1. A.E. Siegman, Lasers (University Science Books, Mill Valley, California, 1986) sect. 14.2
2. M. Born and E. Wolf, Principles of Optics, 6th ed. (Pergamon Press, London 1980) sect. 1.6.5
3. H. Kogelnik and T. Li, Laser Beams and Resonators, Appl. Opt. 5, 1550 (1966)
4. Reference [1], Chap. 19
5. A.G. Fox and T. Li, Resonant Modes in a Maser Interferometer, Bell. Syst. Tech. J. 40, 453 (1961)