Mode discrimination with rimmed optical resonator.

A rimmed optical resonator is studied both theoretically and experimentally. It consists of a convex mirror that spreads out the mode volume and an annular concave mirror that controls the diffraction loss. It is found that such a system is definitely superior to a conventional stable resonator for Fresnel numbers larger than unity. It utilizes larger mode volume, yields higher power, and discriminates more against higher order modes. However, our system fails to a certain extent when it is operated at high power. Methods to remove this difficulty are discussed.