The beam quality of annular lasers and related problems

Abstract

Abstract A detailed study of the beam quality of annular lasers, for example, lasers with or without phase distortions emitted from unstable resonators, is made, where the power in the bucket (PIB) and β-parameter are chosen as criteria for characterizing the beam quality in the far field. It is shown that better focusability is achieved at the real focal plane rather than at the geometrical focal plane due to the focal shift, and the negative quartic phase distortions may improve the beam quality measured in terms of the PIB and/or β-parameter. From a practical point of view the PIB and β can be chosen as beam quality characteristic parameters for such lasers. However, some related problems remain, which are discussed briefly.