In the analysis of the propagation of electromagnetic waves in
cyclotron frequency range, in both isotropic media and magnetoactive plasmas,
the role of diffractive effects, which are not accounted for by geometrical
may no longer be neglected when highly collimated beams are to be employed.
Moreover, when lenses, mirrors, refractive gradients and/or wave cut-offs
placed along the beam trajectory, the very concept of independent optical
tends to introduce singularities, which do not always correspond to physical
features. A quasi-optical approach has previously been shown to present
advantage of allowing a description (at the lowest order of approximation)
the diffractive widening of the beam. The specific aim of this paper is
when reflection, refraction or beam focusing indicates the need for particular
attention, the solution method employed within such an approach. The results
presented here concern the propagation and power deposition profiles, in
number of crucial physical situations, of narrow electron cyclotron beams
launched, in Gaussian form, either into isotropic transparent media or
anisotropic toroidal plasmas of fusion interest.