Energy- and angle-resolved triply differential cross sections have been mea
sured in the double photoionization of helium under equal and unequal energ
y sharing conditions using right- and left-elliptically polarized photons.
Linear dichroism in these cross sections has been observed under the equal
energy sharing. For the unequal energy sharing a pure circular polarization
effect has been deduced by eliminating the linear polarization contributio
n.