  The radiation caused by particles of one bunch in the collective
electromagnetic field of the short oncoming bunch is studied. Quantum effects
are calculated for the spectrum of radiated photons. Using this spectrum, the
dependence of the relative energy loss delta on a quantum parameter kappa is
dicussed. It is shown that the behaviour of delta changes considerably with the
increase of that parameter. In the classical regime (kappa << 1) the energy
loss is proportional to the incoming particle energy, while in the extreme
quantum regime (kappa >> 1) the energy loss becomes a constant. The coherent
e+e- pair production for gamma-e colliders as cross-channel to CBS is
considered.
