A few examples are presented to show that the possibilities of developing new promising resonators based on standard optical elements with plane or spherical surfaces are far from being exhausted. Methods of constructing field-rotation linear resonators using a modified Sagnac interferometer are discussed; the properties and application potential of the simplest resonators with spatial filtration of radiation are considered; and a method of constructing multi-pass unstable resonators with a radically reduced sensitivity to misalignment is presented.
Yurii A. Anan'ev,
"Some unusual resonators", Proc. SPIE 1868, Laser Resonators and Coherent Optics: Modeling, Technology, and Applications, (13 August 1993); doi: 10.1117/12.150611; https://doi.org/10.1117/12.150611