  We perform a theoretical study of finesse limitations of a Fabry-Perot (FP)
cavity occurring due to finite size, asymmetry, as well as imperfections of the
cavity mirrors. A method of numerical simulations of the eigenvalue problem
applicable for both the fundamental and high order cavity modes is suggested.
Using this technique we find spatial profile of the modes and their round-trip
diffraction loss. The results of the numerical simulations and analytical
calculations are nearly identical when we consider a conventional FP cavity.
The proposed numerical technique has much broader applicability range and is
valid for any FP cavity with arbitrary non-spherical mirrors which have
cylindrical symmetry but disturbed in an asymmetric way, for example, by tilt
or roughness of their mirrors.
