High-energy photon colliders

Using the laser backscattering method in future linear colliders one can obtain γγ and γe colliding beams (photon colliders) with energy and luminosity comparable to that in e+e− collisions. A key element of a photon collider is a laser with high peak power and repetition rate. One very promising way to overcome this problem is the optical cavity. A very high γγ luminosity could be achieved by further decreasing the beam emittances. One possible way is laser cooling of electron beams. The solution to the first problem is vital for photon colliders and provides an interesting physics program. Solution of the second problem makes photon colliders a very powerful instrument for study of matter. Ways to these goals are discussed in this talk.