Nonlinear effects in Compton scattering at photon colliders

The backward Compton scattering is a basic process at future higher energy photon colliders. To obtain a high probability of e --> gamma conversion th e density of laser photons in the conversion region should be so high that simultaneous interaction of one electron with several laser photons is poss ible (nonlinear Compton effect). In this paper, a detailed consideration of energy spectra, helicities of final photons and electrons in nonlinear bac kward Compton scattering of circularly polarized laser photons is given. Di stributions of gamma gamma luminosities with total helicities 0 and 2 are i nvestigated. Very high intensity of laser wave leads to broadening of the e nergy (luminosity) spectra and shift to lower energies (invariant masses). Beside complicated exact formulae, approximate formulae for energy spectrum and polarization of backscattered photons are given for relatively small n onlinear parameter xi (2) (first order correction). All this is necessary f or optimization of the conversion region at photon colliders and study of p hysics processes, where a sharp edge of the luminosity spectrum and monochr omaticity of collisions are important. (C) 2001 Elsevier Science B.V. All r ights reserved.