Probing the parton densities of polarized photons at a linear e+e- collider

The present theoretical status of spin-dependent parton densities Δfγ(x, Q2) of circularly polarized photons is briefly reviewed. It is then demonstrated that measurements of the deep-inelastic spin asymmetry Aγ1 ≅ gγ1/Fγ1 and of di-jet rapidity distributions at a future linear e+e- collider appear to be particularly suited for a determination the spin-dependent photonic quark and gluon densities, respectively. Special emphasis is devoted to a comparison of the different sources of polarized photons at a linear collider: the equivalent photon approximation and backscattered laser (Compton) photons. It is shown that backscattered laser photons are highly favorable, even indispensable, for decent measurements of the Δfγ(x, Q2)