  In most supersymmetric theories, charginos $\tilde{\chi}^\pm_{1,2}$ belong to
the class of the lightest supersymmetric particles and the couplings of Higgs
bosons to charginos are in general complex so that the CP--violating chargino
contributions to the loop--induced coupling of the lightest Higgs boson to
photon pairs can be sizable even in the decoupling limit of large pseudoscalar
mass $m_A$ with only the lightest Higgs boson kinematically accessible at
future high energy colliders. We introduce a specific benchmark scenario of CP
violation consistent with the electric dipole moment constraints and with a
commonly accepted baryogenesis mechanism in the minimal supersymmetric Standard
Model. Based on the benchmark scenario of CP violation, we demonstrate that the
fusion of the lightest Higgs boson in linearly polarized photon--photon
collisions can allow us to confirm the existence of the CP--violating chargino
contributions {\it even in the decoupling regime of the Higgs sector} for
nearly degenerate SU(2) gaugino and higgsino mass parameters of about the
electroweak scale.
