We present a characterization of the dot-mirror output coupler in the case of low losses. The numerical procedure computes the eigenvalue and field distribution through the Fox-Li method applied to a bare laser cavity. The field associated with the lowest-order mode closely follows the Airy pattern. This fact allows estimating the effective reflectivity and the beam diameter in a simple way. The computed values are compared with the experimental data obtained in a transversely-excited-atmosphere laser. The measured reflectivity approximates the expected figure for the lowest-order mode and thus suggests that this cavity discriminates against the higher-order modes. © 2002 Society of Photo-Optical Instrumentation Engineers.