  We have developed a scattering-matrix approach for numerical calculation of
resonant states and Q-values of a nonideal optical disk cavity of an arbitrary
shape and of an arbitrary varying refraction index. The developed method has
been applied to study the effect of surface roughness and inhomogeneity of the
refraction index on Q-values of microdisk cavities for lasing applications. We
demonstrate that even small surface roughness can lead to a drastic degradation
of high-Q cavity modes by many orders of magnitude. The results of numerical
simulation are analyzed and explained in terms of wave reflection at a curved
dielectric interface combined with the examination of Poincare surfaces of
section and Husimi distributions.

Optics