium double photoionization with elliptically polarized light has been determined, both experimentally and theoretically, at the photon energy of 88 eV. The excess energy was shared between the photoelectron pair as 1 + 8, 3 + 6 and 4.5 + 4.5 eV. Simultaneous sign reversal of the Stokes parameters S₁, S₃ resulted in a profound change of shape of the TDCS. This effect can be attributed to the linear dichroism in the case of equal energy sharing, and a combination of the circular and linear dichroisms in the case of unequal energy sharing. Theoretical TDCS was obtained by employing the convergent close-coupling (CCC) method. In contrast to the previous work of Mergel et al (1998 Phys. Rev. Lett. 80 5301) who investigated the circular dichroism at 99 eV photon energy, good agreement is found between experimental and calculated TDCS in all cases.