High-energy photon colliders

Using the laser backscattering method in future linear colliders one can ob tain yy and ye colliding beams (photon colliders) with energy and luminosit y comparable to that in e(+)e(-) collisions. A key element of a photon coll ider is a laser with high peak power and repetition rate. One very promisin g way to overcome this problem is the optical cavity. A very high gamma gam ma luminosity could be achieved by further decreasing the beam emittances. One possible Ray is laser cooling of electron beams. The solution to the fi rst problem is vital for photon colliders and provides an interesting physi cs program, Solution of the second problem makes photon colliders a very po werful instrument for study of matter. Ways to these goals are discussed in this talk. (C) 2000 Elsevier Science B.V. All rights reserved.