Ultimate luminosities and energies of photon colliders ∗

A photon collider luminosity and its energy are determined by the parameters of an electron-electron linear collider (energy, power, beam emittances) and collision effects. The main collision effect is the coherent e+e− pair creation. At low energies (2E< 0.5–1 TeV) this process is suppressed due to repulsion of electron beams. In this region Lγγ(z > 0.65) ≥ 1035cm−2s−1 is possible (1033 − 1034 is sufficient). At higher energies the limited average beam power and coherent pair creation restrict the maximum energy of photon colliders (with sufficient luminosity) at Ecm ∼ 5 TeV. Obtaining high luminosities requires the development of new methods of production beams with low emittances such as a laser cooling.