ABSTRACT
The need for large mode volume and output-coupling control for applications to high-power lasers has focused interest on unstable resonators. However, good performance can be obtained with planar geometries modified by means of rims along the edges of the mirrors (Checcacci and Scheggi 1969, 1970, Checcacci et al 1971). Rims can compensate for the curvature of the wavefront due to diffraction and hence control output and mode volume.
