▎ 摘　　要

We have investigated the effect of imperfect circular polarization on the angle-resolved photoemission spectroscopy signal, using graphene as a prototypical system that can be understood within tight-binding formalism. We found that perfect left- and right-circularly polarized lights give the same photoelectron intensity distribution around a constant energy contour of the graphene pi band. On the other hand, upon breaking the purity of the polarization, photoelectron intensity starts to show circular dichroism, which is enhanced with further increasing the imperfection. Our results predict the existence of an additional factor for the circular dichroism observed in the photoemission signal from graphene and hence suggest the importance of experimental conditions to understand circular dichroism observed via photoemission spectroscopy. (C) 2014 Elsevier B.V. All rights reserved.