  We study the helicity amplitudes of the process gamma gamma to ZZ in the
Standard Model at high energy. These amplitudes receive contributions from the
W and charged quark and lepton loops, analogous to those encountered in the
gamma gamma to gamma gamma, gamma Z cases studied before. But gamma gamma to ZZ
also receives contributions from the Higgs s-channel poles involving the
effective Higgs-gamma gamma vertex. At energies of about 300 GeV, the
amplitudes in all three processes are mainly helicity-conserving and almost
purely imaginary; which renders them a very useful tool in searching for New
Physics. As an example, a SUSY case is studied, and the signatures due to the
virtual effects induced by a chargino-, charged slepton- or a lightest
stop-loop in gamma gamma to ZZ, are explored. These signatures, combined with
the analogous ones in gamma gamma to gamma gamma and gamma gamma to gamma Z,
should help identifying the nature of possible New Physics particles.
