Production of Scalar Higgs and Pseudoscalar Higgs in Multi-Higgs Doublet Models at $\gamma \gamma$ Colliders

We present the effects of heavy CP-even (H) and CP-odd (A) Higgs bosons on the production cross section of the process $\gamma \gamma$ $\to t\bar{t}$ at the energy around the mass poles of the Higgs bosons. It is found that the interference between H and A with the small mass gap, as well as the ones between Higgs bosons and the continuum, contributes to the cross section, if the photon beams are polarized and if we observe the helicity of the top quarks. It is demonstrated in the framework of the minimal supersymmetric extension of the standard model that the H and A contributions can be sizable at future $\gamma \gamma$ colliders for small value of $\tan \beta$. The methods to measure the CP-parity of the Higgs boson are also presented. The statistical significances of detecting the Higgs signals and measuring the Higgs CP-parity are evaluated.