Spatial structure of radiation from an optical klystron

An equation describing the spatial structure of radiation from an optical klystron is derived. The transverse structure of the field in an optical klystron is investigated using a specially written program which allows from nonlocal saturation. It is shown that stable normal modes (eigenmodes) may exist in a resonator and the structure of these modes depends little on the adopted saturation model. At low values of the Fresnel number the divergence of the output radiation is governed primarily by the optical configuration of the resonator.