Modes in misaligned unstable resonators.

A previously developed technique for the calculation of modes of perfectly aligned unstable resonators in the limit of large Fresnel number is here extended to include effects of misalignment. It is shown how asymptotic techniques may be employed to simplify the calculation of near- and far-field patterns produced by such modes. The basic conclusion is that rectangular aperture unstable resonators are quite insensitive to misalignment, in the sense that the lowest-loss mode continues to be essentially diffraction limited as long as the feedback mirror remains well within the output beam.