Beam modes beyond the paraxial approximation: A scalar treatment

Beam modes are considered by a high-aperture scalar theory based on the complex source-point method. A different form for the beam mode that avoids nonphysical singularities in intensity is introduced. The amplitude in the focal region is explored for the lowest-order mode. Conditions for oscillation of a high-aperture resonator, such as a microcavity, are derived. The amplitude in the focal region is explored for higher-order modes in systems with cylindrical symmetry. These modes are expressed in terms of Jacobi polynomials. @S1050-2947~98!01103-2#