A brief review of transverse mode structure in various curved mirror laser cavities is given. Cavities considered are those consisting of two concave mirrors, a concave and a plane mirror, and a concave and a convex mirror. The volume of the TEM00 mode in the various cavities is discussed, and the alignment tolerance on the mirrors is considered. It is shown that the maximum volume of the TEM00 mode in the near-hemispherical cavity is roughly one-third of the volume in the plane-parallel cavity, but that for a given mode volume, the near-hemispherical cavity is the easiest of all curved mirror cavities to align. It is suggested on the basis of the above consideration that the near-hemispherical cavity is the most practical cavity to use in a laser.
Douglas C. Sinclair, "Choice of Mirror Curvatures for Gas Laser Cavities," Appl. Opt. 3, 1067-1071 (1964)