  A theoretical model for magnetooptic imaging is presented. The model gives a
detailed description of the magnetooptic indicator and the optical imaging
system, where the intensity at the detector plane is described by a set of
diffraction integrals. To demonstrate the applicability of the model, some
issues concerning imaging of single vortices in superconductors are studied. It
is found that the useful signal is strongly dependent on the penetration depth
of the superconductor, and also the sensitivity and thickness of the indicator.
