A theory of the modes in a resonator bounded by the surface of a triaxial ellipsoid was given previously by Weinstein. We have applied this theory to characterize the modes observed in a large-aperture Brewster-window laser. Recognizing that Brewster windows impart astigmatism to the laser cavity, we can find an equivalent ellipsoidal cavity with which to associate the modes. The theory predicts various forms of mode structure, depending on the total astigmatism present. We have verified the theory experimentally and show that high-order modes having rectangular symmetry may be obtained even though a circular aperture is used in the cavity.
© 1975 Optical Society of AmericaPDF Article