Patent ID: 8014433

Claim:
An optical system comprising: a relatively larger concave spherical mirror, a first relatively smaller concave spherical mirror and a second relatively smaller concave spherical mirror, at least one of said first and second relatively smaller concave spherical mirrors being an active mirror, a center of curvature of said relatively larger concave spherical mirror being at a central point between said first and second relatively smaller concave spherical mirrors, the centers of curvature of said first and second relatively smaller concave spherical mirrors being at said relatively larger concave spherical mirror, and a source generating a pump light beam which enters and leaves said system after multiple reflections between said relatively larger mirror and said first and second relatively smaller mirrors, said beam being focused and reflected at substantially unchanged positions at said first and second relatively smaller concave spherical mirrors, said beam striking and being reflected by said relatively larger concave spherical mirror at changing positions.