2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/36989A 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_γ, to be probed.5 pages, 2 figures. To appear in "The THERA Book", DESY-LC-REV-2001-062. IFT 2001/13High Energy Physics - Experimenttext