Reach of future colliders in probing the structure of the photon

5 pp. (2001).
A comparison of the potentials of ep and $e^+e^-$machines to probe the structure of the photon is performed. In particular, the kinematic reach of a proposed future ep facility, THERA, is compared with those of current colliders, LEP and HERA, and with the proposed linear collider, TESLA. THERA like HERA will use a proton beam of 920 GeV but with an increased electron beam energy of 250 GeV allowing higher scales, $Q^2$, and lower values of parton momentum fraction in the photon, x_\gamma, to be probed.