Properties of unstable resonators with field rotation. I. Theoretical principles

A theoretical analysis is made of the characteristics of the mode structure in unstable resonators with field rotation (URFR's). The results of estimating the influence of the optical inhomogeneities of the active medium on the structure of the dominant URFR transverse mode are presented. It is concluded that URFR's are potentially useful for lasers with low gains per pass and active media with large transverse cross sections. Designs of URFR's and calculation methods are discussed.