Low-magnification unstable resonators used with ruby and alexandrite lasers

Low-magnification unstable resonators that utilize radially birefringent elements and that have been shown to be suitable for use with ruby and alexandrite lasers are described. From these resonators, 400 mJ of energy in a Q-switched pulse with ~2.5x diffraction-limited output has been obtained from alexandrite, and 250-mJ Q-switched output that is near diffraction limited has been obtained from ruby.