  We present results of an investigation to study CP violation in the Higgs
sector in $t\bar t$ production at a $\gamma\gamma$-collider, via the process $
\gamgam \ra \phi \ra t \bar t$ where the $\phi$ is a scalar with indeterminate
CP parity. The study is performed in a model independent way parametrising the
CP violating couplings in terms of six form factors $\{\Re(S_{\gamma}),
\Im(S_{\gamma}), \Re(P_{\gamma}), \Im(P_{\gamma}), S_t, P_t\}$. The CP
violation is reflected in the polarisation asymmetry of the produced top quark.
We use the angular distribution of the decay lepton from $t/\bar t$ as a
diagnostic of this polarisation asymmetry and hence of the CP mixing, after
showing that the asymmetries in the angular distribution are indpendent of any
CP violation in the $tbW$ vertex. We construct combined asymmetries in the
initial state lepton (photon) polarization and the final state lepton charge
and study how well different combinations of these form factors can be probed
by measurements of these asymmetries, using circularly polarized photons. We
demonstrate the feasibility of the method to probe CP violation in the Higgs
sector at the level induced by loop effects in supersymmetric theories, using
realistic photon spectra expected for a TESLA like $e^+ e^-$ collider. We
investigate the sensitivity of our method for for different widths of the
scalar as well as for the more realistic backscattered laser photon spectrum
resulting from the inlcusion of the nonlinear effects.
