  Physical Higgs particles in the Minimal Supersymmetric Standard Model (MSSM)
with explicit CP violation are CP mixed states. The decay of these Higgs
particles can be analysed to study the CP properties of the MSSM. In the
present work we consider the di-photon channel of the lightest neutral Higgs
boson for this purpose. Compared to earlier studies on effects of
scalar/pseudo-scalar mixing, our analysis also investigates the effect due to
Higgs-sfermion-sfermion couplings along with that of mixing. We find that a
light stop may have a strong impact on the width and Branching Ratio (BR) of
the decay process H1 --> gamma.gamma, whereas other light sparticles have only
little influence. In some regions of the MSSM parameter space with large
CP-violating phase phi-mu ~ 90 deg a light (~ 200 GeV) stop can change the
di-photon BR by more than 50 % compared to the case with heavy (~ 1 TeV) stop
and otherwise same MSSM parameters.
