Optical resonators and the problem of laser radiation divergence

The fundamental theory of optical resonators is presented and factors influencing the divergence of laser radiation in resonators with small diffraction losses are examined. The use of optical resonators for the production of narrow-beam laser outputs is discussed, and light propagation, divergence, and the various types of oscillations, and energy transformation characteristics of laser resonators are reviewed. The divergence of the radiation of lasers with stable and planar resonators is considered, with attention given to the types of oscillations encountered, boundary diffraction, multimode generation, the effects of resonator deformations and methods for the angular selection of radiation. The theory of unstable resonators, including resonators with slightly inhomogeneous media, central holes, multiple mirrors or prisms and rotating fields is then developed and their applications in pulsed and CW lasers are discussed. Finally, problems relating to the optical nonuniformity of active media and means of resolving them are examined.