Propagation of partially coherent beams in a periodic sequence of lenses and Gaussian apertures

The evolution of the cross-spectral density of an initially spatially incoherent beam propagating through an iterated sequence of spherical lenses and Gaussian apertures is studied. The global degree of spatial coherence, the spot size and the radius of wavefront curvature are calculated as functions of the number of transits. Steady-state values of the beam parameters are also given in a closed form. The dependence of the results on the aperture width and the focal length is discussed.