  Reflection and transmission of narrow beams at a dielectric interface is
analysed. It is confirmed that for arbitrary incidence two types of beams -
Elegant Hermite-Gaussians of linear polarization and Elegant Laguerre-Gaussians
of circular polarization, both defined in the interface plane - can be treated
as vector normal modes of the interface. Excitation of higher-order modes by
cross-polarization coupling is described by changes of mode indices induced by
generalised transmission and reflection matrices. It is explicitly shown that,
off-axis in general, spectral placements of the excited optical vortices are
determined by elements of these matrices, depended in turn on beam incidence.
Numerical simulations of beam reflection entirely confirm theoretical
predictions. The current paper is a continuation and extension of a previous
work by W. Nasalski [Phys. Rev. E 74, 056613 (2006)].
