Three-dimensional field structure in open unstable cavities - Part II: Active cavity results

The three-dimensional field distribution of the diffractive cavity mode str ucture in an active, open, unstable laser resonator is presented as a funct ion of the equivalent Fresnel number of the cavity. The active cavity mode structures are compared to that of the corresponding passive cavity so that the effects of a spatially extended, homogeneously broadened, saturable ga in medium on the cavity field structure may be ascertained. The qualitative structure of this intracavity field distribution, including the central in tensity core (or oscillator filament), is explained in terms of the Fresnel zone structure defined over the cavity feedback aperture. (C) 1999 Optical Society of America.