  We study double Higgs production in photon-photon collisions as a probe of
the new dynamics of Higgs interactions in the framework of two Higgs Doublet
Models. We analyze neutral Higgs bosons production and decay in the fusion
processes, $\gamma \gamma \to S_iS_j$, $S_i=h^0, H^0, A^0$, and show that both
$h^0h^0$ and $A^0A^0$ production can be enhanced by threshold effects in the
region $E_{\gamma\gamma}\approx 2 m_{H\pm}$. Resonant effects due to the heavy
Higgs, $H^0$, can also play a role in the cross section enhancement when it is
allowed to decay to two light CP-even $h^0$ or to two light CP-odd $A^0$
scalars. We have scanned the allowed parameter space of the Two Higgs Doublet
Model and found a vast region of the parameter space where the cross section is
two orders of magnitude above the Standard Model cross section. We further show
that the Standard Model experimental analysis can be used to discover or to
constraint the two Higgs doublet model parameter space.
